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Clin Microbiol Rev. 2009 January; 22(1): 161–182.
PMCID: PMC2620637

AmpC β-Lactamases


Summary: AmpC β-lactamases are clinically important cephalosporinases encoded on the chromosomes of many of the Enterobacteriaceae and a few other organisms, where they mediate resistance to cephalothin, cefazolin, cefoxitin, most penicillins, and β-lactamase inhibitor-β-lactam combinations. In many bacteria, AmpC enzymes are inducible and can be expressed at high levels by mutation. Overexpression confers resistance to broad-spectrum cephalosporins including cefotaxime, ceftazidime, and ceftriaxone and is a problem especially in infections due to Enterobacter aerogenes and Enterobacter cloacae, where an isolate initially susceptible to these agents may become resistant upon therapy. Transmissible plasmids have acquired genes for AmpC enzymes, which consequently can now appear in bacteria lacking or poorly expressing a chromosomal blaAmpC gene, such as Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis. Resistance due to plasmid-mediated AmpC enzymes is less common than extended-spectrum β-lactamase production in most parts of the world but may be both harder to detect and broader in spectrum. AmpC enzymes encoded by both chromosomal and plasmid genes are also evolving to hydrolyze broad-spectrum cephalosporins more efficiently. Techniques to identify AmpC β-lactamase-producing isolates are available but are still evolving and are not yet optimized for the clinical laboratory, which probably now underestimates this resistance mechanism. Carbapenems can usually be used to treat infections due to AmpC-producing bacteria, but carbapenem resistance can arise in some organisms by mutations that reduce influx (outer membrane porin loss) or enhance efflux (efflux pump activation).


The first bacterial enzyme reported to destroy penicillin was the AmpC β-lactamase of Escherichia coli, although it had not been so named in 1940 (1). Swedish investigators began a systematic study of the genetics of penicillin resistance in E. coli in 1965. Mutations with stepwise-enhanced resistance were termed ampA and ampB (84, 85). A mutation in an ampA strain that resulted in reduced resistance was then designated ampC. ampA strains overproduced β-lactamase, suggesting a regulatory role for the ampA gene (180). ampB turned out not to be a single locus, and such strains were found to have an altered cell envelope (236). ampC strains made little if any β-lactamase, suggesting that ampC was the structural gene for the enzyme (46). Most of the amp nomenclature has changed over the years, but the designation ampC has persisted. The sequence of the ampC gene from E. coli was reported in 1981 (144). It differed from the sequence of penicillinase-type β-lactamases such as TEM-1 but, like them, had serine at its active site (161). In the Ambler structural classification of β-lactamases (7), AmpC enzymes belong to class C, while in the functional classification scheme of Bush et al. (47), they were assigned to group 1.


When the functional classification scheme was published in 1995, chromosomally determined AmpC β-lactamases in Enterobacteriaceae and also in a few other families were known (47). Since then, the number of sequenced bacterial genes and genomes has grown enormously. In GenBank, ampC genes are included in COG 1680, where COG stands for cluster of orthologous groups. COG 1680 comprises other penicillin binding proteins as well as class C β-lactamases and includes proteins from archaea as well as bacteria, gram-positive as well as gram-negative organisms, strict anaerobes along with facultative ones, and soil and water denizens as well as human pathogens, such as species of Legionella and Mycobacterium. Sequence alone is insufficient to differentiate an AmpC β-lactamase from ubiquitous low-molecular-weight penicillin binding proteins involved in cell wall biosynthesis, such as d-peptidase (d-alanyl-d-alanine carboxypeptidase/transpeptidase). Both have the same general structure and share conserved sequence motifs near an active-site serine (149, 162). E. coli even produces a β-lactam binding protein, AmpH, which is related to AmpC structurally but lacks β-lactamase activity (121). The AmpC name is not trustworthy since several enzymes so labeled in the literature actually belong to class A (177, 337). Cephalosporinase activity is not reliable either, since some β-lactamases with predominant activity on cephalosporins belong to class A (97, 205, 278, 298). Accordingly, the conservative listing of AmpC β-lactamases in Table Table11 includes proteins with the requisite structure from organisms that have been demonstrated to possess appropriate AmpC-type β-lactamase activity. It is undoubtedly incomplete. For example, organisms not yet shown to produce a functional AmpC-type enzyme but with identified ampC genes include such diverse bacteria as Agrobacterium tumefaciens (110), Coxiella burnetii (GenBank accession number YP_001424134), Legionella pneumophila (56), Rickettsia felis (239), and Sinorhizobium meliloti (127). For other organisms, supportive MIC or enzymatic but not structural data are available for the presence of AmpC β-lactamase, including Enterobacter sakazakii (258), Ewingella americana (311), Providencia rettgeri (207), and several species of Serratia (306, 307) and Yersinia (215, 288, 313). The phylum Proteobacteria contains the largest number, but at least one acid-fast actinobacterium also produces AmpC β-lactamase. Sequence variation occurs within each type. For example, more than 25 varieties of AmpC β-lactamase that share ≥94% protein sequence identity have been described for Acinetobacter spp. (137; G. Bou et al., personal communication), and GenBank contains similar multiple listings for E. coli, Enterobacter cloacae, Pseudomonas aeruginosa, and other organisms. Some frequently encountered Enterobacteriaceae are conspicuous by their absence. Klebsiella pneumoniae, Klebsiella oxytoca, Proteus mirabilis, and Salmonella spp. (31) lack a chromosomal blaAmpC gene, as do Citrobacter amalonaticus (328), Citrobacter farmeri, Citrobacter gillenii (224), Citrobacter koseri (formerly Citrobacter diversus and Levinea malonatica), Citrobacter rodentium, Citrobacter sedlakii (252), Edwardsiella hoshinae, Edwardsiella ictaluri (312), Kluyvera ascorbata (138, 305), Kluyvera cryocrescens (72), Plesiomonas shigelloides (9), Proteus penneri (175), Proteus vulgaris (60), Rahnella aquatilis (30, 308), Yersinia pestis, and Yersinia pseudotuberculosis (313) as well as, probably, Escherichia hermannii (91), Francisella tularensis (27), Shewanella algae (123), and Stenotrophomonas maltophilia (111). However, since blaAmpC genes occur on transmissible plasmids, the clinical microbiologist needs to consider this resistance mechanism whatever the identification of an organism.

Taxonomy of bacteria expressing chromosomally determined AmpC β-lactamases


AmpC enzymes typically have molecular masses of 34 to 40 kDa and isoelectric points of >8.0, although the isoelectric points of plasmid-mediated FOX enzymes are lower (6.7 to 7.2) (254), and an AmpC enzyme from Morganella morganii has an isoelectric point of 6.6 (264). The enzymes are located in the bacterial periplasm, with the exception of the AmpC β-lactamase of Psychrobacter immobilis, which is secreted mainly into the external medium (88). They are active on penicillins but even more active on cephalosporins and can hydrolyze cephamycins such as cefoxitin and cefotetan; oxyiminocephalosporins such as ceftazidime, cefotaxime, and ceftriaxone; and monobactams such as aztreonam but at a rate <1% of that of benzylpenicillin (Table (Table2,2, which also shows data for class A and D β-lactamases for comparison). Although the hydrolysis rate for such substrates is low due to slow deacylation (99), the enzyme affinity, as reflected by a low Km, is high (Table (Table3),3), a factor that becomes important at low substrate concentrations. The hydrolysis rates for cefepime, cefpirome, and carbapenems are also very low, and the estimated Km values for cefepime and cefpirome are high, reflecting lower enzyme affinity (283).

Physical and kinetic parameters
Enzyme kinetics

With preferred cephalosporin substrates, the turnover rate of the E. cloacae P99 β-lactamase is diffusion limited rather than catalysis limited, implying that AmpC enzymes have evolved to maximal efficiency (45). Such data also suggest that AmpC β-lactamase evolved to deal with cephalosporins rather than for some other cellular function, although there is some evidence to suggest that these enzymes play a morphological role (121).

Inhibitors of class A enzymes such as clavulanic acid, sulbactam, and tazobactam have much less effect on AmpC β-lactamases, although some are inhibited by tazobactam or sulbactam (48, 157, 218). AmpC β-lactamases are poorly inhibited by p-chloromercuribenzoate and not at all by EDTA. Cloxacillin, oxacillin, and aztreonam, however, are good inhibitors (47).


The known three-dimensional structures of AmpC enzymes are very similar (Fig. (Fig.1).1). There is an α-helical domain on one side of the molecule (Fig. (Fig.1,1, left) and an α/β domain on the other (Fig (Fig1,1, right). The active site lies in the center of the enzyme at the left edge of the five-stranded β-sheet with the reactive serine residue at the amino terminus of the central α-helix (162, 190). The active site can be further subdivided into an R1 site, accommodating the R1 side chain of the β-lactam nucleus, and an R2 site for the R2 side chain (Fig. (Fig.2).2). The R1 site is bounded by the Ω-loop, while the R2 site is enclosed by the R2 loop containing the H-10 and H-11 helices. Overall, the AmpC structure is similar to that of class A β-lactamases (and dd-peptidase) except that the binding site is more open in class C enzymes, reflecting their greater ability to accommodate the bulkier side chains of cephalosporins. Key catalytic residues in addition to Ser64 for AmpC enzymes include Lys67, Tyr150, Asn152, Lys315, and Ala318, with substitutions at these sites lowering enzymatic activity dramatically (54). In the folded protein, most of these essential residues are found at the active site, with Lys67 hydrogen bonded to Ser64 and Tyr150 acting as a transient catalytic base (79).

FIG. 1.
Diagram of AmpC from E. coli complexed with acylated ceftazidime (PDB accession number 1IEL) (265) created with Cn3CD, version 4.1 (available at The R2 loop at the top of the molecule and conserved residues S64, K67, Y150, ...
FIG. 2.
Schematic representation of ceftazidime with the R1 side chain at C7 and the R2 side chain at C3. (Adapted from reference 158 with permission from Blackwell Publishing Ltd.)


In many Enterobacteriaceae, AmpC expression is low but inducible in response to β-lactam exposure. The induction mechanism is complex (118, 139, 140). The disruption of murein biosynthesis by a β-lactam agent leads to an accumulation of N-acetylglucosamine-1,6-anhydro-N-acetylmuramic acid oligopeptides. The N-acetylglucosamine moiety is removed to produce a series of 1,6-anhydro-N-acetylmuramic acid tri-, tetra-, and pentapeptides. These oligopeptides compete with oligopeptides of UDP-N-acetylmuramic acid for a binding site on AmpR, a member of the LysR transcriptional regulator family. Displacement of the UDP-N-acetylmuramic acid peptides signals a conformational change in AmpR, which activates the transcription of ampC. In addition, the cell has an enzyme, AmpD, a cytoplasmic N-acetyl-muramyl-l-alanine amidase, that removes stem peptides from the 1,6-anhydro-N-acetylmuramic acid and N-acetylglucosamine-1,6-anhydro-N-acetylmuramic acid oligopeptide derivatives, thus reducing their concentrations and preventing the overexpression of AmpC.

The most common cause of AmpC overexpression in clinical isolates is a mutation in ampD leading to AmpC hyperinducibility or constitutive hyperproduction (289). AmpR mutations are less common but can also result in high-constitutive or hyperinducible phenotypes (118, 153, 165). Least common are mutations in AmpG, which result in constitutive low-level expression. AmpG is an inner membrane permease that transports the oligopeptides involved in cell wall recycling and AmpC regulation into the cytosol (179).

Different organisms add additional features to AmpC regulation. E. coli lacks an ampR gene (129). Consequently, AmpC in E. coli is noninducible but is regulated by promoter and attenuator mechanisms (145), as is AmpC production in Shigella (33). Acinetobacter baumannii also lacks an ampR gene so that its AmpC β-lactamase is noninducible (39). AmpC in Serratia marcescens is regulated by ampR, but the ampC transcript has an unusual untranslated region of 126 bases forming a stem-loop structure that influences the transcript half-life (191). P. aeruginosa PAO1 has three ampD genes, explaining the stepwise upregulation of AmpC production seen in this organism with the successive inactivation of each ampD gene (151). The multiple ampD loci contribute to virulence since a P. aeruginosa strain partially derepressed by the inactivation of one ampD allele remains fully virulent, while double or triple ampD mutants lose the ability to compete in a mouse model of systemic infection (219). Other aspects of AmpC regulation in P. aeruginosa are also more complex than that in the Enterobacteriaceae. AmpR is involved in the regulation of other genes besides AmpC (164), an ampE gene encoding a cytoplasmic membrane protein acting as a sensory transducer has a role in ampC expression as part of an ampDE operon (150), and the CreBCD system as well as dacB, encoding a nonessential penicillin binding protein, are involved in AmpC hyperproduction as well (219a).

β-Lactams differ in their inducing abilities (184, 189, 285, 302). Benzylpenicillin, ampicillin, amoxicillin, and cephalosporins such as cefazolin and cephalothin are strong inducers and good substrates for AmpC β-lactamase. Cefoxitin and imipenem are also strong inducers but are much more stable for hydrolysis (Table (Table4).4). Cefotaxime, ceftriaxone, ceftazidime, cefepime, cefuroxime, piperacillin, and aztreonam are weak inducers and weak substrates but can be hydrolyzed if enough enzyme is made. Consequently, MICs of weakly inducing oxyimino-β-lactams are dramatically increased with AmpC hyperproduction. Conversely, MICs of agents that are strong inducers show little change with regulatory mutations because the level of induced ampC expression is already high (Table (Table4).4). β-Lactamase inhibitors are also inducers, especially clavulanate, which has little inhibitory effect on AmpC β-lactamase activity (336) but can paradoxically appear to increase AmpC-mediated resistance in an inducible organism (160). The inducing effect of clavulanate is especially important for P. aeruginosa, where clinically achieved concentrations of clavulanate by inducing AmpC expression have been shown to antagonize the antibacterial activity of ticarcillin (181).

Susceptibility of inducible and stably derepressed clinical isolatesa

The AmpC enzyme in Aeromonas spp. is controlled, along with two other chromosomally encoded β-lactamases, not by an AmpR-type system but by a two-component regulator, termed brlAB in Aeromonas hydrophila (5, 234). BrlB is a histidine sensor kinase, the regulated β-lactamase genes are preceded by a short sequence tag (TTCAC), and an inner membrane protein is also involved in regulation, but the chemical signal for induction is not yet known (10). E. coli has a homologous regulatory system, and there is some evidence that two-component regulators also play a role in the expression of E. coli ampC (128).


In addition to the amount and intrinsic activity of β-lactamase, the rate at which the substrate is delivered to the enzyme is an important determinant of the resistance spectrum. The concentration of β-lactam substrate in the periplasm is a function of the permeability of the cell's outer membrane, in particular the presence of porin channels through which β-lactams penetrate and of efflux pumps, which transport them out of the cell. At one time, the binding of substrate to AmpC β-lactamase was entertained as a mechanism to explain resistance to β-lactams that appeared to be poorly hydrolyzed (316). Vu and Nikaido pointed out, however, that at the concentration of β-lactams in the periplasm needed to inhibit target penicillin binding proteins, AmpC β-lactamases can hydrolyze cephalosporins despite a low Vmax if the substrate also has a low Km (330). Decreasing the number of porin entry channels or increasing efflux pump expression can lower influx and further augment enzyme efficiency. Thus, carbapenem resistance in clinical isolates of P. aeruginosa involves various combinations of overproduction of AmpC β-lactamase, decreased production of the OprD porin channel for imipenem entry, and activation of MexAB-OprM and other efflux systems (114, 163, 185, 268). Also, cephalosporins with both positive and negative charges (i.e., zwitterionic molecules) such as cefepime and cefpirome have the advantage of penetrating the outer bacterial membrane more rapidly than those with a net positive charge, such as cefotaxime and ceftriaxone, thus more easily reaching their lethal targets without β-lactamase inactivation (233).


The serine β-lactamases are ancient enzymes estimated to have originated more than 2 billion years ago. A structure-based phylogeny indicates that the divergence of AmpC-type enzymes predated the divergence of class A and class D β-lactamases from a common ancestor (116). Figure Figure33 provides an overview of the phylogenetic relationship between the enzymes listed in Table Table1.1. As would be expected, AmpC enzymes from organisms belonging to the same genus cluster together, while the AmpC β-lactamases of Enterobacteriaceae, Pseudomonas, and Acinetobacter are more distantly related.

FIG. 3.
Phylogram of AmpC enzymes listed in Table Table11 constructed with ClustalX (available at


Plasmid-encoded AmpC genes have been known since 1989 (Table (Table5)5) (254, 335). They have been found around the world in nosocomial and nonnosocomial isolates, having been most easily detected in those enterobacteria not expected to produce an AmpC β-lactamase. Minor differences in amino acid sequence have given rise to families. Forty-three CMY alleles are currently known (, and in GenBank, sequence data can be found (some of it unpublished) for seven varieties of FOX; four varieties of ACC, LAT, and MIR; three varieties of ACT and MOX; and two varieties of DHA. Some of these varieties are determined by chromosomal genes and represent possible progenitors for the plasmid-determined enzymes.

Chronology and homology of plasmid-mediated AmpC β-lactamases

As indicated in Table Table5,5, the plasmid-determined enzymes are related, sometimes very closely, to chromosomally determined AmpC β-lactamases. CMY is represented twice since it has two quite different origins. Six current varieties (CMY-1, -8, -9, -10, -11, and -19) are related to chromosomally determined AmpC enzymes in Aeromonas spp., while the remainder (including CMY-2, the most common plasmid-mediated AmpC β-lactamase worldwide) are related to AmpC β-lactamases of Citrobacter freundii. The LAT enzymes have a similar origin, but of the four original LAT enzymes, improved sequencing disclosed that LAT-2 was identical to CMY-2, LAT-3 was identical to CMY-6, and LAT-4 was identical to LAT-1, which is the only one remaining unique (15).

Like the chromosomally determined AmpC β-lactamases, the plasmid-mediated enzymes confer resistance to a broad spectrum of β-lactams (Table (Table6)6) including penicillins, oxyimino-β-cephalosporins, cephamycins, and (variably) aztreonam. Susceptibility to cefepime, cefpirome, and carbapenems is little, if at all, affected. Note that ACC-1 is exceptional in not conferring resistance to cephamycins and is actually cefoxitin inhibited (21, 106).

In vitro susceptibilities of E. coli derivatives producing plasmid-encoded AmpC β-lactamases

The genes for ACT-1, DHA-1, DHA-2, and CMY-13 are linked to ampR genes and are inducible (16, 93, 214, 274), while other plasmid-mediated AmpC genes are not, including other CMY alleles and apparently CFE-1 despite its linkage to an ampR gene (142, 229). Nonetheless, the level of expression of both inducible ACT-1 and noninducible MIR-1 is 33- to 95-fold higher than the level of expression of the chromosomally determined AmpC gene of E. cloacae thanks to a higher gene copy number for the plasmid-determined enzymes (2 copies for blaACT-1 and 12 copies for blaMIR-1) and greater promoter strength for the plasmid genes (8-fold increased from the hybrid MIR-1 promoter and 17-fold increased because of a single base change relative to the wild type in the ACT-1 promoter) (275, 276). AmpC plasmids lack ampD genes, but the level of ACT-1 expression is increased with the loss of chromosomal AmpD function (276).

An AmpD-deficient E. coli strain producing ACT-1 remains susceptible to imipenem (MIC, 2 μg/ml) (276), but imipenem MICs of ≥16 μg/ml have been found in clinical isolates of K. pneumoniae carrying ACT-1 plasmids associated with a loss of outer membrane porins (41). In a porin-deficient K. pneumoniae isolate, other plasmid-mediated AmpC enzymes also provide imipenem, ertapenem, and meropenem resistance (141). Such strains generally remain susceptible to cefepime but are otherwise also resistant to oxyimino-β-cephalosporins.

Plasmids carrying genes for AmpC β-lactamases often carry multiple other resistances including genes for resistance to aminoglycosides, chloramphenicol, quinolones, sulfonamide, tetracycline, and trimethoprim as well as genes for other β-lactamases such as TEM-1, PSE-1 (6), CTX-M-3 (55), SHV varieties (119), and VIM-1 (214). The AmpC gene is usually part of an integron but is not incorporated into a gene cassette with an affiliated 59-base element (273). Note that the same blaAmpC gene can be incorporated into different backbones on different plasmids (50).

A variety of genetic elements have been implicated in the mobilization of AmpC genes onto plasmids (Fig. (Fig.4).4). The insertion sequence ISEcp1 (or truncated versions thereof) is associated with many CMY alleles including CMY-2 (105, 115, 155), CMY-4 (228), CMY-5 (343), CMY-7 (135), CMY-12 (182), CMY-14 (182), CMY-15 (182), CMY-16 (69), CMY-21 (133), CMY-31 (GenBank accession number EU331425), and CMY-36 (GenBank accession number EU331426) as well as the β-lactamases ACC-1 (78, 249) and ACC-4 (247). ISEcp1 plays a dual role. It is involved in the transposition of adjacent genes (261) and has been shown able to mobilize a chromosomal bla gene onto a plasmid (166), and it also can supply an efficient promoter for the high-level expression of neighboring genes. The transcription of at least CMY-7 has been shown to start within the ISEcp1 element and takes place at a much higher level than the expression of the corresponding AmpC gene in C. freundii (135).

FIG. 4.
Genetic environment of representative AmpC genes: CMY-3 (GenBank accession number DQ164214), CMY-9 (accession number AB061794), CMY-13 (accession number AY339625), and DHA-1 (accession number SEN237702).

Other blaAmpC genes are found adjacent to an insertion sequence common region (ISCR1) involved in gene mobilization into (typically) complex class 1 integrons (322). Genes for several CMY varieties (CMY-1, -8, -9, -10, -11, and -19), DHA-1, and MOX-1 are so linked (322, 332). On the other hand, the gene for CMY-13 and its attendant ampR gene are bounded by directly repeated IS26 elements made up of a transposase gene (tnpA) with flanking inverted terminal repeat segments (214). Other elements are associated with and may have been involved in capturing the genes for FOX-5 (269), MIR-1 (142), and MOX-2 (271).


Just as amino acid alterations in TEM and SHV β-lactamase have given rise to extended-spectrum enzymes with broader substrate specificities, amino acid insertions, deletions, and substitutions have been described for AmpC β-lactamases that enhance catalytic efficiency toward oxyimino-β-lactam substrates (235). Such changes in both plasmid-determined and chromosomally mediated AmpC enzymes have been described. Their properties are shown in Table Table7.7. The alterations occur either in the Ω-loop, making the enzyme more accessible for substrates with bulky R1 side chains, or at or near the R2 loop, widening the R2 binding site. At both locations, the amino acid alterations can have opposite effects on enzyme kinetics. Generally, the catalytic constant for ceftazidime increased along with the Km, or the Km decreased (reflecting greater affinity), but the kcat decreased as well. In either case, the kcat/Km ratio or catalytic efficiency for ceftazidime and related substrates increased compared to that of the wild-type enzyme with the result that the ceftazidime MICs for a strain carrying such enzymes were in the resistance range (MIC ≥ 32 μg/ml), while the MICs for cefotaxime and cefepime usually reflected only reduced susceptibility, such as a cefepime MIC of 8 μg/ml for E. coli with the AmpC enzymes from E. cloacae CHE or Enterobacter aerogenes Ear2. The enzyme from S. marcescens HD, however, when expressed in E. coli, conferred a cefepime MIC of 512 μg/ml (196), and those from E. coli strains EC14, EC18, and BER were associated with cefepime MICs of 16 μg/ml (197, 199). MICs for aztreonam and imipenem were usually little affected except that an aztreonam MIC of 128 μg/ml was produced by CMY-10 (172). Structural gene mutations were often accompanied by promoter mutations that increased the level of expression of the mutant gene (193). Modifications at additional enzyme sites in laboratory mutant have been described (14). Interestingly, the AmpC variant from E. coli HKY28 became more susceptible to inhibition by clavulanic acid, sulbactam, and tazobactam, a curious phenotype previously described for a few other AmpC variants (13, 341).

Properties of extended-spectrum cephalosporinases


Chromosomal AmpC Enzymes

For enteric organisms with the potential for high-level AmpC β-lactamase production by mutation, the development of resistance upon therapy is a concern. In a landmark study of 129 patients with bacteremia due to Enterobacter spp., Chow et al. identified 6 out of 31 patients treated with broad-spectrum cephalosporins who developed decreased susceptibility (cephalosporin MIC posttherapy of >16 μg/ml) and augmented β-lactamase production after treatment with cefotaxime, ceftazidime, or ceftizoxime, a much higher frequency (19%) than that for the emergence of resistance to aminoglycosides or other β-lactams (58). A subsequent study of 477 patients with initially susceptible Enterobacter spp. also found that 19% of patients receiving broad-spectrum cephalosporins developed resistant Enterobacter isolates and that resistance was more likely to appear if the original isolate came from blood (156). A recent study evaluated 732 patients with infections due to Enterobacter spp., S. marcescens, C. freundii, or M. morganii (57). Resistance emerged in 11 of 218 patients (5%) treated with broad-spectrum cephalosporins, more often in Enterobacter spp. (10/121, or 8.3%) than in C. freundii (1/39 or 2.6%) and not at all in 37 infections with S. marcescens or 21 infections with M. morganii. A single patient died as a result. Biliary tract infection with malignant bile duct obstruction was identified as being a risk factor for resistance development. Combination therapy did not prevent resistance emergence. The clonal spread of AmpC-hyperproducing E. cloacae strains to other patients has been documented at some medical centers but seems not to be a widespread problem (253). Once selected, however, hyperproduction is stable so that 30 to 40% of E. cloacae isolates from inpatients in the United Kingdom (188) and 15 to 25% of North American isolates (147) currently have this mechanism of β-lactam resistance.

These studies did not address mortality, but in a study of 46 patients initially infected with cephalosporin-susceptible Enterobacter spp. that became resistant matched to 113 control patients with persistently susceptible isolates of the same organism, the patients were more likely to die as a result of the infection (26% versus 13%), had a longer hospital stay, and sustained higher attributable hospital charges (63).

Despite normally low-level expression of AmpC β-lactamase in E. coli, high-level producers have been identified in clinical specimens, typically as cefoxitin-resistant isolates with stronger AmpC promoters or mutations that destabilize the normal AmpC attenuator (32, 51, 52, 94, 241, 242, 297). For example, the screening of 29,323 clinical isolates of E. coli collected in 1999 to 2000 from 12 hospitals in Canada identified 232 strains that were resistant to cefoxitin, with 182 of them identified as being unique by pulsed-field gel electrophoresis (220). PCR and sequencing identified 51 different promoter or attenuator variants (323). In a few strains, the integration of an insertion element created a new and stronger ampC promoter (146, 220). Such strains are not only resistant to cefoxitin but also typically resistant to ampicillin, ticarcillin, cephalothin, and β-lactam combinations with clavulanic acid and have reduced susceptibility or are even resistant to expanded-spectrum cephalosporins. Some E. coli strains with up promoter mutations have alterations in blaAmpC as well, expanding its resistance spectrum (193). An accompanying loss of outer membrane porins can augment the resistance phenotype further (195). These strains usually remain susceptible to cefepime and imipenem (201) but may become ertapenem resistant. At least for the E. coli strains isolated in France that overproduce chromosomal AmpC β-lactamase, most belong to phylogenetic group A, a group which fortunately lacks a number of virulence factors (62). E. coli strains overexpressing AmpC β-lactamase have also been isolated from calves with diarrhea (40), so such strains can be veterinary as well as human pathogens.

Acinetobacter spp. have a variety of acquired β-lactamases, but the oxyimino-β-lactam resistance seen increasingly in this opportunistic pathogen is often attributable to its AmpC enzyme (42). The enzyme is normally expressed at low levels and is not inducible, but overexpression occurs with the upstream insertion of an insertion element (ISAba1) common in A. baumannii, which provides an efficient promoter for the blaAmpC gene (61, 122, 292). The overexpression of AmpC β-lactamase plays a role in the increasing resistance of P. aeruginosa as well, although acquired β-lactamases, pumps, and porins are also important (53, 186, 245). Because P. aeruginosa has at least three ampD genes (151, 290), enhanced AmpC production occurs in a stepwise fashion, producing resistance to antipseudomonas penicillins, oxyiminocephalosporins, and, with full derepression, cefepime (151, 186).

Plasmid-Mediated AmpC Enzymes

Plasmid-mediated AmpC β-lactamases have been found worldwide but are less common than extended-spectrum β-lactamases (ESBLs), and in E. coli, they appear to be less often a cause of cefoxitin resistance than an increased production of chromosomal AmpC β-lactamase (Table (Table8).8). The β-lactamase CMY-2 has the broadest geographic spread and is an important cause of β-lactam resistance in nontyphoid Salmonella strains in many countries (81, 213). In the United States between 1996 and 1998, 13 ceftriaxone-resistant but otherwise unrelated Salmonella strains were isolated from symptomatic patients in eight states and were found to produce CMY-2 β-lactamase (50, 80). Such strains have been isolated from cats, cattle, chickens, dogs, horses, pigs, and turkeys (112, 340), and in one case, they were spread from infected calves to the farmer's 12-year-old son (89). Another small outbreak was traced to contaminated pet dog treats containing dried beef (259). In a survey of U.S. isolates from 2000, 44 of 1,378 (3.2%) nontyphoid Salmonella strains were positive for CMY β-lactamase by PCR, as were 7 Shigella sonnei and 4 E. coli O157:H7 strains (339). When treatment is indicated, fluoroquinolones are as effective as they are with pansusceptible Salmonella strains (74), but a few strains that are resistant to both fluoroquinolones and extended-spectrum cephalosporins have appeared (338). CMY-2-producing nontyphoid Salmonella strains have been isolated in other countries, as have Salmonella strains producing AmpC β-lactamases CMY-4, CMY-7, ACC-1, and DHA-1 (19, 135, 213, 314). CMY producers belong to several serogroups, with Salmonella enterica serovars Typhimurium and Newport (113) being the most common. CMY-2 has also been responsible for ceftriaxone resistance in a Shigella sonnei outbreak (136).

Population studies of plasmid-mediated AmpC β-lactamases

Most other strains with plasmid-mediated AmpC enzymes have been isolated from patients after several days of hospitalization, but recently, AmpC-producing isolates in cultures from long-term care facilities, rehabilitation centers, and outpatient clinics have been reported (117, 210). Risk factors for bloodstream infections caused by AmpC-producing strains of K. pneumoniae include long hospital stay, care in an intensive care unit (ICU), central venous catheterization, need for an indwelling urinary catheter, and prior administration of antibiotics, especially broad-spectrum cephalosporins and β-lactamase inhibitor combinations, and are thus similar to risk factors for infection by ESBL-producing K. pneumoniae strains (244, 347). Patients with leukemia (244, 303), cancer (134, 222, 244), and organ transplantation (222) have been affected. Outbreaks with MIR-1 (11 patients) (248), a BIL-1 (CMY-2)-like enzyme (5 patients) (222), CMY-16 (8 patients) (69), ACC-1 (13 patients [227] and 19 patients [240]), ACT-1 (17 patients) (41), and a LAT-type β-lactamase (6 patients) (103) have been reported. Sources of positive cultures included urine, blood, wounds, sputum, and stool. A CMY-2-producing E. coli isolate caused meningitis in a neonate (86). Often, the strain with a plasmid-mediated AmpC enzyme also produced other β-lactamases such as TEM-1 or an ESBL such as SHV-5, the presence of which may complicate detection of the AmpC phenotype.


There are presently no CLSI or other approved criteria for AmpC detection (76). Organisms producing enough AmpC β-lactamase will typically give a positive ESBL screening test but fail the confirmatory test involving increased sensitivity with clavulanic acid (29, 304). This phenotype is not, however, specific for an AmpC producer, since it can occur with certain complex TEM mutants (277), OXA-type ESBLs, and carbapenemases and in strains with high levels of TEM-1 β-lactamase. Except for non-lactose-fermenting gram-negative organisms intrinsically resistant to cephamycins, resistance to cefoxitin as well as oxyimino-β-lactams is suggestive of an AmpC enzyme, but it is not specific since cefoxitin resistance can also be produced by certain carbapenemases (262) and a few class A β-lactamases (331) and by decreased levels of production of outer membrane porins in both K. pneumoniae and E. coli (124, 125, 202, 203). Furthermore, some plasmid-mediated AmpC strains test susceptible to ceftriaxone, cefotaxime, and ceftazidime by current CLSI criteria and could easily be overlooked (315). Other confirmatory tests are needed (Table (Table99).

Laboratory tests for AmpC detection

The three-dimensional test was designed to detect both AmpC and ESBL production. In the “indirect” form used for AmpC detection, a conventional disk diffusion susceptibility assay is carried out with a susceptible strain, such as E. coli ATCC 25922, as the lawn and a suspension of the test organism, which is added to a circular slit in the agar 3 mm from a disk containing cefoxitin or some other agent. Distortion of the zone of inhibition indicates a positive test, as cefoxitin is hydrolyzed by the presence of an AmpC enzyme (319). In subsequent modifications, a radial slit was employed, and rather than using intact cells, the test organisms were concentrated by centrifugation, and the pellet was freeze-thawed five to seven times to release β-lactamase (66, 200). Direct spot inoculation of the test organism 7 to 8 mm from the cefoxitin disk has also been used successfully (295), as has a heavy inoculum streaked radially from the cefoxitin disk on the agar surface without using a slit (169), although the latter procedure missed some CMY-2- and DHA-1-producing strains. In a further modification, the test organism has been applied to a filter paper disk containing Tris-EDTA to enhance membrane permeability, with the disk then placed onto a lawn of E. coli ATCC 25922 adjacent to a cefoxitin disk (35). In every case, the presence of an AmpC β-lactamase is indicated by a distortion of the inhibition zone around the cefoxitin disk. Organisms producing a carbapenemase can mimic an AmpC β-lactamase in cefoxitin inactivation, so reduced carbapenem susceptibility is important to exclude since otherwise, a carbapenem might be selected for therapy (35).

A variation on the three-dimensional test is to plate the sensitive indicator strain on agar containing 4 μg/ml cefoxitin and add the freeze-thawed cell extract to a well in the plate. After incubation, growth around the well indicates the presence of a cefoxitin-hydrolyzing enzyme (230). This method is reported to be just as sensitive and specific as the three-dimensional test for AmpC detection, is easier to perform, and allows multiple samples per plate to be tested.

Another approach for AmpC detection is the use of an inhibitor for this β-lactamase class analogous to the use of clavulanic acid in a confirmatory test for class A ESBLs. The β-lactams LN-2-128, Ro 48-1220, and Syn 2190 have been evaluated for this purpose, with the best results from the combination of Syn 2190 and cefotetan, which was 100% specific and 91% sensitive in AmpC β-lactamase detection (36, 37). Unfortunately, these inhibitors are not commercially available.

A double-disk test with a 500-μg cloxacillin disk placed between disks containing ceftazidime and cefotaxime on a lawn of the test organism has been explored using 15 AmpC-producing strains. All showed synergy. A central cefoxitin disk produced synergy with ceftazidime and cefotaxime only with ACC-1 β-lactamase and also revealed the inducibility of enzymes such as DHA-1 (280).

Etest strips with a gradient of cefotetan or cefoxitin on one half and the same combined with a constant concentration of cloxacillin on the other half have been evaluated for AmpC detection (38). Either a reduction in cephamycin MIC of at least three dilutions, deformation of the ellipse of inhibition, or a “phantom zone” was interpreted as a positive test. With almost 500 test strains, the overall sensitivity and specificity were 88 to 93% (83).

Boronic acids have long been known as AmpC inhibitors (28). Various boronic acid derivatives have been either added to a blank disk placed near a β-lactam disk or added to the β-lactam disk for comparison with an unmodified β-lactam disk. For example, Yagi et al. found that a disk potentiation test utilizing a ≥5-mm enhancement of the zone of inhibition around a ceftazidime or cefotaxime disk when 300 μg 3-aminophenylboronic acid was added reliably detected all AmpC varieties tested but was negative with strains producing ESBLs and carbapenemases (344), findings that have been confirmed with a different set of strains (143). Strains producing both a plasmid-mediated AmpC β-lactamase and an ESBL have been reliably detected (301), but such a test cannot differentiate between an AmpC enzyme encoded on a plasmid or on the chromosome. Specificity is also a concern since boronic acids also enhance the sensitivity of strains making a non-AmpC enzyme, class A KPC β-lactamase (250, 324).

Phenotypic tests cannot distinguish among the various families of plasmid-mediated AmpC enzymes and may also overlook chromosomally determined AmpC β-lactamases with an extended spectrum (193). For these purposes, and as the current “gold standard” for plasmid-mediated AmpC β-lactamase detection, multiplex PCR has been developed by utilizing six primer pairs (251) to which a seventh pair for CFE-1 β-lactamase (229) could be added. Chromosomal blaAmpC did not interfere in testing strains of K. pneumoniae, E. coli, P. mirabilis, or S. enterica but could be a problem with blaAmpC genes in one of the genera from which the plasmid-mediated enzymes are derived. (Table (Table5).5). A multiplex asymmetric PCR-based microarray method for detecting genes for both plasmid-mediated AmpC β-lactamases and mutations responsible for the ESBL phenotype in blaSHV has been described (351). Perfection of a PCR array technology may ultimately allow the automation of AmpC β-lactamase detection for a suitably equipped clinical laboratory.

Is the recognition of plasmid-mediated AmpC enzymes necessary for the average laboratory? Therapeutic and infection control considerations argue that it is. AmpC-producing isolates may appear to be susceptible in vitro to some cephalosporins and aztreonam yet fail to respond if those agents are used so that a specific test for their presence is necessary (318). Compared to ESBL producers, isolates producing AmpC β-lactamase are resistant to additional β-lactams and insusceptible to currently available β-lactamase inhibitors and have the potential for developing resistance to carbapenems. Furthermore, plasmid mediation of AmpC carries the threat of spread to other organisms within a hospital or geographic region. Time will tell whether these considerations will still apply if cephalosporin breakpoints are significantly lowered so that decisions about therapy become based only on low-MIC susceptibility.


Strains with ampC genes are often resistant to multiple agents, making the selection of an effective antibiotic difficult. β-Lactam/β-lactamase inhibitor combinations and most cephalosporins and penicillins should be avoided because of in vitro resistance, the potential for AmpC induction or selection of high-enzyme-level mutants, and documented poor clinical outcomes with ceftazidime, cefotaxime (244), and, in an animal model, piperacillin-tazobactam (329). Whether cefepime can be used is unsettled. Cefepime is a poor inducer of AmpC β-lactamase, rapidly penetrates through the outer cell membrane, and is little hydrolyzed by the enzyme (232, 283), so many AmpC-producing organisms test cefepime susceptible with a conventional inoculum (see Table Table66 for examples). If a 100-fold-higher inoculum is used, however, cefepime MICs increase dramatically for some AmpC producers, suggesting caution in its use (154, 256), and some strains are frankly resistant (238). In a pneumonia model using guinea pigs, cefepime, imipenem, and meropenem were equally effective against a porin-deficient K. pneumoniae strain producing FOX-5 β-lactamase (255). Also, in a rat pneumonia model with a K. pneumoniae strain producing ACT-1, β-lactam therapy with imipenem, meropenem, ertapenem, or cefepime gave equivalent results, even if the test strain was porin deficient (243). However, in a mouse pneumonia model with a porin-deficient strain of K. pneumoniae producing CMY-2 β-lactamase, survival with cefepime therapy was no better than that without antibiotic and significantly inferior to that with imipenem treatment (256). Nonetheless, cefepime has cured infections due to multiply resistant Enterobacter spp. including those with reduced susceptibility to ceftazidime (286), and in a prospective, randomized study of ICU patients with nosocomial pneumonia having P. aeruginosa as the most common isolate, cefepime proved to be just as effective as imipenem (350). The jury is still out, but cefepime seems to be an exception to the recommendation to avoid all cephalosporin therapy even if an AmpC-producing isolate tests susceptible to an individual agent.

Temocillin, a 6-α-methoxy derivative of ticarcillin, is active in vitro against many AmpC-producing Enterobacteriaceae whether the enzyme is determined by chromosomal or plasmid genes and is also active against ESBL producers (108, 187), but clinical experience is limited, and it is available in only a few countries. Amdinocillin is also effective in vitro against AmpC-producing E. coli strains but shows a marked inoculum effect unless clavulanic acid is present (43) and is also not available in the United States.

Carbapenem therapy has usually been successful (244) but has also been followed by the emergence of carbapenem-resistant K. pneumoniae associated with ACT-1 β-lactamase production and outer membrane porin loss (3, 41, 152). Reduced imipenem susceptibility (MIC 8 to 32 μg/ml) has also been reported in porin-deficient clinical isolates of K. pneumoniae making AmpC enzymes ACC-1 (34), CMY-2 (171), CMY-4 (49), DHA-1 (171), or an uncharacterized AmpC-type enzyme (246). The same scenario has been described for clinical isolates of E. aerogenes (59, 71, 317, 325, 349), E. cloacae (168), and C. freundii (192) as well as laboratory mutants (131, 270, 327). In E. coli, reduced carbapenem susceptibility or frank resistance (imipenem MIC of 8 to 128 μg/ml) in porin-deficient clinical isolates producing CMY-2 (183) or CMY-4 (303) has been described, while a Salmonella enterica strain lacking a porin and making CMY-4 reached an imipenem MIC of 32 μg/ml (8).

If the isolate is susceptible, fluoroquinolone therapy is an option especially for non-life-threatening infections such as urinary tract infection. Tigecycline is another option. It had good activity in vitro against 88% of AmpC-hyperproducing isolates of E. coli, Enterobacter spp., Klebsiella spp., and Citrobacter spp. from the United Kingdom (130), but few P. aeruginosa isolates (282) and, in some centers, only 22% of nosocomial Acinetobacter isolates (231) were tigecycline susceptible.


AmpC β-lactamases are clinically important cephalosporinases encoded on the chromosome of many Enterobacteriaceae and a few other organisms where they mediate resistance to cephalothin, cefazolin, cefoxitin, most penicillins, and β-lactamase inhibitor/β-lactam combinations. In many bacteria, AmpC enzymes are inducible and can be expressed at high levels by mutation. Overexpression confers resistance to broad-spectrum cephalosporins including cefotaxime, ceftazidime, and ceftriaxone and is a problem especially in infections due to E. aerogenes and E. cloacae, where an isolate initially susceptible to these agents may become resistant upon therapy. Transmissible plasmids have acquired genes for AmpC enzymes, which consequently can now appear in bacteria lacking or poorly expressing a chromosomal blaAmpC gene, such as E. coli, K. pneumoniae, and P. mirabilis. Resistance due to plasmid-mediated AmpC enzymes is less common than ESBL production in most parts of the world but may be both harder to detect and broader in spectrum. AmpC enzymes encoded by both chromosomal and plasmid genes are also evolving to hydrolyze broad-spectrum cephalosporins more efficiently. Techniques to identify AmpC β-lactamase-producing isolates are available but are still evolving and are not yet optimized for the clinical laboratory, which probably now underestimates this resistance mechanism. Carbapenems can usually be used to treat infections due to AmpC-producing bacteria, but carbapenem resistance can arise in some organisms by mutations that reduce influx (outer membrane porin loss) or enhance efflux (efflux pump activation).


1. Abraham, E. P., and E. Chain. 1940. An enzyme from bacteria able to destroy penicillin. Nature 146:837. [PubMed]
2. Adler, H., L. Fenner, P. Walter, D. Hohler, E. Schultheiss, S. Oezcan, and R. Frei. 2008. Plasmid-mediated AmpC β-lactamases in Enterobacteriaceae lacking inducible chromosomal ampC genes: prevalence at a Swiss university hospital and occurrence of the different molecular types in Switzerland. J. Antimicrob. Chemother. 61:457-458. [PubMed]
3. Ahmad, M., C. Urban, N. Mariano, P. A. Bradford, E. Calcagni, S. J. Projan, K. Bush, and J. J. Rahal. 1999. Clinical characteristics and molecular epidemiology associated with imipenem-resistant Klebsiella pneumoniae. Clin. Infect. Dis. 29:352-355. [PubMed]
4. Ahmed, A. M., and T. Shimamoto. 2008. Emergence of a cefepime- and cefpirome-resistant Citrobacter freundii clinical isolate harbouring a novel chromosomally encoded AmpC β-lactamase, CMY-37. Int. J. Antimicrob. Agents 32:256-261. [PubMed]
5. Alksne, L. E., and B. A. Rasmussen. 1997. Expression of the AsbA1, OXA-12, and AsbM1 β-lactamases in Aeromonas jandaei AER 14 is coordinated by a two-component regulon. J. Bacteriol. 179:2006-2013. [PMC free article] [PubMed]
6. Alvarez, M., J. H. Tran, N. Chow, and G. A. Jacoby. 2004. Epidemiology of conjugative plasmid-mediated AmpC β-lactamases in the United States. Antimicrob. Agents Chemother. 48:533-537. [PMC free article] [PubMed]
7. Ambler, R. P. 1980. The structure of β-lactamases. Philos. Trans. R. Soc. Lond. B 289:321-331. [PubMed]
8. Armand-Lefèvre, L., V. Leflon-Guibout, J. Bredin, F. Barguellil, A. Amor, J. M. Pagès, and M. H. Nicolas-Chanoine. 2003. Imipenem resistance in Salmonella enterica serovar Wien related to porin loss and CMY-4 β-lactamase production. Antimicrob. Agents Chemother. 47:1165-1168. [PMC free article] [PubMed]
9. Avison, M. B., P. M. Bennett, and T. R. Walsh. 2000. β-Lactamase expression in Plesiomonas shigelloides. J. Antimicrob. Chemother. 45:877-880. [PubMed]
10. Avison, M. B., P. Niumsup, K. Nurmahomed, T. R. Walsh, and P. M. Bennett. 2004. Role of the ‘cre/blr-tag’ DNA sequence in regulation of gene expression by the Aeromonas hydrophila β-lactamase regulator, BlrA. J. Antimicrob. Chemother. 53:197-202. [PubMed]
11. Avison, M. B., P. Niumsup, T. R. Walsh, and P. M. Bennett. 2000. Aeromonas hydrophila AmpH and CepH β-lactamases: derepressed expression in mutants of Escherichia coli lacking creB. J. Antimicrob. Chemother. 46:695-702. [PubMed]
12. Avison, M. B., S. Underwood, A. Okazaki, T. R. Walsh, and P. M. Bennett. 2004. Analysis of AmpC β-lactamase expression and sequence in biochemically atypical ceftazidime-resistant Enterobacteriaceae from paediatric patients. J. Antimicrob. Chemother. 53:584-591. [PubMed]
13. Babini, G. S., F. Danel, S. D. Munro, P. A. Micklesen, and D. M. Livermore. 1998. Unusual tazobactam-sensitive AmpC β-lactamase from two Escherichia coli isolates. J. Antimicrob. Chemother. 41:115-118. [PubMed]
14. Barlow, M., and B. G. Hall. 2003. Experimental prediction of the evolution of cefepime resistance from the CMY-2 AmpC β-lactamase. Genetics 164:23-29. [PubMed]
15. Barlow, M., and B. G. Hall. 2002. Origin and evolution of the AmpC β-lactamases of Citrobacter freundii. Antimicrob. Agents Chemother. 46:1190-1198. [PMC free article] [PubMed]
16. Barnaud, G., G. Arlet, C. Verdet, O. Gaillot, P. H. Lagrange, and A. Philippon. 1998. Salmonella enteritidis: AmpC plasmid-mediated inducible β-lactamase (DHA-1) with an ampR gene from Morganella morganii. Antimicrob. Agents Chemother. 42:2352-2358. [PMC free article] [PubMed]
17. Barnaud, G., Y. Benzerara, J. Gravisse, L. Raskine, M. J. Sanson-Le Pors, R. Labia, and G. Arlet. 2004. Selection during cefepime treatment of a new cephalosporinase variant with extended-spectrum resistance to cefepime in an Enterobacter aerogenes clinical isolate. Antimicrob. Agents Chemother. 48:1040-1042. [PMC free article] [PubMed]
18. Barnaud, G., R. Labia, L. Raskine, M. J. Sanson-Le Pors, A. Philippon, and G. Arlet. 2001. Extension of resistance to cefepime and cefpirome associated to a six amino acid deletion in the H-10 helix of the cephalosporinase of an Enterobacter cloacae clinical isolate. FEMS Microbiol. Lett. 195:185-190. [PubMed]
19. Batchelor, M., K. L. Hopkins, E. J. Threlfall, F. A. Clifton-Hadley, A. D. Stallwood, R. H. Davies, and E. Liebana. 2005. Characterization of AmpC-mediated resistance in clinical Salmonella isolates recovered from humans during the period 1992 to 2003 in England and Wales. J. Clin. Microbiol. 43:2261-2265. [PMC free article] [PubMed]
20. Bauernfeind, A., Y. Chong, and S. Schweighart. 1989. Extended broad spectrum β-lactamase in Klebsiella pneumoniae including resistance to cephamycins. Infection 17:316-321. [PubMed]
21. Bauernfeind, A., I. Schneider, R. Jungwirth, H. Sahly, and U. Ullmann. 1999. A novel type of AmpC β-lactamase, ACC-1, produced by a Klebsiella pneumoniae strain causing nosocomial pneumonia. Antimicrob. Agents Chemother. 43:1924-1931. [PMC free article] [PubMed]
22. Bauernfeind, A., I. Stemplinger, R. Jungwirth, and H. Giamarellou. 1996. Characterization of the plasmidic β-lactamase CMY-2, which is responsible for cephamycin resistance. Antimicrob. Agents Chemother. 40:221-224. [PMC free article] [PubMed]
23. Bauernfeind, A., I. Stemplinger, R. Jungwirth, R. Wilhelm, and Y. Chong. 1996. Comparative characterization of the cephamycinase blaCMY-1 gene and its relationship with other β-lactamase genes. Antimicrob. Agents Chemother. 40:1926-1930. [PMC free article] [PubMed]
24. Baumann, M., H. Simon, K. H. Schneider, H. J. Danneel, U. Küster, and F. Giffhorn. 1989. Susceptibility of Rhodobacter sphaeroides to β-lactam antibiotics: isolation and characterization of a periplasmic β-lactamase (cephalosporinase). J. Bacteriol. 171:308-313. [PMC free article] [PubMed]
25. Bauvois, C., A. S. Ibuka, A. Celso, J. Alba, Y. Ishii, J. M. Frère, and M. Galleni. 2005. Kinetic properties of four plasmid-mediated AmpC β-lactamases. Antimicrob. Agents Chemother. 49:4240-4246. [PMC free article] [PubMed]
26. Beceiro, A., F. J. Pérez-Llarena, A. Pérez, M. Tomás, A. Fernández, S. Mallo, R. Villanueva, and G. Bou. 2007. Molecular characterization of the gene encoding a new AmpC β-lactamase in Acinetobacter baylyi. J. Antimicrob. Chemother. 59:996-1000. [PubMed]
27. Beckstrom-Sternberg, S. M., R. K. Auerbach, S. Godbole, J. V. Pearson, J. S. Beckstrom-Sternberg, Z. Deng, C. Munk, K. Kubota, Y. Zhou, D. Bruce, J. Noronha, R. H. Scheuermann, A. Wang, X. Wei, J. Wang, J. Hao, D. M. Wagner, T. S. Brettin, N. Brown, P. Gilna, and P. S. Keim. 2007. Complete genomic characterization of a pathogenic A.II strain of Francisella tularensis subspecies tularensis. PLoS ONE 2:e947. [PMC free article] [PubMed]
28. Beesley, T., N. Gascoyne, V. Knott-Hunziker, S. Petursson, S. G. Waley, B. Jaurin, and T. Grundstrom. 1983. The inhibition of class C β-lactamases by boronic acids. Biochem. J. 209:229-233. [PubMed]
29. Bell, J. M., M. Chitsaz, J. D. Turnidge, M. Barton, L. J. Walters, and R. N. Jones. 2007. Prevalence and significance of a negative extended-spectrum β-lactamase (ESBL) confirmation test result after a positive ESBL screening test result for isolates of Escherichia coli and Klebsiella pneumoniae: results from the SENTRY Asia-Pacific surveillance program. J. Clin. Microbiol. 45:1478-1482. [PMC free article] [PubMed]
30. Bellais, S., L. Poirel, N. Fortineau, J. W. Decousser, and P. Nordmann. 2001. Biochemical-genetic characterization of the chromosomally encoded extended-spectrum class A β-lactamase from Rahnella aquatilis. Antimicrob. Agents Chemother. 45:2965-2968. [PMC free article] [PubMed]
31. Bergström, S., F. P. Lindberg, O. Olsson, and S. Normark. 1983. Comparison of the overlapping frd and ampC operons of Escherichia coli with the corresponding DNA sequences in other gram-negative bacteria. J. Bacteriol. 155:1297-1305. [PMC free article] [PubMed]
32. Bergstrom, S., and S. Normark. 1979. β-Lactam resistance in clinical isolates of Escherichia coli caused by elevated production of the ampC-mediated chromosomal β-lactamase. Antimicrob. Agents Chemother. 16:427-433. [PMC free article] [PubMed]
33. Bergström, S., O. Olsson, and S. Normark. 1982. Common evolutionary origin of chromosomal beta-lactamase genes in enterobacteria. J. Bacteriol. 150:528-534. [PMC free article] [PubMed]
34. Bidet, P., B. Burghoffer, V. Gautier, N. Brahimi, P. Mariani-Kurkdjian, A. El-Ghoneimi, E. Bingen, and G. Arlet. 2005. In vivo transfer of plasmid-encoded ACC-1 AmpC from Klebsiella pneumoniae to Escherichia coli in an infant and selection of impermeability to imipenem in K. pneumoniae. Antimicrob. Agents Chemother. 49:3562-3565. [PMC free article] [PubMed]
35. Black, J. A., E. S. Moland, and K. S. Thomson. 2005. AmpC disk test for detection of plasmid-mediated AmpC β-lactamases in Enterobacteriaceae lacking chromosomal AmpC β-lactamases. J. Clin. Microbiol. 43:3110-3113. [PMC free article] [PubMed]
36. Black, J. A., K. S. Thomson, J. D. Buynak, and J. D. Pitout. 2005. Evaluation of β-lactamase inhibitors in disk tests for detection of plasmid-mediated AmpC β-lactamases in well-characterized clinical strains of Klebsiella spp. J. Clin. Microbiol. 43:4168-4171. [PMC free article] [PubMed]
37. Black, J. A., K. S. Thomson, and J. D. Pitout. 2004. Use of β-lactamase inhibitors in disk tests to detect plasmid-mediated AmpC β-lactamases. J. Clin. Microbiol. 42:2203-2206. [PMC free article] [PubMed]
38. Bolmström, A., A. Engelhardt, L. Bylund, P. Ho, and Å. Karlsson. 2006. Evaluation of two new Etest strips for AmpC detection, abstr. D-0451. Abstr. 46th Intersci. Conf. Antimicrob. Agents Chemother.
39. Bou, G., and J. Martinez-Beltran. 2000. Cloning, nucleotide sequencing, and analysis of the gene encoding an AmpC β-lactamase in Acinetobacter baumannii. Antimicrob. Agents Chemother. 44:428-432. [PMC free article] [PubMed]
40. Bradford, P. A., P. J. Petersen, I. M. Fingerman, and D. G. White. 1999. Characterization of expanded-spectrum cephalosporin resistance in E. coli isolates associated with bovine calf diarrhoeal disease. J. Antimicrob. Chemother. 44:607-610. [PubMed]
41. Bradford, P. A., C. Urban, N. Mariano, S. J. Projan, J. J. Rahal, and K. Bush. 1997. Imipenem resistance in Klebsiella pneumoniae is associated with the combination of ACT-1, a plasmid-mediated AmpC β-lactamase, and the loss of an outer membrane protein. Antimicrob. Agents Chemother. 41:563-569. [PMC free article] [PubMed]
42. Bratu, S., D. Landman, D. A. Martin, C. Georgescu, and J. Quale. 2008. Correlation of antimicrobial resistance with β-lactamases, the OmpA-like porin, and efflux pumps in clinical isolates of Acinetobacter baumannii endemic to New York City. Antimicrob. Agents Chemother. 52:2999-3005. [PMC free article] [PubMed]
43. Brenwald, N. P., J. Andrews, and A. P. Fraise. 2006. Activity of mecillinam against AmpC β-lactamase-producing Escherichia coli. J. Antimicrob. Chemother. 58:223-224. [PubMed]
44. Brenwald, N. P., G. Jevons, J. Andrews, L. Ang, and A. P. Fraise. 2005. Disc methods for detecting AmpC β-lactamase-producing clinical isolates of Escherichia coli and Klebsiella pneumoniae. J. Antimicrob. Chemother. 56:600-601. [PubMed]
45. Bulychev, A., and S. Mobashery. 1999. Class C β-lactamases operate at the diffusion limit for turnover of their preferred cephalosporin substrates. Antimicrob. Agents Chemother. 43:1743-1746. [PMC free article] [PubMed]
46. Burman, L. G., J. T. Park, E. B. Lindström, and H. G. Boman. 1973. Resistance of Escherichia coli to penicillins: identification of the structural gene for the chromosomal penicillinase. J. Bacteriol. 116:123-130. [PMC free article] [PubMed]
47. Bush, K., G. A. Jacoby, and A. A. Medeiros. 1995. A functional classification scheme for β-lactamases and its correlation with molecular structure. Antimicrob. Agents Chemother. 39:1211-1233. [PMC free article] [PubMed]
48. Bush, K., C. Macalintal, B. A. Rasmussen, V. J. Lee, and Y. Yang. 1993. Kinetic interactions of tazobactam with β-lactamases from all major structural classes. Antimicrob. Agents Chemother. 37:851-858. [PMC free article] [PubMed]
49. Cao, V. T., G. Arlet, B. M. Ericsson, A. Tammelin, P. Courvalin, and T. Lambert. 2000. Emergence of imipenem resistance in Klebsiella pneumoniae owing to combination of plasmid-mediated CMY-4 and permeability alteration. J. Antimicrob. Chemother. 46:895-900. [PubMed]
50. Carattoli, A., F. Tosini, W. P. Giles, M. E. Rupp, S. H. Hinrichs, F. J. Angulo, T. J. Barrett, and P. D. Fey. 2002. Characterization of plasmids carrying CMY-2 from expanded-spectrum cephalosporin-resistant Salmonella strains isolated in the United States between 1996 and 1998. Antimicrob. Agents Chemother. 46:1269-1272. [PMC free article] [PubMed]
51. Caroff, N., E. Espaze, I. Berard, H. Richet, and A. Reynaud. 1999. Mutations in the ampC promoter of Escherichia coli isolates resistant to oxyiminocephalosporins without extended spectrum β-lactamase production. FEMS Microbiol. Lett. 173:459-465. [PubMed]
52. Caroff, N., E. Espaze, D. Gautreau, H. Richet, and A. Reynaud. 2000. Analysis of the effects of −42 and −32 ampC promoter mutations in clinical isolates of Escherichia coli hyperproducing ampC. J. Antimicrob. Chemother. 45:783-788. [PubMed]
53. Cavallo, J. D., R. Fabre, F. Leblanc, M. H. Nicolas-Chanoine, and A. Thabaut. 2000. Antibiotic susceptibility and mechanisms of β-lactam resistance in 1310 strains of Pseudomonas aeruginosa: a French multicentre study (1996). J. Antimicrob. Chemother. 46:133-136. [PubMed]
54. Chen, Y., G. Minasov, T. A. Roth, F. Prati, and B. K. Shoichet. 2006. The deacylation mechanism of AmpC β-lactamase at ultrahigh resolution. J. Am. Chem. Soc. 128:2970-2976. [PMC free article] [PubMed]
55. Chen, Y. T., T. L. Lauderdale, T. L. Liao, Y. R. Shiau, H. Y. Shu, K. M. Wu, J. J. Yan, I. J. Su, and S. F. Tsai. 2007. Sequencing and comparative genomic analysis of pK29, a 269-kilobase conjugative plasmid encoding CMY-8 and CTX-M-3 β-lactamases in Klebsiella pneumoniae. Antimicrob. Agents Chemother. 51:3004-3007. [PMC free article] [PubMed]
56. Chien, M., I. Morozova, S. Shi, H. Sheng, J. Chen, S. M. Gomez, G. Asamani, K. Hill, J. Nuara, M. Feder, J. Rineer, J. J. Greenberg, V. Steshenko, S. H. Park, B. Zhao, E. Teplitskaya, J. R. Edwards, S. Pampou, A. Georghiou, I. C. Chou, W. Iannuccilli, M. E. Ulz, D. H. Kim, A. Geringer-Sameth, C. Goldsberry, P. Morozov, S. G. Fischer, G. Segal, X. Qu, A. Rzhetsky, P. Zhang, E. Cayanis, P. J. De Jong, J. Ju, S. Kalachikov, H. A. Shuman, and J. J. Russo. 2004. The genomic sequence of the accidental pathogen Legionella pneumophila. Science 305:1966-1968. [PubMed]
57. Choi, S. H., J. E. Lee, S. J. Park, S. O. Lee, J. Y. Jeong, M. N. Kim, J. H. Woo, and Y. S. Kim. 2008. Emergence of antibiotic resistance during therapy for infections caused by Enterobacteriaceae producing AmpC β-lactamase: implications for antibiotic use. Antimicrob. Agents Chemother. 52:995-1000. [PMC free article] [PubMed]
58. Chow, J. W., M. J. Fine, D. M. Shlaes, J. P. Quinn, D. C. Hooper, M. P. Johnson, R. Ramphal, M. M. Wagener, D. K. Miyashiro, and V. L. Yu. 1991. Enterobacter bacteremia: clinical features and emergence of antibiotic resistance during therapy. Ann. Intern. Med. 115:585-590. [PubMed]
59. Chow, J. W., and D. M. Shlaes. 1991. Imipenem resistance associated with the loss of a 40 kDa outer membrane protein in Enterobacter aerogenes. J. Antimicrob. Chemother. 28:499-504. [PubMed]
60. Cole, S. T. 1987. Nucleotide sequence and comparative analysis of the frd operon encoding the fumarate reductase of Proteus vulgaris. Extensive sequence divergence of the membrane anchors and absence of an frd-linked ampC cephalosporinase gene. Eur. J. Biochem. 167:481-488. [PubMed]
61. Corvec, S., N. Caroff, E. Espaze, C. Giraudeau, H. Drugeon, and A. Reynaud. 2003. AmpC cephalosporinase hyperproduction in Acinetobacter baumannii clinical strains. J. Antimicrob. Chemother. 52:629-635. [PubMed]
62. Corvec, S., A. Prodhomme, C. Giraudeau, S. Dauvergne, A. Reynaud, and N. Caroff. 2007. Most Escherichia coli strains overproducing chromosomal AmpC β-lactamase belong to phylogenetic group A. J. Antimicrob. Chemother. 60:872-876. [PubMed]
63. Cosgrove, S. E., K. S. Kaye, G. M. Eliopoulous, and Y. Carmeli. 2002. Health and economic outcomes of the emergence of third-generation cephalosporin resistance in Enterobacter species. Arch. Intern. Med. 162:185-190. [PubMed]
64. Coudron, P. E. 2005. Inhibitor-based methods for detection of plasmid-mediated AmpC β-lactamases in Klebsiella spp., Escherichia coli, and Proteus mirabilis. J. Clin. Microbiol. 43:4163-4167. [PMC free article] [PubMed]
65. Coudron, P. E., N. D. Hanson, and M. W. Climo. 2003. Occurrence of extended-spectrum and AmpC beta-lactamases in bloodstream isolates of Klebsiella pneumoniae: isolates harbor plasmid-mediated FOX-5 and ACT-1 AmpC beta-lactamases. J. Clin. Microbiol. 41:772-777. [PMC free article] [PubMed]
66. Coudron, P. E., E. S. Moland, and K. S. Thomson. 2000. Occurrence and detection of AmpC beta-lactamases among Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis isolates at a veterans medical center. J. Clin. Microbiol. 38:1791-1796. [PMC free article] [PubMed]
67. Crichlow, G. V., A. P. Kuzin, M. Nukaga, K. Mayama, T. Sawai, and J. R. Knox. 1999. Structure of the extended-spectrum class C β-lactamase of Enterobacter cloacae GC1, a natural mutant with a tandem tripeptide insertion. Biochemistry 38:10256-10261. [PubMed]
68. Curtis, N. A. C., R. L. Eisenstadt, C. Rudd, and A. J. White. 1986. Inducible type I β-lactamases of gram-negative bacteria and resistance to β-lactam antibiotics. J. Antimicrob. Chemother. 17:51-61. [PubMed]
69. D'Andrea, M. M., E. Nucleo, F. Luzzaro, T. Giani, R. Migliavacca, F. Vailati, V. Kroumova, L. Pagani, and G. M. Rossolini. 2006. CMY-16, a novel acquired AmpC-type β-lactamase of the CMY/LAT lineage in multifocal monophyletic isolates of Proteus mirabilis from northern Italy. Antimicrob. Agents Chemother. 50:618-624. [PMC free article] [PubMed]
70. da Silva Dias, R. C., A. A. Borges-Neto, G. I. D'Almeida Ferraiuoli, M. P. de-Oliveira, L. W. Riley, and B. M. Moreira. 2008. Prevalence of AmpC and other β-lactamases in enterobacteria at a large urban university hospital in Brazil. Diagn. Microbiol. Infect. Dis. 60:79-87. [PMC free article] [PubMed]
71. de Champs, C., C. Henquell, D. Guelon, D. Sirot, N. Gazuy, and J. Sirot. 1993. Clinical and bacteriological study of nosocomial infections due to Enterobacter aerogenes resistant to imipenem. J. Clin. Microbiol. 31:123-127. [PMC free article] [PubMed]
72. Decousser, J. W., L. Poirel, and P. Nordmann. 2001. Characterization of a chromosomally encoded extended-spectrum class A β-lactamase from Kluyvera cryocrescens. Antimicrob. Agents Chemother. 45:3595-3598. [PMC free article] [PubMed]
73. Deshpande, L. M., R. N. Jones, T. R. Fritsche, and H. S. Sader. 2006. Occurrence of plasmidic AmpC type β-lactamase-mediated resistance in Escherichia coli: report from the SENTRY Antimicrobial Surveillance Program (North America, 2004). Int. J. Antimicrob. Agents 28:578-581. [PubMed]
74. Devasia, R. A., J. K. Varma, J. Whichard, S. Gettner, A. B. Cronquist, S. Hurd, S. Segler, K. Smith, D. Hoefer, B. Shiferaw, F. J. Angulo, and T. F. Jones. 2005. Antimicrobial use and outcomes in patients with multidrug-resistant and pansusceptible Salmonella Newport infections, 2002-2003. Microb. Drug Resist. 11:371-377. [PubMed]
75. Ding, H., Y. Yang, Q. Lu, Y. Wang, Y. Chen, L. Deng, A. Wang, Q. Deng, H. Zhang, C. Wang, L. Liu, X. Xu, L. Wang, and X. Shen. 2008. The prevalence of plasmid-mediated AmpC β-lactamases among clinical isolates of Escherichia coli and Klebsiella pneumoniae from five children's hospitals in China. Eur. J. Clin. Microbiol. Infect. Dis. 27:915-921. [PubMed]
76. Doi, Y., and D. L. Paterson. 2007. Detection of plasmid-mediated class C β-lactamases. Int. J. Infect. Dis. 11:191-197. [PubMed]
77. Doi, Y., J. Wachino, M. Ishiguro, H. Kurokawa, K. Yamane, N. Shibata, K. Shibayama, K. Yokoyama, H. Kato, T. Yagi, and Y. Arakawa. 2004. Inhibitor-sensitive AmpC β-lactamase variant produced by an Escherichia coli clinical isolate resistant to oxyiminocephalosporins and cephamycins. Antimicrob. Agents Chemother. 48:2652-2658. [PMC free article] [PubMed]
78. Doloy, A., C. Verdet, V. Gautier, D. Decre, E. Ronco, A. Hammami, A. Philippon, and G. Arlet. 2006. Genetic environment of acquired blaACC-1 β-lactamase gene in Enterobacteriaceae isolates. Antimicrob. Agents Chemother. 50:4177-4181. [PMC free article] [PubMed]
79. Dubus, A., P. Ledent, J. Lamotte-Brasseur, and J. M. Frère. 1996. The roles of residues Tyr150, Glu272, and His314 in class C β-lactamases. Proteins 25:473-485. [PubMed]
80. Dunne, E. F., P. D. Fey, P. Kludt, R. Reporter, F. Mostashari, P. Shillam, J. Wicklund, C. Miller, B. Holland, K. Stamey, T. J. Barrett, J. K. Rasheed, F. C. Tenover, E. M. Ribot, and F. J. Angulo. 2000. Emergence of domestically acquired ceftriaxone-resistant Salmonella infections associated with AmpC β-lactamase. JAMA 284:3151-3156. [PubMed]
81. Egorova, S., M. Timinouni, M. Demartin, S. A. Granier, J. M. Whichard, V. Sangal, L. Fabre, A. Delauné, M. Pardos, Y. Millemann, E. Espié, M. Achtman, P. A. Grimont, and F. X. Weill. 2008. Ceftriaxone-resistant Salmonella enterica serotype Newport, France. Emerg. Infect. Dis. 14:954-957. [PMC free article] [PubMed]
82. Empel, J., A. Baraniak, E. Literacka, A. Mrowka, J. Fiett, E. Sadowy, W. Hryniewicz, and M. Gniadkowski. 2008. Molecular survey of β-lactamases conferring resistance to newer β-lactams in Enterobacteriaceae isolates from Polish hospitals. Antimicrob. Agents Chemother. 52:2449-2454. [PMC free article] [PubMed]
83. Engelhardt, A., A. Yusof, P. Ho, K. Sjöström, and C. Johansson. 2008. Evaluation of a new Etest strip for AmpC detection using a large collection of genotypically characterized strains, abstr. D-280. Abstr. 48th Intersci. Conf. Antimicrob. Agents Chemother.
84. Eriksson-Grennberg, K. G. 1968. Resistance of Escherichia coli to penicillins. II. An improved mapping of the ampA gene. Genet. Res. 12:147-156. [PubMed]
85. Eriksson-Grennberg, K. G., H. G. Boman, J. A. Jansson, and S. Thorén. 1965. Resistance of Escherichia coli to penicillins. I. Genetic study of some ampicillin-resistant mutants. J. Bacteriol. 90:54-62. [PMC free article] [PubMed]
86. Fakioglu, E., A. M. Queenan, K. Bush, S. G. Jenkins, and B. C. Herold. 2006. AmpC β-lactamase-producing Escherichia coli in neonatal meningitis: diagnostic and therapeutic challenge. J. Perinatol. 26:515-517. [PubMed]
87. Farrar, W. E., Jr., and N. M. O'Dell. 1976. β-Lactamase activity in Chromobacterium violaceum. J. Infect. Dis. 134:290-293. [PubMed]
88. Feller, G., Z. Zekhnini, J. Lamotte-Brasseur, and C. Gerday. 1997. Enzymes from cold-adapted microorganisms. The class C β-lactamase from the antarctic psychrophile Psychrobacter immobilis A5. Eur. J. Biochem. 244:186-191. [PubMed]
89. Fey, P. D., T. J. Safranek, M. E. Rupp, E. F. Dunne, E. Ribot, I. P. C., P. A. Bradford, F. J. Angulo, and S. H. Hinrichs. 2000. Ceftriaxone-resistant Salmonella infection acquired by a child from cattle. N. Engl. J. Med. 342:1242-1249. [PubMed]
90. Fihman, V., M. Rottman, Y. Benzerara, F. Delisle, R. Labia, A. Philippon, and G. Arlet. 2002. BUT-1: a new member in the chromosomal inducible class C β-lactamases family from a clinical isolate of Buttiauxella sp. FEMS Microbiol. Lett. 213:103-111. [PubMed]
91. Fitoussi, F., G. Arlet, P. A. Grimont, P. Lagrange, and A. Philippon. 1995. Escherichia hermannii: susceptibility pattern to β-lactams and production of β-lactamase. J. Antimicrob. Chemother. 36:537-543. [PubMed]
92. Flores, A. R., L. M. Parsons, and M. S. Pavelka, Jr. 2005. Genetic analysis of the β-lactamases of Mycobacterium tuberculosis and Mycobacterium smegmatis and susceptibility to β-lactam antibiotics. Microbiology 151:521-532. [PubMed]
93. Fortineau, N., L. Poirel, and P. Nordmann. 2001. Plasmid-mediated and inducible cephalosporinase DHA-2 from Klebsiella pneumoniae. J. Antimicrob. Chemother. 47:207-210. [PubMed]
94. Forward, K. R., B. M. Willey, D. E. Low, A. McGeer, M. A. Kapala, M. M. Kapala, and L. L. Burrows. 2001. Molecular mechanisms of cefoxitin resistance in Escherichia coli from the Toronto area hospitals. Diagn. Microbiol. Infect. Dis. 41:57-63. [PubMed]
95. Fosse, T., C. Giraud-Morin, I. Madinier, and R. Labia. 2003. Sequence analysis and biochemical characterisation of chromosomal CAV-1 (Aeromonas caviae), the parental cephalosporinase of plasmid-mediated AmpC ‘FOX’ cluster. FEMS Microbiol. Lett. 222:93-98. [PubMed]
96. Franceschini, N., L. Boschi, S. Pollini, R. Herman, M. Perilli, M. Galleni, J. M. Frère, G. Amicosante, and G. M. Rossolini. 2001. Characterization of OXA-29 from Legionella (Fluoribacter) gormanii: molecular class D β-lactamase with unusual properties. Antimicrob. Agents Chemother. 45:3509-3516. [PMC free article] [PubMed]
97. Franceschini, N., M. Galleni, J. M. Frère, A. Oratore, and G. Amicosante. 1993. A class-A β-lactamase from Pseudomonas stutzeri that is highly active against monobactams and cefotaxime. Biochem. J. 292:697-700. [PubMed]
98. Gaillot, O., C. Clement, M. Simonet, and A. Philippon. 1997. Novel transferable β-lactam resistance with cephalosporinase characteristics in Salmonella enteritidis. J. Antimicrob. Chemother. 39:85-87. [PubMed]
99. Galleni, M., G. Amicosante, and J. M. Frère. 1988. A survey of the kinetic parameters of class C β-lactamases. Cephalosporins and other β-lactam compounds. Biochem. J. 255:123-129. [PubMed]
100. Galleni, M., and J. M. Frère. 1988. A survey of the kinetic parameters of class C β-lactamases. Penicillins. Biochem. J. 255:119-122. [PubMed]
101. Galleni, M., F. Lindberg, S. Normark, S. Cole, N. Honore, B. Joris, and J. M. Frere. 1988. Sequence and comparative analysis of three Enterobacter cloacae ampC β-lactamase genes and their products. Biochem. J. 250:753-760. [PubMed]
102. Gates, M. L., C. C. Sanders, R. V. Goering, and W. E. Sanders, Jr. 1986. Evidence for multiple forms of type I chromosomal β-lactamase in Pseudomonas aeruginosa. Antimicrob. Agents Chemother. 30:453-457. [PMC free article] [PubMed]
103. Gazouli, M., M. E. Kaufmann, E. Tzelepi, H. Dimopoulou, O. Paniara, and L. S. Tzouvelekis. 1997. Study of an outbreak of cefoxitin-resistant Klebsiella pneumoniae in a general hospital. J. Clin. Microbiol. 35:508-510. [PMC free article] [PubMed]
104. Gazouli, M., L. S. Tzouvelekis, A. C. Vatopoulos, and E. Tzelepi. 1998. Transferable class C β-lactamases in Escherichia coli strains isolated in Greek hospitals and characterization of two enzyme variants (LAT-3 and LAT-4) closely related to Citrobacter freundii AmpC β-lactamase. J. Antimicrob. Chemother. 42:419-425. [PubMed]
105. Giles, W. P., A. K. Benson, M. E. Olson, R. W. Hutkins, J. M. Whichard, P. L. Winokur, and P. D. Fey. 2004. DNA sequence analysis of regions surrounding blaCMY-2 from multiple Salmonella plasmid backbones. Antimicrob. Agents Chemother. 48:2845-2852. [PMC free article] [PubMed]
106. Girlich, D., T. Naas, S. Bellais, L. Poirel, A. Karim, and P. Nordmann. 2000. Biochemical-genetic characterization and regulation of expression of an ACC-1-like chromosome-borne cephalosporinase from Hafnia alvei. Antimicrob. Agents Chemother. 44:1470-1478. [PMC free article] [PubMed]
107. Girlich, D., T. Naas, S. Bellais, L. Poirel, A. Karim, and P. Nordmann. 2000. Heterogeneity of AmpC cephalosporinases of Hafnia alvei clinical isolates expressing inducible or constitutive ceftazidime resistance phenotypes. Antimicrob. Agents Chemother. 44:3220-3223. [PMC free article] [PubMed]
108. Glupczynski, Y., T. D. Huang, C. Berhin, G. Claeys, M. Delmée, L. Ide, G. Ieven, D. Pierard, H. Rodriguez-Villalobos, M. Struelens, and J. Vaneldere. 2007. In vitro activity of temocillin against prevalent extended-spectrum beta-lactamases producing Enterobacteriaceae from Belgian intensive care units. Eur. J. Clin. Microbiol. Infect. Dis. 26:777-783. [PubMed]
109. Gonzalez Leiza, M., J. C. Perez-Diaz, J. Ayala, J. M. Casellas, J. Martinez-Beltran, K. Bush, and F. Baquero. 1994. Gene sequence and biochemical characterization of FOX-1 from Klebsiella pneumoniae, a new AmpC-type plasmid-mediated β-lactamase with two molecular variants. Antimicrob. Agents Chemother. 38:2150-2157. [PMC free article] [PubMed]
110. Goodner, B., G. Hinkle, S. Gattung, N. Miller, M. Blanchard, B. Qurollo, B. S. Goldman, Y. Cao, M. Askenazi, C. Halling, L. Mullin, K. Houmiel, J. Gordon, M. Vaudin, O. Iartchouk, A. Epp, F. Liu, C. Wollam, M. Allinger, D. Doughty, C. Scott, C. Lappas, B. Markelz, C. Flanagan, C. Crowell, J. Gurson, C. Lomo, C. Sear, G. Strub, C. Cielo, and S. Slater. 2001. Genome sequence of the plant pathogen and biotechnology agent Agrobacterium tumefaciens C58. Science 294:2323-2328. [PubMed]
111. Gould, V. C., A. Okazaki, and M. B. Avison. 2006. β-Lactam resistance and β-lactamase expression in clinical Stenotrophomonas maltophilia isolates having defined phylogenetic relationships. J. Antimicrob. Chemother. 57:199-203. [PubMed]
112. Gray, J. T., L. L. Hungerford, P. J. Fedorka-Cray, and M. L. Headrick. 2004. Extended-spectrum-cephalosporin resistance in Salmonella enterica isolates of animal origin. Antimicrob. Agents Chemother. 48:3179-3181. [PMC free article] [PubMed]
113. Gupta, A., J. Fontana, C. Crowe, B. Bolstorff, A. Stout, S. Van Duyne, M. P. Hoekstra, J. M. Whichard, T. J. Barrett, and F. J. Angulo. 2003. Emergence of multidrug-resistant Salmonella enterica serotype Newport infections resistant to expanded-spectrum cephalosporins in the United States. J. Infect. Dis. 188:1707-1716. [PubMed]
114. Gutiérrez, O., C. Juan, E. Cercenado, F. Navarro, E. Bouza, P. Coll, J. L. Pérez, and A. Oliver. 2007. Molecular epidemiology and mechanisms of carbapenem resistance in Pseudomonas aeruginosa isolates from Spanish hospitals. Antimicrob. Agents Chemother. 51:4329-4335. [PMC free article] [PubMed]
115. Haldorsen, B., B. Aasnaes, K. H. Dahl, A. M. Hanssen, G. S. Simonsen, T. R. Walsh, A. Sundsfjord, and E. W. Lundblad. 2008. The AmpC phenotype in Norwegian clinical isolates of Escherichia coli is associated with an acquired ISEcp1-like ampC element or hyperproduction of the endogenous AmpC. J. Antimicrob. Chemother. 62:694-702. [PubMed]
116. Hall, B. G., and M. Barlow. 2004. Evolution of the serine β-lactamases: past, present and future. Drug Resist. Updates 7:111-123. [PubMed]
117. Hanson, N. D., E. S. Moland, S. G. Hong, K. Propst, D. J. Novak, and S. J. Cavalieri. 2008. Surveillance of community-based reservoirs reveals the presence of CTX-M, imported AmpC, and OXA-30 β-lactamases in urine isolates of Klebsiella pneumoniae and Escherichia coli in a U.S. community. Antimicrob. Agents Chemother. 52:3814-3816. [PMC free article] [PubMed]
118. Hanson, N. D., and C. C. Sanders. 1999. Regulation of inducible AmpC β-lactamase expression among Enterobacteriaceae. Curr. Pharm. Des. 5:881-894. [PubMed]
119. Hanson, N. D., K. S. Thomson, E. S. Moland, C. C. Sanders, G. Berthold, and R. G. Penn. 1999. Molecular characterization of a multiply resistant Klebsiella pneumoniae encoding ESBLs and a plasmid-mediated AmpC. J. Antimicrob. Chemother. 44:377-380. [PubMed]
120. Hayes, M. V., C. J. Thomson, and S. G. Amyes. 1994. Three beta-lactamases isolated from Aeromonas salmonicida, including a carbapenemase not detectable by conventional methods. Eur. J. Clin. Microbiol. Infect. Dis. 13:805-811. [PubMed]
121. Henderson, T. A., K. D. Young, S. A. Denome, and P. K. Elf. 1997. AmpC and AmpH, proteins related to the class C β-lactamases, bind penicillin and contribute to the normal morphology of Escherichia coli. J. Bacteriol. 179:6112-6121. [PMC free article] [PubMed]
122. Héritier, C., L. Poirel, and P. Nordmann. 2006. Cephalosporinase over-expression resulting from insertion of ISAba1 in Acinetobacter baumannii. Clin. Microbiol. Infect. 12:123-130. [PubMed]
123. Héritier, C., L. Poirel, and P. Nordmann. 2004. Genetic and biochemical characterization of a chromosome-encoded carbapenem-hydrolyzing Ambler class D β-lactamase from Shewanella algae. Antimicrob. Agents Chemother. 48:1670-1675. [PMC free article] [PubMed]
124. Hernández-Allés, S., V. J. Benedí, L. Martínez-Martínez, A. Pascual, A. Aguilar, J. M. Tomás, and S. Albertí. 1999. Development of resistance during antimicrobial therapy caused by insertion sequence interruption of porin genes. Antimicrob. Agents Chemother. 43:937-939. [PMC free article] [PubMed]
125. Hernández-Allés, S., M. Conejo, A. Pascual, J. M. Tomás, V. J. Benedí, and L. Martínez-Martínez. 2000. Relationship between outer membrane alterations and susceptibility to antimicrobial agents in isogenic strains of Klebsiella pneumoniae. J. Antimicrob. Chemother. 46:273-277. [PubMed]
126. Hidri, N., G. Barnaud, D. Decré, C. Cerceau, V. Lalande, J. C. Petit, R. Labia, and G. Arlet. 2005. Resistance to ceftazidime is associated with a S220Y substitution in the omega loop of the AmpC β-lactamase of a Serratia marcescens clinical isolate. J. Antimicrob. Chemother. 55:496-499. [PubMed]
127. Higgins, C. S., M. B. Avison, L. Jamieson, A. M. Simm, P. M. Bennett, and T. R. Walsh. 2001. Characterization, cloning and sequence analysis of the inducible Ochrobactrum anthropi AmpC β-lactamase. J. Antimicrob. Chemother. 47:745-754. [PubMed]
128. Hirakawa, H., K. Nishino, J. Yamada, T. Hirata, and A. Yamaguchi. 2003. β-Lactam resistance modulated by the overexpression of response regulators of two-component signal transduction systems in Escherichia coli. J. Antimicrob. Chemother. 52:576-582. [PubMed]
129. Honoré, N., M. H. Nicolas, and S. T. Cole. 1986. Inducible cephalosporinase production in clinical isolates of Enterobacter cloacae is controlled by a regulatory gene that has been deleted from Escherichia coli. EMBO J. 5:3709-3714. [PubMed]
130. Hope, R., M. Warner, N. A. Potz, E. J. Fagan, D. James, and D. M. Livermore. 2006. Activity of tigecycline against ESBL-producing and AmpC-hyperproducing Enterobacteriaceae from south-east England. J. Antimicrob. Chemother. 58:1312-1314. [PubMed]
131. Hopkins, J. M., and K. J. Towner. 1990. Enhanced resistance to cefotaxime and imipenem associated with outer membrane protein alterations in Enterobacter aerogenes. J. Antimicrob. Chemother. 25:49-55. [PubMed]
132. Hopkins, K. L., M. J. Batchelor, E. Liebana, A. P. Deheer-Graham, and E. J. Threlfall. 2006. Characterisation of CTX-M and ampC genes in human isolates of Escherichia coli identified between 1995 and 2003 in England and Wales. Int. J. Antimicrob. Agents 28:180-192. [PubMed]
133. Hopkins, K. L., A. Deheer-Graham, E. Karisik, M. J. Batchelor, E. Liebana, and E. J. Threlfall. 2006. New plasmid-mediated AmpC β-lactamase (CMY-21) in Escherichia coli isolated in the UK. Int. J. Antimicrob. Agents 28:80-82. [PubMed]
134. Horii, T., Y. Arakawa, M. Ohta, S. Ichiyama, R. Wacharotayankun, and N. Kato. 1993. Plasmid-mediated AmpC-type β-lactamase isolated from Klebsiella pneumoniae confers resistance to broad-spectrum β-lactams, including moxalactam. Antimicrob. Agents Chemother. 37:984-990. [PMC free article] [PubMed]
135. Hossain, A., M. D. Reisbig, and N. D. Hanson. 2004. Plasmid-encoded functions compensate for the biological cost of AmpC overexpression in a clinical isolate of Salmonella typhimurium. J. Antimicrob. Chemother. 53:964-970. [PubMed]
136. Huang, I. F., C. H. Chiu, M. H. Wang, C. Y. Wu, K. S. Hsieh, and C. C. Chiou. 2005. Outbreak of dysentery associated with ceftriaxone-resistant Shigella sonnei: first report of plasmid-mediated CMY-2-type AmpC β-lactamase resistance in S. sonnei. J. Clin. Microbiol. 43:2608-2612. [PMC free article] [PubMed]
137. Hujer, K. M., N. S. Hamza, A. M. Hujer, F. Perez, M. S. Helfand, C. R. Bethel, J. M. Thomson, V. E. Anderson, M. Barlow, L. B. Rice, F. C. Tenover, and R. A. Bonomo. 2005. Identification of a new allelic variant of the Acinetobacter baumannii cephalosporinase, ADC-7 β-lactamase: defining a unique family of class C enzymes. Antimicrob. Agents Chemother. 49:2941-2948. [PMC free article] [PubMed]
138. Humeniuk, C., G. Arlet, V. Gautier, P. Grimont, R. Labia, and A. Philippon. 2002. β-Lactamases of Kluyvera ascorbata, probable progenitors of some plasmid-encoded CTX-M types. Antimicrob. Agents Chemother. 46:3045-3049. [PMC free article] [PubMed]
139. Jacobs, C., J. M. Frère, and S. Normark. 1997. Cytosolic intermediates for cell wall biosynthesis and degradation control inducible β-lactam resistance in gram-negative bacteria. Cell 88:823-832. [PubMed]
140. Jacobs, C., L. Huang, E. Bartowsky, S. Normark, and J. T. Park. 1994. Bacterial cell wall recycling provides cytosolic muropeptides as effector for β-lactamase induction. EMBO J. 13:4684-4694. [PubMed]
141. Jacoby, G. A., D. M. Mills, and N. Chow. 2004. Role of β-lactamases and porins in resistance to ertapenem and other β-lactams in Klebsiella pneumoniae. Antimicrob. Agents Chemother. 48:3203-3206. [PMC free article] [PubMed]
142. Jacoby, G. A., and J. Tran. 1999. Sequence of the MIR-1 β-lactamase gene. Antimicrob. Agents Chemother. 43:1759-1760. [PMC free article] [PubMed]
143. Jacoby, G. A., K. E. Walsh, and V. J. Walker. 2006. Identification of extended-spectrum, AmpC, and carbapenem-hydrolyzing β-lactamases in Escherichia coli and Klebsiella pneumoniae by disk tests. J. Clin. Microbiol. 44:1971-1976. [PMC free article] [PubMed]
144. Jaurin, B., and T. Grundström. 1981. ampC cephalosporinase of Escherichia coli K-12 has a different evolutionary origin from that of β-lactamases of the penicillinase type. Proc. Natl. Acad. Sci. USA 78:4897-4901. [PubMed]
145. Jaurin, B., T. Grundström, T. Edlund, and S. Normark. 1981. The E. coli β-lactamase attenuator mediates growth rate-dependent regulation. Nature 290:221-225. [PubMed]
146. Jaurin, B., and S. Normark. 1983. Insertion of IS2 creates a novel ampC promoter in Escherichia coli. Cell 32:809-816. [PubMed]
147. Jones, R. N., J. T. Kirby, and P. R. Rhomberg. 2008. Comparative activity of meropenem in US medical centers (2007): initiating the 2nd decade of MYSTIC program surveillance. Diagn. Microbiol. Infect. Dis. 61:203-213. [PubMed]
148. Joris, B., F. De Meester, M. Galleni, S. Masson, J. Dusart, J. M. Frère, J. Van Beeumen, K. Bush, and R. Sykes. 1986. Properties of a class C β-lactamase from Serratia marcescens. Biochem. J. 239:581-586. [PubMed]
149. Joris, B., P. Ledent, O. Dideberg, E. Fonzé, J. Lamotte-Brasseur, J. A. Kelly, J. M. Ghuysen, and J. M. Frère. 1991. Comparison of the sequences of class A β-lactamases and of the secondary structure elements of penicillin-recognizing proteins. Antimicrob. Agents Chemother. 35:2294-2301. [PMC free article] [PubMed]
150. Juan, C., M. D. Macia, O. Gutierrez, C. Vidal, J. L. Perez, and A. Oliver. 2005. Molecular mechanisms of β-lactam resistance mediated by AmpC hyperproduction in Pseudomonas aeruginosa clinical strains. Antimicrob. Agents Chemother. 49:4733-4738. [PMC free article] [PubMed]
151. Juan, C., B. Moyá, J. L. Pérez, and A. Oliver. 2006. Stepwise upregulation of the Pseudomonas aeruginosa chromosomal cephalosporinase conferring high-level β-lactam resistance involves three AmpD homologues. Antimicrob. Agents Chemother. 50:1780-1787. [PMC free article] [PubMed]
152. Kaczmarek, F. M., F. Dib-Hajj, W. Shang, and T. D. Gootz. 2006. High-level carbapenem resistance in a Klebsiella pneumoniae clinical isolate is due to the combination of blaACT-1 β-lactamase production, porin OmpK35/36 insertional inactivation, and down-regulation of the phosphate transport porin PhoE. Antimicrob. Agents Chemother. 50:3396-3406. [PMC free article] [PubMed]
153. Kaneko, K., R. Okamoto, R. Nakano, S. Kawakami, and M. Inoue. 2005. Gene mutations responsible for overexpression of AmpC β-lactamase in some clinical isolates of Enterobacter cloacae. J. Clin. Microbiol. 43:2955-2958. [PMC free article] [PubMed]
154. Kang, C. I., H. Pai, S. H. Kim, H. B. Kim, E. C. Kim, M. D. Oh, and K. W. Choe. 2004. Cefepime and the inoculum effect in tests with Klebsiella pneumoniae producing plasmid-mediated AmpC-type β-lactamase. J. Antimicrob. Chemother. 54:1130-1133. [PubMed]
155. Kang, M. S., T. E. Besser, and D. R. Call. 2006. Variability in the region downstream of the blaCMY-2 β-lactamase gene in Escherichia coli and Salmonella enterica plasmids. Antimicrob. Agents Chemother. 50:1590-1593. [PMC free article] [PubMed]
156. Kaye, K. S., S. Cosgrove, A. Harris, G. M. Eliopoulos, and Y. Carmeli. 2001. Risk factors for emergence of resistance to broad-spectrum cephalosporins among Enterobacter spp. Antimicrob. Agents Chemother. 45:2628-2630. [PMC free article] [PubMed]
157. Kazmierczak, A., X. Cordin, J. M. Duez, E. Siebor, A. Pechinot, and J. Sirot. 1990. Differences between clavulanic acid and sulbactam in induction and inhibition of cephalosporinases in enterobacteria. J. Int. Med. Res. 18(Suppl. 4):67D-77D. [PubMed]
158. Kim, J. Y., H. I. Jung, Y. J. An, J. H. Lee, S. J. Kim, S. H. Jeong, K. J. Lee, P. G. Suh, H. S. Lee, S. H. Lee, and S. S. Cha. 2006. Structural basis for the extended substrate spectrum of CMY-10, a plasmid-encoded class C β-lactamase. Mol. Microbiol. 60:907-916. [PubMed]
159. Kimura, H., M. Izawa, and Y. Sumino. 1996. Molecular analysis of the gene cluster involved in cephalosporin biosynthesis from Lysobacter lactamgenus YK90. Appl. Microbiol. Biotechnol. 44:589-596. [PubMed]
160. Kitzis, M. D., B. Ferre, A. Coutrot, J. F. Acar, and L. Gutmann. 1989. In vitro activity of combinations of beta-lactam antibiotics with beta-lactamase inhibitors against cephalosporinase-producing bacteria. Eur. J. Clin. Microbiol. Infect. Dis. 8:783-788. [PubMed]
161. Knott-Hunziker, V., S. Petursson, G. S. Jayatilake, S. G. Waley, B. Jaurin, and T. Grundström. 1982. Active sites of β-lactamases. Biochem. J. 201:621-627. [PubMed]
162. Knox, J. R., P. C. Moews, and J. M. Frere. 1996. Molecular evolution of bacterial β-lactam resistance. Chem. Biol. 3:937-947. [PubMed]
163. Kohler, T., M. Michea-Hamzehpour, S. F. Epp, and J. C. Pechere. 1999. Carbapenem activities against Pseudomonas aeruginosa: respective contributions of OprD and efflux systems. Antimicrob. Agents Chemother. 43:424-427. [PMC free article] [PubMed]
164. Kong, K. F., S. R. Jayawardena, S. D. Indulkar, A. Del Puerto, C. L. Koh, N. Hoiby, and K. Mathee. 2005. Pseudomonas aeruginosa AmpR is a global transcriptional factor that regulates expression of AmpC and PoxB β-lactamases, proteases, quorum sensing, and other virulence factors. Antimicrob. Agents Chemother. 49:4567-4575. [PMC free article] [PubMed]
165. Kuga, A., R. Okamoto, and M. Inoue. 2000. ampR gene mutations that greatly increase class C β-lactamase activity in Enterobacter cloacae. Antimicrob. Agents Chemother. 44:561-567. [PMC free article] [PubMed]
166. Lartigue, M. F., L. Poirel, D. Aubert, and P. Nordmann. 2006. In vitro analysis of ISEcp1B-mediated mobilization of naturally occurring β-lactamase gene blaCTX-M of Kluyvera ascorbata. Antimicrob. Agents Chemother. 50:1282-1286. [PMC free article] [PubMed]
167. Lau, S. K., P. L. Ho, M. W. Li, H. W. Tsoi, R. W. Yung, P. C. Woo, and K. Y. Yuen. 2005. Cloning and characterization of a chromosomal class C β-lactamase and its regulatory gene in Laribacter hongkongensis. Antimicrob. Agents Chemother. 49:1957-1964. [PMC free article] [PubMed]
168. Lee, E. H., M. H. Nicolas, M. D. Kitzis, G. Pialoux, E. Collatz, and L. Gutmann. 1991. Association of two resistance mechanisms in a clinical isolate of Enterobacter cloacae with high-level resistance to imipenem. Antimicrob. Agents Chemother. 35:1093-1098. [PMC free article] [PubMed]
169. Lee, K., S. G. Hong, Y. J. Park, H. S. Lee, W. Song, J. Jeong, D. Yong, and Y. Chong. 2005. Evaluation of phenotypic screening methods for detecting plasmid-mediated AmpC β-lactamases-producing isolates of Escherichia coli and Klebsiella pneumoniae. Diagn. Microbiol. Infect. Dis. 53:319-323. [PubMed]
170. Lee, K., M. Lee, J. H. Shin, M. H. Lee, S. H. Kang, A. J. Park, D. Yong, and Y. Chong. 2006. Prevalence of plasmid-mediated AmpC β-lactamases in Escherichia coli and Klebsiella pneumoniae in Korea. Microb. Drug Resist. 12:44-49. [PubMed]
171. Lee, K., D. Yong, Y. S. Choi, J. H. Yum, J. M. Kim, N. Woodford, D. M. Livermore, and Y. Chong. 2007. Reduced imipenem susceptibility in Klebsiella pneumoniae clinical isolates with plasmid-mediated CMY-2 and DHA-1 β-lactamases co-mediated by porin loss. Int. J. Antimicrob. Agents 29:201-206. [PubMed]
172. Lee, S. H., S. H. Jeong, and Y. M. Park. 2003. Characterization of blaCMY-10 a novel, plasmid-encoded AmpC-type β-lactamase gene in a clinical isolate of Enterobacter aerogenes. J. Appl. Microbiol. 95:744-752. [PubMed]
173. Lee, S. H., J. H. Lee, M. J. Heo, I. K. Bae, S. H. Jeong, and S. S. Cha. 2007. Exact location of the region responsible for the extended substrate spectrum in class C β-lactamases. Antimicrob. Agents Chemother. 51:3778-3779. [PMC free article] [PubMed]
174. Li, Y., Q. Li, Y. Du, X. Jiang, J. Tang, J. Wang, G. Li, and Y. Jiang. 2008. Prevalence of plasmid-mediated AmpC β-lactamases in a Chinese university hospital from 2003 to 2005: first report of CMY-2-type AmpC β-lactamase resistance in China. J. Clin. Microbiol. 46:1317-1321. [PMC free article] [PubMed]
175. Liassine, N., S. Madec, B. Ninet, C. Metral, M. Fouchereau-Peron, R. Labia, and R. Auckenthaler. 2002. Postneurosurgical meningitis due to Proteus penneri with selection of a ceftriaxone-resistant isolate: analysis of chromosomal class A β-lactamase HugA and its LysR-type regulatory protein HugR. Antimicrob. Agents Chemother. 46:216-219. [PMC free article] [PubMed]
176. Liebana, E., M. Gibbs, C. Clouting, L. Barker, F. A. Clifton-Hadley, E. Pleydell, B. Abdalhamid, N. D. Hanson, L. Martin, C. Poppe, and R. H. Davies. 2004. Characterization of β-lactamases responsible for resistance to extended-spectrum cephalosporins in Escherichia coli and Salmonella enterica strains from food-producing animals in the United Kingdom. Microb. Drug Resist. 10:1-9. [PubMed]
177. Lin, J. W., S. F. Weng, Y. F. Chao, and Y. T. Chung. 2005. Characteristic analysis of the ampC gene encoding β-lactamase from Photobacterium phosphoreum. Biochem. Biophys. Res. Commun. 326:539-547. [PubMed]
178. Linberg, F., and S. Normark. 1986. Sequence of the Citrobacter freundii OS60 chromosomal ampC β-lactamase gene. Eur. J. Biochem. 156:441-445. [PubMed]
179. Lindquist, S., K. Weston-Hafer, H. Schmidt, C. Pul, G. Korfmann, J. Erickson, C. Sanders, H. H. Martin, and S. Normark. 1993. AmpG, a signal transducer in chromosomal β-lactamase induction. Mol. Microbiol. 9:703-715. [PubMed]
180. Linström, E. B., H. G. Boman, and B. B. Steele. 1970. Resistance of Escherichia coli to penicillins. VI. Purification and characterization of the chromosomally mediated penicillinase present in ampA-containing strains. J. Bacteriol. 101:218-231. [PMC free article] [PubMed]
181. Lister, P. D., V. M. Gardner, and C. C. Sanders. 1999. Clavulanate induces expression of the Pseudomonas aeruginosa AmpC cephalosporinase at physiologically relevant concentrations and antagonizes the antibacterial activity of ticarcillin. Antimicrob. Agents Chemother. 43:882-889. [PMC free article] [PubMed]
182. Literacka, E., J. Empel, A. Baraniak, E. Sadowy, W. Hryniewicz, and M. Gniadkowski. 2004. Four variants of the Citrobacter freundii AmpC-type cephalosporinases, including novel enzymes CMY-14 and CMY-15, in a Proteus mirabilis clone widespread in Poland. Antimicrob. Agents Chemother. 48:4136-4143. [PMC free article] [PubMed]
183. Liu, Y. F., J. J. Yan, W. C. Ko, S. H. Tsai, and J. J. Wu. 2008. Characterization of carbapenem-non-susceptible Escherichia coli isolates from a university hospital in Taiwan. J. Antimicrob. Chemother. 61:1020-1023. [PubMed]
184. Livermore, D. M. 1987. Clinical significance of beta-lactamase induction and stable derepression in gram-negative rods. Eur. J. Clin. Microbiol. 6:439-445. [PubMed]
185. Livermore, D. M. 1992. Interplay of impermeability and chromosomal β-lactamase activity in imipenem-resistant Pseudomonas aeruginosa. Antimicrob. Agents Chemother. 36:2046-2048. [PMC free article] [PubMed]
186. Livermore, D. M. 2002. Multiple mechanisms of antimicrobial resistance in Pseudomonas aeruginosa: our worst nightmare? Clin. Infect. Dis. 34:634-640. [PubMed]
187. Livermore, D. M., R. Hope, E. J. Fagan, M. Warner, N. Woodford, and N. Potz. 2006. Activity of temocillin against prevalent ESBL- and AmpC-producing Enterobacteriaceae from south-east England. J. Antimicrob. Chemother. 57:1012-1014. [PubMed]
188. Livermore, D. M., and N. Woodford. 2006. The β-lactamase threat in Enterobacteriaceae, Pseudomonas and Acinetobacter. Trends Microbiol. 14:413-420. [PubMed]
189. Livermore, D. M., and Y. J. Yang. 1987. β-Lactamase lability and inducer power of newer β-lactam antibiotics in relation to their activity against β-lactamase-inducibility mutants of Pseudomonas aeruginosa. J. Infect. Dis. 155:775-782. [PubMed]
190. Lobkovsky, E., P. C. Moews, H. Liu, H. Zhao, J. M. Frere, and J. R. Knox. 1993. Evolution of an enzyme activity: crystallographic structure at 2-Å resolution of cephalosporinase from the ampC gene of Enterobacter cloacae P99 and comparison with a class A penicillinase. Proc. Natl. Acad. Sci. USA 90:11257-11261. [PubMed]
191. Mahlen, S. D., S. S. Morrow, B. Abdalhamid, and N. D. Hanson. 2003. Analyses of ampC gene expression in Serratia marcescens reveal new regulatory properties. J. Antimicrob. Chemother. 51:791-802. [PubMed]
192. Mainardi, J. L., P. Mugnier, A. Coutrot, A. Buu-Hoï, E. Collatz, and L. Gutmann. 1997. Carbapenem resistance in a clinical isolate of Citrobacter freundii. Antimicrob. Agents Chemother. 41:2352-2354. [PMC free article] [PubMed]
193. Mammeri, H., F. Eb, A. Berkani, and P. Nordmann. 2008. Molecular characterization of AmpC-producing Escherichia coli clinical isolates recovered in a French hospital. J. Antimicrob. Chemother. 61:498-503. [PubMed]
194. Mammeri, H., H. Nazic, T. Naas, L. Poirel, S. Leotard, and P. Nordmann. 2004. AmpC β-lactamase in an Escherichia coli clinical isolate confers resistance to expanded-spectrum cephalosporins. Antimicrob. Agents Chemother. 48:4050-4053. [PMC free article] [PubMed]
195. Mammeri, H., P. Nordmann, A. Berkani, and F. Eb. 2008. Contribution of extended-spectrum AmpC (ESAC) β-lactamases to carbapenem resistance in Escherichia coli. FEMS Microbiol. Lett. 282:238-240. [PubMed]
196. Mammeri, H., L. Poirel, P. Bemer, H. Drugeon, and P. Nordmann. 2004. Resistance to cefepime and cefpirome due to a 4-amino-acid deletion in the chromosome-encoded AmpC β-lactamase of a Serratia marcescens clinical isolate. Antimicrob. Agents Chemother. 48:716-720. [PMC free article] [PubMed]
197. Mammeri, H., L. Poirel, N. Fortineau, and P. Nordmann. 2006. Naturally occurring extended-spectrum cephalosporinases in Escherichia coli. Antimicrob. Agents Chemother. 50:2573-2576. [PMC free article] [PubMed]
198. Mammeri, H., L. Poirel, H. Nazik, and P. Nordmann. 2006. Cloning and functional characterization of the Ambler class C β-lactamase of Yersinia ruckeri. FEMS Microbiol. Lett. 257:57-62. [PubMed]
199. Mammeri, H., L. Poirel, and P. Nordmann. 2007. Extension of the hydrolysis spectrum of AmpC β-lactamase of Escherichia coli due to amino acid insertion in the H-10 helix. J. Antimicrob. Chemother. 60:490-494. [PubMed]
200. Manchanda, V., and N. P. Singh. 2003. Occurrence and detection of AmpC β-lactamases among gram-negative clinical isolates using a modified three-dimensional test at Guru Tegh Bahadur Hospital, Delhi, India. J. Antimicrob. Chemother. 51:415-418. [PubMed]
201. Martínez-Martínez, L., M. C. Conejo, A. Pascual, S. Hernández-Allés, S. Ballesta, E. Ramírez De Arellano-Ramos, V. J. Benedí, and E. J. Perea. 2000. Activities of imipenem and cephalosporins against clonally related strains of Escherichia coli hyperproducing chromosomal β-lactamase and showing altered porin profiles. Antimicrob. Agents Chemother. 44:2534-2536. [PMC free article] [PubMed]
202. Martínez-Martínez, L., S. Hernández-Allés, S. Albertí, J. M. Tomás, V. J. Benedi, and G. A. Jacoby. 1996. In vivo selection of porin-deficient mutants of Klebsiella pneumoniae with increased resistance to cefoxitin and expanded-spectrum cephalosporins. Antimicrob. Agents Chemother. 40:342-348. [PMC free article] [PubMed]
203. Martínez-Martínez, L., A. Pascual, S. Hernández-Allés, D. Alvarez-Díaz, A. I. Suárez, J. Tran, V. J. Benedí, and G. A. Jacoby. 1999. Roles of β-lactamases and porins in activities of carbapenems and cephalosporins against Klebsiella pneumoniae. Antimicrob. Agents Chemother. 43:1669-1673. [PMC free article] [PubMed]
204. Matagne, A., A. M. Misselyn-Bauduin, B. Joris, T. Erpicum, B. Granier, and J. M. Frère. 1990. The diversity of the catalytic properties of class A β-lactamases. Biochem. J. 265:131-146. [PubMed]
205. Matsubara, N., A. Yotsuji, K. Kumano, M. Inoue, and S. Mitsuhashi. 1981. Purification and some properties of a cephalosporinase from Proteus vulgaris. Antimicrob. Agents Chemother. 19:185-187. [PMC free article] [PubMed]
206. Matsumura, N., S. Minami, and S. Mitsuhashi. 1998. Sequences of homologous β-lactamases from clinical isolates of Serratia marcescens with different substrate specificities. Antimicrob. Agents Chemother. 42:176-179. [PMC free article] [PubMed]
207. Matsuura, M., H. Nakazawa, M. Inoue, and S. Mitsuhashi. 1980. Purification and biochemical properties of β-lactamase produced by Proteus rettgeri. Antimicrob. Agents Chemother. 18:687-690. [PMC free article] [PubMed]
208. Maurelli, A. T., R. E. Fernandez, C. A. Bloch, C. K. Rode, and A. Fasano. 1998. “Black holes” and bacterial pathogenicity: a large genomic deletion that enhances the virulence of Shigella spp. and enteroinvasive Escherichia coli. Proc. Natl. Acad. Sci. USA 95:3943-3948. [PubMed]
209. Michaux, C., J. Massant, F. Kerff, J. M. Frère, J. D. Docquier, I. Vandenberghe, B. Samyn, A. Pierrard, G. Feller, P. Charlier, J. Van Beeumen, and J. Wouters. 2008. Crystal structure of a cold-adapted class C β-lactamase. FEBS J. 275:1687-1697. [PubMed]
210. Migliavacca, R., E. Nucleo, M. M. D'Andrea, M. Spalla, T. Giani, and L. Pagani. 2007. Acquired AmpC type beta-lactamases: an emerging problem in Italian long-term care and rehabilitation facilities. New Microbiol. 30:295-298. [PubMed]
211. Minami, S., M. Inoue, and S. Mitsuhashi. 1980. Purification and properties of a cephalosporinase from Enterobacter cloacae. Antimicrob. Agents Chemother. 18:853-857. [PMC free article] [PubMed]
212. Minami, S., M. Inoue, and S. Mitsuhashi. 1980. Purification and properties of cephalosporinase in Escherichia coli. Antimicrob. Agents Chemother. 18:77-80. [PMC free article] [PubMed]
213. Miriagou, V., P. T. Tassios, N. J. Legakis, and L. S. Tzouvelekis. 2004. Expanded-spectrum cephalosporin resistance in non-typhoid Salmonella. Int. J. Antimicrob. Agents 23:547-555. [PubMed]
214. Miriagou, V., L. S. Tzouvelekis, L. Villa, E. Lebessi, A. C. Vatopoulos, A. Carattoli, and E. Tzelepi. 2004. CMY-13, a novel inducible cephalosporinase encoded by an Escherichia coli plasmid. Antimicrob. Agents Chemother. 48:3172-3174. [PMC free article] [PubMed]
215. Mittal, S., S. Mallik, S. Sharma, and J. S. Virdi. 2007. Characteristics of β-lactamases and their genes (blaA and blaB) in Yersinia intermedia and Y. frederiksenii. BMC Microbiol. 7:25. [PMC free article] [PubMed]
216. Moland, E. S., J. A. Black, J. Ourada, M. D. Reisbig, N. D. Hanson, and K. S. Thomson. 2002. Occurrence of newer β-lactamases in Klebsiella pneumoniae isolates from 24 U.S. hospitals. Antimicrob. Agents Chemother. 46:3837-3842. [PMC free article] [PubMed]
217. Moland, E. S., N. D. Hanson, J. A. Black, A. Hossain, W. Song, and K. S. Thomson. 2006. Prevalence of newer β-lactamases in gram-negative clinical isolates collected in the United States from 2001 to 2002. J. Clin. Microbiol. 44:3318-3324. [PMC free article] [PubMed]
218. Monnaie, D., and J. M. Frere. 1993. Interaction of clavulanate with class C β-lactamases. FEBS Lett. 334:269-271. [PubMed]
219. Moya, B., C. Juan, S. Albertí, J. L. Pérez, and A. Oliver. 2008. Benefit of having multiple ampD genes for acquiring β-lactam resistance without losing fitness and virulence in Pseudomonas aeruginosa. Antimicrob. Agents Chemother. 52:3694-3700. [PMC free article] [PubMed]
219a. Moya, B., C. Juan, J. Blazquez, L. Zamorano, J. L. Perez, A. Oliver, and H. Son Dureta. 2008. Abstr. 48th Intersci. Conf. Antimicrob. Agents Chemother., abstr. C1-3729.
220. Mulvey, M. R., E. Bryce, D. A. Boyd, M. Ofner-Agostini, A. M. Land, A. E. Simor, and S. Paton. 2005. Molecular characterization of cefoxitin-resistant Escherichia coli from Canadian hospitals. Antimicrob. Agents Chemother. 49:358-365. [PMC free article] [PubMed]
221. Murata, T., S. Minami, K. Yasuda, S. Iyobe, M. Inoue, and S. Mitsuhashi. 1981. Purification and properties of cephalosporinase from Pseudomonas aeruginosa. J. Antibiot. (Tokyo) 34:1164-1170. [PubMed]
222. M'Zali, F. H., J. Heritage, D. M. Gascoyne-Binzi, M. Denton, N. J. Todd, and P. M. Hawkey. 1997. Transcontinental importation into the UK of Escherichia coli expressing a plasmid-mediated AmpC-type β-lactamase exposed during an outbreak of SHV-5 extended-spectrum β-lactamase in a Leeds hospital. J. Antimicrob. Chemother. 40:823-831. [PubMed]
223. Naas, T., D. Aubert, N. Fortineau, and P. Nordmann. 2002. Cloning and sequencing of the β-lactamase gene and surrounding DNA sequences of Citrobacter braakii, Citrobacter murliniae, Citrobacter werkmanii, Escherichia fergusonii and Enterobacter cancerogenus. FEMS Microbiol. Lett. 215:81-87. [PubMed]
224. Naas, T., D. Aubert, A. Özcan, and P. Nordmann. 2007. Chromosome-encoded narrow-spectrum Ambler class A β-lactamase GIL-1 from Citrobacter gillenii. Antimicrob. Agents Chemother. 51:1365-1372. [PMC free article] [PubMed]
225. Naas, T., D. Aubert, S. Vimont, and P. Nordmann. 2004. Identification of a chromosome-borne class C β-lactamase from Erwinia rhapontici. J. Antimicrob. Chemother. 54:932-935. [PubMed]
226. Nadjar, D., R. Labia, C. Cerceau, C. Bizet, A. Philippon, and G. Arlet. 2001. Molecular characterization of chromosomal class C β-lactamase and its regulatory gene in Ochrobactrum anthropi. Antimicrob. Agents Chemother. 45:2324-2330. [PMC free article] [PubMed]
227. Nadjar, D., M. Rouveau, C. Verdet, J. Donay, J. Herrmann, P. H. Lagrange, A. Philippon, and G. Arlet. 2000. Outbreak of Klebsiella pneumoniae producing transferable AmpC-type β-lactamase (ACC-1) originating from Hafnia alvei. FEMS Microbiol. Lett. 187:35-40. [PubMed]
228. Nakano, R., R. Okamoto, N. Nagano, and M. Inoue. 2007. Resistance to gram-negative organisms due to high-level expression of plasmid-encoded ampC β-lactamase blaCMY-4 promoted by insertion sequence ISEcp1. J. Infect. Chemother. 13:18-23. [PubMed]
229. Nakano, R., R. Okamoto, Y. Nakano, K. Kaneko, N. Okitsu, Y. Hosaka, and M. Inoue. 2004. CFE-1, a novel plasmid-encoded AmpC β-lactamase with an ampR gene originating from Citrobacter freundii. Antimicrob. Agents Chemother. 48:1151-1158. [PMC free article] [PubMed]
230. Nasim, K., S. Elsayed, J. D. Pitout, J. Conly, D. L. Church, and D. B. Gregson. 2004. New method for laboratory detection of AmpC β-lactamases in Escherichia coli and Klebsiella pneumoniae. J. Clin. Microbiol. 42:4799-4802. [PMC free article] [PubMed]
231. Navon-Venezia, S., A. Leavitt, and Y. Carmeli. 2007. High tigecycline resistance in multidrug-resistant Acinetobacter baumannii. J. Antimicrob. Chemother. 59:772-774. [PubMed]
232. Neu, H. C., N. X. Chin, K. Jules, and P. Labthavikul. 1986. The activity of BMY 28142 a new broad spectrum β-lactamase stable cephalosporin. J. Antimicrob. Chemother. 17:441-452. [PubMed]
233. Nikaido, H., W. Liu, and E. Y. Rosenberg. 1990. Outer membrane permeability and β-lactamase stability of dipolar ionic cephalosporins containing methoxyimino substituents. Antimicrob. Agents Chemother. 34:337-342. [PMC free article] [PubMed]
234. Niumsup, P., A. M. Simm, K. Nurmahomed, T. R. Walsh, P. M. Bennett, and M. B. Avison. 2003. Genetic linkage of the penicillinase gene, amp, and blrAB, encoding the regulator of β-lactamase expression in Aeromonas spp. J. Antimicrob. Chemother. 51:1351-1358. [PubMed]
235. Nordmann, P., and H. Mammeri. 2007. Extended-spectrum cephalosporinases: structure, detection and epidemiology. Future Microbiol. 2:297-307. [PubMed]
236. Nordström, K., L. G. Burman, and K. G. Eriksson-Grennberg. 1970. Resistance of Escherichia coli to penicillins. 8. Physiology of a class II ampicillin-resistant mutant. J. Bacteriol. 101:659-668. [PMC free article] [PubMed]
237. Nukaga, M., S. Haruta, K. Tanimoto, K. Kogure, K. Taniguchi, M. Tamaki, and T. Sawai. 1995. Molecular evolution of a class C β-lactamase extending its substrate specificity. J. Biol. Chem. 270:5729-5735. [PubMed]
238. Odeh, R., S. Kelkar, A. M. Hujer, R. A. Bonomo, P. C. Schreckenberger, and J. P. Quinn. 2002. Broad resistance due to plasmid-mediated AmpC β-lactamases in clinical isolates of Escherichia coli. Clin. Infect. Dis. 35:140-145. [PubMed]
239. Ogata, H., P. Renesto, S. Audic, C. Robert, G. Blanc, P. E. Fournier, H. Parinello, J. M. Claverie, and D. Raoult. 2005. The genome sequence of Rickettsia felis identifies the first putative conjugative plasmid in an obligate intracellular parasite. PLoS Biol. 3:e248. [PMC free article] [PubMed]
240. Ohana, S., V. Leflon, E. Ronco, M. Rottman, D. Guillemot, S. Lortat-Jacob, P. Denys, G. Loubert, M. H. Nicolas-Chanoine, J. L. Gaillard, and C. Lawrence. 2005. Spread of a Klebsiella pneumoniae strain producing a plasmid-mediated ACC-1 AmpC β-lactamase in a teaching hospital admitting disabled patients. Antimicrob. Agents Chemother. 49:2095-2097. [PMC free article] [PubMed]
241. Olsson, O., S. Bergström, F. P. Lindberg, and S. Normark. 1983. ampC β-lactamase hyperproduction in Escherichia coli: natural ampicillin resistance generated by horizontal chromosomal DNA transfer from Shigella. Proc. Natl. Acad. Sci. USA 80:7556-7560. [PubMed]
242. Olsson, O., S. Bergström, and S. Normark. 1982. Identification of a novel ampC β-lactamase promoter in a clinical isolate of Escherichia coli. EMBO J. 1:1411-1416. [PubMed]
243. Padilla, E., D. Alonso, A. Doménech-Sánchez, C. Gomez, J. L. Pérez, S. Albertí, and N. Borrell. 2006. Effect of porins and plasmid-mediated AmpC β-lactamases on the efficacy of β-lactams in rat pneumonia caused by Klebsiella pneumoniae. Antimicrob. Agents Chemother. 50:2258-2260. [PMC free article] [PubMed]
244. Pai, H., C. I. Kang, J. H. Byeon, K. D. Lee, W. B. Park, H. B. Kim, E. C. Kim, M. D. Oh, and K. W. Choe. 2004. Epidemiology and clinical features of bloodstream infections caused by AmpC-type-β-lactamase-producing Klebsiella pneumoniae. Antimicrob. Agents Chemother. 48:3720-3728. [PMC free article] [PubMed]
245. Pai, H., J. Kim, J. H. Lee, K. W. Choe, and N. Gotoh. 2001. Carbapenem resistance mechanisms in Pseudomonas aeruginosa clinical isolates. Antimicrob. Agents Chemother. 45:480-484. [PMC free article] [PubMed]
246. Palasubramaniam, S., R. Karunakaran, G. G. Gin, S. Muniandy, and N. Parasakthi. 2007. Imipenem-resistance in Klebsiella pneumoniae in Malaysia due to loss of OmpK36 outer membrane protein coupled with AmpC hyperproduction. Int. J. Infect. Dis. 11:472-474. [PubMed]
247. Papagiannitsis, C. C., L. S. Tzouvelekis, E. Tzelepi, and V. Miriagou. 2007. Plasmid-encoded ACC-4, an extended-spectrum cephalosporinase variant from Escherichia coli. Antimicrob. Agents Chemother. 51:3763-3767. [PMC free article] [PubMed]
248. Papanicolaou, G. A., A. A. Medeiros, and G. A. Jacoby. 1990. Novel plasmid-mediated β-lactamase (MIR-1) conferring resistance to oxyimino- and α-methoxy β-lactams in clinical isolates of Klebsiella pneumoniae. Antimicrob. Agents Chemother. 34:2200-2209. [PMC free article] [PubMed]
249. Partridge, S. R. 2007. Genetic environment of ISEcp1 and blaACC-1. Antimicrob. Agents Chemother. 51:2658-2659. [PMC free article] [PubMed]
250. Pasteran, F. G., L. Otaegui, L. Guerriero, G. Radice, R. Maggiora, M. Rapoport, D. Faccone, A. Di Martino, and M. Galas. 2008. Klebsiella pneumoniae carbapenemase-2, Buenos Aires, Argentina. Emerg. Infect. Dis. 14:1178-1180. [PMC free article] [PubMed]
251. Pérez-Pérez, F. J., and N. D. Hanson. 2002. Detection of plasmid-mediated AmpC β-lactamase genes in clinical isolates by using multiplex PCR. J. Clin. Microbiol. 40:2153-2162. [PMC free article] [PubMed]
252. Petrella, S., D. Clermont, I. Casin, V. Jarlier, and W. Sougakoff. 2001. Novel class A β-lactamase Sed-1 from Citrobacter sedlakii: genetic diversity of β-lactamases within the Citrobacter genus. Antimicrob. Agents Chemother. 45:2287-2298. [PMC free article] [PubMed]
253. Pfaller, M. A., R. N. Jones, S. A. Marshall, S. L. Coffman, R. J. Hollis, M. B. Edmond, and R. P. Wenzel. 1997. Inducible ampC β-lactamase producing gram-negative bacilli from blood stream infections: frequency, antimicrobial susceptibility, and molecular epidemiology in a national surveillance program (SCOPE). Diagn. Microbiol. Infect. Dis. 28:211-219. [PubMed]
254. Philippon, A., G. Arlet, and G. A. Jacoby. 2002. Plasmid-determined AmpC-type β-lactamases. Antimicrob. Agents Chemother. 46:1-11. [PMC free article] [PubMed]
255. Pichardo, C., M. del Carmen Conejo, M. Bernabéu-Wittel, A. Pascual, M. E. Jiménez-Mejías, M. de Cueto, M. E. Pachón-Ibáñez, I. García, J. Pachón, and L. Martínez-Martínez. 2005. Activity of cefepime and carbapenems in experimental pneumonia caused by porin-deficient Klebsiella pneumoniae producing FOX-5 β-lactamase. Clin. Microbiol. Infect. 11:31-38. [PubMed]
256. Pichardo, C., J. M. Rodríguez-Martínez, M. E. Pachón-Ibañez, C. Conejo, J. Ibáñez-Martínez, L. Martínez-Martínez, J. Pachón, and A. Pascual. 2005. Efficacy of cefepime and imipenem in experimental murine pneumonia caused by porin-deficient Klebsiella pneumoniae producing CMY-2 β-lactamase. Antimicrob. Agents Chemother. 49:3311-3316. [PMC free article] [PubMed]
257. Pitout, J. D., D. B. Gregson, D. L. Church, and K. B. Laupland. 2007. Population-based laboratory surveillance for AmpC β-lactamase-producing Escherichia coli, Calgary. Emerg. Infect. Dis. 13:443-448. [PMC free article] [PubMed]
258. Pitout, J. D., E. S. Moland, C. C. Sanders, K. S. Thomson, and S. R. Fitzsimmons. 1997. β-Lactamases and detection of β-lactam resistance in Enterobacter spp. Antimicrob. Agents Chemother. 41:35-39. [PMC free article] [PubMed]
259. Pitout, J. D., M. D. Reisbig, M. Mulvey, L. Chui, M. Louie, L. Crowe, D. L. Church, S. Elsayed, D. Gregson, R. Ahmed, P. Tilley, and N. D. Hanson. 2003. Association between handling of pet treats and infection with Salmonella enterica serotype Newport expressing the AmpC β-lactamase, CMY-2. J. Clin. Microbiol. 41:4578-4582. [PMC free article] [PubMed]
260. Poirel, L., M. Guibert, D. Girlich, T. Naas, and P. Nordmann. 1999. Cloning, sequence analyses, expression, and distribution of ampC-ampR from Morganella morganii clinical isolates. Antimicrob. Agents Chemother. 43:769-776. [PMC free article] [PubMed]
261. Poirel, L., M. F. Lartigue, J. W. Decousser, and P. Nordmann. 2005. ISEcp1B-mediated transposition of blaCTX-M in Escherichia coli. Antimicrob. Agents Chemother. 49:447-450. [PMC free article] [PubMed]
262. Poirel, L., T. Naas, D. Nicolas, L. Collet, S. Bellais, J. D. Cavallo, and P. Nordmann. 2000. Characterization of VIM-2, a carbapenem-hydrolyzing metallo-β-lactamase and its plasmid- and integron-borne gene from a Pseudomonas aeruginosa clinical isolate in France. Antimicrob. Agents Chemother. 44:891-897. [PMC free article] [PubMed]
263. Potz, N. A., R. Hope, M. Warner, A. P. Johnson, and D. M. Livermore. 2006. Prevalence and mechanisms of cephalosporin resistance in Enterobacteriaceae in London and South-East England. J. Antimicrob. Chemother. 58:320-326. [PubMed]
264. Power, P., M. Galleni, J. A. Ayala, and G. Gutkind. 2006. Biochemical and molecular characterization of three new variants of AmpC β-lactamases from Morganella morganii. Antimicrob. Agents Chemother. 50:962-967. [PMC free article] [PubMed]
265. Powers, R. A., E. Caselli, P. J. Focia, F. Prati, and B. K. Shoichet. 2001. Structures of ceftazidime and its transition-state analogue in complex with AmpC β-lactamase: implications for resistance mutations and inhibitor design. Biochemistry 40:9207-9214. [PubMed]
266. Preston, K. E., C. C. Radomski, and R. A. Venezia. 2000. Nucleotide sequence of the chromosomal ampC gene of Enterobacter aerogenes Antimicrob. Agents Chemother. 44:3158-3162. [PMC free article] [PubMed]
267. Qin, X., D. M. Zerrt, S. J. Weissman, J. A. Englund, D. M. Denno, E. J. Klein, P. I. Tarr, J. Kwong, J. R. Stapp, L. G. Tulloch, and E. Galanakis. 2008. Prevalence and mechanisms of broad-spectrum β-lactam resistance in Enterobacteriaceae: a children's hospital experience. Antimicrob. Agents Chemother. 52:3909-3914. [PMC free article] [PubMed]
268. Quale, J., S. Bratu, J. Gupta, and D. Landman. 2006. Interplay of efflux system, ampC, and oprD expression in carbapenem resistance of Pseudomonas aeruginosa clinical isolates. Antimicrob. Agents Chemother. 50:1633-1641. [PMC free article] [PubMed]
269. Queenan, A. M., S. Jenkins, and K. Bush. 2001. Cloning and biochemical characterization of FOX-5, an AmpC-type plasmid-encoded β-lactamase from a New York City Klebsiella pneumoniae clinical isolate. Antimicrob. Agents Chemother. 45:3189-3194. [PMC free article] [PubMed]
270. Raimondi, A., A. Traverso, and H. Nikaido. 1991. Imipenem- and meropenem-resistant mutants of Enterobacter cloacae and Proteus rettgeri lack porins. Antimicrob. Agents Chemother. 35:1174-1180. [PMC free article] [PubMed]
271. Raskine, L., I. Borrel, G. Barnaud, S. Boyer, B. Hanau-Bercot, J. Gravisse, R. Labia, G. Arlet, and M. J. Sanson-Le-Pors. 2002. Novel plasmid-encoded class C β-lactamase (MOX-2) in Klebsiella pneumoniae from Greece. Antimicrob. Agents Chemother. 46:2262-2265. [PMC free article] [PubMed]
272. Rasmussen, B. A., D. Keeney, Y. Yang, and K. Bush. 1994. Cloning and expression of a cloxacillin-hydrolyzing enzyme and a cephalosporinase from Aeromonas sobria AER 14M in Escherichia coli: requirement for an E. coli chromosomal mutation for efficient expression of the class D enzyme. Antimicrob. Agents Chemother. 38:2078-2085. [PMC free article] [PubMed]
273. Recchia, G. D., and R. M. Hall. 1995. Gene cassettes: a new class of mobile element. Microbiology 141:3015-3027. [PubMed]
274. Reisbig, M. D., and N. D. Hanson. 2002. The ACT-1 plasmid-encoded AmpC β-lactamase is inducible: detection in a complex β-lactamase background. J. Antimicrob. Chemother. 49:557-560. [PubMed]
275. Reisbig, M. D., and N. D. Hanson. 2004. Promoter sequences necessary for high-level expression of the plasmid-associated ampC β-lactamase gene blaMIR-1. Antimicrob. Agents Chemother. 48:4177-4182. [PMC free article] [PubMed]
276. Reisbig, M. D., A. Hossain, and N. D. Hanson. 2003. Factors influencing gene expression and resistance for gram-negative organisms expressing plasmid-encoded ampC genes of Enterobacter origin. J. Antimicrob. Chemother. 51:1141-1151. [PubMed]
277. Robin, F., J. Delmas, M. Archambaud, C. Schweitzer, C. Chanal, and R. Bonnet. 2006. CMT-type β-lactamase TEM-125, an emerging problem for extended-spectrum β-lactamase detection. Antimicrob. Agents Chemother. 50:2403-2408. [PMC free article] [PubMed]
278. Rogers, M. B., A. C. Parker, and C. J. Smith. 1993. Cloning and characterization of the endogenous cephalosporinase gene, cepA, from Bacteroides fragilis reveals a new subgroup of Ambler class A β-lactamases. Antimicrob. Agents Chemother. 37:2391-2400. [PMC free article] [PubMed]
279. Rottman, M., Y. Benzerara, B. Hanau-Bercot, C. Bizet, A. Philippon, and G. Arlet. 2002. Chromosomal ampC genes in Enterobacter species other than Enterobacter cloacae, and ancestral association of the ACT-1 plasmid-encoded cephalosporinase to Enterobacter asburiae. FEMS Microbiol. Lett. 210:87-92. [PubMed]
280. Ruppé, E., P. Bidet, C. Verdet, G. Arlet, and E. Bingen. 2006. First detection of the Ambler class C 1 AmpC β-lactamase in Citrobacter freundii by a new, simple double-disk synergy test. J. Clin. Microbiol. 44:4204-4207. [PMC free article] [PubMed]
281. Sabath, L. D., M. Jago, and E. P. Abraham. 1965. Cephalosporinase and penicillinase activities of a β-lactamase from Pseudomonas pyocyanea. Biochem. J. 96:739-752. [PubMed]
282. Sader, H. S., R. N. Jones, M. G. Stilwell, M. J. Dowzicky, and T. R. Fritsche. 2005. Tigecycline activity tested against 26,474 bloodstream infection isolates: a collection from 6 continents. Diagn. Microbiol. Infect. Dis. 52:181-186. [PubMed]
283. Sanders, C. C. 1993. Cefepime: the next generation? Clin. Infect. Dis. 17:369-379. [PubMed]
284. Reference deleted.
285. Sanders, C. C., and W. E. Sanders, Jr. 1986. Type I β-lactamases of gram-negative bacteria: interaction with β-lactam antibiotics. J. Infect. Dis. 154:792-800. [PubMed]
286. Sanders, W. E., Jr., J. H. Tenney, and R. E. Kessler. 1996. Efficacy of cefepime in the treatment of infections due to multiply resistant Enterobacter species. Clin. Infect. Dis. 23:454-461. [PubMed]
287. Sawai, T., A. Yamaguchi, and K. Tsukamoto. 1988. Amino acid sequence, active-site residue, and effect of suicide inhibitors on cephalosporinase of Citrobacter freundii GN346. Rev. Infect. Dis. 10:721-725. [PubMed]
288. Schiefer, A. M., I. Wiegand, K. J. Sherwood, B. Wiedemann, and I. Stock. 2005. Biochemical and genetic characterization of the β-lactamases of Y. aldovae, Y. bercovieri, Y. frederiksenii and “Y. ruckeri” strains. Int. J. Antimicrob. Agents 25:496-500. [PubMed]
289. Schmidtke, A. J., and N. D. Hanson. 2006. Model system to evaluate the effect of ampD mutations on AmpC-mediated β-lactam resistance. Antimicrob. Agents Chemother. 50:2030-2037. [PMC free article] [PubMed]
290. Schmidtke, A. J., and N. D. Hanson. 2008. Role of ampD homologs in overproduction of AmpC in clinical isolates of Pseudomonas aeruginosa. Antimicrob. Agents Chemother. 52:3922-3927. [PMC free article] [PubMed]
291. Schumacher, H., M. Nir, B. Mansa, and A. Grassy. 1992. β-Lactamases in Shigella. APMIS 100:954-956. [PubMed]
292. Segal, H., E. C. Nelson, and B. G. Elisha. 2004. Genetic environment and transcription of ampC in an Acinetobacter baumannii clinical isolate. Antimicrob. Agents Chemother. 48:612-614. [PMC free article] [PubMed]
293. Seoane, A., M. V. Francia, and J. M. Garcia Lobo. 1992. Nucleotide sequence of the ampC-ampR region from the chromosome of Yersinia enterocolitica. Antimicrob. Agents Chemother. 36:1049-1052. [PMC free article] [PubMed]
294. Seoane, A., and J. M. Garcia Lobo. 1991. Cloning of chromosomal β-lactamase genes from Yersinia enterocolitica. J. Gen. Microbiol. 137:141-146. [PubMed]
295. Shahid, M., A. Malik, M. Agrawal, and S. Singhal. 2004. Phenotypic detection of extended-spectrum and AmpC β-lactamases by a new spot-inoculation method and modified three-dimensional extract test: comparison with the conventional three-dimensional extract test. J. Antimicrob. Chemother. 54:684-687. [PubMed]
296. Sharma, S., P. Ramnani, and J. S. Virdi. 2004. Detection and assay of β-lactamases in clinical and non-clinical strains of Yersinia enterocolitica biovar 1A. J. Antimicrob. Chemother. 54:401-405. [PubMed]
297. Siu, L. K., P. L. Lu, J. Y. Chen, F. M. Lin, and S. C. Chang. 2003. High-level expression of ampC β-lactamase due to insertion of nucleotides between −10 and −35 promoter sequences in Escherichia coli clinical isolates: cases not responsive to extended-spectrum-cephalosporin treatment. Antimicrob. Agents Chemother. 47:2138-2144. [PMC free article] [PubMed]
298. Smith, C. J., T. K. Bennett, and A. C. Parker. 1994. Molecular and genetic analysis of the Bacteroides uniformis cephalosporinase gene, cblA, encoding the species-specific β-lactamase. Antimicrob. Agents Chemother. 38:1711-1715. [PMC free article] [PubMed]
299. Sohn, S. G., J. J. Lee, E. S. Sohn, L. W. Kang, and S. H. Lee. 2008. Extension of the hydrolysis spectrum of AmpC β-lactamase of Escherichia coli due to amino acid insertion in the H-10 helix. J. Antimicrob. Chemother. 61:965-966. [PubMed]
300. Song, W., I. K. Bae, Y. N. Lee, C. H. Lee, S. H. Lee, and S. H. Jeong. 2007. Detection of extended-spectrum β-lactamases by using boronic acid as an AmpC β-lactamase inhibitor in clinical isolates of Klebsiella spp. and Escherichia coli. J. Clin. Microbiol. 45:1180-1184. [PMC free article] [PubMed]
301. Song, W., S. H. Jeong, J. S. Kim, H. S. Kim, D. H. Shin, K. H. Roh, and K. M. Lee. 2007. Use of boronic acid disk methods to detect the combined expression of plasmid-mediated AmpC β-lactamases and extended-spectrum β-lactamases in clinical isolates of Klebsiella spp., Salmonella spp., and Proteus mirabilis. Diagn. Microbiol. Infect. Dis. 57:315-318. [PubMed]
302. Stapleton, P., K. Shannon, and I. Phillips. 1995. The ability of β-lactam antibiotics to select mutants with derepressed β-lactamase synthesis from Citrobacter freundii. J. Antimicrob. Chemother. 36:483-496. [PubMed]
303. Stapleton, P. D., K. P. Shannon, and G. L. French. 1999. Carbapenem resistance in Escherichia coli associated with plasmid-determined CMY-4 β-lactamase production and loss of an outer membrane protein. Antimicrob. Agents Chemother. 43:1206-1210. [PMC free article] [PubMed]
304. Steward, C. D., J. K. Rasheed, S. K. Hubert, J. W. Biddle, P. M. Raney, G. J. Anderson, P. P. Williams, K. L. Brittain, A. Oliver, J. E. McGowan, Jr., and F. C. Tenover. 2001. Characterization of clinical isolates of Klebsiella pneumoniae from 19 laboratories using the National Committee for Clinical Laboratory Standards extended-spectrum β-lactamase detection methods. J. Clin. Microbiol. 39:2864-2872. [PMC free article] [PubMed]
305. Stock, I. 2005. Natural antimicrobial susceptibility patterns of Kluyvera ascorbata and Kluyvera cryocrescens strains and review of the clinical efficacy of antimicrobial agents used for the treatment of Kluyvera infections. J. Chemother. 17:143-160. [PubMed]
306. Stock, I., S. Burak, K. J. Sherwood, T. Gruger, and B. Wiedemann. 2003. Natural antimicrobial susceptibilities of strains of ‘unusual’ Serratia species: S. ficaria, S. fonticola, S. odorifera, S. plymuthica and S. rubidaea. J. Antimicrob. Chemother. 51:865-885. [PubMed]
307. Stock, I., T. Grueger, and B. Wiedemann. 2003. Natural antibiotic susceptibility of strains of Serratia marcescens and the S. liquefaciens complex: S. liquefaciens sensu stricto, S. proteamaculans and S. grimesii. Int. J. Antimicrob. Agents 22:35-47. [PubMed]
308. Stock, I., T. Grüger, and B. Wiedemann. 2000. Natural antibiotic susceptibility of Rahnella aquatilis and R. aquatilis-related strains. J. Chemother. 12:30-39. [PubMed]
309. Stock, I., B. Henrichfreise, and B. Wiedemann. 2002. Natural antibiotic susceptibility and biochemical profiles of Yersinia enterocolitica-like strains: Y. bercovieri, Y. mollaretii, Y. aldovae and ‘Y. ruckeri.’ J. Med. Microbiol. 51:56-69. [PubMed]
310. Stock, I., M. Rahman, K. J. Sherwood, and B. Wiedemann. 2005. Natural antimicrobial susceptibility patterns and biochemical identification of Escherichia albertii and Hafnia alvei strains. Diagn. Microbiol. Infect. Dis. 51:151-163. [PubMed]
311. Stock, I., K. J. Sherwood, and B. Wiedemann. 2003. Natural antibiotic susceptibility of Ewingella americana strains. J. Chemother. 15:428-441. [PubMed]
312. Stock, I., and B. Wiedemann. 2001. Natural antibiotic susceptibilities of Edwardsiella tarda, E. ictaluri, and E. hoshinae. Antimicrob. Agents Chemother. 45:2245-2255. [PMC free article] [PubMed]
313. Stock, I., and B. Wiedemann. 2003. Natural antimicrobial susceptibilities and biochemical profiles of Yersinia enterocolitica-like strains: Y. frederiksenii, Y. intermedia, Y. kristensenii and Y. rohdei. FEMS Immunol. Med. Microbiol. 38:139-152. [PubMed]
314. Su, L. H., T. L. Wu, J. H. Chia, C. Chu, A. J. Kuo, and C. H. Chiu. 2005. Increasing ceftriaxone resistance in Salmonella isolates from a university hospital in Taiwan. J. Antimicrob. Chemother. 55:846-852. [PubMed]
315. Tan, T. Y., S. Y. Ng, L. Teo, Y. Koh, and C. H. Teok. 2008. Detection of plasmid-mediated AmpC in Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis. J. Clin. Pathol. 61:642-644. [PubMed]
316. Then, R. L., and P. Angehrn. 1982. Trapping of nonhydrolyzable cephalosporins by cephalosporinases in Enterobacter cloacae and Pseudomonas aeruginosa as a possible resistance mechanism. Antimicrob. Agents Chemother. 21:711-717. [PMC free article] [PubMed]
317. Thiolas, A., C. Bollet, B. La Scola, D. Raoult, and J. M. Pagès. 2005. Successive emergence of Enterobacter aerogenes strains resistant to imipenem and colistin in a patient. Antimicrob. Agents Chemother. 49:1354-1358. [PMC free article] [PubMed]
318. Thomson, K. S. 2001. Controversies about extended-spectrum and AmpC beta-lactamases. Emerg. Infect. Dis. 7:333-336. [PMC free article] [PubMed]
319. Thomson, K. S., and C. C. Sanders. 1992. Detection of extended-spectrum β-lactamases in members of the family Enterobacteriaceae: comparison of the double-disk and three-dimensional tests. Antimicrob. Agents Chemother. 36:1877-1882. [PMC free article] [PubMed]
320. Thomson, K. S., C. C. Sanders, and J. A. Washington II. 1993. Ceftazidime resistance in Hafnia alvei. Antimicrob. Agents Chemother. 37:1375-1376. [PMC free article] [PubMed]
321. Tokunaga, H., M. Ishibashi, T. Arakawa, and M. Tokunaga. 2004. Highly efficient renaturation of β-lactamase isolated from moderately halophilic bacteria. FEBS Lett. 558:7-12. [PubMed]
322. Toleman, M. A., P. M. Bennett, and T. R. Walsh. 2006. ISCR elements: novel gene-capturing systems of the 21st century? Microbiol. Mol. Biol. Rev. 70:296-316. [PMC free article] [PubMed]
323. Tracz, D. M., D. A. Boyd, R. Hizon, E. Bryce, A. McGeer, M. Ofner-Agostini, A. E. Simor, S. Paton, and M. R. Mulvey. 2007. ampC gene expression in promoter mutants of cefoxitin-resistant Escherichia coli clinical isolates. FEMS Microbiol. Lett. 270:265-271. [PubMed]
324. Tsakris, A., I. Kristo, A. Poulou, F. Markou, A. Ikonomidis, and S. Pournaras. 2008. First occurrence of KPC-2-possessing Klebsiella pneumoniae in a Greek hospital and recommendation for detection with boronic acid disc tests. J. Antimicrob. Chemother. 62:1257-1260. [PubMed]
325. Tzouvelekis, L. S., E. Tzelepi, M. E. Kaufmann, and A. F. Mentis. 1994. Consecutive mutations leading to the emergence in vivo of imipenem resistance in a clinical strain of Enterobacter aerogenes. J. Med. Microbiol. 40:403-407. [PubMed]
326. Tzouvelekis, L. S., E. Tzelepi, A. F. Mentis, and A. Tsakris. 1993. Identification of a novel plasmid-mediated β-lactamase with chromosomal cephalosporinase characteristics from Klebsiella pneumoniae. J. Antimicrob. Chemother. 31:645-654. [PubMed]
327. Tzouvelekis, L. S., E. Tzelepi, A. F. Mentis, A. C. Vatopoulos, and A. Tsakris. 1992. Imipenem resistance in Enterobacter aerogenes is associated with derepression of chromosomal cephalosporinases and impaired permeability. FEMS Microbiol. Lett. 74:195-199. [PubMed]
328. Underwood, S., and M. B. Avison. 2004. Citrobacter koseri and Citrobacter amalonaticus isolates carry highly divergent β-lactamase genes despite having high levels of biochemical similarity and 16S rRNA sequence homology. J. Antimicrob. Chemother. 53:1076-1080. [PubMed]
329. Vimont, S., D. Aubert, J. X. Mazoit, L. Poirel, and P. Nordmann. 2007. Broad-spectrum β-lactams for treating experimental peritonitis in mice due to Escherichia coli producing plasmid-encoded cephalosporinases. J. Antimicrob. Chemother. 60:1045-1050. [PubMed]
330. Vu, H., and H. Nikaido. 1985. Role of β-lactam hydrolysis in the mechanism of resistance of a β-lactamase-constitutive Enterobacter cloacae strain to expanded-spectrum β-lactams. Antimicrob. Agents Chemother. 27:393-398. [PMC free article] [PubMed]
331. Wachino, J., Y. Doi, K. Yamane, N. Shibata, T. Yagi, T. Kubota, and Y. Arakawa. 2004. Molecular characterization of a cephamycin-hydrolyzing and inhibitor-resistant class A β-lactamase, GES-4, possessing a single G170S substitution in the Ω-loop. Antimicrob. Agents Chemother. 48:2905-2910. [PMC free article] [PubMed]
332. Wachino, J., H. Kurokawa, S. Suzuki, K. Yamane, N. Shibata, K. Kimura, Y. Ike, and Y. Arakawa. 2006. Horizontal transfer of blaCMY-bearing plasmids among clinical Escherichia coli and Klebsiella pneumoniae isolates and emergence of cefepime-hydrolyzing CMY-19. Antimicrob. Agents Chemother. 50:534-541. [PMC free article] [PubMed]
333. Walsh, T. R., L. Hall, A. P. MacGowan, and P. M. Bennett. 1995. Sequence analysis of two chromosomally mediated inducible β-lactamases from Aeromonas sobria, strain 163a, one a class D penicillinase, the other an AmpC cephalosporinase. J. Antimicrob. Chemother. 36:41-52. [PubMed]
334. Walsh, T. R., R. A. Stunt, J. A. Nabi, A. P. MacGowan, and P. M. Bennett. 1997. Distribution and expression of β-lactamase genes among Aeromonas spp. J. Antimicrob. Chemother. 40:171-178. [PubMed]
335. Walther-Rasmussen, J., and N. Høiby. 2002. Plasmid-borne AmpC β-lactamases. Can. J. Microbiol. 48:479-493. [PubMed]
336. Weber, D. A., and C. C. Sanders. 1990. Diverse potential of β-lactamase inhibitors to induce class I enzymes. Antimicrob. Agents Chemother. 34:156-158. [PMC free article] [PubMed]
337. Weng, S. F., Y. F. Chao, and J. W. Lin. 2004. Identification and characteristic analysis of the ampC gene encoding β-lactamase from Vibrio fischeri. Biochem. Biophys. Res. Commun. 314:838-843. [PubMed]
338. Whichard, J., K. Gay, J. E. Stevenson, K. Joyce, K. Cooper, M. Omondi, M. F., G. A. Jacoby, and T. J. Barrett. 2007. Human Salmonella and concurrent decreased susceptibility to quinolones and extended-spectrum cephalosporins. Emerg. Infect. Dis. 13:1681-1688. [PMC free article] [PubMed]
339. Whichard, J. M., K. Joyce, P. D. Fey, J. M. Nelson, F. J. Angulo, and T. J. Barrett. 2005. β-Lactam resistance and Enterobacteriaceae, United States. Emerg. Infect. Dis. 11:1464-1466. [PMC free article] [PubMed]
340. Winokur, P. L., A. Brueggemann, D. L. DeSalvo, L. Hoffmann, M. D. Apley, E. K. Uhlenhopp, M. A. Pfaller, and G. V. Doern. 2000. Animal and human multidrug-resistant, cephalosporin-resistant Salmonella isolates expressing a plasmid-mediated CMY-2 AmpC β-lactamase. Antimicrob. Agents Chemother. 44:2777-2783. [PMC free article] [PubMed]
341. Wong-Beringer, A., J. Hindler, M. Loeloff, A. M. Queenan, N. Lee, D. A. Pegues, J. P. Quinn, and K. Bush. 2002. Molecular correlation for the treatment outcomes in bloodstream infections caused by Escherichia coli and Klebsiella pneumoniae with reduced susceptibility to ceftazidime. Clin. Infect. Dis. 34:135-146. [PubMed]
342. Woodford, N., S. Reddy, E. J. Fagan, R. L. Hill, K. L. Hopkins, M. E. Kaufmann, J. Kistler, M. F. Palepou, R. Pike, M. E. Ward, J. Cheesbrough, and D. M. Livermore. 2007. Wide geographic spread of diverse acquired AmpC β-lactamases among Escherichia coli and Klebsiella spp. in the UK and Ireland. J. Antimicrob. Chemother. 59:102-105. [PubMed]
343. Wu, S. W., K. Dornbusch, G. Kronvall, and M. Norgren. 1999. Characterization and nucleotide sequence of a Klebsiella oxytoca cryptic plasmid encoding a CMY-type β-lactamase: confirmation that the plasmid-mediated cephamycinase originated from the Citrobacter freundii AmpC β-lactamase. Antimicrob. Agents Chemother. 43:1350-1357. [PMC free article] [PubMed]
344. Yagi, T., J. Wachino, H. Kurokawa, S. Suzuki, K. Yamane, Y. Doi, N. Shibata, H. Kato, K. Shibayama, and Y. Arakawa. 2005. Practical methods using boronic acid compounds for identification of class C β-lactamase-producing Klebsiella pneumoniae and Escherichia coli. J. Clin. Microbiol. 43:2551-2558. [PMC free article] [PubMed]
345. Yan, J. J., P. R. Hsueh, J. J. Lu, F. Y. Chang, J. M. Shyr, J. H. Wan, Y. C. Liu, Y. C. Chuang, Y. C. Yang, S. M. Tsao, H. H. Wu, L. S. Wang, T. P. Lin, H. M. Wu, H. M. Chen, and J. J. Wu. 2006. Extended-spectrum β-lactamases and plasmid-mediated AmpC enzymes among clinical isolates of Escherichia coli and Klebsiella pneumoniae from seven medical centers in Taiwan. Antimicrob. Agents Chemother. 50:1861-1864. [PMC free article] [PubMed]
346. Yan, J. J., W. C. Ko, H. M. Wu, S. H. Tsai, C. L. Chuang, and J. J. Wu. 2004. Complexity of Klebsiella pneumoniae isolates resistant to both cephamycins and extended-spectrum cephalosporins at a teaching hospital in Taiwan. J. Clin. Microbiol. 42:5337-5340. [PMC free article] [PubMed]
347. Yan, J. J., W. C. Ko, J. J. Wu, S. H. Tsai, and C. L. Chuang. 2004. Epidemiological investigation of bloodstream infections by extended spectrum cephalosporin-resistant Escherichia coli in a Taiwanese teaching hospital. J. Clin. Microbiol. 42:3329-3332. [PMC free article] [PubMed]
348. Yatsuyanagi, J., S. Saito, T. Konno, S. Harata, N. Suzuki, J. Kato, and K. Amano. 2006. Nosocomial outbreak of ceftazidime-resistant Serratia marcescens strains that produce a chromosomal AmpC variant with N235K substitution. Jpn. J. Infect. Dis. 59:153-159. [PubMed]
349. Yigit, H., G. J. Anderson, J. W. Biddle, C. D. Steward, J. K. Rasheed, L. L. Valera, J. E. McGowan, Jr., and F. C. Tenover. 2002. Carbapenem resistance in a clinical isolate of Enterobacter aerogenes is associated with decreased expression of OmpF and OmpC porin analogs. Antimicrob. Agents Chemother. 46:3817-3822. [PMC free article] [PubMed]
350. Zanetti, G., F. Bally, G. Greub, J. Garbino, T. Kinge, D. Lew, J. A. Romand, J. Bille, D. Aymon, L. Stratchounski, L. Krawczyk, E. Rubinstein, M. D. Schaller, R. Chiolero, M. P. Glauser, and A. Cometta. 2003. Cefepime versus imipenem-cilastatin for treatment of nosocomial pneumonia in intensive care unit patients: a multicenter, evaluator-blind, prospective, randomized study. Antimicrob. Agents Chemother. 47:3442-3447. [PMC free article] [PubMed]
351. Zhu, L. X., Z. W. Zhang, D. Liang, D. Jiang, C. Wang, N. Du, Q. Zhang, K. Mitchelson, and J. Cheng. 2007. Multiplex asymmetric PCR-based oligonucleotide microarray for detection of drug resistance genes containing single mutations in Enterobacteriaceae. Antimicrob. Agents Chemother. 51:3707-3713. [PMC free article] [PubMed]

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