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1.  Longitudinal Farm Study of Extended-Spectrum β-Lactamase-Mediated Resistance 
Journal of Clinical Microbiology  2006;44(5):1630-1634.
Extended-spectrum β-lactamase (ESBL)-mediated resistance is of considerable importance in human medicine. Recently, such enzymes have been reported in bacteria from animals. We describe a longitudinal study of a dairy farm suffering calf scour with high mortality rates. In November 2004, two Escherichia coli isolates with resistance to a wide range of β-lactams (including amoxicillin-clavulanate and cefotaxime) were isolated from scouring calves. Testing by PCR and sequence analysis confirmed the isolates as being both blaCTX-M14/17 and blaTEM-35 (IRT-4) positive. They had indistinguishable plasmid and pulsed-field gel electrophoresis (PFGE) profiles. Transferability studies demonstrated that blaCTX-M was located on a conjugative 65-MDa IncK plasmid. Following a farm visit in December 2004, 31/48 calves and 2/60 cows were positive for E. coli with blaCTX-M. Also, 5/48 calf and 28/60 cow samples yielded blaCTX- and blaTEM-negative E. coli isolates that were resistant to cefotaxime, and sequence analysis confirmed that these presented mutations in the promoter region of the chromosomal ampC gene. Fingerprinting showed 11 different PFGE types (seven in blaCTX-M-positive isolates). Six different PFGE clones conjugated the same blaCTX-M-positive IncK plasmid. One clone carried a different-sized, blaCTX-M-positive, transformable plasmid. This is the first report of blaCTX-M from livestock in the United Kingdom, and this report demonstrates the complexity of ESBL epidemiology. Results indicate that horizontal plasmid transfer between strains as well as horizontal gene transfer between plasmids have contributed to the spread of resistance. We have also shown that some clones can persist for months, suggesting that clonal spread also contributes to the perpetuation of resistance.
PMCID: PMC1479190  PMID: 16672386
2.  Commensal Enterobacteriaceae as reservoirs of extended-spectrum beta-lactamases, integrons, and sul genes in Portugal 
Bacteria colonizing the human intestine have a relevant role in the spread of antimicrobial resistance. We investigated the faecal carriage of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae in healthy humans from Portugal and analyzed the distribution of sul genes and class 1 and 2 integrons. Faecal samples (n = 113) were recovered from healthy persons (North/Centre of Portugal, 2001–2004) and plated on MacConkey agar with and without ceftazidime (1 mg/L) or cefotaxime (1 mg/L). Isolates representing different morphotypes/plate and antibiotic susceptibility patterns (n = 201) were selected. Isolates resistant to sulfonamides and/or streptomycin, gentamicin, and trimethoprim were screened (PCR and sequencing) for sul genes (sul1, sul2, sul3) and class 1 and 2 integrons. Presence of ESBLs was inferred using the double disk synergy test (DDST) and further confirmed by PCR and sequencing. ESBL producers were selected for clonal analysis, plasmid characterization and conjugation assays by standard methods. ESBL-producing isolates were found in 1.8% (2/113) of samples, corresponding to Escherichia coli of phylogroups A (n = 1) and B1 (n = 1) carrying transferable blaCTX-M-14 and the new blaTEM-153, respectively. A 80kb IncK plasmid bearing blaCTX-M-14 was found, being highly related to that widely spread among CTX-M-14 producers of humans and animals from Portugal and other European countries. sul genes were found in 88% (22/25; sul2-60%, sul1-48%, sul3-4%) of the sulfonamide resistant isolates. Class 1 integrons were more frequently found than class 2 (7%, 14/201 vs. 3%, 6/201). Interestingly, gene cassette arrangements within these platforms were identical to those commonly observed among Enterobacteriaceae from Portuguese food-producing animals, although aadA13 is here firstly described in Morganella morganii. These results reinforce the relevance of human commensal flora as reservoir of clinically relevant antibiotic resistance genes including blaESBLs, and highly transferable genetic platforms as IncK epidemic plasmids.
PMCID: PMC3619534  PMID: 23579192
ESBLs; CTX-M-14; TEM-153; class 1 and class 2 integrons; healthy volunteers
3.  The Sudden Dominance of blaCTX–M Harbouring Plasmids in Shigella spp. Circulating in Southern Vietnam 
Plasmid mediated antimicrobial resistance in the Enterobacteriaceae is a global problem. The rise of CTX-M class extended spectrum beta lactamases (ESBLs) has been well documented in industrialized countries. Vietnam is representative of a typical transitional middle income country where the spectrum of infectious diseases combined with the spread of drug resistance is shifting and bringing new healthcare challenges.
We collected hospital admission data from the pediatric population attending the hospital for tropical diseases in Ho Chi Minh City with Shigella infections. Organisms were cultured from all enrolled patients and subjected to antimicrobial susceptibility testing. Those that were ESBL positive were subjected to further investigation. These investigations included PCR amplification for common ESBL genes, plasmid investigation, conjugation, microarray hybridization and DNA sequencing of a blaCTX–M encoding plasmid.
Principal Findings
We show that two different blaCTX-M genes are circulating in this bacterial population in this location. Sequence of one of the ESBL plasmids shows that rather than the gene being integrated into a preexisting MDR plasmid, the blaCTX-M gene is located on relatively simple conjugative plasmid. The sequenced plasmid (pEG356) carried the blaCTX-M-24 gene on an ISEcp1 element and demonstrated considerable sequence homology with other IncFI plasmids.
The rapid dissemination, spread of antimicrobial resistance and changing population of Shigella spp. concurrent with economic growth are pertinent to many other countries undergoing similar development. Third generation cephalosporins are commonly used empiric antibiotics in Ho Chi Minh City. We recommend that these agents should not be considered for therapy of dysentery in this setting.
Author Summary
Shigellosis is a disease caused by bacteria belonging to Shigella spp. and is a leading cause of bacterial gastrointestinal infections in infants in unindustrialized countries. The Shigellae are dynamic and capable of rapid change when placed under selective pressure in a human population. Extended spectrum beta lactamases (ESBLs) are enzymes capable of degrading cephalosporins (a group of antimicrobial agents) and the genes that encode them are common in pathogenic E. coli and other related organisms in industrialized countries. In southern Vietnam, we have isolated multiple cephalosporin-resistant Shigella that express ESBLs. Furthermore, over two years these strains have replaced strains isolated from patients with shigellosis that cannot express ESBLs. Our work describes the genes responsible for this characteristic and we investigate one of the elements carrying one of these genes. These finding have implications for treatment of shigellosis and support the growing necessity for vaccine development. Our findings also may be pertinent for other countries undergoing a similar economic transition to Vietnam's and the corresponding effect on bacterial populations.
PMCID: PMC2882334  PMID: 20544028
4.  Characterization of Extended-Spectrum β-Lactamase Genes Found among Escherichia coli Isolates from Duck and Environmental Samples Obtained on a Duck Farm 
Applied and Environmental Microbiology  2012;78(10):3668-3673.
In this study, we focused on evaluating the occurrence of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli in fecal samples of healthy ducks and environmental samples from a duck farm in South China. Duck cloacal swabs and pond water samples were cultivated on MacConkey agar plates supplemented with ceftiofur. Individual colonies were examined for ESBL production. Bacteria identified as E. coli were screened for the presence of ESBL and plasmid-borne AmpC genes. The genetic relatedness, plasmid replicon type, and genetic background were determined. Of 245 samples analyzed, 123 had E. coli isolates with ceftiofur MICs higher than 8 μg/ml (116 [50.4%] from 230 duck samples and 7 [46.7%] from 15 water samples). blaCTX-M, blaSHV-12, blaCMY-2, and blaDHA-1 were identified in 108, 5, 9, and 1 isolates, respectively. The most common blaCTX-M genes were blaCTX-M-27 (n = 34), blaCTX-M-55 (n = 27), blaCTX-M-24e (n = 22), and blaCTX-M-105 (n = 20), followed by blaCTX-M-14a, blaCTX-M-14b, blaCTX-M-24a, and blaCTX-M-24b. Although most of the CTX-M producers had distinct pulsotypes, clonal transmission between duck and water isolates was observed. blaCTX-M genes were carried by transferable IncN, IncF, and untypeable plasmids. The novel CTX-M gene blaCTX-M-105 was flanked by two hypothetical protein sequences, partial ISEcp1 upstream and truncated IS903D, iroN, orf1, and a Tn1721-like element downstream. It is suggested that the horizontal transfer of blaCTX-M genes mediated by mobile elements and the clonal spread of CTX-M-producing E. coli isolates contributed to the dissemination of blaCTX-M in the duck farm. Our findings highlight the importance of ducks for the dissemination of transferable antibiotic resistance genes into the environment.
PMCID: PMC3346353  PMID: 22407683
5.  Dissemination and Characterization of Plasmids Carrying oqxAB-blaCTX-M Genes in Escherichia coli Isolates from Food-Producing Animals 
PLoS ONE  2013;8(9):e73947.
The association of PMQR and ESBLs in negative-bacteria isolates has been of great concern. The present study was performed to investigate the prevalence of co-transferability of oqxAB and blaCTX-M genes among the 696 Escherichia coli (E. coli) isolates from food-producing animals in South China, and to characterize these plasmids.
The ESBL-encoding genes (blaCTX-M, blaTEM and blaSHV), and PMQR (qnrA, qnrB, qnrS, qnrC, qnrD, aac(6’)-Ib-cr, qepA, and oqxAB) of these 696 isolates were determined by PCR and sequenced directionally. Conjugation, S1 nuclease pulsed-field gel electrophoresis (PFGE) and Southern blotting experiments were performed to investigate the co-transferability and location of oqxAB and blaCTX-M. The EcoRI digestion profiles of the plasmids with oqxAB-blaCTX-M were also analyzed. The clonal relatedness was investigated by PFGE.
Of the 696 isolates, 429 harbored at least one PMQR gene, with oqxAB (328) being the most common type; 191 carried blaCTX-M, with blaCTX-M-14 the most common. We observed a significant higher prevalence of blaCTX-M among the oqxAB-positive isolates (38.7%) than that (17.4%) in the oqxAB-negative isolates. Co-transferability of oqxAB and blaCTX-M was found in 18 of the 127 isolates carrying oqxAB-blaCTX-M. These two genes were located on the same plasmid in all the 18 isolates, with floR being on these plasmids in 13 isolates. The co-dissemination of these genes was mainly mediated by F33:A-: B- and HI2 plasmids with highly similar EcoRI digestion profiles. Diverse PFGE patterns indicated the high prevalence of oqxAB was not caused by clonal dissemination.
blaCTX-M was highly prevalent among the oqxAB-positive isolates. The co-dissemination of oqxAB-blaCTX-M genes in E. coli isolates from food-producing animals is mediated mainly by similar F33:A-: B- and HI2 plasmids. This is the first report of the co-existence of oqxAB, blaCTX-M, and floR on the same plasmids in E. coli.
PMCID: PMC3767592  PMID: 24040123
6.  Spread of blaCTX-M-14 Is Driven Mainly by IncK Plasmids Disseminated among Escherichia coli Phylogroups A, B1, and D in Spain▿  
Antimicrobial Agents and Chemotherapy  2009;53(12):5204-5212.
Since its first description in 2000, CTX-M-14 has become one of the most widespread extended-spectrum β-lactamases in Spain. In the present Escherichia coli multilevel population genetic study involving the characterization of phylogroups, clones, plasmids, and genetic platforms, 61 isolates from 16 hospitalized patients and 40 outpatients and healthy volunteers recovered from 2000 to 2005 were analyzed. Clonal relatedness (XbaI pulsed-field gel electrophoresis [PFGE] type, phylogenetic group, multilocus sequence type [MLST]) was established by standard methods. Analysis of transferred plasmids (I-CeuI; S1 nuclease; restriction fragment length polymorphism analysis; and analysis of RNA interference, replicase, and relaxase) was performed by PCR, sequencing, and hybridization. The genetic environment of blaCTX-M-14 was characterized by PCR on the basis of known associated structures (ISEcp1, IS903, ISCR1). The isolates were mainly recovered from patients in the community (73.8%; 45/61) with urinary tract infections (62.2%; 28/45). They were clonally unrelated by PFGE and corresponded to phylogenetic groups A (36.1%), D (34.4%), and B1 (29.5%). MLST revealed a high degree of sequence type (ST) diversity among phylogroup D isolates and the overrepresentation of the ST10 complex among phylogroup A isolates and ST359/ST155 among phylogroup B1 isolates. Two variants of blaCTX-M-14 previously designated blaCTX-M-14a (n = 59/61) and blaCTX-M-14b (n = 2/61) were detected. blaCTX-M-14a was associated with either ISEcp1 within IncK plasmids (n = 27), ISCR1 linked to an IncHI2 plasmid (n = 1), or ISCR1 linked to IncI-like plasmids (n = 3). The blaCTX-M-14b identified was associated with an ISCR1 element located in an IncHI2 plasmid (n = 1) or with ISEcp1 located in IncK (n = 1). The CTX-M-14-producing E. coli isolates in our geographic area are frequent causes of community-acquired urinary tract infections. The increase in the incidence of such isolates is mostly due to the dissemination of IncK plasmids among E. coli isolates of phylogroups A, B1, and D.
PMCID: PMC2786348  PMID: 19786598
7.  Three Cefotaximases, CTX-M-9, CTX-M-13, and CTX-M-14, among Enterobacteriaceae in the People's Republic of China 
Of 15 extended-spectrum β-lactamase (ESBL)-producing isolates of the family Enterobacteriaceae collected from the First Municipal People's Hospital of Guangzhou, in the southern part of the People's Republic of China, 9 were found to produce CTX-M ESBLs, 3 produced SHV-12, and 3 produced both CTX-M and SHV-12. Eleven isolates produced either TEM-1B or SHV-11, in addition to an ESBL. Nucleotide sequence analysis of the 12 isolates carrying blaCTX-M genes revealed that they harbored three different blaCTX-M genes, blaCTX-M-9 (5 isolates), blaCTX-M-13 (1 isolate), and blaCTX-M-14 (6 isolates). These genes have 98% nucleotide homology with blaToho-2. The blaCTX-M genes were carried on plasmids that ranged in size from 35 to 150 kb. Plasmid fingerprints and pulsed-field gel electrophoresis showed the dissemination of the blaCTX-M genes through transfer of different antibiotic resistance plasmids to different bacteria, suggesting that these resistance determinants are highly mobile. Insertion sequence ISEcp1, found on the upstream region of these genes, may be involved in the translocation of the blaCTX-M genes. This is the first report of the occurrence of SHV-12 and CTX-M ESBLs in China. The presence of strains with these ESBLs shows both the evolution of blaCTX-M genes and their dissemination among at least three species of the family Enterobacteriaceae, Escherichia coli, Klebsiella pneumoniae, and Enterobacter cloacae, isolated within a single hospital. The predominance of CTX-M type enzymes seen in this area of China appears to be similar to that seen in South America but is different from those seen in Europe and North America, suggesting different evolutionary routes and selective pressures. A more comprehensive survey of the ESBL types from China is urgently needed.
PMCID: PMC127467  PMID: 11850241
8.  Molecular epidemiology of extended-spectrum beta-lactamase-producing Escherichia coli in Tunisia and characterization of their virulence factors and plasmid addiction systems 
BMC Microbiology  2013;13:147.
Extended-spectrum β-lactamases (ESBLs), particularly CTX-M- type ESBLs, are among the most important resistance determinants spreading worldwide in Enterobacteriaceae. The aim of this study was to characterize a collection of 163 ESBL-producing Escherichia coli collected in Tunisia, their ESBL-encoding plasmids and plasmid associated addiction systems.
The collection comprised 163 ESBL producers collected from two university hospitals of Sfax between 1989 and 2009. 118 isolates harbored blaCTX-M gene (101 blaCTX-M-15 gene and 17 blaCTX-M-14 gene). 49 isolates carried blaSHV-12 gene, 9 blaSHV-2a gene and only 3 blaTEM-26 gene. 16 isolates produced both CTX-M and SHV-12. The 101 CTX-M-15-producing isolates were significantly associated to phylogroup B2 and exhibiting a high number of virulence factors. 24 (23.7%) of the group B2 isolates belonged to clonal complex ST131. Pulsed-field gel electrophoresis (PFGE) typing revealed a genetic diversity of the isolates. 144 ESBL determinants were transferable mostly by conjugation. The majority of plasmid carrying blaCTX-M-15 genes (72/88) were assigned to various single replicon or multireplicon IncF types and had significantly a higher frequency of addiction systems, notably the VagCD module.
This study demonstrates that the dissemination of CTX-M-15 producing E. coli in our setting was due to the spread of various IncF-type plasmids harboring multiple addiction systems, into related clones with high frequency of virulence determinants.
PMCID: PMC3701463  PMID: 23800277
E. coli; ESBL; CTX-M-15; Plasmid; Addiction systems; Virulence
9.  Molecular Epidemiological Analysis of Escherichia coli Sequence Type ST131 (O25:H4) and blaCTX-M-15 among Extended-Spectrum-β-Lactamase-Producing E. coli from the United States, 2000 to 2009 
Escherichia coli sequence type ST131 (from phylogenetic group B2), often carrying the extended-spectrum-β-lactamase (ESBL) gene blaCTX-M-15, is an emerging globally disseminated pathogen that has received comparatively little attention in the United States. Accordingly, a convenience sample of 351 ESBL-producing E. coli isolates from 15 U.S. centers (collected in 2000 to 2009) underwent PCR-based phylotyping and detection of ST131 and blaCTX-M-15. A total of 200 isolates, comprising 4 groups of 50 isolates each that were (i) blaCTX-M-15 negative non-ST131, (ii) blaCTX-M-15 positive non-ST131, (iii) blaCTX-M-15 negative ST131, or (iv) blaCTX-M-15 positive ST131, also underwent virulence genotyping, antimicrobial susceptibility testing, and pulsed-field gel electrophoresis (PFGE). Overall, 201 (57%) isolates exhibited blaCTX-M-15, whereas 165 (47%) were ST131. ST131 accounted for 56% of blaCTX-M-15-positive- versus 35% of blaCTX-M-15-negative isolates (P < 0.001). Whereas ST131 accounted for 94% of the 175 total group B2 isolates, non-ST131 isolates were phylogenetically distributed by blaCTX-M-15 status, with groups A (blaCTX-M-15-positive isolates) and D (blaCTX-M-15-negative isolates) predominating. Both blaCTX-M-15 and ST131 occurred at all participating centers, were recovered from children and adults, increased significantly in prevalence post-2003, and were associated with molecularly inferred virulence. Compared with non-ST131 isolates, ST131 isolates had higher virulence scores, distinctive virulence profiles, and more-homogeneous PFGE profiles. blaCTX-M-15 was associated with extensive antimicrobial resistance and ST131 with fluoroquinolone resistance. Thus, E. coli ST131 and blaCTX-M-15 are emergent, widely distributed, and predominant among ESBL-positive E. coli strains in the United States, among children and adults alike. Enhanced virulence and antimicrobial resistance have likely promoted the epidemiological success of these emerging public health threats.
PMCID: PMC3346636  PMID: 22354301
10.  Molecular Characterization of Resistance to Extended-Spectrum Cephalosporins in Clinical Escherichia coli Isolates from Companion Animals in the United States ▿ † 
Antimicrobial Agents and Chemotherapy  2011;55(12):5666-5675.
Resistance to extended-spectrum cephalosporins (ESC) among members of the family Enterobacteriaceae occurs worldwide; however, little is known about ESC resistance in Escherichia coli strains from companion animals. Clinical isolates of E. coli were collected from veterinary diagnostic laboratories throughout the United States from 2008 to 2009. E. coli isolates (n = 54) with reduced susceptibility to ceftazidime or cefotaxime (MIC ≥ 16 μg/ml) and extended-spectrum-β-lactamase (ESBL) phenotypes were analyzed. PCR and sequencing were used to detect mutations in ESBL-encoding genes and the regulatory region of the chromosomal gene ampC. Conjugation experiments and plasmid identification were conducted to examine the transferability of resistance to ESCs. All isolates carried the blaCTX-M-1-group β-lactamase genes in addition to one or more of the following β-lactamase genes: blaTEM, blaSHV-3, blaCMY-2, blaCTX-M-14-like, and blaOXA-1. Different blaTEM sequence variants were detected in some isolates (n = 40). Three isolates harbored a blaTEM-181 gene with a novel mutation resulting in an Ala184Val substitution. Approximately 78% of the isolates had mutations in promoter/attenuator regions of the chromosomal gene ampC, one of which was a novel insertion of adenine between bases −28 and −29. Plasmids ranging in size from 11 to 233 kbp were detected in the isolates, with a common plasmid size of 93 kbp identified in 60% of isolates. Plasmid-mediated transfer of β-lactamase genes increased the MICs (≥16-fold) of ESCs for transconjugants. Replicon typing among isolates revealed the predominance of IncI and IncFIA plasmids, followed by IncFIB plasmids. This study shows the emergence of conjugative plasmid-borne ESBLs among E. coli strains from companion animals in the United States, which may compromise the effective therapeutic use of ESCs in veterinary medicine.
PMCID: PMC3232758  PMID: 21947397
11.  Molecular Characterization of Extended-Spectrum-β-Lactamase-Producing and Plasmid-Mediated AmpC β-Lactamase-Producing Escherichia coli Isolated from Stray Dogs in South Korea 
A total of 47 extended-spectrum-cephalosporin-resistant Escherichia coli strains isolated from stray dogs in 2006 and 2007 in the Republic of Korea were investigated using molecular methods. Extended-spectrum β-lactamase (ESBL) and AmpC β-lactamase phenotypes were identified in 12 and 23 E. coli isolates, respectively. All 12 ESBL-producing isolates carried blaCTX-M genes. The most common CTX-M types were CTX-M-14 (n = 5) and CTX-M-24 (n = 3). Isolates producing CTX-M-3, CTX-M-55, CTX-M-27, and CTX-M-65 were also identified. Twenty-one of 23 AmpC β-lactamase-producing isolates were found to carry blaCMY-2 genes. TEM-1 was associated with CTX-M and CMY-2 β-lactamases in 4 and 15 isolates, respectively. In addition to blaTEM-1, two isolates carried blaDHA-1, and one of them cocarried blaCMY-2. Both CTX-M and CMY-2 genes were located on large (40 to 170 kb) conjugative plasmids that contained the insertion sequence ISEcp1 upstream of the bla genes. Only in the case of CTX-M genes was there an IS903 sequence downstream of the gene. The spread of ESBLs and AmpC β-lactamases occurred via both horizontal gene transfer, accounting for much of the CTX-M gene dissemination, and clonal spread, accounting for CMY-2 gene dissemination. The horizontal dissemination of blaCTX-M and blaCMY-2 genes was mediated by IncF and IncI1-Iγ plasmids, respectively. The clonal spread of blaCMY-2 was driven mainly by E. coli strains of virulent phylogroup D lineage ST648. To our knowledge, this is the first report of blaDHA-1 in E. coli strains isolated from companion animals. This study also represents the first report of CMY-2 β-lactamase-producing E. coli isolates from dogs in the Republic of Korea.
PMCID: PMC3346616  PMID: 22354297
12.  Extended-Spectrum-Beta-Lactamases, AmpC Beta-Lactamases and Plasmid Mediated Quinolone Resistance in Klebsiella spp. from Companion Animals in Italy 
PLoS ONE  2014;9(3):e90564.
We report the genetic characterization of 15 Klebsiella pneumoniae (KP) and 4 isolates of K. oxytoca (KO) from clinical cases in dogs and cats and showing extended-spectrum cephalosporin (ESC) resistance. Extended spectrum beta-lactamase (ESBL) and AmpC genes, plasmid-mediated quinolone resistance (PMQR) and co-resistances were investigated. Among KP isolates, ST101 clone was predominant (8/15, 53%), followed by ST15 (4/15, 27%). ST11 and ST340, belonging to Clonal Complex (CC)11, were detected in 2012 (3/15, 20%). MLST on KP isolates corresponded well with PFGE results, with 11 different PFGE patterns observed, including two clusters of two (ST340) and four (ST101) indistinguishable isolates, respectively. All isolates harbored at least one ESBL or AmpC gene, all carried on transferable plasmids (IncR, IncFII, IncI1, IncN), and 16/19 were positive for PMQR genes (qnr family or aac(6′)-Ib-cr). The most frequent ESBL was CTX-M-15 (11/19, 58%), detected in all KP ST101, in one KP ST15 and in both KP ST340. blaCTX-M-15 was carried on IncR plasmids in all but one KP isolate. All KP ST15 isolates harbored different ESC resistance genes and different plasmids, and presented the non-transferable blaSHV-28 gene, in association with blaCTX-M-15, blaCTX-M-1 (on IncR, or on IncN), blaSHV-2a (on IncR) or blaCMY-2 genes (on IncI1). KO isolates were positive for blaCTX-M-9 gene (on IncHI2), or for the blaSHV-12 and blaDHA-1 genes (on IncL/M). They were all positive for qnr genes, and one also for the aac(6′)-Ib-cr gene. All Klebsiella isolates showed multiresistance towards aminoglycosides, sulfonamides, tetracyclines, trimethoprim and amphenicols, mediated by strA/B, aadA2, aadB, ant (2")-Ia, aac(6′)-Ib, sul, tet, dfr and cat genes in various combinations. The emergence in pets of multidrug-resistant Klebsiella with ESBL, AmpC and PMQR determinants, poses further and serious challenges in companion animal therapy and raise concerns for possible bi-directional transmission between pets and humans, especially at household level.
PMCID: PMC3942433  PMID: 24595207
13.  Epidemic Plasmid Carrying blaCTX-M-15 in Klebsiella penumoniae in China 
PLoS ONE  2013;8(1):e52222.
To investigate the local epidemiology of Klebsiella penumoniae carrying blaCTX-M-15 in southern China and to characterize the genetic environment of blaCTX-M-15.
PCR and DNA sequencing were used to detect and characterize the genetic contexts of blaCTX-M-15. The clonal relatedness of isolates carrying blaCTX-M-15 was determined by pulse-field gel electrophoresis. Conjugative plasmids carrying blaCTX-M-15 were obtained by mating and were further subject to restriction analysis and replicon typing.
A total of 47CTX-M-15 ESBL-producing isolates of K. pneumoniae were collected from nine hospitals in China from October 2007 to October 2008. Isolates were clustered into various clonal groups. The local spread of blaCTX-M-15 was mainly mediated by one major conjugative plasmid as determined by S1-PFGE and restriction analysis. A 90-kb plasmid belonging to incompatible group FII was the major carrier of blaCTX-M-15 in K. pneumoniae. Except blaTEM-1, the resistance genes such as blaSHV, blaDHA-1, blaOXA-1, qnrB, qnrS, aac(3)-II, and aac(6′)-Ib were not found in the plasmid. In the comparing of conjugative gene sequence, it is 100% identical with the plasmid pKF3–94, which was found in K. pneumonia from Zhejiang province of china previously.
blaCTX-M-15 was prevalent in K. pneumonia of southern China. The dissemination of blaCTX-M-15 appeared to be due to the horizontal transfer of a 90-kb epidemic plasmid.
PMCID: PMC3558504  PMID: 23382815
14.  Molecular Characterization of CTX-M β-Lactamase and Associated Addiction Systems in Escherichia coli Circulating among Cattle, Farm Workers, and the Farm Environment 
Applied and Environmental Microbiology  2013;79(13):3898-3905.
A total of 84 extended-spectrum β-lactamase (ESBL)-producing Escherichia coli isolates from cattle, farm workers, and the farm environment isolated from February to September 2008 in the Republic of Korea were investigated. All 84 ESBL-producing isolates carried blaCTX-M genes that belonged to the CTX-M-1 (n = 35) or CTX-M-9 (n = 49) family. The most predominant CTX-M type identified was CTX-M-14 (n = 49), followed by CTX-M-32 (n = 26). The blaCTX-M genes were identified most commonly in E. coli isolates from feces (n = 29), teats (n = 25), and milk (n = 14). A blaCTX-M-14 gene was also detected in an E. coli isolate from a farmer's hand. Transfer of the blaCTX-M gene from 60 blaCTX-M-positive E. coli isolates to the recipient E. coli J53 strain by conjugation was demonstrated. Plasmid isolation from blaCTX-M-positive transconjugants revealed a large (95- to 140-kb) conjugative plasmid. Almost all (82/84) blaCTX-M genes possessed an insertion sequence, ISEcp1, upstream of the blaCTX-M gene. Only in the case of the CTX-M-14 genes was IS903 downstream of the gene. The blaCTX-M genes were associated with seven kinds of addiction systems. Among them, pndAC, hok-sok, and srnBC were the most frequently identified addiction systems in both wild strains and transconjugants. The spread of blaCTX-M genes was attributed to both clonal expansion and horizontal dissemination. Our data suggest that a combination of multiple addiction systems in plasmids carrying blaCTX-M genes could contribute to their maintenance in the host cells. To our knowledge, the blaCTX-M-32 gene has not previously been reported in animal isolates from the Republic of Korea.
PMCID: PMC3697548  PMID: 23584784
15.  Using Nucleic Acid Microarrays To Perform Molecular Epidemiology and Detect Novel β-Lactamases: a Snapshot of Extended-Spectrum β-Lactamases throughout the World 
Journal of Clinical Microbiology  2012;50(5):1632-1639.
The worldwide dissemination of extended-spectrum-β-lactamase (ESBL)- and carbapenemase-producing Enterobacteriaceae is a major concern in both hospital and community settings. Rapid identification of these resistant pathogens and the genetic determinants they possess is needed to assist in clinical practice and epidemiological studies. A collection of Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, and Proteus mirabilis isolates, including phenotypically ESBL-positive (n = 1,093) and ESBL-negative isolates (n = 59), obtained in 2008–2009 from a longitudinal surveillance study (SMART) was examined using an in vitro nucleic acid-based microarray. This approach was used to detect and identify blaESBL (blaSHV, blaTEM, and blaCTX-M genes of groups 1, 2, 9, and 8/25) and blaKPC genes and was combined with selective PCR amplification and DNA sequencing for complete characterization of the blaESBL and blaKPC genes. Of the 1,093 phenotypically ESBL-positive isolates, 1,041 were identified as possessing at least one blaESBL gene (95.2% concordance), and 59 phenotypically ESBL-negative isolates, used as negative controls, were negative. Several ESBL variants of blaTEM (n = 5), blaSHV (n = 11), blaCTX-M (n = 19), and blaKPC (n = 3) were detected. A new blaSHV variant, blaSHV-129, and a new blaKPC variant, blaKPC-11, were also identified. The most common bla genes found in this study were blaCTX-M-15, blaCTX-M-14, and blaSHV-12. Using nucleic acid microarrays, we obtained a “molecular snapshot” of blaESBL genes in a current global population; we report that CTX-M-15 is still the dominant ESBL and provide the first report of the new β-lactamase variants blaSHV-129 and blaKPC-11.
PMCID: PMC3347121  PMID: 22322349
16.  Complete Nucleotide Sequence of CTX-M-15-Plasmids from Clinical Escherichia coli Isolates: Insertional Events of Transposons and Insertion Sequences 
PLoS ONE  2010;5(6):e11202.
CTX-M-producing Escherichia coli strains are regarded as major global pathogens.
Methodology/Principal Findings
The nucleotide sequence of three plasmids (pEC_B24: 73801-bp; pEC_L8: 118525-bp and pEC_L46: 144871-bp) from Escherichia coli isolates obtained from patients with urinary tract infections and one plasmid (pEC_Bactec: 92970-bp) from an Escherichia coli strain isolated from the joint of a horse with arthritis were determined. Plasmid pEC_Bactec belongs to the IncI1 group and carries two resistance genes: blaTEM-1 and blaCTX-M-15. It shares more than 90% homology with a previously published blaCTX-M-plasmid from E. coli of human origin. Plasmid pEC_B24 belongs to the IncFII group whereas plasmids pEC_L8 and pEC_L46 represent a fusion of two replicons of type FII and FIA. On the pEC_B24 backbone, two resistance genes, blaTEM-1 and blaCTX-M-15, were found. Six resistance genes, blaTEM-1, blaCTX-M-15, blaOXA-1, aac6'-lb-cr, tetA and catB4, were detected on the pEC_L8 backbone. The same antimicrobial drug resistance genes, with the exception of tetA, were also identified on the pEC_L46 backbone. Genome analysis of all 4 plasmids studied provides evidence of a seemingly frequent transposition event of the blaCTX-M-15-ISEcp1 element. This element seems to have a preferred insertion site at the tnpA gene of a blaTEM-carrying Tn3-like transposon, the latter itself being inserted by a transposition event. The IS26-composite transposon, which contains the blaOXA-1, aac6'-lb-cr and catB4 genes, was inserted into plasmids pEC_L8 and pEC_L46 by homologous recombination rather than a transposition event. Results obtained for pEC_L46 indicated that IS26 also plays an important role in structural rearrangements of the plasmid backbone and seems to facilitate the mobilisation of fragments from other plasmids.
Collectively, these data suggests that IS26 together with ISEcp1 could play a critical role in the evolution of diverse multiresistant plasmids found in clinical Enterobacteriaceae.
PMCID: PMC2887853  PMID: 20585456
17.  Molecular identification of CTX-M and blaOXY/K1 β-lactamase genes in Enterobacteriaceae by sequencing of universal M13-sequence tagged PCR-amplicons 
Plasmid encoded blaCTX-M enzymes represent an important sub-group of class A β-lactamases causing the ESBL phenotype which is increasingly found in Enterobacteriaceae including Klebsiella spp. Molecular typing of clinical ESBL-isolates has become more and more important for prevention of the dissemination of ESBL-producers among nosocomial environment.
Multiple displacement amplified DNA derived from 20 K. pneumoniae and 34 K. oxytoca clinical isolates with an ESBL-phenotype was used in a universal CTX-M PCR amplification assay. Identification and differentiation of blaCTX-M and blaOXY/K1 sequences was obtained by DNA sequencing of M13-sequence-tagged CTX-M PCR-amplicons using a M13-specific sequencing primer.
Nine out of 20 K. pneumoniae clinical isolates had a blaCTX-M genotype. Interestingly, we found that the universal degenerated primers also amplified the chromosomally located K1-gene in all 34 K. oxytoca clinical isolates. Molecular identification and differentiation between blaCTX-M and blaOXY/K1-genes could only been achieved by sequencing of the PCR-amplicons. In silico analysis revealed that the universal degenerated CTX-M primer-pair used here might also amplify the chromosomally located blaOXY and K1-genes in Klebsiella spp. and K1-like genes in other Enterobacteriaceae.
The PCR-based molecular typing method described here enables a rapid and reliable molecular identification of blaCTX-M, and blaOXY/K1-genes. The principles used in this study could also be applied to any situation in which antimicrobial resistance genes would need to be sequenced.
PMCID: PMC2651175  PMID: 19161622
18.  Neonatal septicaemia caused by diverse clones of Klebsiella pneumoniae & Escherichia coli harbouring blaCTX-M-15 
Background & objectives:
Information about the genetic diversity of the extended-spectrum β-lactamases (ESBLs) and the clonal relationship of the organisms causing neonatal infections is limited, particularly from India where neonatal mortality is high. This study was undertaken to investigate the molecular epidemiology and risk factors associated with neonatal septicaemia caused by ESBL-producing Klebsiella pneumoniae and Escherichia coli.
Bloodstream isolates (n=26) of K. pneumoniae (n=10) and E. coli (n=16) from the neonates admitted in a tertiary care hospital in New Delhi during January to May 2008 were characterized. Antimicrobial susceptibility tests were carried out and ESBL production was assessed phenotypically. PCR was carried out for ESBL and ampC genes. Genotyping was performed by pulsed-field gel electrophoresis (PFGE). Conjugation experiments were done to determine the mobility of ESBL genes. Risk factors associated with ESBL-producing K. pneumoniae and E. coli infections were analysed.
Resistance rates to most of the antibiotics tested were high, except for imipenem. Among the isolates tested, 60 per cent of K. pneumoniae and 75 per cent of E. coli were ESBL producers. PFGE of the isolates demonstrated a vast diversity of genotypes with no epidemic clones. Despite the clonal diversity, blaCTX-M-15 was detected in 100 per cent of ESBL-positive isolates. The other genes present in ESBL-positive isolates were blaTEM-1, blaSHV-1, blaSHV-28, blaSHV-11, and blaSHV-12. Class 1 integrons were detected in 7 of 18 ESBL-positive isolates. Moreover, the plasmid carrying blaCTX-M-15, in E. coli and K. pneumoniae were self transferable. Feeding through an enteral tube was identified as the only risk factor for sepsis by ESBL-producing organisms.
Interpretation & conclusions:
The study emphasises the presence of blaCTX-M-15 in clonally diverse isolates indicating probable horizontal transfer of this gene. The widespread dissemination of CTX-M-15 is of great concern as it further confines the limited therapeutic interventions available for neonates.
PMCID: PMC3724262  PMID: 23703349
CTX-M-15; diverse clones; ESBLs; Escherichia coli; Klebsiella pneumoniae; neonatal sepsis; risk factor
19.  Detection of P. aeruginosa harboring bla CTX-M-2, bla GES-1 and bla GES-5, bla IMP-1 and bla SPM-1 causing infections in Brazilian tertiary-care hospital 
BMC Infectious Diseases  2012;12:176.
Nosocomial infections caused by Pseudomonas aeruginosa presenting resistance to beta-lactam drugs are one of the most challenging targets for antimicrobial therapy, leading to substantial increase in mortality rates in hospitals worldwide. In this context, P. aeruginosa harboring acquired mechanisms of resistance, such as production of metallo-beta-lactamase (MBLs) and extended-spectrum beta-lactamases (ESBLs) have the highest clinical impact. Hence, this study was designed to investigate the presence of genes codifying for MBLs and ESBLs among carbapenem resistant P. aeruginosa isolated in a Brazilian 720-bed teaching tertiary care hospital.
Fifty-six carbapenem-resistant P. aeruginosa strains were evaluated for the presence of MBL and ESBL genes. Strains presenting MBL and/or ESBL genes were submitted to pulsed-field gel electrophoresis for genetic similarity evaluation.
Despite the carbapenem resistance, genes for MBLs (blaSPM-1 or blaIMP-1) were detected in only 26.7% of isolates. Genes encoding ESBLs were detected in 23.2% of isolates. The blaCTX-M-2 was the most prevalent ESBL gene (19.6%), followed by blaGES-1 and blaGES-5 detected in one isolate each. In all isolates presenting MBL phenotype by double-disc synergy test (DDST), the blaSPM-1 or blaIMP-1 genes were detected. In addition, blaIMP-1 was also detected in three isolates which did not display any MBL phenotype. These isolates also presented the blaCTX-M-2 gene. The co-existence of blaCTX-M-2 with blaIMP-1 is presently reported for the first time, as like as co-existence of blaGES-1 with blaIMP-1.
In this study MBLs production was not the major mechanism of resistance to carbapenems, suggesting the occurrence of multidrug efflux pumps, reduction in porin channels and production of other beta-lactamases. The detection of blaCTX-M-2,blaGES-1 and blaGES-5 reflects the recent emergence of ESBLs among antimicrobial resistant P. aeruginosa and the extraordinary ability presented by this pathogen to acquire multiple resistance mechanisms. These findings raise the concern about the future of antimicrobial therapy and the capability of clinical laboratories to detect resistant strains, since simultaneous production of MBLs and ESBLs is known to promote further complexity in phenotypic detection. Occurrence of intra-hospital clonal dissemination enhances the necessity of better observance of infection control practices.
PMCID: PMC3512492  PMID: 22863113
P. aeruginosa; Nosocomial infection; ESBL; MBL; CTX-M-2; GES-1; GES-5; IMP-1; SPM-1
20.  Complete Nucleotide Sequences of Plasmids pEK204, pEK499, and pEK516, Encoding CTX-M Enzymes in Three Major Escherichia coli Lineages from the United Kingdom, All Belonging to the International O25:H4-ST131 Clone ▿  
Antimicrobial Agents and Chemotherapy  2009;53(10):4472-4482.
We determined the complete nucleotide sequences of three plasmids that encode CTX-M extended-spectrum β-lactamases (ESBLs) in pulsed-field gel electrophoresis-defined United Kingdom variants (strains A, C, and D) of the internationally prevalent Escherichia coli O25:H4-ST131 clone. Plasmid pEK499 (strain A; 117,536 bp) was a fusion of type FII and FIA replicons and harbored the following 10 antibiotic resistance genes conferring resistance to eight antibiotic classes: blaCTX-M-15, blaOXA-1, blaTEM-1, aac6′-Ib-cr, mph(A), catB4, tet(A), and the integron-borne dfrA7, aadA5, and sulI genes. pEK516 (strain D; 64,471 bp) belonged to incompatibility group IncFII and carried seven antibiotic resistance genes: blaCTX-M-15, blaOXA-1, blaTEM-1, aac6′-Ib-cr, catB4, and tet(A), all as in pEK499. It also carried aac3-IIa, conferring gentamicin resistance, and was highly related to pC15-1a, a plasmid encoding the CTX-M-15 enzyme in Canada. By contrast, pEK204 (strain C; 93,732 bp) belonged to incompatibility group IncI1 and carried only two resistance genes, blaCTX-M-3 and blaTEM-1. It probably arose by the transposition of Tn3 and ISEcp1-blaCTX-M-3 elements into a pCOLIb-P9-like plasmid. We conclude that (i) United Kingdom variants of the successful E. coli ST131 clone have acquired different plasmids encoding CTX-M ESBLs on separate occasions, (ii) the blaCTX-M-3 and blaCTX-M-15 genes on pEK204 and pEK499/pEK516 represent separate escape events, and (iii) IncFII plasmids harboring blaCTX-M-15 have played a crucial role in the global spread of CTX-M-15 ESBLs in E. coli.
PMCID: PMC2764225  PMID: 19687243
21.  Predominance of Klebsiella pneumoniae ST14 carrying CTX-M-15 causing neonatal sepsis in Tanzania 
BMC Infectious Diseases  2013;13:466.
Klebsiella pneumoniae strains expressing ESBLs are a predominant cause of hospital acquired infections. Here we describe the molecular epidemiology of these isolates in a tertiary hospital in Tanzania, as potential pathogens for neonatal infections.
Between April 2009 and March 2010 all Klebsiella pneumoniae isolates with phenotypic expression Extended Spectrum Beta Lactamase (ESBL) were collected and characterized. Identification was done using in house biochemical tests in case of ambiguous results confirmation was done using API 20E. Susceptibility testing was determined using the disc diffusion method followed by specific PCR and sequencing to determine ESBL genes. Phylogenetic analysis, Pulse field gel electrophoresis (PFGE) and Multi-Locus sequence typing (MLST) to PFGE clusters representative isolates were performed to determine clones of the isolates. Conjugation and hybridization were performed to determine the location of blaCTX-M-15 gene.
A total of 92 non- repetitive ESBL producing K. pneumoniae representing 50.3% of Klebsiella pneumoniae isolates were characterized. These isolates were from blood 61 (66%), wound swab 13 (14%), urine 12 (13%) and pus 6 (7%) were analyzed. Most blood culture strains originated from neonatal unit 39/61(64%) and 22 (36%) of the blood culture isolates were from neonatal ICU. All isolates were resistant to gentamicin and 54% were resistant to ciprofloxacin. Using a similarity index of 80%, the isolates were assigned to thirteen clusters based on PFGE patterns and contained sub-clusters with identical strains indicating clonal outbreaks. Cluster X5, X7 and X8, and X9 were grouped into ST48, ST14 and ST348 respectively. Based on gyrA PCR- RFLP phylogenetic analysis all isolates were grouped as KpI. The predominant ESBL allele detected was blaCTX-M-15 which was found in 76% of isolates, followed by blaTEM-104 (19%), blaSHV-11 (3.2%) and blaTEM-176 (2%). The blaCTX-M-15 gene was located in multiple conjugative IncF plasmids ranging from 25 kb-485 kb in size.
The high prevalence of blaCTX-M-15 observed among ESBL producing K. pneumoniae in Tanzania, is possibly due to the spread of a common IncFII 145 kb plasmid and of certain clones such as ST14 and ST48. Furthermore the 485 kb plasmid detected is the largest plasmid reported to carry blaCTX-M-15 todate.
PMCID: PMC3851032  PMID: 24099282
22.  Molecular characterization of blaESBL–harboring conjugative plasmids identified in multi-drug resistant Escherichia coli isolated from food-producing animals and healthy humans 
Background: Extended-spectrum β-lactamase (ESBL)-encoding genes are frequently mapped to plasmids, yet few of these structures have been characterized at the molecular level, to date.
Methods: Eighty-seven ESBL-producing Escherichia coli were isolated from fecal samples of food-producing animals and healthy humans in Switzerland from 2009 to 2011. Plasmid DNA of all isolates was purified. Broth mating assays were carried out individually for 32 isolates to determine if the ESBL marker could be transferred by conjugation. The plasmid sizes were determined by S1-nuclease pulsed-field gel electrophoresis (PFGE) and the plasmids were typed by PCR-based replicon typing. Susceptibility tests by disk diffusion followed with a re-analysis S1-nuclease PFGE and PCRs were performed to confirm plasmid transfer. Microarray was performed to detect additional antibiotic resistance markers and multi-locus sequence typing was also performed in selected donor strains. The phylotypes were identified by triplex PCR.
Results: About half (n = 46) of the 87 isolates carried small (<20-kb) plasmids. All selected 32 isolates contained large plasmids (ranging in sizes from 20- to 600-kb). Eleven plasmid replicon types were detected. Of these, IncFIA (n = 5), IncFIB (n = 9), and IncK/B (n = 4) were common. Nine isolates demonstrated the ability to transfer their cefotaxime resistance marker at high transfer rates. Plasmid profile re-analysis of these transconjugants identified 16 plasmids. IncFIB and IncI1 were the most prevalent replicon types. Phylogenetic grouping showed that five of the nine donor strains belonged to phylogroup B1. Nine different sequence types were identified in nine tested donor strains.
Conclusion: Characterization of these ESBL-encoding conjugative plasmids extends our understanding on these resistance markers in multi-drug resistant E. coli cultured from healthy human and animal sources.
PMCID: PMC3708134  PMID: 23874325
ESBLs; E. coli; horizontal gene transfer; replicon typing; conjugation; S1-nuclease PFGE; plasmid profiling; plasmids
23.  Spread of extended-spectrum beta-lactamase producing Escherichia coli isolates in Swedish broilers mediated by an incI plasmid carrying blaCTX-M-1 
The already high and increasing occurrence of extended-spectrum beta-lactamases (ESBL) producing Escherichia coli in European broiler populations is of concern due to the fact that third and fourth generation cephalosporins are deemed critically important in human medicine. In Sweden 34% of the broilers carry ESBL/pAmpC producing E. coli in their gut, despite the absence of a known selection pressure such as antimicrobial usages. The aim of the current study was to characterise a selection of E. coli strains carrying the blaCTX-M-1, to determine if the spread was due to a specific clone.
Ten isolates carrying blaCTX-M-1 from Swedish broilers belonged to eight different multi-locus sequence types with three isolates belonging to ST155. The ST155 isolates were identical as assessed by PFGE. The blaCTX-M-1 was in all isolates carried on a plasmid of replicon type incI, which also transferred resistance to tetracycline and sulfamethoxazole.
The occurrence of ESBL-producing E. coli in the Swedish broilers is not due to the emergence of a single clone, but rather the spread of a specific incI plasmid carrying blaCTX-M-1.
PMCID: PMC3557190  PMID: 23336334
Extended spectrum betalactamases; ESBL; Broiler; CTX-M-1; Escherichia coli
24.  Analysis of blaCTX-M-Carrying Plasmids from Escherichia coli Isolates Collected in the BfT-GermVet Study ▿  
Applied and Environmental Microbiology  2011;77(20):7142-7146.
In this study, 417 Escherichia coli isolates from defined disease conditions of companion and farm animals collected in the BfT-GermVet study were investigated for the presence of extended-spectrum β-lactamase (ESBL) genes. Three ESBL-producing E. coli isolates were identified among the 100 ampicillin-resistant isolates. The E. coli isolates 168 and 246, of canine and porcine origins, respectively, harbored blaCTX-M-1, and the canine isolate 913 harbored blaCTX-M-15, as confirmed by PCR and sequence analysis. The isolates 168 and 246 belonged to the novel multilocus sequence typing (MLST) types ST1576 and ST1153, respectively, while isolate 913 had the MLST type ST410. The ESBL genes were located on structurally related IncN plasmids in isolates 168 and 246 and on an IncF plasmid in isolate 913. The blaCTX-M-1 upstream regions of plasmids pCTX168 and pCTX246 were similar, whereas the downstream regions showed structural differences. The genetic environment of the blaCTX-M-15 gene on plasmid pCTX913 differed distinctly from that of both blaCTX-M-1 genes. Detailed sequence analysis showed that the integration of insertion sequences, as well as interplasmid recombination events, accounted for the structural variability in the blaCTX-M gene regions.
PMCID: PMC3194854  PMID: 21685166
25.  CTX-M-2 and a New CTX-M-39 Enzyme Are the Major Extended-Spectrum Beta-Lactamases in Multiple Escherichia coli Clones Isolated in Tel Aviv, Israel 
Antimicrobial Agents and Chemotherapy  2005;49(11):4745-4750.
The rate of occurrence of the extended-spectrum beta-lactamase (ESBL)-producing phenotype among Escherichia coli isolates in Tel Aviv is 12% (22). The aim of this study was to understand the molecular epidemiology of E. coli ESBL producers and to identify the ESBL genes carried by them. We studied 20 single-patient ESBL-producing E. coli clinical isolates. They comprised 11 distinct nonrelated pulsed-field gel electrophoresis (PFGE) genotypes: six isolates belonged to the same PFGE clone, four other clones included two isolates each, and six unrelated clones included only one isolate. All isolates produced various beta-lactamases with pIs ranging from 5.2 to 8.2, varying within similar PFGE clones. The most prevalent ESBL gene was blaCTX-M; 16 isolates carried blaCTX-M-2 and three carried a new ESBL gene designated blaCTX-M-39. Three strains carried blaSHV (two blaSHV-12 and one blaSHV-5), and two strains carried inhibitor-resistant ESBL genes, blaTEM-33 and blaTEM-30; 18 strains carried blaTEM-1 and eight strains carried blaOXA-2. Plasmid mapping and Southern blot analysis with a CTX-M-2 probe demonstrated that blaCTX-M-2 is plasmid borne. The wide dissemination of ESBLs among E. coli isolates in our institution is partly related to clonal spread, but more notably to various plasmid-associated ESBL genes, occurring in multiple clones, wherein the CTX-M gene family appears almost uniformly. We report here a new CTX-M gene, designated blaCTX-M-39, which revealed 99% homology with blaCTX-M-26, with a substitution of arginine for glutamine at position 225.
PMCID: PMC1280129  PMID: 16251320

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