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1.  Sensitive Screening Tests for Suspected Class A Carbapenemase Production in Species of Enterobacteriaceae▿  
Journal of Clinical Microbiology  2009;47(6):1631-1639.
The detection of class A serine-carbapenemases among species of Enterobacteriaceae remains a challenging issue. Methods of identification for routine use in clinical microbiology laboratories have not been standardized to date. We developed a novel screening methodology suitable for countries with high basal levels of carbapenem resistance due to non-carbapenemase-mediated mechanisms and standardized several simple confirmatory methods that allow the recognition of bacteria producing class A carbapenemases, including KPC, Sme, IMI, NMC-A, and GES, by using boronic acid (BA) derivatives. A total of 28 genetically unrelated Enterobacteriaceae strains producing several class A carbapenemases were tested. Thirty-eight genetically unrelated negative controls were included. The isolates were tested against imipenem (IPM), meropenem (MEM), and ertapenem (ETP) by MIC and disk diffusion assays in order to select appropriate tools to screen for suspected carbapenemase production. It was possible to differentiate class A carbapenemase-producing bacteria from non-carbapenemase-producing bacteria by using solely the routine IPM susceptibility tests. The modified Hodge test was evaluated and found to be highly sensitive, although false-positive results were documented. Novel BA-based methods (a double-disk synergy test and combined-disk and MIC tests) using IPM, MEM, and ETP, in combination with 3-aminophenylboronic acid as an inhibitor, were designed as confirmatory tools. On the basis of the performance of these methods, a sensitive flow chart for suspicion and confirmation of class A carbapenemase production in species of Enterobacteriaceae was designed. By using this methodology, isolates producing KPC, GES, Sme, IMI, and NMC-A carbapenemases were successfully distinguished from those producing other classes of β-lactamases (extended-spectrum β-lactamases, AmpCs, and metallo-β-lactamases, etc). These methods will rapidly provide useful information needed for targeting antimicrobial therapy and appropriate infection control.
PMCID: PMC2691115  PMID: 19386850
2.  Controlling False-Positive Results Obtained with the Hodge and Masuda Assays for Detection of Class A Carbapenemase in Species of Enterobacteriaceae by Incorporating Boronic Acid▿  
Journal of Clinical Microbiology  2010;48(4):1323-1332.
The modified Hodge method (MHT) has been recommended by the CLSI for confirmation of suspected class A carbapenemase production in species of Enterobacteriaceae. This test and the Masuda method (MAS) have advantages over traditional phenotypic methods in that they directly analyze carbapenemase activity. In order to identify the potential interferences of these tests, we designed a panel composed of diverse bacterial genera with distinct carbapenem susceptibility patterns (42 carbapenemase producers and 48 nonproducers). About 25% of results among carbapenemase nonproducers, mainly strains harboring CTX-M and AmpC hyperproducers, were observed to be false positive. Subsequently, we developed an optimized approach for more-accurate detection of suspicious isolates of carbapenemase by addition of boronic acid (BA) derivatives (reversible inhibitor of class A carbapenemases and AmpC cephalosporinases) and oxacillin (inhibitor of AmpCs enzymes). The use of the modified BA- and oxacillin-based MHT and MAS resulted in high sensitivity (>90%) and specificity (100%) for class A carbapenemase detection. By use of these methodologies, isolates producing KPCs and GES, Sme, IMI, and NMC-A carbapenemases were successfully distinguished from those producing other classes of ß-lactamases (extended-spectrum β-lactamases [ESBLs], AmpC β-lactamases, metallo-β-lactamases [MBLs], etc.). These methods will provide the fast and useful information needed for targeting of antimicrobial therapy and appropriate infection control.
PMCID: PMC2849613  PMID: 20181912
3.  Rapid Molecular Characterization of Acinetobacter baumannii Clones with rep-PCR and Evaluation of Carbapenemase Genes by New Multiplex PCR in Hospital District of Helsinki and Uusimaa 
PLoS ONE  2014;9(1):e85854.
Multidrug-resistant Acinetobacter baumannii (MDRAB) is an increasing problem worldwide. Prevalence of carbapenem resistance in Acinetobacter spp. due to acquired carbapenemase genes is not known in Finland. The purpose of this study was to examine prevalence and clonal spread of multiresistant A. baumannii group species, and their carbapenemase genes. A total of 55 Acinetobacter isolates were evaluated with repetitive PCR (DiversiLab) to analyse clonality of isolates, in conjunction with antimicrobial susceptibility profile for ampicillin/sulbactam, colistin, imipenem, meropenem, rifampicin and tigecycline. In addition, a new real-time PCR assay, detecting most clinically important carbapenemase genes just in two multiplex reactions, was developed. The assay detects genes for KPC, VIM, IMP, GES-1/-10, OXA-48, NDM, GIM-1, SPM-1, IMI/NMC-A, SME, CMY-10, SFC-1, SIM-1, OXA-23-like, OXA-24/40-like, OXA-58 and ISAbaI-OXA-51-like junction, and allows confident detection of isolates harbouring acquired carbapenemase genes. There was a time-dependent, clonal spread of multiresistant A. baumannii strongly correlating with carbapenamase gene profile, at least in this geographically restricted study material. The new carbapenemase screening assay was able to detect all the genes correctly suggesting it might be suitable for epidemiologic screening purposes in clinical laboratories.
PMCID: PMC3897539  PMID: 24465749
4.  Carbapenemases: the Versatile β-Lactamases 
Clinical Microbiology Reviews  2007;20(3):440-458.
Carbapenemases are β-lactamases with versatile hydrolytic capacities. They have the ability to hydrolyze penicillins, cephalosporins, monobactams, and carbapenems. Bacteria producing these β-lactamases may cause serious infections in which the carbapenemase activity renders many β-lactams ineffective. Carbapenemases are members of the molecular class A, B, and D β-lactamases. Class A and D enzymes have a serine-based hydrolytic mechanism, while class B enzymes are metallo-β-lactamases that contain zinc in the active site. The class A carbapenemase group includes members of the SME, IMI, NMC, GES, and KPC families. Of these, the KPC carbapenemases are the most prevalent, found mostly on plasmids in Klebsiella pneumoniae. The class D carbapenemases consist of OXA-type β-lactamases frequently detected in Acinetobacter baumannii. The metallo-β-lactamases belong to the IMP, VIM, SPM, GIM, and SIM families and have been detected primarily in Pseudomonas aeruginosa; however, there are increasing numbers of reports worldwide of this group of β-lactamases in the Enterobacteriaceae. This review updates the characteristics, epidemiology, and detection of the carbapenemases found in pathogenic bacteria.
PMCID: PMC1932750  PMID: 17630334
5.  Comparative Evaluation of Multiplex PCR and Routine Laboratory Phenotypic Methods for Detection of Carbapenemases among Gram Negative Bacilli 
Background: Carbapenem resistant pathogens cause infections associated with significant morbidity and mortality.
Objective: This study evaluates the use of Multiplex PCR for rapid detection of carbapenemase genes among carbapenem resistant Gram negative bacteria in comparison with the existing phenotypic methods like modified Hodge test (MHT), combined disc test (CDT) and automated methods.
Material and Methods: A total of 100 Carbapenem resistant clinical isolates, [Escherichia coli (25), Klebsiella pneumoniae (35) P. aeruginosa (18) and Acinetobacter baumannii (22)] were screened for the presence of carbapenemases (blaNDM-1, blaVIM, blaIMP and blaKPC genes) by phenotype methods such as the modified Hodge test (MHT) and combined disc test (CDT) and the molecular methods such as Multiplex PCR.
Results: Seventy of the 100 isolates were MHT positive while, 65 isolates were positive by CDT. All the CDT positive isolates with EDTA and APB were Metallo betalactamase (MBL) and K. pneumoniae carbapenemase (KPC) producers respectively. blaNDM-1 was present as a lone gene in 44 isolates. In 14 isolates blaNDM-1 gene was present with blaKPC gene, and in one isolate blaNDM-1 gene was present with blaVIM, gene. Only one E. coli isolate had a lone blaKPC gene. We didn’t find blaIMP gene in any of the isolates. Neither of the genes could be detected in 35 isolates.
Conclusion: Accurate detection of the genes related with carbapenemase production by Molecular methods like Multiplex PCR overcome the limitations of the phenotypic methods and Automated systems.
PMCID: PMC4316255  PMID: 25653949
blaNDM-1; blaVIM; blaIMPblaKPCgenes; Combined disc test; Modified hodge test; Multiplex PCR
6.  Laboratory Detection of Enterobacteriaceae That Produce Carbapenemases 
Journal of Clinical Microbiology  2012;50(12):3877-3880.
A study was designed to evaluate the modified Hodge test (MHT), Mastdiscs ID inhibitor combination disks (MDI), Rosco Diagnostica Neo-Sensitabs (RDS), metallo-β-lactamase (MBL) Etest, and in-house multiplex PCR for the detection of well-characterized carbapenemase-producing Enterobacteriaceae. One hundred forty-two nonrepeat clinical isolates of carbapenemase-producing Enterobacteriaceae (including Klebsiella spp., Escherichia coli, Citrobacter freundii, and Enterobacter spp.) obtained from the SMART worldwide surveillance program during 2008 to 2009 were included. These included 49 KPC-, 27 NDM-, 19 VIM-, 14 OXA-48-like enzyme-, and 5 IMP-producing isolates and 28 carbapenem-resistant, carbapenemase-negative isolates. The manufacturer's instructions were followed for MDI, RDS, and MBL Etest and CLSI guidelines for MHT. A multiplex PCR was designed to detect KPC, NDM, VIM, IMP, and OXA-48-like carbapenemases. Overall, the sensitivity and specificity were 78% and 93% for MDI, 80% and 93% for RDS, 58% and 93% for MHT, and 55% and 100% for MBL Etest, respectively. The PCR had 100% sensitivity and specificity. MDI and RDS performed well for the detection of KPCs and NDMs but poorly for VIMs, IMPs, and OXA-48-like enzymes. MHT performed well for KPCs and OXA-48-like enzymes but poorly for NDMs, VIMs, and IMPs. MDI and RDS were easy to perform and interpret but lacked sensitivity for OXA-48-like enzymes, VIMs, and IMPs. MHT and MBL Etest were often difficult to interpret. We recommend using molecular tests for the optimal detection of carbapenemase-producing Enterobacteriaceae.
PMCID: PMC3503014  PMID: 22993175
7.  KPC-mediated resistance in Klebsiella pneumoniae in two hospitals in Padua, Italy, June 2009-December 2011: massive spreading of a KPC-3-encoding plasmid and involvement of non-intensive care units 
Gut Pathogens  2012;4:7.
Klebsiella pneumoniae carbapenemases (KPCs) producing bacteria have emerged as a cause of multidrug-resistant nosocomial infections worldwide. KPCs are plasmid-encoded enzymes capable of hydrolysing a broad spectrum of beta-lactams, including carbapenems and monobactams, therefore worryingly limiting antimicrobial treatment options. Analysis of circulating bacterial strains and KPC alleles may help understanding the route of KPC dissemination and therefore help containing the infection.
KPC-producing Klebsiella pneumoniae dissemination in two 1580- and 300- bed hospitals in Padua, Italy, from initial outbreak in 2009 to late 2011 was analysed. Molecular and clinical epidemiology, including bacterial strains, KPC-encoding plasmid sequences and associated resistance genes, involved hospital wards and relocation of patients were described. Routine antimicrobial susceptibility testing and MIC of carbapenems on clinical isolates were performed. Detection of resistance genes was obtained by PCR and sequencing. MLST, PFGE and ERIC were used for molecular genotyping. Plasmid analysis was obtained by digestion with restriction enzymes and deep sequencing.
KPC-positive clinical samples were isolated from nearly 200 patients. In the initial outbreak intensive care units were almost exclusively involved, while medical, surgical and long-term wards were successively massively concerned. Analysis of KPC alleles, plasmids and bacterial sequence types (STs) indicated that during the initial outbreak KPC-3 in ST258 and KPC-2 in ST147 were each confined in one of the two surveilled hospitals. While KPC-2 dissemination was effectively contained, KPC-3 in ST258 cross-spreading was observed. The simultaneous presence of two carbapenemases, VIM-1 and KPC-2, in the same isolate was also observed in three patients. Total sequencing of plasmid content of two KPC-3 strains showed novel association of resistance plasmids.
The acquired molecular epidemiology demonstrated that 1) both acquisitions from outward sources and patient relocation within the hospitals were responsible for the observed spreading; 2) KPC-3-encoding Klebsiella pneumoniae ST258 prevailed over other strains. In addition, the described massive transfer of KPC-mediated resistance to non-intensive care units may anticipate spreading of resistance to the non-hospitalized population. Therefore, genotypic analysis alongside phenotypic identification of carbapenemase producers, also at the carriage state, is advisable to prevent and contain further carbapenemase resistance dissemination.
PMCID: PMC3411510  PMID: 22800501
KPC; Carbapenemase; Klebsiella pneumoniae; Plasmid-mediated antimicrobial resistance; Gram-negative; Nosocomial infections
8.  Oligonucleotide Microarray for the Identification of Carbapenemase Genes of Molecular Classes A, B, and D  
Acta Naturae  2010;2(3):101-109.
This work is a report on the development of a method of hybridization analysis on DNA microarrays for the simultaneous identification and typing of carbapenemase-encoding genes. These enzymes are produced by the microorganisms that are responsible for causing infectious diseases. The method involves several steps, including DNA extraction from clinical samples and amplification of carbapenemase genes by multiplex PCR with simultaneous labelling by biotin. Following that, hybridization of the labeled PCR products with oligonucleotide probes immobilized on the surface of a nitrocellulose-based DNA microarray occurs. The biotin molecules attached to the DNA duplexes are detected by using conjugates of streptavidin-horseradish peroxidase, which is then quantified by colorimetric detection of the enzyme. We have designed the required oligonucleotide probes and optimized the conditions of the membrane microarray-based hybridization analysis. Our method allows to identify 7 types of carbapenemase genes belonging to the molecular classes A, B, and D, and it also allows additional typing into genetic subgroups. The microarrays have been tested with the control strains producing the carbapenemase genes which have been characterized by sequencing. The developed method of hybridization analysis was employed to investigate clinical strains ofPseudomonasspp. andAcinetobacterspp., which produce carbapenemases of different classes based on phenotypic testing. All strains ofAcinetobacter baumaniiresistant to carbapenems were producers of two carbapenemase OXA-type genes (OXA-51, in combination with OXA-23 (1 strain), OXA-40 (5 strains), or OXA-58 (4 strains)). The metallo-β-lactamase VIM-2 type gene was detected in allPseudomonas aeruginosastrains resistant to carbapenems. Testing of carbapenem-sensitive strains did not detect any carbapenemase genes. The microarray method for the identification of carbapenemase genes is very accurate and highly productive. It can be employed in clinical microbiological laboratories for the identification and study of carbapenemase epidemiology.
PMCID: PMC3347561  PMID: 22649657
DNA microarrays; horseradish peroxidase; colorimetric detection; antibiotic resistance; carbapenemases
9.  Rapid Detection and Statistical Differentiation of KPC Gene Variants in Gram-Negative Pathogens by Use of High-Resolution Melting and ScreenClust Analyses 
In the United States, the production of the Klebsiella pneumoniae carbapenemase (KPC) is an important mechanism of carbapenem resistance in Gram-negative pathogens. Infections with KPC-producing organisms are associated with increased morbidity and mortality; therefore, the rapid detection of KPC-producing pathogens is critical in patient care and infection control. We developed a real-time PCR assay complemented with traditional high-resolution melting (HRM) analysis, as well as statistically based genotyping, using the Rotor-Gene ScreenClust HRM software to both detect the presence of blaKPC and differentiate between KPC-2-like and KPC-3-like alleles. A total of 166 clinical isolates of Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter baumannii with various β-lactamase susceptibility patterns were tested in the validation of this assay; 66 of these organisms were known to produce the KPC β-lactamase. The real-time PCR assay was able to detect the presence of blaKPC in all 66 of these clinical isolates (100% sensitivity and specificity). HRM analysis demonstrated that 26 had KPC-2-like melting peak temperatures, while 40 had KPC-3-like melting peak temperatures. Sequencing of 21 amplified products confirmed the melting peak results, with 9 isolates carrying blaKPC-2 and 12 isolates carrying blaKPC-3. This PCR/HRM assay can identify KPC-producing Gram-negative pathogens in as little as 3 h after isolation of pure colonies and does not require post-PCR sample manipulation for HRM analysis, and ScreenClust analysis easily distinguishes blaKPC-2-like and blaKPC-3-like alleles. Therefore, this assay is a rapid method to identify the presence of blaKPC enzymes in Gram-negative pathogens that can be easily integrated into busy clinical microbiology laboratories.
PMCID: PMC3536237  PMID: 23077125
10.  Outbreaks of Imipenem Resistant Acinetobacter Baumannii Producing OXA-23 β-Lactamase in a Tertiary Care Hospital in Korea 
Yonsei Medical Journal  2009;50(6):764-770.
Since November 2006, imipenem-resistant Acinetobacter baumannii isolates have increased in Kyung Hee University Hospital in Seoul, Korea. The purpose of this study was to determine the genetic basis and molecular epidemiology of outbreak isolates.
Materials and Methods
Forty-nine non-repetitive isolates of the 734 IRAB strains were investigated in order to determine their characteristics. The modified Hodge and the ethylenediaminetetraacetic acid (EDTA)-disk synergy test were performed for the screening of carbapenemase and metallo-β-lactamase production. Multiplex polymerase chain reaction (PCR) assays were performed for the detection of genes encoding for OXA-23-like, OXA-24-like, OXA-58-like and OXA-51-like carbapenemase. Pulsed-field gel electrophoresis (PFGE) was performed for strain identification.
All isolates showed 100% resistance to ciprofloxacin and gentamicin, 97.9% resistance to cefepime, piperacillin/tazobactam, aztreonam, ceftazidime and piperacillin, 93.9% resistance to tobramycin and 57.1% resistance to amikacin. All of the 49 isolates (100%) showed positive results in the modified Hodge test and negative results in the EDTA-disk synergy test. They all (100%) possessed the encoding gene for an intrinsic OXA-51-like carbapenemase and an acquired OXA-23-like carbapenemase in the multiplex PCR assay. PFGE patterns revealed that all isolates were clonally related from A1 to A14.
It is concluded that all of the 49 IRAB isolates acquired resistance to imipenem by producing OXA-23 carbapenemase and they might have originated from a common source.
PMCID: PMC2796401  PMID: 20046415
Imipenem resistant Acinetobacter baumannii; outbreak; OXA-23
11.  OXA-181 Beta Lactamase is not a Major Mediator of Carbapenem Resistance in Enterobacteriaceae 
Background: Detection of carbapenem hydrolyzing class D beta lactamase OXA-181, (a variant of OXA-48) in Enterobacteriaceae, is important, to institute appropriate therapy and to initiate preventive measures. This study was done to determine the presence of OXA 48 and its derivative OXA-181 in Enterobacteriaceae of pathogenic significance.
Material and Methods: One hundred and eleven non–repetitive Enterobacteriaceae isolates which were resistant to any of the cephalosporin subclasses III and which exhibited reduced susceptibility to carbapenems were included in the study. Minimum inhibitory concentrations (MICs) to imipenem and meropenem was determined by broth microdilution. Production of carbapenamase was screened by Modified Hodge test (MHT). Polymerase Chain Reaction (PCR) was done to detect the presence of bla OXA-181 and bla OXA-48 .Coexistence of other carbapenemase encoding genes, namely, NDM-1, VIM, IMP and KPC were also looked for, by PCR.
Results: Of all the isolates which were tested, only 2 (1.8%) revealed the presence of OXA-181 and OXA-48. These were Klebsiella pneumoniae and Citrobacter freundii. MICs of imipenem and meropenem for Klebsiella pneumoniae were 128mg/l and 64 mg/l and for Citrobacter freundii, they were 32mg/l and 16mg/l respectively. MHT was positive in both isolates.
Conclusion: Production of OXA-48 / OXA-181 is not a major mechanism of carbapenem resistance. PCR is the gold standard for its routine identification in clinical microbiology laboratory.
PMCID: PMC3809655  PMID: 24179916
Enterobacteriaceae; OXA-181 carbapenemase; Polymerase chain reaction
12.  Emergence of KPC-producing Klebsiella pneumoniae in Italy 
BMC Research Notes  2010;3:40.
The emergence of KPC-producing K. pneumoniae has now become a global concern. KPC beta-lactamases are plasmid-borne and, like extended spectrum beta lactamases (ESBLs), can accumulate and transfer resistance determinants to other classes of antibiotics. Therefore, infection control guidelines on early identification and control of the spread of organisms carrying these resistant determinants are needed.
Klebsiella pneumoniae carbapenemase (KPC) was detected in two isolates of carbapenem-resistant K. pneumoniae obtained from patients at an Italian teaching hospital. The first strain was isolated from a culture drawn from a central venous device (CVC) in a patient with Crohn's disease who was admitted to a gastroenterology ward. The second was isolated from a urine sample collected from an indwelling urinary catheter in an intensive care unit (ICU) patient with a subdural haematoma. The patients had not travelled abroad. Both isolates were resistant to all β-lactams and were susceptible to imipenem and meropenem but resistant to ertapenem. Isolates also showed resistance to other classes of non-β-lactam antibiotics, such as quinolones, aminoglycosides (with the exception for amikacin), trimethoprim-sulfamethoxazole (TMP-SMX) and nitrofurantoin. They were determined to contain the plasmid encoding the carbapenemase gene bla-KPC and were also positive in the Hodge test.
This is the second report of KPC-producing isolates in Italy, but the first concerning KPC type 2 gene, and it may have important implications for controlling the transmission of microorganisms resistant to antibiotics.
PMCID: PMC2844393  PMID: 20178590
13.  First report of Klebsiella pneumonia carbapenemase-producing Pseudomonas aeruginosa isolated from burn patients in Iran: phenotypic and genotypic methods 
Wound infection associated with carbapenem-resistant Pseudomonas aeruginosa in burn patients is a growing problem. One of the main mechanisms of resistance to carbapenem antibiotics is the ability of P. aeruginosa to produce carbapenemase enzymes. Klebsiella pneumonia carbapemenase (KPC) is an important type of carbapenemase which can hydrolyze carbapenem antibiotics. The Modified Hodge Test (MHT) and boronic acid as a KPC inhibitor are two phenotypic methods used for detection of carbapenemase. The sensitivity and specificity of these two phenotypic tests for the identification of KPC can be measured by PCR.
In this study, 241 P. aeruginosa strains were isolated from wounds of hospitalized burn patients. Carbapenem-resistant P. aeruginosa isolates were determined by the disk diffusion method. KPC-producing carbapenem-resistant strains were examined using the Modified Hodge Test, followed by boronic acid. Further, strains with positive responses to MHT and boronic acid tests were analyzed with the PCR molecular method. One hundred eighty-six of 241 isolates were resistant to carbapenems and 75 were positive in the MHT. Three exhibited an at least 5-mm diameter difference when meropenem was combined with boronic acid vs meropenem alone in the boronic acid test. Two strains had a specific band with primer No.1 after gel electrophoresis.
This study showed that MHT, despite excellent sensitivity, has variable specificity independent of bacterial species. Further, the use of KPC inhibitors such as boronic acid did not yield favorable sensitivity and specificity among the specimens from Iranian patients. Thus, it seems that sequencing after PCR should be considered the gold standard for the detection of KPC-producing P. aeruginosa.
PMCID: PMC3960934  PMID: 24653970
P. aeruginosa; KPC; boronic acid; Modified Hodge Test; blaKPC
14.  A Combined Disk Test for Direct Differentiation of Carbapenemase-Producing Enterobacteriaceae in Surveillance Rectal Swabs 
Journal of Clinical Microbiology  2013;51(9):2986-2990.
Carbapenemase-producing Enterobacteriaceae (CPE) are rapidly spreading worldwide. Early detection of fecal CPE carriers is essential for effective infection control. Here, we evaluated the performance of a meropenem combined disk test (CDT) for rapidly differentiating CPE isolates directly from rectal swabs. The screening method was applied for 189 rectal swabs from hospitalized patients at high risk for CPE carriage. Swabs were suspended in 1 ml saline and cultured for confluent growth onto a MacConkey agar plate with a meropenem (MER) disk alone, a MER disk plus phenyl boronic acid (PBA), a MER disk plus EDTA, and a MER disk plus PBA and EDTA. An inhibition zone of ≤25 mm around the MER disk alone indicated carriage of carbapenem-resistant organisms. Furthermore, ≥5-mm differences in the inhibition zone between MER disks without and with the inhibitors (PBA, EDTA, or both) were considered positive results for detecting Klebsiella pneumoniae carbapenemase (KPC), metallo-β-lactamase (MBL), or both carbapenemases, respectively. For comparison, rectal suspensions were tested using MacConkey plates with ertapenem (MacERT) disks and PCR (PCR-S) for carbapenemase genes. Of the 189 samples, 97 were genotypically confirmed as CPE positive by one of the three protocols tested. The CDT, MacERT disks, and PCR-S assays exhibited sensitivities of 94.8%, 96.9%, and 94.8% and specificities of 100%, 98.9%, and 100%, respectively, for detecting CPE-positive swabs. Moreover, the CDT correctly differentiated the production of KPC, MBL, or both carbapenemases in 78 of the 97 (80.4%) CPE-positive rectal swabs. Our results demonstrate that the CDT may provide a simple and inexpensive method for detecting and differentiating the carbapenemase type within a single day without requiring further testing and additional delay, supporting the timely implementation of infection control measures.
PMCID: PMC3754636  PMID: 23843486
15.  blaKPC gene Detection in Clinical Isolates of Carbapenem Resistant Enterobacteriaceae in a Tertiary Care Hospital 
Introduction: Carbapenem resistance among Enterobacteriaceae, especially in Klebsiella pneumoniae and Escherichia coli, is an emerging problem worldwide. A common mechanism of carbapenem resistance is the production of class-A, Klebsiella pneumoniae carbapenemase (KPC).
Aims and Objectives: The present study focused on determining the antibiotic resistance pattern and prevalence of bla KPC gene coding for KPC in carbapenem resistant Enterobacteriaceae.
Methodology: Forty six carbapenem resistant isolates belonging to the family Enterobacteriaceae were tested for antibiotic sensitivity pattern. Modified Hodge Test (MHT) and PCR for bla KPC gene detection were performed on these isolates. Of these, 22 were Klebsiella pneumoniae, 21 were Escherichia coli, 2 were Citrobacter species and 1 was Proteus mirabilis
Results: Forty three (93.4%) out of the 46 isolates were resistant to Meropenem, 34 (73.9%) were resistant to Imipenem and 30 (65.2%) were resistant to both Imipenem and Meropenem. Modified Hodge Test was positive in 38 (82.6%) out of 46 isolates and blaKPC gene was detected in 31 (67.4%) isolates. bla KPC gene was detected in 28 out of the 38 MHT positive isolates.
PMCID: PMC3919306  PMID: 24551626
Enterbacteriaceae; Carbapenem resistance; Modified Hodge Test; blaKPC gene
16.  Molecular Characterization of Klebsiella pneumoniae Carbapenemase (KPC)-Producing Enterobacteriaceae in Ontario, Canada, 2008-2011 
PLoS ONE  2014;9(12):e116421.
Due to the lack of detailed reports of Klebsiella pneumoniae carbapenemase (KPC)-producing enterobacteria in Ontario, Canada, we perform a molecular characterization of KPC-producing Enterobacteriaceae submitted to the provincial reference laboratory from 2008 to 2011. Susceptibility profiles were accessed by E-test. Molecular types of isolates were determined by pulse-field gel electrophoresis (PFGE) and multilocus sequence typing. Screening of ß-lactamase genes was performed by multiplex PCR and alleles were identified by DNA sequencing. The genetic platform of blaKPC gene was analyzed by PCR. Plasmid replicons were typed using PCR-based typing approach. KPC-plasmids were also evaluated by S1 nuclease-PFGE and Southern blot. Thirty unique clinical isolates (26 Klebsiella pneumoniae, 2 Enterobacter cloacae, 1 Citrobacter freundii and 1 Raoultella ornithinolytica) were identified as blaKPC positive: 4 in 2008, 3 in 2009, 10 in 2010 and 13 in 2011. The majority exhibited resistance to carbapenems, cephalosporins and fluoroquinolones and two isolates were also resistant to colistin. The isolates harbored blaKPC-2 (n = 23) or blaKPC-3 (n = 7). blaTEM-1 (n = 27) was commonly detected and occasionally blaOXA-1 (n = 3) and blaCTX-M-15 (n = 1). As expected, all K. pneumoniae isolates carried blaSHV-11. blaKPC genes were identified on Tn4401a (n = 20) or b (n = 10) isoforms, on plasmids of different sizes belonging to the incompatibility groups IncFIIA (n = 19), IncN (n = 3), IncI2 (n = 3), IncFrep (n = 2) and IncA/C (n = 1). The occurrence of KPC ß-lactamase in Ontario was mainly associated with the spread of the K. pneumoniae clone ST258.
PMCID: PMC4280202  PMID: 25549365
17.  Phenotypic Screening of Carbapenemases and Associated β-Lactamases in Carbapenem-Resistant Enterobacteriaceae 
Journal of Clinical Microbiology  2012;50(4):1295-1302.
Dissemination of carbapenem resistance among Enterobacteriaceae poses a considerable threat to public health. Carbapenemase gene detection by molecular methods is the gold standard but is available in only a few laboratories. The aim of this study was to test phenotypic methods for the detection of metallo-β-lactamase (MBL)- or Klebsiella pneumoniae carbapenemase (KPC)-producing Enterobacteriaceae and associated mechanisms of β-lactam resistance against a panel of 30 genotypically characterized carbapenem-resistant Enterobacteriaceae : 9 MBL, 7 KPC, 6 OXA-48, and 8 extended-spectrum β-lactamase (ESBL) or AmpC β-lactamases associated with decreased permeability. We used carbapenemase inhibitor-impregnated agar to test for carbapenem-resistant strains. Differences in the inhibition zone sizes of the meropenem, imipenem, ertapenem, and doripenem disks were measured between control and inhibitor (EDTA or phenylboronic acid [PBA] with or without cloxacillin)-impregnated Mueller-Hinton agar with a cutoff of 10 mm. All 9 MBL- and 7 KPC-producing Enterobacteriaceae were identified from the differences in zone size in the presence and absence of specific inhibitors, regardless of the carbapenem MICs and including isolates with low-level resistance to carbapenems. We also detected their associated β-lactam resistance mechanisms (11 ESBL-type and 5 class A β-lactamase 2b). No differences in zone size were observed for OXA-48-producing strains or other carbapenem resistance mechanisms such as ESBL and decreased permeability. We propose a new strategy to detect carbapenemases (MBL- and KPC-type) and associated mechanisms of β-lactam resistance (ESBL or class A β-lactamase 2b) by the use of inhibitor-impregnated agar. A rapid phenotypic detection of resistance mechanisms is important for epidemiological purposes and for limiting the spread of resistant strains by implementing specific infection control measures.
PMCID: PMC3318498  PMID: 22259214
18.  Carbapenemase Genes among Multidrug Resistant Gram Negative Clinical Isolates from a Tertiary Hospital in Mwanza, Tanzania 
BioMed Research International  2014;2014:303104.
The burden of antimicrobial resistance (AMR) is rapidly growing across antibiotic classes, with increased detection of isolates resistant to carbapenems. Data on the prevalence of carbapenem resistance in developing countries is limited; therefore, in this study, we determined the prevalence of carbapenemase genes among multidrug resistant gram negative bacteria (MDR-GNB) isolated from clinical specimens in a tertiary hospital in Mwanza, Tanzania. A total of 227 MDR-GNB isolates were analyzed for carbapenem resistance genes. For each isolate, five different PCR assays were performed, allowing for the detection of the major carbapenemase genes, including those encoding the VIM-, IMP-, and NDM-type metallo-beta-lactamases, the class A KPC-type carbapenemases, and the class D OXA-48 enzyme. Of 227 isolates, 80 (35%) were positive for one or more carbapenemase gene. IMP-types were the most predominant gene followed by VIM, in 49 (21.59%) and 28 (12%) isolates, respectively. Carbapenemase genes were most detected in K. pneumoniae 24 (11%), followed by P. aeruginosa 23 (10%), and E. coli with 19 isolates (8%). We have demonstrated for the first time a high prevalence of MDR-GNB clinical isolates having carbapenem resistance genes in Tanzania. We recommend routine testing for carbapenem resistance among the MDR-GNB particularly in systemic infections.
PMCID: PMC3953670  PMID: 24707481
19.  Identification and Differentiation of Carbapenemases in Klebsiella Pneumoniae: A Phenotypic Test Evaluation Study from Jaipur, India 
Background: Carbapenem resistance is one of the major threats faced in antimicrobial treatment of infections caused by gram negative organisms. In recent years, carbapenem resistance has emerged in Klebsiella pneumoniae isolates due to acquisition of carbapenemases which belong to Ambler class A KPC type enzymes or to Ambler class B metallo-β-lactamases (MBL). Routine lab detection of carbapenemase producing K. pneumoniae isolates is crucial, both for a therapeutic management and an efficient infection control.
Materials and Methods: A study was conducted on 60 carbapenem resistant Klebsiella pneumoniae strains which were isolated from various clinical samples over a period of one year (September 2010-August 2011), at a tertiary care hospital in Jaipur. Phenotypic confirmatory test was done by using discs of Meropenem alone and those with phenyl boronic acid (PBA) or Ethylenediaminetetraacetic acid (EDTA) or both, for detection of carbapenemase production and differentiation of KPC and MBL enzymes.
Results: Of the 60 carbapenem resistant Klebsiella pneumoniae isolates, 53 (88.33%) were found to be MBL producers, 4(6.66%) were found to be MBL and KPC co-producers and the rest of the 3(5%) isolates were negative for both MBL and KPC production, as was seen by combined disc testing.
Conclusion: The combined disc test is a simple test which can be used for differentiation of carbapenemases and it can be easily incorporated in routine microbiology lab testing.
PMCID: PMC4149068  PMID: 25177562
Carbapenem resistance; Klebseilla pneumoniae; Enterobacteriaceae; Modified hodge test; Carbapenemase inhibition tests
20.  Multiplex Real-Time PCR Assay for Detection and Classification of Klebsiella pneumoniae Carbapenemase Gene (blaKPC) Variants▿ 
Journal of Clinical Microbiology  2011;49(2):579-585.
Carbapenem resistance mediated by plasmid-borne Klebsiella pneumoniae carbapenemases (KPC) is an emerging problem of significant clinical importance in Gram-negative bacteria. Multiple KPC gene variants (blaKPC) have been reported, with KPC-2 (blaKPC-2) and KPC-3 (blaKPC-3) associated with epidemic outbreaks in New York City and various international settings. Here, we describe the development of a multiplex real-time PCR assay using molecular beacons (MB-PCR) for rapid and accurate identification of blaKPC variants. The assay consists of six molecular beacons and two oligonucleotide primer pairs, allowing for detection and classification of all currently described blaKPC variants (blaKPC-2 to blaKPC-11). The MB-PCR detection limit was 5 to 40 DNA copies per reaction and 4 CFU per reaction using laboratory-prepared samples. The MB-PCR probes were highly specific for each blaKPC variant, and cross-reactivity was not observed using DNA isolated from several bacterial species. A total of 457 clinical Gram-negative isolates were successfully characterized by our MB-PCR assay, with blaKPC-3 and blaKPC-2 identified as the most common types in the New York/New Jersey metropolitan region. The MB-PCR assay described herein is rapid, sensitive, and specific and should be useful for understanding the ongoing evolution of carbapenem resistance in Gram-negative bacteria. As novel blaKPC variants continue to emerge, the MB-PCR assay can be modified in response to epidemiologic developments.
PMCID: PMC3043520  PMID: 21123529
21.  Adenylyl Cyclase Functions Downstream of the Gα Protein Gpa1 and Controls Mating and Pathogenicity of Cryptococcus neoformans 
Eukaryotic Cell  2002;1(1):75-84.
The signaling molecule cyclic AMP (cAMP) is a ubiquitous second messenger that enables cells to detect and respond to extracellular signals. cAMP is generated by the enzyme adenylyl cyclase, which is activated or inhibited by the Gα subunits of heterotrimeric G proteins in response to ligand-activated G-protein-coupled receptors. Here we identified the unique gene (CAC1) encoding adenylyl cyclase in the opportunistic fungal pathogen Cryptococcus neoformans. The CAC1 gene was disrupted by transformation and homologous recombination. In stark contrast to the situation for Saccharomyces cerevisiae, in which adenylyl cyclase is essential, C. neoformans cac1 mutant strains were viable and had no vegetative growth defect. Furthermore, cac1 mutants maintained the yeast-like morphology of wild-type cells, in contrast to the constitutively filamentous phenotype found upon the loss of adenylyl cyclase in another basidiomycete pathogen, Ustilago maydis. Like C. neoformans mutants lacking the Gα protein Gpa1, cac1 mutants were mating defective and failed to produce two inducible virulence factors: capsule and melanin. As a consequence, cac1 mutant strains were avirulent in animal models of cryptococcal meningitis. Reintroduction of the wild-type CAC1 gene or the addition of exogenous cAMP suppressed cac1 mutant phenotypes. Moreover, the overexpression of adenylyl cyclase restored mating and virulence factor production in gpa1 mutant strains. Physiological studies revealed that the Gα protein Gpa1 and adenylyl cyclase controlled cAMP production in response to glucose, and no cAMP was detectable in extracts from cac1 or gpa1 mutant strains. These findings provide direct evidence that Gpa1 and adenylyl cyclase function in a conserved signal transduction pathway controlling cAMP production, hyphal differentiation, and virulence of this human fungal pathogen.
PMCID: PMC118042  PMID: 12455973
22.  A rapid low-cost real-time PCR for the detection of klebsiella pneumonia carbapenemase genes 
Klebsiella pneumonia carbapenemases (KPCs) are able to hydrolyze the carbapenems, which cause many bacteria resistance to multiple classes of antibiotics, so the rapid dissemination of KPCs is worrisome. Laboratory identification of KPCs-harboring clinical isolates would be a key to limit the spread of the bacteria. This study would evaluate a rapid low-cost real-time PCR assay to detect KPCs.
Real-time PCR assay based on SYBR GreenIwas designed to amplify a 106bp product of the blaKPC gene from the159 clinical Gram-negative isolates resistant to several classes of -lactam antibiotics through antimicrobial susceptibility testing. We confirmed the results of real-time PCR assay by the conventional PCR-sequencing. At the same time, KPCs of these clinical isolates were detected by the modified Hodge test (MHT). Then we compared the results of real-time PCR assay with those of MHT from the sensitivity and specificity. Moreover, we evaluated the sensitivity of the real-time PCR assay.
The sensitivity and specificity of the results of the real-time PCR assay compared with those of MHT was 29/29(100%) and 130/130(100%), respectively. The results of the real-time PCR and the MHT were strongly consistent (Exact Sig. (2-tailed) =1. 000; McNemar test). The real-time PCR detection limit was about 0.8cfu using clinical isolates.
The real-time PCR assay could rapidly and accurately detect KPCs -harboring strains with high analytical sensitivity and specificity.
PMCID: PMC3377543  PMID: 22545713
Real-time polymerase chain reaction; Klebsiella pneumonia carbapenemase
23.  Novel Carbapenem-Hydrolyzing β-Lactamase, KPC-1, from a Carbapenem-Resistant Strain of Klebsiella pneumoniae 
A Klebsiella pneumoniae isolate showing moderate to high-level imipenem and meropenem resistance was investigated. The MICs of both drugs were 16 μg/ml. The β-lactamase activity against imipenem and meropenem was inhibited in the presence of clavulanic acid. The strain was also resistant to extended-spectrum cephalosporins and aztreonam. Isoelectric focusing studies demonstrated three β-lactamases, with pIs of 7.2 (SHV-29), 6.7 (KPC-1), and 5.4 (TEM-1). The presence of blaSHV and blaTEM genes was confirmed by specific PCRs and DNA sequence analysis. Transformation and conjugation studies with Escherichia coli showed that the β-lactamase with a pI of 6.7, KPC-1 (K. pneumoniae carbapenemase-1), was encoded on an approximately 50-kb nonconjugative plasmid. The gene, blaKPC-1, was cloned in E. coli and shown to confer resistance to imipenem, meropenem, extended-spectrum cephalosporins, and aztreonam. The amino acid sequence of the novel carbapenem-hydrolyzing β-lactamase, KPC-1, showed 45% identity to the pI 9.7 carbapenem-hydrolyzing β-lactamase, Sme-1, from Serratia marcescens S6. Hydrolysis studies showed that purified KPC-1 hydrolyzed not only carbapenems but also penicillins, cephalosporins, and monobactams. KPC-1 had the highest affinity for meropenem. The kinetic studies also revealed that clavulanic acid and tazobactam inhibited KPC-1. An examination of the outer membrane proteins of the parent K. pneumoniae strain demonstrated that the strain does not express detectable levels of OmpK35 and OmpK37, although OmpK36 is present. We concluded that carbapenem resistance in K. pneumoniae strain 1534 is mainly due to production of a novel Bush group 2f, class A, carbapenem-hydrolyzing β-lactamase, KPC-1, although alterations in porin expression may also play a role.
PMCID: PMC90438  PMID: 11257029
24.  Crystal structure of KPC-2 
Biochemistry  2007;46(19):5732-5740.
β-lactamases inactivate β-lactam antibiotics and are a major cause of antibiotic resistance. The recent outbreaks of Klebsiella pneumoniae carbapenem-resistant (KPC) infections mediated by KPC type β-lactamases are creating a serious threat to our “last resort” antibiotics, the carbapenems. KPC β-lactamases are thus carbapenemases and are a subclass of Class A β-lactamases that have evolved to efficiently hydrolyze carbapenems and cephamycins which contain substitutions at the α position proximal to the carbonyl group that normally render these β-lactams resistant to hydrolysis. To investigate the molecular basis of this carbapenemase activity, we have determined the structure of KPC-2 at 1.85Å resolution. The active site of KPC-2 reveals the presence of a bicine buffer molecule which interacts via its carboxyl group with conserved active site residues S130, K234, T235, and T237; this likely resembles the interactions the β-lactam carboxyl moiety makes in the Michaelis-Menten complex. Comparison of the KPC-2 structure with non-carbapenemases and previously determined NMC-A and SME-1 carbapenemase structures shows several active site alterations that are unique among carbapenemases. An outward shift of the catalytic S70 residue renders the active sites of the carbapenemases more shallow likely allowing easier access of the bulkier substrates. Further space for the α-substituents is likely provided by shifts in N132 and N170 in addition to concerted movements in the postulated carboxyl binding pocket that might allow the substrates to bind in a slightly different angle to accommodate these α-substituents. The structure of KPC-2 thus provides key insights into the carbapenemase activity of emerging Class A β-lactamases.
PMCID: PMC2596071  PMID: 17441734
25.  Isolation of a Klebsiella pneumoniae Isolate of Sequence Type 258 Producing KPC-2 Carbapenemase in Korea 
Carbapenem-resistant Klebsiella pneumoniae isolates producing K. pneumoniae carbapenemases (KPC) were first reported in the USA in 2001, and since then, this infection has been reported in Europe, Israel, South America, and China. In Korea, the first KPC-2-producing K. pneumoniae sequence type (ST) 11 strain was detected in 2010. We report the case of a patient with a urinary tract infection caused by KPC-2-producing K. pneumoniae. This is the second report of a KPC-2-producing K. pneumoniae infection in Korea, but the multilocus sequence type was ST258. The KPC-2-producing isolate was resistant to all tested β-lactams (including imipenem and meropenem), amikacin, tobramycin, ciprofloxacin, levofloxacin, and trimethoprim-sulfamethoxazole, but was susceptible to gentamicin, colistin, polymyxin B, and tigecycline. The KPC-2-producing isolate was negative to phenotypic extended-spectrum β-lactamase (ESBL) and AmpC detection tests and positive to modified Hodge test and carbapenemase inhibition test with aminophenylboronic acid.
PMCID: PMC3190012  PMID: 22016687
KPC-2; Klebsiella pneumoniae; ST258

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