Hidden VIM-1 metallo-beta-lactamase phenotypes among Acinetobacter baumannii clinical isolates

A total of 87 Acinetobacter baumannii nonrepetitive consecutive clinical isolates were tested for the presence of metallo-β-lactamases (MBLs). Results of phenotypic assays (MBL Etest, imipenem/imipenem-EDTA combined-disk test, and imipenem/EDTA double-disk synergy test) were negative in all cases, but molecular testing revealed the presence of two bla_VIM-1-carrying isolates. One isolate had bla_VIM-1 preceded by a weak P1 promoter, and both had inactivated P2 promoters and reduced bla_VIM-1 expression, partially justifying the results revealing hidden MBL phenotypes.     

Evaluation of Boronic Acid Disk Tests for Differentiating KPC-Possessing Klebsiella pneumoniae Isolates in the Clinical Laboratory

The worldwide increase in the occurrence and dissemination of KPC β-lactamases among gram-negative pathogens makes critical the early detection of these enzymes. Boronic acid disk tests using different antibiotic substrates were evaluated for detection of KPC-possessing Klebsiella pneumoniae isolates. A total of 57 genotypically confirmed KPC-possessing K. pneumoniae isolates with varying carbapenem MICs were examined. To measure the specificity of the tests, 106 non-KPC-possessing isolates (89 K. pneumoniae and 17 Escherichia coli isolates) were randomly selected among those exhibiting reduced susceptibility to cefoxitin, expanded-spectrum cephalosporins, or carbapenems. As many as 56, 53, and 40 of the non-KPC-possessing isolates harbored extended-spectrum β-lactamases, metallo-β-lactamases, and plasmid-mediated AmpC β-lactamases, respectively. By use of CLSI methodology and disks containing imipenem, meropenem, or cefepime, either alone or in combination with 400 μg of boronic acid, all 57 KPC producers gave positive results (sensitivity, 100%) whereas all 106 non-KPC producers were negative (specificity, 100%). The meropenem duplicate disk with or without boronic acid demonstrated the largest differences in inhibition zone diameters between KPC producers and non-KPC producers. By use of disks containing ertapenem, all isolates were correctly differentiated except for five AmpC producers that gave false-positive results (sensitivity, 100%; specificity, 95.3%). These practical and simple boronic acid disk tests promise to be very helpful for the accurate differentiation of KPC-possessing K. pneumoniae isolates, even in regions where different broad-spectrum β-lactamases are widespread.     

Multilocus Sequence Types of Carbapenem-Resistant Pseudomonas aeruginosa in Singapore Carrying Metallo-β-Lactamase Genes,Including the Novel blaIMP-26 Gene

Nine imipenem-resistant Pseudomonas aeruginosa isolates were found to contain a variety of metallo-β-lactamase genes, including bla_IMP-1, bla_IMP-7, bla_VIM-2, bla_VIM-6, and the novel bla_IMP-26. Multilocus sequence typing showed a diversity of sequence types. Comparison with isolates from an earlier study showed that the epidemic clones from 2000 have not become established.Carbapenem-resistant Pseudomonas aeruginosa is an increasing problem worldwide. While many underlying mechanisms may account for carbapenem resistance in this species, the possession of metallo-β-lactamase (MBL) genes is of particular concern because these enzymes are able to hydrolyze all β-lactam antimicrobials with the exception of aztreonam. In addition, these genes may be mobilized and transferred between different species of bacteria. We conducted a study in 2008 to investigate if there were any changes in the epidemiology of P. aeruginosa isolates containing MBL genes in our hospital compared to results from an earlier survey carried out in 2000 (3).Of 2,552 nonduplicate P. aeruginosa organisms isolated in 2008, 123 isolates were imipenem resistant. Of these, 11 were positive for MBL production by imipenem-EDTA disk diffusion (5). Nine of these yielded a product by multiplex PCR for MBL genes (2). The individual MBL genes were then amplified and sequenced. The clonal relationship between isolates with MBL genes was determined by pulsed-field gel electrophoresis (PFGE) of chromosomal DNA restricted with SpeI (3). The PFGE band patterns were analyzed with Bionumerics (Applied Maths NV, Sint-Martens-Latem, Belgium), and all strains with more than 85% similarity were considered to belong to the same clone. All strains were further subjected to multilocus sequence typing (MLST) (1). Because it is a nucleic acid sequence-based method, MLST is able to characterize bacterial types in an unambiguous fashion and establish evolutionary relationships between strains better than band-based methods like PFGE. Representative MBL-producing P. aeruginosa isolates from the 2000 survey were also subjected to PFGE and MLST. MLST profiles were submitted to eBURST V3 (http://eburst.mlst.net/) on 10 March 2010. Isolates sharing six out of seven alleles were assigned to the same BURST group and can be considered to belong to the same clonal complex descended from a common founder genotype. The PFGE, MBL gene sequence, and MLST results are summarized in Fig. ​Fig.11.Open in a separate windowFIG. 1.Dendrogram of PFGE patterns of P. aeruginosa isolates with metallo-β-lactamase genes, showing the year of isolation, MLST sequence type, and BURST group.In our previous study, 21 of 2,094 (1.0%) of all nonduplicate P. aeruginosa isolates in our hospital had MBL genes (3). With the exception of one isolate with bla_IMP-7, all other isolates had bla_IMP-1 and belonged to one of two PFGE clones. Isolates belonging to clone A had sequences identical to that of the original bla_IMP-1 first reported in Japan. Four representatives of clone A isolated from our hospital in 2000 had sequence type 964 (ST964) by MLST. Isolates belonging to clone B isolated in 2000 had sequences for variant bla_IMP-1 (bla_IMP-1v) with four silent mutations. Three representatives of this clone from 2000 had ST233 and one had ST742 based on MLST. All four representatives of clone B belong to the same BURST group, which was different from that of clone A.In contrast, in the 2008 survey, 9 of 2,552 (0.35%) nonduplicate P. aeruginosa isolates had MBL genes. Unlike the earlier study, there were no large clonal outbreaks. Two isolates with bla_IMP-1v had similar PFGE patterns and belonged to the same BURST group as representative isolates from clone B in 2000.Two isolates from 2008 with bla_IMP-7 had similar PFGE patterns and shared the same BURST group. The rest of the isolates from 2008 had distinct PFGE patterns.There was a greater diversity of MBL genes compared to the 2000 survey results. In particular, this is the first time that bla_VIM-2 and bla_VIM-6 have been found in P. aeruginosa in Singapore. bla_IMP-26 is a novel MBL gene that differs from bla_IMP-4 at position 145 (G-to-T change). The translated amino acid sequence differs from IMP-4 at residue 49 (phenylalanine for valine). This sequence has been previously deposited in the GenBank database as IMP-4 from an Acinetobacter calcoaceticus isolate from Malaysia (accession number {"type":"entrez-protein","attrs":{"text":"ABC24668.1","term_id":"83583501"}}ABC24668.1).Three of the isolates in this study (separately containing bla_VIM-2, bla_IMP-1, and bla_IMP-7) belonged to ST235. This sequence type has been described in a VIM-producing P. aeruginosa isolate in Belgrade and is the founder of an international clonal complex of isolates bearing MBL genes found in several countries in Europe (6). Recently, an increasing prevalence of IMP-1-producing P. aeruginosa has been found in Hiroshima, Japan. This was due entirely to the clonal expansion of only two lineages, ST235 (BURST group 3) and ST357 (BURST group 108) (4). This is similar to the situation that existed in Singapore in 2000, where only two lineages (BURST groups 29 and 44) accounted for the majority of MBL-producing P. aeruginosa (3).It is noteworthy that the original fear that a clone of MBL-producing P. aeruginosa would become established in Singapore has not been realized. The BURST group 29 and 44 lineages from 2000 were represented by only one to two isolates in 2008. The two P. aeruginosa isolates with bla_IMP-7 in 2008 are unrelated to the solitary isolate with bla_IMP-7 from 2000. It has been suggested that P. aeruginosa displays an epidemic population structure, with a limited number of clones emerging from a large number of unrelated genotypes (7). Although we did not correlate our study with hospital infection control measures, the Japanese data and our own seem to suggest that controlling the prevalence of MBL-producing P. aeruginosa may be achieved by preventing the transmission of specific epidemic clones.While it is reassuring to note that the prevalence of MBL producers in carbapenem-resistant P. aeruginosa has not increased, the increased diversity of MBL genes represents a new cause for concern. We were unable to characterize the gene responsible for the MBL phenotype in two isolates in this study, and these may represent novel resistance determinants. Although clones of MBL-producing P. aeruginosa have not become established, it seems likely, given the variation of MBL genes and MLST types in this study, that MBL-producing P. aeruginosa continues to be introduced to our hospital from diverse sources.     

Infections with VIM-1 Metallo-β-Lactamase-Producing Enterobacter cloacae and Their Correlation with Clinical Outcome

The aim of this study was to ascertain the incidence and clinical significance of metallo-β-lactamases among Enterobacter strains isolated from patients with nosocomial infections. We prospectively collected data on patients with Enterobacter infection during a 13-month period. All of the strains were investigated for antibiotic susceptibility, the presence and expression of metallo-β-lactamases, and clonality. Of 29 infections (11 involving the urinary tract, 7 pneumonias, 3 skin/soft tissue infections, 3 intra-abdominal infections, 3 bacteremias, and 2 other infections), 7 (24%) were caused by Enterobacter cloacae strains harboring a bla_VIM-1 gene associated or not with a bla_SHV12 gene. Infections caused by VIM-1-producing strains were more frequently associated with a recent prior hospitalization (P = 0.006), cirrhosis (P = 0.03), relapse of infection (P < 0.001), and more prolonged duration of antibiotic therapy (P = 0.01) than were other infections. All of the isolates were susceptible to imipenem and meropenem and had bla_VIM-1 preceded by a weak P1 promoter and inactivated P2 promoters. Most VIM-1-producing Enterobacter isolates belonged to a main clone, but four different clones were found. Multiclonal VIM-1-producing E. cloacae infections are difficult to diagnose due to an apparent susceptibility to various beta-lactams, including carbapenems, and are associated with a high relapse rate and a more prolonged duration of antibiotic therapy.The emergence of metallo-β-lactamases (MBLs) in the Enterobacteriaceae is a matter of major concern for clinicians worldwide (7, 28). Infection with VIM-1-producing Klebsiella pneumoniae has become endemic in some European nations (especially in the intensive care units of tertiary care hospitals in Greece [23]), and sporadic cases of infection due to multidrug-resistant Enterobacteriaceae carrying bla_VIM-1 have also been reported (18, 23). In a recent Italian nationwide survey of acquired MBLs in gram-negative pathogens, among 14,812 consecutive nonreplicate clinical isolates (12,245 Enterobacteriaceae isolates and 2,567 gram-negative nonfermenters) screened for reduced carbapenem susceptibility during a 4-month period, 30 (0.2%) isolates (28 Pseudomonas aeruginosa isolates, 1 Pseudomonas putida isolate, and 1 Enterobacter cloacae isolate) carried acquired MBL determinants (20). Despite the presence of an MBL, the carbapenem MICs are frequently below the current resistance breakpoints (23), and no clinical information is available on the outcomes of patients infected with carbapenem-susceptible MBL-producing Enterobacteriaceae.Enterobacter spp. are an important cause of nosocomial infection, but only a few cases of infection due to MBL-producing E. cloacae have been reported in the English literature worldwide (10, 16, 23, 29). In our hospital, we recently observed a fatal case of hospital-acquired pneumonia caused by a VIM-1-producing E. cloacae strain (18). This first episode prompted us to a careful monitoring of Enterobacter infections, to ascertain the incidence and the outcome of MBL production among cases of severe nosocomial infections caused by this species and to better define the biochemical characteristics of MBL-producing strains.(This work was presented in part at the 48th Interscience Conference on Antimicrobial Agents and Chemotherapy, September 2008, Washington, DC [5a].)     

Increasing Carbapenem-Resistant Gram-Negative Bacilli and Decreasing Metallo-β-Lactamase Producers over Eight Years from Korea

The trends and types of carbapenemase-producing Gram-negative bacilli were analyzed from clinical specimens collected between 2005 and 2012 at a Korean teaching hospital. The proportions of carbapenem-resistant Acinetobacter spp. increased markedly to 66%. Metallo-β-lactamase producers significantly decreased and the majority shifted from the bla_VIM-2 type to the bla_IMP-1 type.     

Population Analysis and Epidemiological Features of Inhibitor-Resistant-TEM-β-Lactamase-Producing Escherichia coli Isolates from both Community and Hospital Settings in Madrid,Spain

Punctual mutations in the TEM-1 or TEM-2 gene may lead to inhibitor-resistant-TEM (IRT) β-lactamases with resistance to β-lactam-β-lactamase inhibitor combinations and susceptibility to cephalosporins. The aim of this work was to analyze the current epidemiology of IRT β-lactamases in contemporary clinical Escherichia coli. Isolates were prospectively collected in our hospital (2007 and 2008) from both outpatients (59.8%) and hospitalized patients (40.2%). The genetic relationships of the isolates were determined by XbaI pulsed-field gel electrophoresis, multilocus sequence typing, and phylogenetic group analysis. IRT genes were sequenced and located by hybridization, and the incompatibility group of the plasmids was determined. From a total of 3,556 E. coli isolates recovered during the study period, 152 (4.3%) showed reduced susceptibility to amoxicillin-clavulanate, with 18 of them producing IRT enzymes (0.5%). These were mostly recovered from urine (77.8%). A high degree of IRT diversity was detected (TEM-30, -32, -33, -34, -36, -37, -40, and -54), and the isolates were clonally unrelated but were mostly associated with phylogenetic group B2 (55.5%). In 12 out of 16 (75%) isolates, the bla_IRT gene was plasmid located and transferred by conjugation in 9 of them, whereas chromosomal localization was demonstrated in 4 isolates (25%). The sizes of the plasmids ranged from 40 kb (IncN) to 100 kb (IncFII, IncFI/FIIA), and they showed different restriction patterns by restriction fragment length polymorphism analysis. Unlike extended-spectrum β-lactamase producers, the frequency of IRT producers remains low in both community and hospital settings, with most of them causing urinary tract infections. Although bla_IRT genes are mainly associated with plasmids, they can be also located in the chromosome. Despite this situation, clonal expansion and/or gene dispersion was not observed, denoting the independent emergence of these enzymes.Resistance to β-lactam-β-lactamase inhibitor combinations in Escherichia coli may be due to different mechanisms, including TEM-1 penicillinase hyperproduction, constitutive AmpC overproduction or plasmid AmpC production, OXA-type β-lactamase production, permeability deficiencies involving OmpF and/or OmpC porins, inhibitor-resistant TEM (IRT)- and complex mutant TEM (CMT)-like ß-lactamase production, and more recently, carbapenemase production (4).IRT enzymes comprise a group of plasmid-encoding variants of TEM-1 and TEM-2 with decreased affinities for amino-, carboxy-, and ureidopenicillins and altered interaction with class A ß-lactamase inhibitors (6). IRT-producing isolates remain susceptible to cephalosporins, cephamycins, carbapenems, and in most cases, piperacillin-tazobactam. They are usually resistant to ampicillin-sulbactam and intermediate or resistant to amoxicillin-clavulanate combinations. IRT enzymes have previously been reported in different organisms, such as E. coli, Klebsiella spp., Enterobacter cloacae, Proteus mirabilis, Citrobacter freundii, and Shigella sonnei (4); but there are only a few recent epidemiological studies concerning these enzymes. Moreover, the population structure of IRT-producing E. coli isolates has not been addressed using a multilocus sequence typing (MLST) technique.The aim of the present work was to analyze the current epidemiology of IRT β-lactamases in contemporary E. coli isolates with reduced susceptibility to amoxicillin-clavulanate recovered in our hospital in 2007 and 2008.     

Molecular epidemiology of extended-spectrum beta-lactamases among Escherichia coli isolates collected in a Swedish hospital and its associated health care facilities from 2001 to 2006

The genetic characteristics and molecular epidemiology of extended-spectrum β-lactamases (ESBLs) among Escherichia coli isolates were investigated at a general hospital and its associated health care facilities in Stockholm, Sweden, during the period from 2001 to 2006. Of 87 consecutive nonduplicate ESBL-positive isolates, 80 isolates encoded CTX-M-type ESBLs, 64 of which were group 1 enzymes. TEM-type and OXA-type β-lactamases were encoded in 63 and 59% of the ESBL isolates, respectively. Pulsed-field gel electrophoresis (PFGE) analysis revealed 40 different pulsotypes, consisting of 11 clones accounting for 66% of all isolates, and 29 unique patterns. Moreover, of the 11 clones, clones 1 and 4 comprised half of the clonally related isolates (28 of 57). Clone 1 was a persistent endemic clone in the area throughout the years, and clone 4 emerged in 2003. However, in recent years, clone 1 isolates were no longer predominant and were gradually replaced by new emerging strains. Concerning β-lactamase gene profiles in relation to PFGE pulsotypes, clone-related bla profiles were observed in certain clones, while in most cases different bla profiles could be observed in the same clone, and the same bla profile could be present in different clones. The molecular epidemiology of ESBL-positive E. coli in the area shows shifts in predominant strains and increased clonal diversity over time. The study also indicated that both clonal spread of epidemic strains and transfer of transposable genetic elements might contribute to the proliferation of ESBLs.     

Can Results Obtained with Commercially Available MicroScan Microdilution Panels Serve as an Indicator of β-Lactamase Production among Escherichia coli and Klebsiella Isolates with Hidden Resistance to ExpandedSpectrum Cephalosporins and Aztreonam?

Among clinical isolates of Escherichia coli, Klebsiella pneumoniae, and Klebsiella oxytoca, there is an ever-increasing prevalence of β-lactamases that may confer resistance to newer β-lactam antibiotics that is not detectable by conventional procedures. Therefore, 75 isolates of these species producing well-characterized β-lactamases were studied using two MicroScan conventional microdilution panels, Gram Negative Urine MIC 7 (NU7) and Gram Negative MIC Plus 2 (N+2), to determine if results could be utilized to provide an accurate indication of β-lactamase production in the absence of frank resistance to expanded-spectrum cephalosporins and aztreonam. The enzymes studied included Bush groups 1 (AmpC), 2b (TEM-1, TEM-2, and SHV-1), 2be (extended spectrum β-lactamases [ESBLs] and K1), and 2br, alone and in various combinations. In tests with E. coli and K. pneumoniae and the NU7 panel, cefpodoxime MICs of ≥2 μg/ml were obtained only for isolates producing ESBLs or AmpC β-lactamases. Cefoxitin MICs of >16 μg/ml were obtained for all strains producing AmpC β-lactamase and only 1 of 33 strains producing ESBLs. For the N+2 panel, ceftazidime MICs of ≥4 μg/ml correctly identified 90% of ESBL producers and 100% of AmpC producers among isolates of E. coli and K. pneumoniae. Cefotetan MICs of ≥ 8 μg/ml were obtained for seven of eight producers of AmpC β-lactamase and no ESBL producers. For tests performed with either panel and isolates of K. oxytoca, MICs of ceftazidime, cefotaxime, and ceftizoxime were elevated for strains producing ESBLs, while ceftriaxone and aztreonam MICs separated low-level K1 from high-level K1 producers within this species. These results suggest that microdilution panels can be used by clinical laboratories as an indicator of certain β-lactamases that may produce hidden but clinically significant resistance among isolates of E. coli, K. pneumoniae, and K. oxytoca. Although it may not always be possible to differentiate between strains that produce ESBLs and those that produce AmpC, this differentiation is not critical since therapeutic options for patients infected with such organisms are similarly limited.     

Coproduction of KPC-18 and VIM-1 Carbapenemases by Enterobacter cloacae: Implications for Newer β-Lactam–β-Lactamase Inhibitor Combinations

Enterobacter cloacae strain G6809 with reduced susceptibility to carbapenems was identified from a patient in a long-term acute care hospital in Kentucky. G6809 belonged to sequence type (ST) 88 and carried two carbapenemase genes, bla_KPC-18 and bla_VIM-1. Whole-genome sequencing localized bla_KPC-18 to the chromosome and bla_VIM-1 to a 58-kb plasmid. The strain was highly resistant to ceftazidime-avibactam. Insidious coproduction of metallo-β-lactamase with KPC-type carbapenemase has implications for the use of next-generation β-lactam–β-lactamase inhibitor combinations.     

Dissemination of IMP-6-producing Pseudomonas aeruginosa ST244 in multiple cities in China

Pseudomonas aeruginosa is an important opportunistic pathogen responsible for nosocomial infections and is currently reported to be a worldwide nosocomial menace. The aim of this study was to investigate the epidemiological traits and the distribution of metallo-β-lactamases (MBLs)-producing P. aeruginosa clinical isolates in ten cities in China between January 2010 and May 2012. Antimicrobial susceptibility was determined by disc diffusion assay and the minimum inhibitory concentrations (MICs) of imipenem and meropenem were also determined by the Etest according to Clinical and Laboratory Standards Institute (CLSI) guidelines. In addition, polymerase chain reaction (PCR) and DNA sequencing were applied to detect bla _MBL genes, and their epidemiological relationships were investigated by multilocus sequence typing (MLST). Of 368 P. aeruginosa isolates, MLST analysis identified 138 sequence types (STs), including 122 known and 16 novel STs, and the most frequently detected clone was ST244, followed by ST235. Besides, our study revealed that 25 isolates carried the bla _IMP-6 gene and three isolates carried the bla _VIM-2 gene, and a probe specific for both genes could be hybridised to an ~1,125-kb fragment in all isolates. Interestingly, all of the bla _IMP-6-producing isolates shared an identical ST, ST244, and exhibited a higher level of resistance to several antibiotics. Overall, these observations suggest that P. aeruginosa ST244 carrying the chromosomally located bla _IMP-6 gene is widely disseminated in multiple cites in China.     

Rapid detection of blaKPC carbapenemase genes by real-time PCR

Carbapenem resistance among Enterobacteriaceae is an emerging problem worldwide. Klebsiella pneumoniae carbapenemase (bla_KPC) enzymes are among the most common β-lactamases described. In this study, we report the development and validation of a real-time PCR (q-PCR) assay for the detection of bla_KPC genes using TaqMan chemistry. The q-PCR amplification of bla_KPC DNA was linear over 7 log dilutions (r² = 0.999; slope, 3.54), and the amplification efficiency was 91.6%. The q-PCR detection limit was 1 CFU, and there was no cross-reaction with DNA extracted from several multidrug-resistant bacteria. Perianal/rectal swabs (n = 187) collected in duplicate from 128 patients admitted to Sheba Medical Center surgical intensive care units were evaluated for the presence of carbapenem-resistant bacteria by culturing on MacConkey agar-plus-carbapenem disks and for bla_KPC genes by q-PCR. Carbapenem-resistant organisms, all K. pneumoniae, were isolated from 47 (25.1%) of the 187 samples collected, while bla_KPC genes were detected in 54 (28.9%) of the patient samples extracted by the NucliSENS easyMAG system. Of these, seven samples were positive for bla_KPC genes by q-PCR but negative for carbapenem resistance by culture, while all samples in which no carbapenem-resistant bacteria were detected by culture also tested negative by q-PCR. Thus, the sensitivity and specificity of the q-PCR assay after extraction by the NucliSENS easyMAG system were 100% and 95%, respectively. Similar values were obtained after DNA extraction by the Roche MagNA Pure LC instrument: 97.9% sensitivity and 96.4% specificity. Overall, the bla_KPC q-PCR assay appears to be highly sensitive and specific. The utilization of q-PCR will shorten the time to bla_KPC detection from 24 h to 4 h and will help in rapidly isolating colonized or infected patients and assigning them to cohorts.     

Spread of Multidrug-Resistant Pseudomonas aeruginosa Clones in a University Hospital

An outbreak of multidrug-resistant Pseudomonas aeruginosa (MDRPA) infections in a university hospital is described. Phenotypic and genotypic analysis of 240 isolates revealed that 152 patients, mainly in the intensive care unit (ICU), were colonized or infected with MDRPA, the majority with O11. All metallo-β-lactamase (MBL)-positive isolates carried the bla_VIM-2 or bla_VIM-1 gene. One or more type III secretion system toxin genes were detected in most isolates. Five dominant pulsed-field gel electrophoresis (PFGE) types were characterized, associated with ST235, ST111, ST253, ST309, and ST639.     

Prevalence of CTX-M β-Lactamases in Philadelphia,Pennsylvania

CTX-M β-lactamases were thought to be rare in the United States, but a recent study in Texas showed that up to 70% of extended-spectrum β-lactamase (ESBL)-containing members of the Enterobacteriaceae family were CTX-M positive (J. S. Lewis, M. Herrera, B. Wickes, J. E. Patterson, and J. H. Jorgensen, Antimicrob. Agents Chemother. 51:4015-4021, 2007). We used PCR to detect CTX-M in all 291 extended-spectrum cephalosporin-resistant gram-negative bacteria isolated in our laboratory during 2007. Thirty (48%) Escherichia coli isolates, 6 (3%) Klebsiella sp. isolates, and 7 (100%) Proteus mirabilis isolates tested were CTX-M positive, with 15% of all Enterobacteriaceae tested being positive. The E. coli CTX-M groups were I (57%), IV (37%), II (3%), and not groupable (3%); three of the group IV isolates were positive for CTX-M-18, and three of the group I isolates were positive for CTX-M-15. One of seven positive P. mirabilis isolates was in group II, with the remainder being positive for a CTX-M-25-like β-lactamase; and 33% of the Klebsiella sp. isolates were in group I or IV, with the remainder not being in groups I to IV. CTX-M-producing bacteria were isolated from urine (n = 13), blood (n = 13), wounds (n = 12), and the respiratory tract (n = 4). All 31 CTX-M-positive isolates tested for the presence of ESBL were confirmed to produce ESBLs by the use of tests recommended by the CLSI. Pulsed-field gel electrophoresis of the CTX-M-positive isolates showed that six P. mirabilis isolates were clonal and that there were seven different E. coli clusters. Five of seven P. mirabilis isolates were from blood cultures. The CLSI tests for the confirmation of ESBL production reliably detect these isolates if both cefotaxime and ceftazidime are tested, but only about half would be classified as a possible CTX-M producers on the basis of the antibiogram alone. A new panprimer set increases the ability to detect CTX-M-producing strains. CTX-M-positive bacteria are common in our geographic region, are often invasive, and, with the exception of P. mirabilis, are multiclonal.CTX-M β-lactamases were thought to be uncommon in North America, although they are common on many other continents (1, 8, 10). CTX-M β-lactamases are extended-spectrum β-lactamases (ESBLs) that mainly inactivate cefotaxime and ceftriaxone and that have less activity against ceftazidime (8). As opposed to the usual epidemiology of other ESBL-positive members of the Enterobacteriaceae family, which are mainly nosocomial, CTX-M β-lactamase producers often appear to be community acquired, albeit in debilitated people with prior antibiotic exposure (8). The recognition of this group of resistant bacteria could have importance for decisions on empirical antibiotic therapy and could influence the accuracy of current procedures for screening for ESBLs. On the basis of the findings of a recent study from Texas showing that 70% of recent ESBL-producing isolates contained CTX-M β-lactamases (7), we tested all extended-spectrum cephalosporin-resistant Enterobacteriaceae isolated in the Clinical Microbiology Laboratory at the Hospital of the University of Pennsylvania (HUP) in 2007, as well as all multidrug-resistant Acinetobacter baumannii isolates recovered during the same time period. We show that CTX-M β-lactamases are common among extended-spectrum cephalosporin-resistant Escherichia coli and Proteus mirabilis isolates recovered from patients in hospitals in Philadelphia, PA.(This study was presented in abstract form at the 48th Interscience Conference on Antimicrobial Agents and Chemotherapy, Washington, DC, 2008.)     

Molecular Characterization and Antimicrobial Susceptibility of Salmonella Isolates from Infections in Humans in Henan Province, China

We characterized 208 human Salmonella isolates from 2006 to 2007 and 27 human Salmonella enterica serovar Typhimurium isolates from 1987 to 1993 from Henan Province, China, by serotyping, by antimicrobial susceptibility testing, and, for the most common serovars, by pulsed-field gel electrophoresis (PFGE). The most common serovars among the 2006-2007 isolates were S. enterica serovar Typhimurium (27%), S. enterica serovar Enteritidis (17%), S. enterica serovar Derby (10%), S. enterica serovar Indiana (6%), and S. enterica serovar Litchfield (6%). A high percentage of the isolates were multiple-drug resistant, and 54% were resistant to both nalidixic acid and ciprofloxacin. Of these, 42% were resistant to a high level of ciprofloxacin (MIC > 4 μg/ml), whereas for the remaining isolates, the MICs ranged from 0.125 to 2 μg/ml. Five isolates (2%) were ceftiofur resistant and harbored bla_CTX-M14 or bla_CTX-M15. With the possible exception of the quinolones and cephalosporins, the 1987-1993 S. enterica serovar Typhimurium isolates were almost as resistant as the recent isolates. PFGE typing of S. enterica serovar Typhimurium showed that the most common cluster predominated over time. Two other clusters have emerged, and another cluster has disappeared.     

Multiple carbapenem hydrolyzing genes in clinical isolates of Acinetobacter baumannii

Purpose: Carbapenem resistance in Acinetobacter baumannii has become highly rampant, which has been ascribed to the presence of multiple carbapenemases. The objective of the present study was to prospectively investigate the presence of multiple carbapenemase encoding genes in clinical isolates of A. baumannii. Materials and Methods: A total of 30 imipenem resistant, consecutive non-repeat clinical isolates A. baumannii from a Tertiary Care Centre of Delhi were subjected to antimicrobial susceptibility testing (AST), screening for carbapenemase production by modified Hodge test (MHT) and determination of minimum inhibitory concentration for imipenem by E-Test®. These were subjected to Real time PCR for bla_{IMP-1 and 2}, bla_{VIM-1 and 2}, bla_{OXA23, 24, 51 and 58} using SYBR green-I. These were grouped together on the basis of their genotype as each isolate harboured multiple carbapenemases and correlated with their AST profile. Detection of the novel carbapenemase bla_NDM-1 was performed by real time PCR using TaqMan probes on 14 isolates. Results: Colistin appeared to be the most effective drug in vitro, followed by tetracycline and beta lactam/beta lactamase inhibitor combinations. All, but one isolate were positive for the MHT. All 30 isolates were positive for bla_OXA-51 like gene as well as bla_IMP-1 and bla_VIM-1 genes. bla_{OXA 24 and 58} were not detected in any of the isolates. bla_IMP-2, bla_VIM-2, bla_OXA-23 were present in 15, 6 and 14 isolates respectively. Grouping based on the genotypic profile did not correlate with susceptibility pattern. Nine among the 14 isolates also harboured the novel bla_NDM-1 gene. Conclusions: This is the first study from North India, which comprehensively detected the presence of multiple carbapenemases as well the bla_NDM-1 gene. The presence of the novel gene bla_NDM-1indicated ability of A. baumannii to acquire new carbapenemase genes despite the existence of multiple carbapenemase genes. The present study confirmed the presence of multiple genetic mechanisms for carbapenemases production among the clinical isolates of A. baumannii in north India.     

Emergence of Pseudomonas aeruginosa strains producing metallo-β-lactamases of the IMP-15 and VIM-2 types in Mexico

Eighty-six carbapenem non-susceptible Pseudomonas aeruginosa isolates collected in the National Institute of Respiratory Diseases of Mexico City were screened for the presence of metallo-β-lactamase (MBL) activity using both E-test strips and a microbiological assay with EDTA-imipenem. Genomic comparisons and sequence analyses conducted with these isolates revealed the presence of bla_VIM-2 in two clonally related isolates, and bla_IMP-15 in a clonally unrelated isolate. Both genes were found to be carried by class 1 integrons, and bla_IMP-15 was additionally present on a broad host-range plasmid. This is the first report of co-existing P. aeruginosa strains producing different MBLs in a Mexican hospital, highlighting the necessity of appropriate surveillance to prevent dissemination of carbapenem resistance.     

Related carbapenemase-producing <Emphasis Type="Italic">Klebsiella</Emphasis> isolates detected in both a hospital and associated aquatic environment in Sweden

Carbapenem antibiotics are one of the last-resort agents against multidrug-resistant (MDR) bacteria. The occurrence of carbapenemase-producing Enterobacteriaceae (CPE) in wastewater and aquatic environments is an indication of MDR bacteria in the community. This study evaluated CPE in aquatic environments and compared them to the local hospital isolates in Sweden. Phenotypic and genotypic analyses of antibiotic resistance of environmental and clinical CPE were performed. The relatedness of the isolates and possible clonal dissemination was evaluated using phylogenetic and phyloproteomic analysis. Klebsiella oxytoca carrying carbapenemase genes (bla_VIM-1, bla_IMP-29) were isolated from wastewater and the recipient river, while K. oxytoca (bla_VIM-1) and Klebsiella pneumoniae (bla_VIM-1, bla_OXA-48, bla_NDM-1, bla_KPC-3) were isolated from patients at the local clinics or hospital. The K. oxytoca classified as sequence type 172 (ST172) isolated from the river was genotypically related to two clinical isolates recovered from patients. The similarity between environmental and clinical isolates suggests the dispersion of bla_VIM-1 producing K. oxytoca ST172 from hospital to aquatic environment and the likelihood of its presence in the community. This is the first report of CPE in aquatic environments in Sweden; therefore, surveillance of aquatic and hospital environments for CPE in other urban areas is important to determine the major transfer routes in order to formulate strategies to prevent the spread of MDR bacteria.     

Laboratory Surveillance for Prospective Plasmid-Mediated AmpC β-Lactamases in the Kinki Region of Japan

Extended-spectrum β-lactamases, plasmid-mediated AmpC β-lactamases (PABLs), and plasmid-mediated metallo-β-lactamases confer resistance to many β-lactams. In Japan, although several reports exist on the prevalence of extended-spectrum β-lactamases and metallo-β-lactamases, the prevalence and characteristics of PABLs remain unknown. To investigate the production of PABLs, a total of 22,869 strains of 4 enterobacterial species, Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, and Proteus mirabilis, were collected during six 6-month periods from 17 clinical laboratories in the Kinki region of Japan. PABLs were detected in 29 (0.13%) of 22,869 isolates by the 3-dimensional test, PCR analysis, and DNA sequencing analysis. PABL-positive isolates were detected among isolates from 13 laboratories. Seventeen of 13,995 (0.12%) E. coli isolates, 8 of 5,970 (0.13%) K. pneumoniae isolates, 3 of 1,722 (0.17%) K. oxytoca isolates, and 1 of 1,182 (0.08%) P. mirabilis isolates were positive for PABLs. Of these 29 PABL-positive strains, 20 (69.0%), 6 (20.7%), 2 (6.9%), and 1 (3.4%) carried the genes for CMY-2, DHA-1, CMY-8, and MOX-1 PABLs, respectively. Pattern analysis of randomly amplified polymorphic DNA and pulsed-field gel electrophoretic analysis revealed that the prevalence of CMY-2-producing E. coli strains was not due to epidemic strains and that 3 DHA-1-producing K. pneumoniae strains were identical, suggesting their clonal relatedness. In conclusion, the DHA-1 PABLs were predominantly present in K. pneumoniae strains, but CMY-2 PABLs were predominantly present in E. coli strains. The present findings will provide significant information to assist in preventing the emergence and further spread of PABL-producing bacteria.β-Lactamase production is the most important factor for β-lactam resistance in Gram-negative rods (16). Plasmid-mediated β-lactamases, such as extended-spectrum β-lactamases (ESBLs), plasmid-mediated AmpC β-lactamases (PABLs), and plasmid-mediated metallo-β-lactamases (MBLs), hydrolyze broad-spectrum β-lactams. Detection of these plasmid-mediated β-lactamase-producing isolates is important for epidemiological studies and hospital infection control, because plasmid-mediated genes can spread to other organisms.The Study of Bacterial Resistance in the Kinki Region of Japan (SBRK) Antimicrobial Surveillance Program was established in 1997 to monitor the predominant pathogens and antimicrobial resistance patterns of nosocomial and community-acquired infections via a broad network of clinical laboratories differing in geographic location and size. Our previously reported survey data from the Kinki region of Japan revealed the prevalence of ESBLs and plasmid-mediated MBLs (21, 30); however, the epidemiology of PABLs remains unknown. For this reason, a laboratory-based surveillance study was conducted to determine the presence and prevalence of PABLs among members of the family Enterobacteriaceae.PABL CMY-1 was first found in a Klebsiella pneumoniae isolate in South Korea in 1989 (4, 5). Since then, additional organisms producing PABLs have been reported worldwide (25). PABLs are a heterogeneous group of enzymes that originated from the chromosomal genes of Enterobacter spp. (ACT-1/MIR-1 type), Citrobacter freundii (CMY/LAT type), Morganella morganii (DHA type), Hafnia alvei (ACC-1), and Aeromonas spp. (CMY/MOX type and FOX type). The most prevalent and most widely distributed PABLs are the CMY/LAT-type enzymes (25). In addition to these enzyme types, DHA-type enzymes have been identified in Taiwan (31) and China (15). In Korea (14, 26), DHA-, CMY/MOX-, and ACT-1/MIR-1-type enzymes have also been identified, while in the United States (1, 17), in addition to the types mentioned above, DHA-, ACT-1/MIR-1-, and FOX-type enzymes have been identified. To date, in Japan, MOX-1 (11), CMY-9 (9, 28), CMY-19 (28), CFE-1 (19), CMY-2 (18), and DHA-1 (18) have been found in clinical isolates. Muratani et al. (18) reported PABL producers among cephem-resistant K. pneumoniae isolates, but this report did not indicate the rate of occurrence of PABLs.For the present study, we collected 22,869 isolates from 17 clinical laboratories in the Kinki region of Japan, and we assessed the prevalence and types of PABL-positive bacteria.     

Metallo-��-Lactamase-Producing Pseudomonas spp. in Korea: High Prevalence of Isolates with VIM-2 Type and Emergence of Isolates with IMP-1 Type

Purpose

Two Korean nationwide studies showed that metallo-β-lactamases (MBLs)-producing-Pseudomonas spp. are not rare. The aim of this study was to assess the trends of MBL-producing isolates among imipenem-resistant isolates of Pseudomonas spp.

Materials and Methods

Imipenem-resistant clinical isolates were collected from 23 hospitals and one commercial laboratory participating in the KONSAR program in 2005. Polymerase chain reaction (PCR) was used to detect MBL genes.

Results

Alleles of MBL genes were detected in 10.8% of 415 Pseudomonas aeruginosa and 66.7% of 12 P. putida isolates from 18 of 24 hospitals/laboratory. Among the 14 IMP-1-like and 39 VIM-2-like MBLs, emergence of IMP-6 was detected for the first time.

Conclusion

Prevalence of MBL-producing P. aeruginosa has not significantly increased, but IMP-6 emerged in P. aeruginosa.     

Molecular characterization of VIM-producing Klebsiella pneumoniae from Scandinavia reveals genetic relatedness with international clonal complexes encoding transferable multidrug resistance

VIM-producing Klebsiella pneumoniae (VPKP) has been identified as a source of hospital outbreaks and is prevalent particularly in the Mediterranean region. In this study we have characterized eight VPKP isolates identified in Scandinavia during 2005–2008. With the exception of one isolate, all were from patients with recent history of hospitalization abroad (Greece, n = 6; Turkey, n = 1). Multilocus sequence typing (MLST) resulted in five sequence types (STs), ST36 (n = 1), ST147 (n = 4), ST272 (n = 1), ST273 (n = 1) and ST383 (n = 1), which except for ST272 were part of putative international clonal complexes. All were multidrug resistant due to the presence of other resistance determinants, including extended-spectrum β-lactamases (CTX-M-3, SHV-5 and SHV-12), 16S rRNA methylases (ArmA) and plasmid-mediated quinolone resistance determinants (QnrS). One isolate harboured a novel VIM-variant (VIM-26) while VIM-1 and VIM-19 were detected in six and one isolate, respectively. Two different genetic structures surrounding the bla_VIM gene were identified in four isolates. In two isolates bla_VIM-1 and bla_VIM-26 were located in an integron similar to In-e541 (intI1;bla_VIM-1/-26;aacA7; dhfrI;aadA1;3’CS) while in the other two isolates bla_VIM-1 was located in an integron lacking 3’CS but with an IS26 element in the 3’end (intI1;bla_VIM-1;aac(6’)-Ib;IS26), as identified in the IncN plasmid pKOX105. The bla_VIM-genes were located on transferable plasmids ranging from -40 to -240 kb and associated with Tn21 in four isolates. PCR-based replicon typing indicated association of bla_VIM with IncN (n = 3) and A/C (n = 1) broad-host-range plasmids but also with unknown replicons (n = 4). In conclusion, Scandinavian VPKP is associated with importation and genetically related to international clones encoding transferable plasmid-mediated multidrug resistance.