Outbreak of Klebsiella pneumoniae producing a new carbapenem-hydrolyzing class A beta-lactamase, KPC-3, in a New York Medical Center

Emergence of carbapenem-non-susceptible extended-spectrum β-lactamase-producing Klebsiella pneumoniae isolates at the university hospital of Tübingen, Germany

The spread of Gram-negative bacteria with plasmid-borne extended-spectrum β-lactamases (ESBLs) has become a worldwide problem. This study analysed a total of 366 ESBL-producing Enterobacteriaceae strains isolated from non-selected patient specimens at the university hospital of Tübingen in the period January 2003 to December 2007. Although the overall ESBL rate was comparatively low (1.6 %), the percentages of ESBL-producing Enterobacter spp. and Escherichia coli increased from 0.8 and 0.5 %, respectively, in 2003 to 4.6 and 3.8 % in 2007. In particular, the emergence was observed of one carbapenem-resistant ESBL-producing E. coli isolate and five carbapenem-non-susceptible ESBL-positive Klebsiella pneumoniae isolates, in two of which carbapenem resistance development was documented in vivo under a meropenem-containing antibiotic regime. The possible underlying mechanism for this carbapenem resistance in three of the K. pneumoniae isolates was loss of the Klebsiella porin channel protein OmpK36 as shown by PCR analysis. The remaining two K. pneumoniae isolates exhibited increased expression of a tripartite AcrAB–TolC efflux pump as demonstrated by SDS-PAGE and mass spectrometry analysis of bacterial outer-membrane extracts, which, in addition to other unknown mechanisms, may contribute towards increasing the carbapenem MIC values further. Carbapenem-non-susceptible ESBL isolates may pose a new problem in the future due to possible outbreak situations and limited antibiotic treatment options. Therefore, a systematic exploration of intestinal colonization with ESBL isolates should be reconsidered, at least for haemato-oncological departments from where four of the five carbapenem-non-susceptible ESBL isolates originated.

Contribution of OmpK36 to carbapenem susceptibility in KPC-producing Klebsiella pneumoniae

Isolates of Klebsiella pneumoniae harbouring the carbapenemase KPC may have carbapenem MICs that remain in the susceptible range, and may therefore go unrecognized. To understand the mechanisms contributing to the variability in carbapenem MICs, 20 clinical isolates, all belonging to either of two clonal groups of KPC-possessing K. pneumoniae endemic to New York City, were examined. Expression of genes encoding KPC, the porins OmpK35 and OmpK36, and the efflux pump AcrAB was examined by real-time RT-PCR. Outer-membrane profiles of selected KPC-producing isolates were examined by SDS-PAGE, and proteins were identified by matrix-assisted laser desorption/ionization mass spectrometry. The identification of SHV and TEM beta-lactamases and the genomic sequences of ompK35 and ompK36 were determined by PCR and DNA sequencing, respectively. For one clonal group, carbapenem MICs increased with decreasing expression of ompK36. A second clonal group also had carbapenem MICs that correlated with ompK36 expression. However, all of the isolates in this latter group continued to produce OmpK36, suggesting that porin configuration may affect entry of carbapenems. For isolates that had the greatest expression of ompK36, carbapenem MICs tended to be lower when determined by the broth microdilution technique, and scattered colonies were seen around the Etest zones of inhibition. All of the KPC-producing isolates were highly resistant to ertapenem, regardless of ompK36 expression. In conclusion, isolates of KPC-possessing K. pneumoniae that express ompK36 tend to have lower MICs to carbapenems and therefore may be more difficult to detect by clinical laboratories. Regardless of ompK36 expression, all of the KPC producers were consistently resistant to ertapenem.

Molecular epidemiology of KPC-producing Klebsiella pneumoniae isolates in the United States: clonal expansion of multilocus sequence type 258

Klebsiella pneumoniae carbapenemase (KPC)-producing Enterobacteriaceae have become more common in the United States and throughout the world. We used pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) to examine the molecular epidemiology of KPC-producing K. pneumoniae isolates sent to the Centers for Disease Control and Prevention (CDC) for reference testing from 1996 to 2008. A dominant strain, sequence type 258 (ST 258), was found and likely accounts for 70% of the CDC's K. pneumoniae PFGE database. Isolates with PFGE patterns related to ST 258 were identified in 10 of the 19 U.S. states currently reporting KPC-producing K. pneumoniae, in addition to one isolate from Israel. KPC subtyping and analysis of the surrounding genetic environment were subsequently performed on 23 representative isolates. Thirteen isolates identified as ST 258 possessed either bla(KPC-2) or bla(KPC-3) and some variability in the Tn4401 element upstream of the bla(KPC) gene. Escherichia coli DH10B was successfully transformed by electroporation with KPC-encoding plasmid DNA from 20 of the 23 isolates. Restriction analysis of plasmid DNA prepared from transformants revealed a diversity of band patterns, suggesting the presence of different plasmids harboring the bla(KPC) gene, even among isolates of the same ST.

The real threat of Klebsiella pneumoniae carbapenemase-producing bacteria

From early this decade, Enterobacteriaceae that produce Klebsiella pneumoniae carbapenemases (KPC) were reported in the USA and subsequently worldwide. These KPC-producing bacteria are predominantly involved in nosocomial and systemic infections; although they are mostly Enterobacteriaceae, they can also be, rarely, Pseudomonas aeruginosa isolates. KPC beta lactamases (KPC-1 to KPC-7) confer decreased susceptibility or resistance to virtually all beta lactams. Carbapenems (imipenem, meropenem, and ertapenem) may thus become inefficient for treating enterobacterial infections with KPC-producing bacteria, which are, in addition, resistant to many other non-beta-lactam molecules, leaving few available therapeutic options. Detection of KPC-producing bacteria may be difficult based on routine antibiotic susceptibility testing. It is therefore crucial to implement efficient infection control measures to limit the spread of these pathogens.

Clinical outcomes of patients with Klebsiella pneumoniae carbapenemase-producing K. pneumoniae after treatment with imipenem or meropenem

Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae may appear susceptible to imipenem or meropenem by routine susceptibility testing. We report a series of patients with infections caused by K. pneumoniae isolates, which yielded imipenem-susceptible results but were subsequently KPC-positive by polymerase chain reaction. When these infections were treated with imipenem or meropenem, frequent clinical and microbiologic failures were observed.

Genetic organization of transposase regions surrounding blaKPC carbapenemase genes on plasmids from Klebsiella strains isolated in a New York City hospital

Carbapenem-resistant Klebsiella strains carrying Klebsiella pneumoniae carbapenemases (KPC) are endemic to New York City and are spreading across the United States and internationally. Recent studies have indicated that the KPC structural gene is located on a 10-kb plasmid-borne element designated Tn4401. Fourteen Klebsiella pneumoniae strains and one Klebsiella oxytoca strain isolated at a New York City hospital in 2005 carrying either bla(KPC-2) or bla(KPC-3) were examined for isoforms of Tn4401. Ten of the Klebsiella strains contained a 100-bp deletion in Tn4401, corresponding to the Tn4401a isoform. The presence of this deletion adjacent to the upstream promoter region of bla(KPC) in Tn4401a resulted in a different -35 promoter sequence of TGGAGA than that of CTGATT present in isoform Tn4401b. Complete sequencing of one plasmid carrying bla(KPC) from each of three nonclonal isolates indicated the presence of genes encoding other types of antibiotic resistance determinants. The 70.6-kb plasmid from K. pneumoniae strain S9 carrying bla(KPC-2) revealed two identical copies of Tn4401b inserted in an inverse fashion, but in this case, one of the elements disrupted a group II self-splicing intron. In K. pneumoniae strain S15, the Tn4401a element carrying bla(KPC-2) was found on both a large 120-kb plasmid and a smaller 24-kb plasmid. Pulsed-field gel electrophoresis results indicate that the isolates studied represent a heterogeneous group composed of unrelated as well as closely related Klebsiella strains. Our results suggest that endemic KPC-positive Klebsiella strains constitute a generally nonclonal population comprised of various alleles of bla(KPC) on several distinct plasmid genetic backgrounds. This study increases our understanding of the genetic composition of the evolving and expanding role of KPC-producing, healthcare-associated, gram-negative pathogens.

Cluster of bloodstream infections caused by KPC-2 carbapenemase-producing Klebsiella pneumoniae in Manhattan

BACKGROUND

Carbapenems are considered the agents of choice for treatment of serious infections caused by resistant gram-negative organisms. A new group of class A beta-lactamases, known as KPC-type carbapenemases, has recently been described and poses a serious clinical challenge.

METHODS

Seven patients with bloodstream infections caused by Klebsiella pneumoniae isolates with decreased susceptibility to carbapenems were identified between January and April 2005 in the intensive care units of a hospital in Manhattan. Isolate identification and susceptibility testing were performed according to National Committee for Clinical Laboratory Standards methodology. All isolates were ribotyped and screened for (bla)KPC by polymerase chain reaction. The polymerase chain reaction product underwent nucleotide sequencing for one of the isolates. Medical records were reviewed retrospectively.

RESULTS

Six isolates were carbapenem-resistant with minimum inhibitory concentrations for imipenem of >8microg/mL. Ribotyping showed that all isolates belonged to a single clone. All isolates possessed (bla)KPC and nucleotide sequencing identified the allelic type KPC-2. Patients' median age was 68 years. The median duration of hospitalization was 25.5 days before the first positive blood culture. Five of 6 patients received previous broad-spectrum beta-lactam antibiotics but none received prior carbapenems. Five of 6 isolates were susceptible to polymyxin B. Three of the 5 patients were treated with polymyxin B and 1 survived. Overall, only 2 of the 6 patients survived.

CONCLUSION

This report describes the first outbreak of KPC-2 carbapenemase-producing K pneumoniae bloodstream infections in a hospital in Manhattan.

Outbreak of infections due to KPC-2-producing Klebsiella pneumoniae in a hospital in Crete (Greece)

Starting in May 2007, an ongoing outbreak of infections due to carbapenem resistant KPC-2-producing Klebsiella pneumoniae occurred in a tertiary care hospital in Crete (Greece). The outbreak involved 22 patients, none of whom had travelled in a country with known high prevalence of such isolates. KPC-producing K. pneumoniae strains were mainly isolated from patients admitted in the Intensive Care Unit, on mechanical ventilation, with prolonged hospitalization, prolonged administration of antibiotics, and prolonged administration of carbapenems. Clinical diagnoses were: pneumonia (62% of cases), surgical site infection (19%), bacteremia (9.5%), urinary tract infection (4.7%), and peritonitis (4.7%). Overall, 61 KPC-producing K. pneumoniae isolates were recovered, mainly from the respiratory tract (59.1%), catheter tip (22.7%), surgical site (18.2%), and blood (18.2%). Among 16 patients for whom therapeutic data were available, 14 (87.5%) were treated with a combination of colistin and/or tigecycline and/or garamycin. Clinical failure was noted in 22.2% of 18 patients available for assessment of clinical outcome, and microbiologic failure in 87.5% of 8 patients available for assessment of microbiologic outcome. In conclusion, an outbreak of KPC-producing K. pneumoniae infections has occurred in a tertiary care hospital in Greece, with significant associated morbidity and mortality. Prospective studies are required to evaluate the available therapeutic options for these infections. Our efforts should focus on rational use of available antibiotics, enhancement of infection control measures, and implementation of active antibiotic resistance surveillance.

Fatal cross infection by carbapenem-resistant Klebsiella in two liver transplant recipients

Members of the family Enterobacteriaceae including Klebsiella have re-emerged as major pathogens in solid organ transplantation. The recent appearance and dissemination of carbapenemase-producing Enterobacteriaceae in Europe and the northeastern United States represents a major challenge to the treatment of enteric gram-negative bacterial infections in immunocompromised patients; however, few reports have detailed the outcomes of such infections. Here we report 2 cases of Klebsiella pneumoniae carbapenemase (KPC)-producing Klebsiella infections in orthotopic liver transplant recipients, which were the index case and initial secondary case for an outbreak of KPC-producing Enterobacteriaceae in our institution. In both instances, the pathogens were initially misidentified as being carbapenem sensitive, the infections recurred after cessation of directed therapy, and the patients ultimately succumbed to their infections.

Combined porin loss and extended spectrum beta-lactamase production is associated with an increasing imipenem minimal inhibitory concentration in clinical Klebsiella pneumoniae strains

For this study, 150 clinical isolates of Klebsiella pneumoniae were collected from one hospital in Beijing, China, and assayed for minimal inhibitory concentration (MIC) of imipenem. To elucidate the mechanisms responsible for imipenem MIC variation among extended-spectrum beta-lactamase (ESBL)-positive and -negative K. pneumoniae strains, a variety of beta-lactamase genes (bla(TEM), bla(CTX-M), bla(SHV), and bla(OXA)) were screened by polymerase chain reaction (PCR). The outer membrane profile and expression of related genes (ompK35 and ompK36) then were analyzed and evaluated, respectively. None of the tested isolates were clinically resistant to imipenem, but the range of MICs among ESBL-positive and -negative strains was significantly different. Deficiency in the expression of outer membrane proteins (OmpK35,36) was observed in some of both ESBL-positive(17.6%) and -negative strains (10.9%), but only the ESBL-positive strains depressed by the expression of ompK35/36 had an increased MIC of imipenem (>or=0.5 mg/l). These results confirmed that the combination of SHV-1, CTX-M-3, CTX-M-14, TEM-1, or OXA-11 production and reduced expression of ompK35/36 may not result in clinical resistance to imipenem but does correlate with increasing imipenem MIC.

Characterization of blaKPC-containing Klebsiella pneumoniae isolates detected in different institutions in the Eastern USA

BACKGROUND

The emergence of bla(KPC)-containing Klebsiella pneumoniae (KPC-Kp) isolates is attracting significant attention. Outbreaks in the Eastern USA have created serious treatment and infection control problems. A comparative multi-institutional analysis of these strains has not yet been performed.

METHODS

We analysed 42 KPC-Kp recovered during 2006-07 from five institutions located in the Eastern USA. Antimicrobial susceptibility tests, analytical isoelectric focusing (aIEF), PCR and sequencing of bla genes, PFGE and rep-PCR were performed. Results By in vitro testing, KPC-Kp isolates were highly resistant to all non-carbapenem beta-lactams (MIC(90)s >or= 128 mg/L). Among carbapenems, MIC(50/90)s were 4/64 mg/L for imipenem and meropenem, 4/32 mg/L for doripenem and 8/128 for ertapenem. Combinations of clavulanate or tazobactam with a carbapenem or cefepime did not significantly lower the MIC values. Genetic analysis revealed that the isolates possessed the following bla genes: bla(KPC-2) (59.5%), bla(KPC-3) (40.5%), bla(TEM-1) (90.5%), bla(SHV-11) (95.2%) and bla(SHV-12) (50.0%). aIEF of crude beta-lactamase extracts from these strains supported our findings, showing beta-lactamases at pIs of 5.4, 7.6 and 8.2. The mean number of beta-lactamases was 3.5 (range 3-5). PFGE demonstrated that 32 (76.2%) isolates were clonally related (type A). Type A KPC-Kp isolates (20 bla(KPC-2) and 12 bla(KPC-3)) were detected in each of the five institutions. rep-PCR showed patterns consistent with PFGE.

CONCLUSIONS

We demonstrated the complex beta-lactamase background of KPC-Kp isolates that are emerging in multiple centres in the Eastern USA. The prevalence of a single dominant clone suggests that interstate transmission has occurred.

New developments in carbapenems

Antibiotic resistance among Gram-negative pathogens in hospitals is a growing threat to patients and is driving the increased use of carbapenems. Carbapenems are potent members of the beta-lactam family of antibiotics, with a history of safety and efficacy for serious infections that exceeds 20 years. Original and review articles were identified from a Medline search (1979-2008). Reference citations from identified publications, abstracts from the Interscience Conferences on Antimicrobial Agents and Chemotherapy and package inserts were also used. Carbapenems are effective in treating severe infections at diverse sites, with relatively low resistance rates and a favourable safety profile. Carbapenems are the beta-lactams of choice for the treatment of infections caused by multidrug-resistant organisms. Optimized dosing of carbapenems should limit the emergence of resistance and prolong the utility of these agents. The newly approved doripenem should prove to be a valuable addition to the currently available carbapenems: imipenem, meropenem and ertapenem.

Multiresistant Enterobacteriaceae: new threat of an old problem

The Enterobacteriaceae are among the most important causes of serious nosocomial and community-onset bacterial infections in humans, and resistance to antimicrobial agents in these species has become an increasingly relevant problem for healthcare providers. beta-lactam and fluoroquinolone antibiotics are important drug classes used to treat infections caused by Enterobacteriaceae. Emerging resistance mechanisms against these agents have recently been described in Enterobacteriaceae and include the production of newer beta-lactamases and plasmid-mediated quinolone resistance. The newer beta-lactamases consist of the following: plasmid-mediated AmpC beta-lactamases (e.g., ephamycin [CMY], CMY types), extended-spectrum beta-lactamases (e.g., cefotaxime [CTX], CTX-M first isolated at Munich) and carbapenem-hydrolyzing enzymes (e.g., Klebsiella pneumoniae carbapenemase [KPC], KPC types and the metallo-beta-lactamases). Recent developments in the epidemiology, clinical relevance and laboratory detection of infections caused by multiresistant Enterobacteriaceae with these new types of resistance mechanisms will be addressed in this review.

Development and evaluation of a real-time PCR assay for detection of Klebsiella pneumoniae carbapenemase genes

We developed a novel real-time PCR assay to detect Klebsiella pneumoniae carbapenemases (KPCs) and used this assay to screen clinical isolates of K. pneumoniae and Klebsiella oxytoca for the presence of bla(KPC) genes. The TaqMan real-time PCR assay amplified a 399-bp product from the bla(KPC) gene. The amplicon was designed so that the genes for isoenzymes KPC-1, -2, and -3 could be easily distinguished by subsequent restriction digestion of the amplicon with the enzymes BstNI and RsaI. The assay was validated with reference strains obtained from the Centers for Disease Control and Prevention that contained each of the three described isoenzymes and 69 extended-spectrum beta-lactamase-producing clinical isolates (39 K. pneumoniae and 30 K. oxytoca isolates). Subsequently, the bla(KPC) PCR assay was used to confirm the presence of bla(KPC) genes in any meropenem-resistant Klebsiella spp. The PCR assay detected bla(KPC) in all of the reference strains, in 6 of 7 meropenem-resistant isolates, and in 0 of 62 meropenem-susceptible clinical isolates. The PCR assay was then used to confirm the presence of bla(KPC) in an additional 20 meropenem-resistant isolates from 16 patients. Restriction digestion of the PCR amplicons identified two bla(KPC) gene variants in our patient population: 9 isolates with C and 17 with T at nucleotide 944, consistent with bla(KPC-2) and bla(KPC-3), respectively. The real-time PCR assay is a rapid and accurate method to detect all KPC isoenzymes and was useful in documenting the presence and dissemination of KPC-producing strains in our patient population.

First report on a hyperepidemic clone of KPC-3-producing Klebsiella pneumoniae in Israel genetically related to a strain causing outbreaks in the United States

A highly epidemic carbapenem-resistant clone of KPC-3-producing Klebsiella pneumoniae emerged in Israel in 2006, causing a nationwide outbreak. This clone was genetically related to outbreak strains from the United States isolated in 2000 but differed in KPC-carrying plasmids. The threat of the global spread of hyperepidemic, extensively drug-resistant bacterial strains should be recognized and confronted.

Presence of the KPC carbapenemase gene in Enterobacteriaceae causing bacteremia and its correlation with in vitro carbapenem susceptibility

During 6 months, we obtained Enterobacteriaceae isolates from patients with gram-negative bacteremia at a 1,250-bed teaching hospital in St. Louis, MO, and compared carbapenem susceptibilities with the presence of bla(KPC), a transferable carbapenemase gene. Three (1.2%) out of 243 isolates were bla(KPC) positive. Ertapenem nonsusceptibility had a low positive predictive value.

Phenotypic and enzymatic comparative analysis of the novel KPC variant KPC-5 and its evolutionary variants, KPC-2 and KPC-4

A novel Klebsiella pneumoniae carbapenemase (KPC) variant, designated bla(KPC-5), was discovered in a carbapenem-resistant Pseudomonas aeruginosa clinical isolate from Puerto Rico. Characterization of the upstream region of bla(KPC-5) showed significant differences from the flanking regions of other bla(KPC) variants. Comparison of amino acid sequences with those of other KPC enzymes revealed that KPC-5 was an intermediate between KPC-2 and KPC-4, differing from KPC-2 by a single amino acid substitution (Pro(103)-->Arg), while KPC-4 contained Pro(103)-->Arg plus an additional amino acid change (Val(239)-->Gly). Transformation studies with an Escherichia coli recipient strain showed differences in the properties of the KPC variants. KPC-4 and KPC-5 both had pIs of 7.65, in contrast with the pI of 6.7 for KPC-2. KPC-2 transformants were less susceptible to the carbapenems than KPC-4 and KPC-5 transformants. These data correlated with higher rates of imipenem hydrolysis for KPC-2 than for KPC-4 and KPC-5. However, KPC-4 and KPC-5 transformants had higher ceftazidime MICs, and the enzymes from these transformants had slightly better hydrolysis of this drug than KPC-2. KPC-4 and KPC-5 were more sensitive than KPC-2 to inhibition by clavulanic acid in both susceptibility testing and hydrolysis assays. Thus, KPC enzymes may be evolving through stepwise mutations to alter their spectra of activity.

Non-susceptibility trends among Enterobacteriaceae from bacteraemias in the UK and Ireland, 2001-06

BACKGROUND

Enterobacteriaceae are common agents of bacteraemia, with Escherichia coli accounting for 20% of the cases. Reflecting this importance, members of the family constitute 4 of the 12 collection groups in the British Society for Antimicrobial Chemotherapy (BSAC) Bacteraemia Surveillance Programme.

METHODS

MICs from the BSAC surveillance programme were reviewed, along with bacteraemia reports received by the Health Protection Agency (HPA) via its CoSurv/LabBase system. Isolates with unusual resistances were subjected to molecular analysis.

RESULTS

The BSAC and HPA systems both revealed dramatically increasing resistance to cephalosporins, ciprofloxacin and gentamicin among E. coli and Klebsiella spp., with cephalosporin resistance largely contingent on the spread of CTX-M extended-spectrum beta-lactamases (ESBLs); fluoroquinolone resistance also increased among Proteus mirabilis and ESBL-negative E. coli. Carbapenem resistance remained extremely rare, but two Enterobacter spp., from the same patient in different years, had KPC carbapenemases, while a few isolates had carbapenem resistance contingent upon combinations of beta-lactamase and impermeability, and ertapenem MICs for AmpC-derepressed Enterobacter spp. rose over time. Three new agents-ceftobiprole, doripenem and tigecycline-were tested. Ceftobiprole was broadly active, except against ESBL producers and Klebsiella oxytoca hyperproducing K1 enzyme, and was variable against AmpC-derepressed Enterobacter spp. and against Proteus vulgaris. Doripenem was more potent than imipenem. Tigecycline was almost universally active against E. coli, but low-level non-susceptibility (MIC 2 mg/L) was frequent among Klebsiella spp.

CONCLUSIONS

E. coli and Klebsiella spp. showed dramatic shifts, with sharply rising non-susceptibility to cephalosporins, ciprofloxacin and gentamicin. The rise in cephalosporin resistance reflected dissemination of CTX-M ESBLs. Carbapenems remain broadly active and new agents offer potential.

Plasmid-mediated 16S rRNA methylases in aminoglycoside-resistant Enterobacteriaceae isolates in Shanghai, China

High-level resistance to aminoglycosides produced by 16S rRNA methylases in Enterobacteriaceae isolates was investigated. The prevalences of armA in Escherichia coli, Klebsiella pneumoniae, and Enterobacter cloacae were 0.6%, 3.0%, and 10%, respectively. rmtB was more prevalent than armA. Pulsed-field gel electrophoresis patterns indicated that armA and rmtB have spread horizontally and clonally.

Simple disk-based method for detection of Klebsiella pneumoniae carbapenemase-type beta-lactamase by use of a boronic acid compound

A disk potentiation method using carbapenems as substrates and 3-aminophenyl boronic acid as an inhibitor was evaluated for the detection of Klebsiella pneumoniae carbapenemase (KPC)-type beta-lactamases. When combined with nonsusceptibility to ertapenem, the method was easy to perform and reliably differentiated isolates producing KPC-type beta-lactamases from those producing other types of beta-lactamases.

High-level carbapenem resistance in a Citrobacter freundii clinical isolate is due to a combination of KPC-2 production and decreased porin expression

An imipenem-resistant isolate of Citrobacter freundii ZJ163 (MIC 256 microg ml(-1)) isolated from a Chinese hospital was investigated. The C. freundii ZJ163 isolate exhibited high-level resistance to carbapenems, penicillins, cephalosporins, cefoxitin, aztreonam, quinolones and aminoglycosides. Isoelectric focusing (IEF) demonstrated three beta-lactamases with pIs of 5.4 (TEM-1), 6.7 (KPC-2) and 7.9 (CTX-M-14). Two different transconjugants (types A and B) were obtained by conjugation studies. The type A transconjugant exhibited reduced susceptibility or resistance to penicillins, cephalosporins and aztreonam, but was susceptible to carbapenems, quinolones and aminoglycosides. The antimicrobial susceptibility patterns of the type B transconjugant were similar to that of type A, except for its significantly reduced carbapenem susceptibility (imipenem MIC 2 microg ml(-1)). IEF, specific PCRs and DNA sequence analysis indicated that the type A transconjugant produced CTX-M-14 beta-lactamase with a pI of 7.9, that the type B transconjugant produced KPC-2 beta-lactamase with a pI of 6.7 and that the beta-lactamase with a pI of 5.4 was TEM-1. PCR analysis and sequencing confirmed the presence of the ampC gene in the chromosomal DNA from C. freundii ZJ163, although no activity of AmpC beta-lactamase was detected by IEF. Urea/SDS-PAGE analysis of outer-membrane proteins revealed that the levels of the 41 and 38 kDa porins were decreased in C. freundii ZJ163. It was concluded that production of KPC-2 combined with decreased expression of porins contributes to high-level resistance to carbapenems in C. freundii ZJ163.

Carbapenem-resistant Escherichia coli and Klebsiella pneumoniae isolates from Turkey with OXA-48-like carbapenemases and outer membrane protein loss

Treatment options are limited in infections caused by extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae, with carbapenems generally preferred. Disturbingly, however, carbapenem-resistant strains are emerging worldwide. Here we report two clinical isolates, one Escherichia coli and one Klebsiella pneumoniae, each with high-level carbapenem resistance (imipenem minimum inhibitory concentration of 32 microg/mL). They were isolated following imipenem therapy from two hospital patients who had received imipenem therapy in different regions of Turkey. Both isolates produced OXA-48-like carbapenemases, enzymes so far reported only from Turkey. Both isolates also had group 1 CTX-M-type ESBLs and had lost major outer membrane proteins. OXA-48-like carbapenemases appear to be scattered in Turkey and surveillance to determine their prevalence is warranted.

Emergence of Serratia marcescens, Klebsiella pneumoniae, and Escherichia coli Isolates possessing the plasmid-mediated carbapenem-hydrolyzing beta-lactamase KPC-2 in intensive care units of a Chinese hospital

Twenty-one Serratia marcescens, ten Klebsiella pneumoniae, and one Escherichia coli isolate with carbapenem resistance or reduced carbapenem susceptibility were recovered from intensive care units (ICUs) in our hospital. Enterobacterial repetitive intergenic consensus-PCR and pulsed-field gel electrophoresis demonstrated that all the S. marcescens isolates belonged to a clonal strain and the 10 K. pneumoniae isolates were indistinguishable or closely related to each other. The MICs of imipenem, meropenem, and ertapenem for all isolates were 2 to 8 microg/ml, except for K. pneumoniae K10 (MICs of 128, 256, and >256 microg/ml). Isoelectric focusing, PCRs, and DNA sequencing indicated that all S. marcescens isolates produced KPC-2 and a beta-lactamase with a pI of 6.5. All K. pneumoniae isolates produced TEM-1, KPC-2, CTX-M-14, and a beta-lactamase with a pI of 7.3. The E. coli E1 isolate produced KPC-2, CTX-M-15, and a beta-lactamase with a pI of 7.3. Conjugation studies with E. coli (EC600) resulted in the transfer of reduced carbapenem susceptibility compared to that of the original isolates, and only the bla(KPC-2) gene was detected in E. coli transconjugants. Plasmid restriction analysis showed identical restriction patterns among all E. coli transconjugants. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and ompK35/36 gene sequence analysis of outer membrane proteins revealed that K. pneumoniae K10 failed to express OmpK36, because of insertional inactivation by an insertion sequence ISEcp1. All these results indicate that KPC-2-producing S. marcescens, K. pneumoniae, and E. coli isolates emerged in ICUs in our hospital. KPC-2 combined with porin deficiency results in high-level carbapenem resistance in K. pneumoniae. The same bla(KPC-2)-encoding plasmid was spread among the three different genera.

Identification of carbapenem-resistant klebsiella pneumoniae harboring KPC enzymes in New Jersey

Klebsiella pneumoniae isolates harboring KPC enzymes have been identified in many geographical areas since 2001. Numerous problems exist in the detection and treatment of patients with such isolates. The clinical characteristics and molecular epidemiology associated with 12 randomly chosen patients in whom these enzymes were detected by molecular methods are described. This is the first description of the identification of carbapenem-resistant K. pneumoniae isolates harboring KPC beta-lactamases at the Veterans Administration Hospital in New Jersey (VA NJHCS). Because recognition of carbapenem resistance in K. pneumoniae due to KPC enzymes can only be achieved by molecular methods, detection in the Clinical Microbiology Laboratory by routine methods will continue to be difficult, leading to dilemmas in treatment.

Genetic structures at the origin of acquisition of the beta-lactamase bla KPC gene

Genetic structures surrounding the carbapenem-hydrolyzing Ambler class A bla KPC gene were characterized in several KPC-positive Klebsiella pneumoniae and Pseudomonas aeruginosa strains isolated from the United States, Colombia, and Greece. The bla KPC genes were associated in all cases with transposon-related structures. In the K. pneumoniae YC isolate from the United States, the beta-lactamase bla KPC-2 gene was located on a novel Tn3-based transposon, Tn4401. Tn4401 was 10 kb in size, was delimited by two 39-bp imperfect inverted repeat sequences, and harbored, in addition to the beta-lactamase bla KPC-2 gene, a transposase gene, a resolvase gene, and two novel insertion sequences, ISKpn6 and ISKpn7. Tn4401 has been identified in all isolates. However, two isoforms of this transposon were found: Tn4401a was found in K. pneumoniae YC and K. pneumoniae GR from the United States and Greece, respectively, and differed by a 100-bp deletion, located just upstream of the bla KPC-2 gene, compared to the sequence of Tn4401b, which was found in the Colombian isolates. In all isolates tested, Tn4401 was flanked by a 5-bp target site duplication, the signature of a recent transposition event, and was inserted in different open reading frames located on plasmids that varied in size and nature. Tn4401 is likely at the origin of carbapenem-hydrolyzing beta-lactamase KPC mobilization to plasmids and its further insertion into various-sized plasmids identified in nonclonally related K. pneumoniae and P. aeruginosa isolates.

Predictors of carbapenem-resistant Klebsiella pneumoniae acquisition among hospitalized adults and effect of acquisition on mortality

Carbapenem-resistant Klebsiella pneumoniae (CRKP) is an emerging nosocomial pathogen. Little is known about its risk factors or mortality. We performed a case-case-control study to assess the risks for CRKP isolation and a retrospective cohort study to assess mortality in three groups of hospitalized adults: (i) patients from whom CRKP was isolated, (ii) patients from whom carbapenem-susceptible Klebsiella spp. (CSKS) were isolated, and (iii) controls from whom no Klebsiella spp. were isolated. After adjustment for length of stay (LOS), the demographics, comorbidities, and exposures of each case group were compared with those of the controls. Significant covariates were incorporated into LOS-adjusted multivariable models. In the mortality study, we evaluated the effect of CRKP on in-hospital death. There were 48 patients with CRKP isolation (21 died [44%]), 56 patients with CSKS isolation (7 died [12.5%]), and 59 controls (1 died [2%]). Independent risk factors for CRKP isolation were poor functional status (odds ratio [OR], 15.4; 95% confidence interval [CI], 4.0 to 58.6; P < 0.001); intensive care unit (ICU) stay (OR, 17.4; 95% CI, 1.5 to 201.9; P = 0.02); and receipt of antibiotics (OR, 4.4; 95% CI, 1.0 to 19.2; P = 0.05), particularly fluoroquinolones (OR, 7.2; 95% CI, 1.1 to 49.4; P = 0.04). CRKP was independently associated with death when patients with CRKP were compared with patients with CSKS (OR, 5.4; 95% CI, 1.7 to 17.1; P = 0.005) and with controls (OR, 6.7; 95% CI, 2.4 to 18.8; P < 0.001). After adjustment for the severity of illness, CRKP isolation remained predictive of death, albeit with a lower OR (for the CRKP group versus the CSKS group, OR, 3.9; 95% CI, 1.1 to 13.6; and P = 0.03; for the CRKP group versus the controls, OR, 5.0; 95% CI, 1.7 to 14.8; and P = 0.004). CRKP affects patients with poor functional status, an ICU stay, and antibiotic exposure and is an independent predictor of death.

Carbapenemases: molecular diversity and clinical consequences

Carbapenemases are beta-lactamases that hydrolyze most beta-lactams including carbapenems. Carbapenemases are classified in four molecular classes; those belonging to class A are the chromosomally-encoded and clavulanic acid-inhibited IMI, NMC-A and SME, identified in Enterobacter cloacae and Serratia marcescens; the plasmid-encoded KPC enzymes identified in Enterobacteriaceae (and rarely in Pseudomonas aeruginosa); and the GES-type enzymes identified in Enterobacteriaceae and P. aeruginosa. The class B enzymes are the most clinically-significant carbapenemases; they are metallo-beta-lactamases, mostly of the IMP and the VIM series. They have been reported worldwide and their genes are plasmid- and integron-located, hydrolyzing all beta-lactams with the exception of aztreonam. One single plasmid-mediated AmpC beta-lactamase, CMY-10, identified in an Enterobacter aerogenes isolate, has been shown to be a cephaslosporinase with some carbapenemase properties. Finally, the class D carbapenemases are being increasingly reported, mostly in Acinetobacter baumannii, and they compromise the efficacy of imipenem and meropenem significantly.

Current concepts in antibiotic-resistant gram-negative bacteria

Gram-negative bacteria are the dominant killers among bacterial pathogens in the intensive care unit. Antibiotic resistance has become a threat in hospital settings and efforts are being made to understand the underlying mechanisms. This review describes current data on the most important mechanisms of resistance in prevalent gram-negative pathogens as well as newer therapeutic options.

Antimicrobial resistance prevention initiative--an update: proceedings of an expert panel on resistance

Antimicrobial resistance is a growing problem that complicates the treatment of important nosocomial and community-acquired infections. It is a worldwide problem that spans the range of human pathogens, including bacteria, fungi, and viruses. This update from the Antimicrobial Resistance Prevention Initiative (ARPI) provides a review of some important trends in antibiotic, antifungal, and antiviral resistance. Areas of focus include multidrug-resistant bacteria in the hospital setting; the growing problem of community-acquired methicillin-resistant Staphylococcus aureus; triazole and polyene resistance in nosocomial infections caused by non-Candida albicans or Aspergillus species, and the utility of in vitro susceptibility testing for these fungal infections; antiviral resistance in alpha- or beta-herpesviruses causing genital herpes or cytomegalovirus infection in immunocompromised hosts; and concerns about a possible pandemic involving avian influenza A and the importance of minimizing emergence of resistant strains of this highly pathogenic virus. The challenges in each area are different, but the general keys to addressing the growing problem of antimicrobial resistance continue to be responsible antimicrobial stewardship and the development of newer antimicrobial agents.

The changing face of Klebsiella pneumoniae infections in the community

Klebsiella pneumoniae (Kp) is an important pathogen both in the community and the hospital setting. In the community the emergence of virulent organisms with predominantly K1/K2 capsular serotypes has been observed over the last 20 years, these pathogens cause a distinct clinical syndrome consisting of pyogenic liver abscesses, sometimes accompanied by meningitis and abscesses elsewhere. In the hospital environment, under heavy antibiotic usage, multiple drug resistance has been increasingly observed in Kp. Kp strains harbouring extended spectrum beta-lactamases (ESBL) and more recently metallocarbapenemase, conferring resistance to many of the antibiotics available, have been described in many parts of the world. These multi-drug-resistant organisms are affecting the choice of antimicrobial therapy, are a major cause for increasing hospital costs and duration of hospitalisations. Some of the ESBL-producing Kp have already moved into the community and are creating therapeutic problems in a setting where empiric, oral antimicrobial therapy is a common practice. In this review we will discuss these two Kp emerging trends.

Carbapenemases: the versatile beta-lactamases

Carbapenemases are beta-lactamases with versatile hydrolytic capacities. They have the ability to hydrolyze penicillins, cephalosporins, monobactams, and carbapenems. Bacteria producing these beta-lactamases may cause serious infections in which the carbapenemase activity renders many beta-lactams ineffective. Carbapenemases are members of the molecular class A, B, and D beta-lactamases. Class A and D enzymes have a serine-based hydrolytic mechanism, while class B enzymes are metallo-beta-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 beta-lactamases frequently detected in Acinetobacter baumannii. The metallo-beta-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 beta-lactamases in the Enterobacteriaceae. This review updates the characteristics, epidemiology, and detection of the carbapenemases found in pathogenic bacteria.

Activity of meropenem as serine carbapenemases evolve in US Medical Centers: monitoring report from the MYSTIC Program (2006)

The Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Surveillance Program was designed to monitor the antimicrobial potency and spectrum of meropenem, and selected broad-spectrum comparison agents against pathogens from hospitalized patients. In the 2006 (year 8 of the study) United States sample, a total of 2841 isolates (94.7% compliance) including 641 Escherichia coli, 619 Klebsiella spp., 606 Pseudomonas aeruginosa, 456 oxacillin-susceptible Staphylococcus aureus, 300 streptococci, 149 Enterococcus faecalis, and 70 Gram-positive anaerobic organisms were tested by reference broth microdilution or agar dilution susceptibility methods. The carbapenems, especially meropenem, consistently demonstrated the lowest resistance rates against Enterobacteriaceae strains, and the fluoroquinolones had the highest and increasing resistance rates. The presence of qnr-mediated fluoroquinolone resistance was investigated using polymerase chain reaction methods but was only observed at very low levels (2.1%) and was not clonally associated. Confirmed extended-spectrum beta-lactamase rates for E. coli and Klebsiella spp. were only 4.8% and 5.0%, respectively, with mobile AmpC (CMY-2 and FOX-5) enzymes shown in 13 additional Enterobacteriaceae isolates. Clonally related KPC-type serine carbapenemase production (57 strains, 9.5%) was observed at a rate 2-fold greater than the prior year among Klebsiella spp. isolates, primarily from 1 geographic region (Middle Atlantic States). These MYSTIC Program (2006) results demonstrate the continued need to monitor the carbapenem class potency and spectrum of activity against Enterobacteriaceae as well as P. aeruginosa because of the documented presence of serine carbapenemases and rare incidence of metallo-beta-lactamases that may further compromise their activity and that of other beta-lactam agents.

Tigecycline for Treatment of Pneumonia and Empyema Caused by Carbapenemase-ProducingKlebsiella pneumoniae

Strains of Klebsiella pneumoniae that produce one of three possible carbapenemases--KPC--have recently been identified with increasing frequency among isolates recovered from patients residing along the East Coast of the United States, particularly within the New York City metropolitan region. These strains have exhibited resistance to multiple antibiotic classes, including carbapenem agents. We report a case of nosocomial pneumonia and empyema caused by a KPC-producing isolate of K. pneumoniae at a large midwestern U.S. tertiary care facility in which the patient was treated with tigecycline. Although the pneumonia was treated successfully, the empyema recurred in association with a treatment-emergent tigecycline minimum inhibitory concentration (MIC) increase from 0.75 to 2 microg/ml. Clinicians should be aware of the potential occurrence of this treatment-emergent MIC increase, especially in the setting of sustained tigecycline therapy. In addition, the emergence of carbapenem-resistant Enterobacteriaceae reinforces the importance of antibiotic stewardship and strict infection control practices.

Antimicrobial resistance prevention initiative--an update: proceedings of an expert panel on resistance

Antimicrobial resistance is a growing problem that complicates the treatment of important nosocomial and community-acquired infections. It is a worldwide problem that spans the range of human pathogens, including bacteria, fungi, and viruses. This update from the Antimicrobial Resistance Prevention Initiative (ARPI) provides a review of some important trends in antibiotic, antifungal, and antiviral resistance. Areas of focus include multidrug-resistant bacteria in the hospital setting; the growing problem of community-acquired methicillin-resistant Staphylococcus aureus; triazole and polyene resistance in nosocomial infections caused by non-Candida albicans or Aspergillus species, and the utility of in vitro susceptibility testing for these fungal infections; antiviral resistance in alpha- or beta-herpesviruses causing genital herpes or cytomegalovirus infection in immunocompromised hosts; and concerns about a possible pandemic involving avian influenza A and the importance of minimizing emergence of resistant strains of this highly pathogenic virus. The challenges in each area are different, but the general keys to addressing the growing problem of antimicrobial resistance continue to be responsible antimicrobial stewardship and the development of newer antimicrobial agents.

Comparison of Phoenix and VITEK 2 extended-spectrum-beta-lactamase detection tests for analysis of Escherichia coli and Klebsiella isolates with well-characterized beta-lactamases

The VITEK 2 and Phoenix extended-spectrum beta-lactamase (ESBL) detection systems, which comprise confirmatory tests and expert systems, were evaluated for their ability to discriminate between 102 well-characterized strains of ESBL-positive or -negative Escherichia coli, Klebsiella pneumoniae, and Klebsiella oxytoca. At least 38 distinct ESBLs were included. The strains were chosen to include some known to cause false-positive and false-negative CLSI ESBL confirmatory test results. Therefore, enzyme characterizations, rather than CLSI tests, were the reference methods for the Phoenix and VITEK 2 evaluations. A third arm of the study was conducted with the Phoenix test using two normally inactive expert rules intended to enhance ESBL detection, in addition to using the currently available software. The Phoenix ESBL confirmatory test and unmodified expert system exhibited 96% sensitivity and 81% specificity for ESBL detection. Activation of the two additional rules increased sensitivity to 99% but reduced the specificity to 58%. The VITEK 2 ESBL confirmatory test exhibited 91% sensitivity, which was reduced to 89% sensitivity by its expert system, while its specificity was 85%. Many of the expert system interpretations of both instruments were helpful, but some were suboptimal. The VITEK 2 expert system was potentially more frustrating because it provided more inconclusive interpretations of the results. Considering the high degree of diagnostic difficulty posed by the strains, both ESBL confirmatory tests were highly sensitive. The expert systems of both instruments require modification to update and enhance their utility.

Class A carbapenemases

Carbapenems, such as imipenem and meropenem, are most often used to treat infections caused by enterobacteria that produce extended-spectrum beta-lactamases, and the emergence of enzymes capable of inactivating carbapenems would therefore limit the options for treatment. Carbapenem resistance in Enterobacteriaceae is rare, but class A beta-lactamases with activity against the carbapenems are becoming more prevalent within this bacterial family. The class A carbapenemases can phylogenetically be segregated into six different groups of which four groups are formed by members of the GES, KPC, SME, IMI/NMC-A enzymes, while SHV-38 and SFC-1 each separately constitute a group. The genes encoding the class A carbapenemases are either plasmid-borne or located on the chromosome of the host. The bla(GES) genes reside as gene cassettes on mainly class I integrons, whereas the bla(KPC) genes and a single bla(IMI-2) gene are flanked by transposable elements on plasmids. Class A carbapenemases hydrolyse penicillins, classical cephalosporins, monobactam, and imipenem and meropenem, and the enzymes are divided into four phenotypically different groups, namely group 2br, 2be, 2e and 2f, according to the Bush-Jacoby-Medeiros classification system. Class A carbapenemases are inhibited by clavulanate and tazobactam like other class A beta-lactamases.