Simona Bratu

Emergence of Carbapenem-Resistant Klebsiella Species Possessing the Class A Carbapenem-Hydrolyzing KPC-2 and Inhibitor-Resistant TEM-30 β-Lactamases in New York City

Nineteen isolates of carbapenem-resistant Klebsiella species were recovered from 7 hospitals in New York City. Most K. pneumoniae belonged to a single ribotype. Nucleotide sequencing identified KPC-2, a carbapenem-hydrolyzing beta -lactamase. In 3 strains, TEM-30, an inhibitor-resistant beta -lactamase, was detected. Carbapenem-resistant Klebsiella species possessing KPC-2 are endemic in New York City. This study documents the identification of an inhibitor-resistant TEM beta -lactamase in the United States.

Interplay of Efflux System, ampC, and oprD Expression in Carbapenem Resistance of Pseudomonas aeruginosa Clinical Isolates

ABSTRACT Carbapenems are important agents for the therapy of infections due to multidrug-resistant Pseudomonas aeruginosa; the development of carbapenem resistance hampers effective therapeutic options. To assess the mechanisms leading to resistance, 33 clinical isolates with differing degrees of carbapenem susceptibility were analyzed for the expression of the chromosomal β-lactamase (ampC), the porin that is important for the entry of carbapenems (oprD), and the proteins involved in four efflux systems (mexA, mexC, mexE, and mexX). Real-time reverse transcriptase PCR was performed using primers and fluorescent probes for each of the target genes. The sequencing of regulatory genes (ampR, mexR, nalC, nalD, mexT, and mexZ) was also performed. Diminished expression of oprD was present in all imipenem- and meropenem-resistant isolates but was not required for ertapenem resistance. Increased expression of ampC was not observed in several isolates that were overtly resistant to carbapenems. Increased expression of several efflux systems was observed in many of the carbapenem-resistant isolates. Increased efflux activity correlated with high-level ertapenem resistance and reduced susceptibility to meropenem and aztreonam. Most isolates with increased expression of mexA had mutations affecting nalC and/or nalD. Two isolates with mutations leading to a premature stop codon in mexZ had markedly elevated mexX expressions, although mutations in mexZ were not a prerequisite for overexpression. β-Lactam resistance in clinical isolates of P. aeruginosa is a result of the interplay between diminished production of oprD, increased activity of ampC, and several efflux systems.

Emergence of KPC-Possessing Klebsiella pneumoniae in Brooklyn, New York: Epidemiology and Recommendations for Detection

ABSTRACT Among 257 isolates of Klebsiella pneumoniae collected in Brooklyn, NY, 24% were found to possess blaKPC. Clinical microbiology laboratories that used automated broth microdilution systems reported 15% of the KPC-possessing isolates as susceptible to imipenem. The imipenem MIC was found to be markedly affected by the inoculum. For accurate detection of KPC-possessing K. pneumoniae, particular attention should be paid to proper inoculum preparation for broth-based susceptibility methods. In addition, using ertapenem or meropenem for class reporting of carbapenem susceptibility will improve detection.

Molecular Epidemiology and Mechanisms of Carbapenem Resistance in Acinetobacter baumannii Endemic in New York City

Multidrug-resistant Acinetobacter baumannii has emerged as a serious nosocomial pathogen in certain areas. In Brooklyn, New York, citywide surveillance revealed that approximately 2 of every 3 isolates were resistant to carbapenem antibiotics. Genetic fingerprinting revealed that 2 strains accounted for 82% of these resistant isolates. Compared with carbapenem-susceptible isolates, carbapenem-resistant isolates had reduced expression of 47-, 44-, and 37-kDa outer-membrane proteins. No specific carbapenemase was found; however, carbapenem-resistant isolates expressed greater levels of a class C cephalosporinase. Although expression of penicillin-binding proteins varied among strains, no consistent pattern appeared to account for carbapenem resistance. An efflux pump, present in several strains, did not appear to contribute to carbapenem resistance. Clonal spread of carbapenem-resistant A. baumannii has occurred in hospitals in Brooklyn. The preliminary findings for a small number of strains suggest that diminished production of outer-membrane porins, together with increased expression of a class C cephalosporinase, appear to be important factors leading to carbapenem resistance in this region.

Success of an Infection Control Program to Reduce the Spread of Carbapenem-Resistant Klebsiella pneumoniae

OBJECTIVE To assess the effect of enhanced infection control measures with screening for gastrointestinal colonization on limiting the spread of carbapenem-resistant Klebsiella pneumoniae in a New York City hospital endemic for this pathogen. DESIGN Retrospective observational study with pre- and postinterventional phases. METHODS Beginning in 2006, a comprehensive infection control program was instituted in a 10-bed medical and surgical intensive care unit at a university-based medical center. In addition to being placed in contact isolation, all patients colonized or infected with carbapenem-resistant gram-negative bacilli, vancomycin-resistant Enterococcus, or methicillin-resistant Staphylococcus aureus were cohorted to one end of the unit. Improved decontamination of hands and environmental surfaces was encouraged. In addition, routine rectal surveillance cultures were screened for the presence of carbapenem-resistant pathogens. The number of patients per quarter with clinical cultures positive for carbapenem-resistant K. pneumoniae was compared during the approximately 2-year periods before and after the intervention. RESULTS The mean number (+/-SD) of new patients per 1,000 patient-days per quarter with cultures yielding carbapenem-resistant K. pneumoniae decreased from 9.7 +/- 2.2 before the intervention to 3.7 +/- 1.6 after the intervention (P < .001). There was no change in the mean number of patient-days or the mean number of patients per quarter with cultures yielding methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus, or carbapenem-resistant Acinetobacter baumannii or Pseudomonas aeruginosa after the intervention. There was no association between antibiotic usage patterns and carbapenem-resistant K. pneumoniae. CONCLUSIONS The comprehensive intervention that combined intensified infection control measures with routine rectal surveillance cultures was helpful in reducing the incidence of carbapenem-resistant K. pneumoniae in an intensive care unit where strains producing the carbapenemase KPC were endemic.

Community-associated Methicillin-resistant Staphylococcus aureus in Hospital Nursery and Maternity Units

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has rarely been reported in the hospital setting. We report an outbreak of 7 cases of skin and soft tissue infections due to a strain of CA-MRSA. All patients were admitted to the labor and delivery, nursery, or maternity units during a 3-week period. Genetic fingerprinting showed that the outbreak strain was closely related to the USA 400 strain that includes the midwestern strain MW2. All isolates contained the staphylococcal chromosome cassette mec type IV. Genes for Panton-Valentine leukocidin and staphylococcal enterotoxin K were detected in all isolates, and most contained other enterotoxin genes. Testing of nearly 2,000 MRSA isolates collected during citywide surveillance studies from 1999 to 2003 showed that ≈1% were genetically related to MW2. CA-MRSA strain MW2 has been present in this region at least since 1999. This study documents the spread of this strain among healthy newborns at 1 hospital.

Detection and Spread of Escherichia coli Possessing the Plasmid-Borne Carbapenemase KPC-2 in Brooklyn, New York

A carbapenem-resistant isolate of Escherichia coli was identified that possessed a 23-kb plasmid encoding Klebsiella pneumoniae carbapenemase type 2 (KPC-2). A subsequent surveillance study involving hospitals in Brooklyn, New York, revealed that, among 1417 E. coli isolates, 7 isolates (from 3 hospitals) possessed bla(KPC-2). E. coli possessing KPC-2 is emerging in our region, and improved methods for detection are urgently needed.

Detection of KPC carbapenem-hydrolyzing enzymes in Enterobacter spp. from Brooklyn, New York.

ABSTRACT Enterobacter spp. are rarely resistant to carbapenems. In this report, one Enterobacter sp. isolate possessed blaKPC-3 and two possessed blaKPC-2. For all three strains, the imipenem MICs were dependent on the inoculum and testing method; two were reported by the clinical laboratories to be carbapenem susceptible. Improved detection methods will be necessary to identify these enzymes.

Correlation of Antimicrobial Resistance with β-Lactamases, the OmpA-Like Porin, and Efflux Pumps in Clinical Isolates of Acinetobacter baumannii Endemic to New York City

ABSTRACT Acinetobacter baumannii strains resistant to all β-lactams, aminoglycosides, and fluoroquinolones have emerged in many medical centers. Potential mechanisms contributing to antimicrobial resistance were investigated in 40 clinical isolates endemic to New York City. The isolates were examined for the presence of various β-lactamases, aminoglycoside-modifying enzymes, and mutations in gyrA and parC. Expression of the genes encoding the β-lactamase AmpC, the efflux systems AdeABC and AbeM, and the OmpA-like porin was also examined by real-time reverse transcription-PCR. No VIM, IMP, KPC, OXA-23-type, OXA-24-type, or OXA-58 β-lactamases were detected, although several isolates had acquired blaSHV-5. Most cephalosporin-resistant isolates had increased levels of expression of ampC and/or had acquired blaSHV-5; however, isolates without these features still had reduced susceptibility to cefepime that was mediated by the AdeABC efflux system. Although most isolates with ISAba1 upstream of the blaOXA-51-like carbapenemase gene were resistant to meropenem, several remained susceptible to imipenem. The presence of aminoglycoside-modifying enzymes and gyrase mutations accounted for aminoglycoside and fluoroquinolone resistance, respectively. The increased expression of adeABC was not an important contributor to aminoglycoside or fluoroquinolone resistance but did correlate with reduced susceptibility to tigecycline. The expression of abeM and ompA and phenotypic changes in OmpA did not correlate with antimicrobial resistance. A. baumannii has become a well-equipped nosocomial pathogen; defining the relative contribution of these and other mechanisms of antimicrobial resistance will require further investigation.

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.