Abstract
BackgroundSimultaneous resistance to aminoglycosides and fluoroquinolones in carbapeneme non-susceptible (CNS) isolates will inevitably create problems. The present study was performed to characterize the prevalence of the plasmid-mediated quinolone resistance determinants (QRDs) and aminoglycoside resistance determinants (ARDs) among the CNS Enterobacter cloacae (E. cloacae) isolates in a Chinese teaching hospital, and to acquire their molecular epidemiological characteristics.MethodsThe β-lactamases genes (including class A carbapenemase genes blaKPC and blaSME, metallo-β-lactamase genes (MBLs) blaIMP, blaVIM and blaNDM, and extended spectrum β-lactamases (ESBLs),blaCTX-M, blaTEM and blaSHV), QRDs (including qnrA, qnrB, qnrS and aac(6′)-Ib-cr) and ARDs (including aac(6′)-Ib, armA and rmtB) of these 35 isolates were determined by PCR and sequenced bidirectionally. The clonal relatedness was investigated by pulsed-field gel electrophoresis (PFGE).ResultsOf the 35 isolates, 9 (25.7%) harbored a carbapenemase gene; 23 (65.7%) carried ESBLs; 24 (68.6%) were QRD positive; and 27 (77.1%) were ARD positive. Among the 5 blaIMP-8 positive strains, 4 (80%) contained both ESBL and QRD genes, and all the 5 (100%) harbored ARD genes. Of the 23 ESBLs positive isolates, 6 (26.1%) were carbapenemase positive, 14 (60.9%) were QRD positive, and 18 (78.3%) were ARD positive. PFGE revealed genetic diversity among the 35 isolates, indicating that the high prevalence of CNS E. cloacae isolates was not caused by clonal dissemination.ConclusionQRD and ARD genes were highly prevalent among the CNS E. cloacae isolates. Multiple resistant genes were co-expressed in the same isolates. The CNS E. cloacae isolate co-expressing blaNDM-1, blaIMP-26, qnrA1 and qnrS1 was first reported.
Highlights
Enterobacter cloacae (E. cloacae) has recently emerged as an important hospital pathogen [1]
All the 35 E. cloacae isolates with reduced susceptibility to imipenem (MIC$2 mg/ml) or ertapenem (MIC$1 mg/ml) were defined as carbapeneme non-susceptible (CNS) isolates, which were than PCR screened using custom primers (Table 1) targeting b-lactamases genes, quinolone resistance determinants (QRDs) and aminoglycoside resistance determinants (ARDs) genes
The qnrA, qnrB, qnrS and aac(69)-Ib-cr genes and any QRD genes were detected in 13.0% (3/23), 30.4% (7/23), 26.1% (6/23), 30.4% (7/23) and 60.9% (14/23) of the extendedspectrum b-lactamases (ESBLs) positive isolates, respectively
Summary
Enterobacter cloacae (E. cloacae) has recently emerged as an important hospital pathogen [1]. Several mechanisms of carbapenem resistance have been reported, most of the mechanisms are related to the spread of plasmid-mediated acquired carbapenemases belonging to Ambler class A (KPCs) and class B (VIMs, IMPs, and NDM-1) b-lactamases [5]. These enzymes compromise the clinical efficacy of almost the whole armamentarium of antimicrobial drugs, leaving clinicians with only a limited number of ‘‘last-line’’ agents such as colistin [6]. The present study was performed to characterize the prevalence of the plasmidmediated quinolone resistance determinants (QRDs) and aminoglycoside resistance determinants (ARDs) among the CNS Enterobacter cloacae (E. cloacae) isolates in a Chinese teaching hospital, and to acquire their molecular epidemiological characteristics
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