Prevalence and Characterization of Plasmid-Medicated Quinolone Resistance Genes among Clinical Isolates of Extended-Spectrum Cephalosporin Resistant Enterobacter cloacae / 감염과화학요법

ABSTRACT

BACKGROUND: Extended-spectrum cephalosporins (ESCs)-resistant Enterobacter cloacae is one of the pathogens of nosocomial infection the incidence of which is on the rise. Moreover, plasmid-mediated quinolone resistance genes (PMQR genes) that reduce quinolone sensitivity have been shown to be widely distributed among clinical isolates of Enterobacteriaceae. This study was carried out to observe the distribution of PMQR genes in clinical isolates of E. cloacae resistant to ESCs. MATERIALS AND METHODS: Fourty-three ESCs-resistant E. cloacae strains from the blood collected during the span of 7 years, from 1994 to 2001, at Seoul National University Children's Hospital (SNUCH) were included in this study. Isoelectric focusing and enzyme specific PCR were performed to characterize beta-lactamase. The presence of qnrA, qnrB, qnrC, qnrS, qepA, and aac(6')-Ib-cr was determined by PCR, restriction enzyme analyses of PCR products, and DNA sequencing. Minimal inhibitory concentration (MIC) of several quinolones was measured by agar dilution method. RESULTS: The PMQR genes were detected in 9 (21%) of 43 ESCs-resistant E. cloacae isolates. Among them, five isolates were positive for qnrB2, and each two isolates harbored qnrB4 or qnrB5, respectively. qnrA, qnrC, qnrS or qepA was not identified. aac(6')-Ib was detected in 27 isolates, but aac(6')-Ib-cr was not found. Among the 9 qnrB-positive isolates, 5 produced SHV-12, 3 were derepressed mutants, and 1 produced pI 7.5 beta-lactamase. MIC ranges and percent resistances of nalidixic acid, ofloxacin, levofloxacin, and moxifloxacin for the PMQR genes-positive isolates were higher than PMQR genes-negative isolates. CONCLUSION: In this study, ESCs-resistant E. cloacae showed a high prevalence of PMQR genes, and qnrB was the only PMQR gene identified.