Infect Chemother.  2009 Oct;41(5):279-285. 10.3947/ic.2009.41.5.279.

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

• Kim YJ
• Seo MR
• Kim J
• Choi EH
• Lee HJ
• Pai H

• KMID: 1473653
• DOI: http://doi.org/10.3947/ic.2009.41.5.279

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.

Keyword

Enterobacter cloacae; qnr; Extended-spectrum cephalosporin resistance

MeSH Terms

Agar
Aza Compounds
beta-Lactamases
Cephalosporins
Cloaca
Cross Infection
Enterobacter
Enterobacter cloacae
Enterobacteriaceae
Incidence
Isoelectric Focusing
Nalidixic Acid
Ofloxacin
Polymerase Chain Reaction
Prevalence
Quinolines
Quinolones
Restriction Mapping
Sequence Analysis, DNA
Agar
Aza Compounds
Cephalosporins
Nalidixic Acid
Ofloxacin
Quinolines
Quinolones
beta-Lactamases

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