Prevalence of the Extended-Spectrum β -Lactamase and qnr Genes in Clinical Isolates of Escherichia coli

Abstract

Background: This study was performed to investigate the prevalence of qnr genes in clinical isolates of Escherichia coli from Korea that produce extended-spectrum β-lactamases (ESBLs). Methods: During the period of May to June 2005, we collected clinical isolates of E. coli that were intermediate or resistant to ceftazidime and/or cefotaxime from 11 Korean hospitals. Antimicrobial susceptibility was determined by the disk diffusion and agar dilution methods. ESBL production was confirmed phenotypically by the double-disk synergy test. ESBL and qnr genes were searched for by PCR amplification, and the PCR products were then subjected to direct sequencing. Results: Double-disk synergy tests were positive in 84.3% (118/140) of ceftazidime-and/or cefotaxime-nonsusceptible E. coli isolates. The most prevalent types of ESBL in E. coli isolates were CTXM-14 (N=41) and CTX-M-15 (N=58). Other ESBLs were also identified, including CTX-M-3 (N=7), CTX-M-9 (N=8), CTX-M-12 (N=1), CTX-M-57 (N=1), SHV-2a (N=2), SHV-12 (N=17) and TEM-52 (N=4). The qnrA1 and qnrB4 genes were identified in 4 and 7 ESBL-producing isolates, respectively. Conclusions: CTX-M-type enzymes were the most common type of ESBL in E. coli isolates from Korea, and the qnr genes were not uncommon in ESBL-producing E. coli isolates. Dissemination of E. coli containing both ESBL and qnr genes could compromise the future usefulness of the expanded-spectrum antibiotics for the treatment of infections.