RESUMEN
BACKGROUND: Clinical isolates of Escherichia coli were evaluated to determine the prevalence and genotypes of Ambler class A extended-spectrum beta -lactamases (ESBLs). METHODS: Clinical isolates of E. coli were collected from 12 hospitals from February through July, 2004. Antimicrobial susceptibility was tested by disk diffusion and agar dilution methods, and ESBLproduction was determined by double-disk synergy test. TEM, SHV, CTX-M, PER-1, VEB, IBC, GES, and TLA type ESBL genes were detected by PCR amplifications, and the PCR products were subjected to direct sequencing. RESULTS: The double-disk synergy test was positive in 90.9% (149 in 164) of the ceftazidime- or cefotaxime-resistant E. coli isolates. The most prevalent types of Ambler class A ESBLs in E. coliisolates were CTX-M-15 (n=53). CTX-M-14 (n=24), CTX-M-3 (n=9), CTX-M-9 (n=3), CTX-M-12 (n=3), SHV-2a (n=1), SHV-12 (n=5) and TEM-52 (n=3) were also found. CTX-M-12 ESBL had never been reported before in Korea. CONCLUSIONS: CTX-M type ESBL-producing E. coli isolates are spreading and CTX-M-12 is emerging in Korea.