Dissemination of SHV-12 and CTX-M-type extended-spectrum β-lactamases among clinical isolates of Escherichia coli and Klebsiella pneumoniae and emergence of GES-3 in Korea

Objectives: To assess the prevalence and genotypes of Ambler class A extended-spectrum β-lactamases (ESBLs) in Korea. Methods: Clinical isolates of Escherichia coli and Klebsiella pneumoniae collected from 12 Korean hospitals during February-July 2003 were evaluated. Antimicrobial susceptibilities were determined by disc diffusion and agar dilution methods, and the putative ESBL-producing strains were tested by the double-disc synergy method. Detection of genes encoding class A β-lactamases was performed by PCR amplification, and the PCR products were subjected to direct sequencing. Results: The double-disc synergy test showed positive results in 9.3% (23/246) of E. coli and 23.0% (55/239) of K. pneumoniae isolates. The most prevalent types of Ambler class A ESBLs in E. coli isolates were CTX-M-15 (n=4) and CTX-M-3 (n=3), and those in K. pneumoniae isolates were SHV-12 (n=30) and CTX-M-3 (n=13). Two isolates produced both SHV-12 and GES-3, simultaneously. Conclusions: CTX-M-type and/or SHV-12 ESBL-producing E. coli and K. pneumoniae isolates are spreading, and a GES-type ESBL has emerged in Korea.