CTX-M and SHV-12 β-lactamases are the most common extended-spectrum enzymes in clinical isolates of Escherichia coli and Klebsiella pneumoniae collected from 3 university hospitals within Korea

Among the 443 clinical isolates of Escherichia coli and Klebsiella spp. collected between June and November 2003 from 3 university hospitals in Korea, 62 isolates were confirmed as extended-spectrum β-lactamase (ESBL)- or plasmid-mediated AmpC β-lactamase-producers by double disk synergy test, PCR and sequencing for β-lactamase genes. The most frequently identified ESBL gene among E. coli and K. pneumoniae isolates was blaSHV-12 and blaCTX-M (blaCTX-M-9, blaCTX-M-14, blaCTX-M-3, and blaCTX-M-15). Four kinds of plasmid-mediated AmpC β-lactamases, ACT-1, CMY-1, CMY-2, and DHA-1, were detected. ESBL production was associated with high levels of resistance to tetracycline, sulfisoxazole, streptomycin, kanamycin, gentamicin and tobramycin when compared to non-ESBL producing isolates. Conclusively, this study suggests that the CTX-M β-lactamases are prevalent and various kinds of plasmid-mediated AmpC enzymes are distributed in clinical isolates of E. coli and Klebsiella spp. in Korea.