Emergence of CTX-M-12 and A Novel CTX-M Type Extended-Spectrum β-Lactamase producing Klebsiella pneumoniae

BACKGROUND: The aims of this study were to survey the nation-wide susceptibilities of Klebsiella pneumoniae isolates against ceftazidime and cefotaxime and to determine the prevalence of class A extended-spectrum beta-lactamases (ESBLs). METHODS: During the period of February to July 2004, K. pneumoniae isolates intermediate or resistant to ceftazidime and/or cefotaxime were collected from 12 hospitals in Korea. Antimicrobial susceptibilities were determined by the disk diffusion and the agar dilution methods and ESBL-production was by double-disk synergy test. Ceftazidime or cefotaxime-resistance determinants of the ESBLproducers were transfered to Escherichia coli J53 by transconjugation. Searches for class A ESBL genes were performed by PCR amplication. RESULTS: Among 212 clinical K. pneumoniae isolates, 172 (81%) isolates showed positive results in double-disk synergy test; the most prevalent ESBL was SHV-12 (n=104). Genes encoding ESBLs including SHV-2 (n=6), SHV-2a (n=17), CTX-M-3 (n=18), CTX-M-9 (n=6), CTX-M-12 (n=1), CTX-M- 14 (n=27), CTX-M-15 (n=3), and a novel CTX-M-type beta-lactamases were also detected. CONCLUSIONS: It is concluded that diversity of ESBLs in K. pneumoniae isolates are increasing in Korea. CTX-M-12 has never been reported in Asia, and a novel CTX-M-type ESBL has emerged.