Background: The aim of this study is to assess the prevalence and to investigate the molecular epidemiology of Ambler class A extended-spectrum β-lactamase (ESBL)-producing Enterobacter cloacae isolates in a university hospital in Busan, Korea.

Methods: Non-duplicated clinical isolates of E. cloacae from patients admitted in Kosin University Gospel Hospital were collected during the period from January through September, 2003. ESBL-production was examined by the double-disk synergy test (DDST) and the transferability of cefotaxime-resistance by conjugation. MICs of β-lactam antibiotics were determined by the agar dilution method and Ambler class A ESBL genes were searched by PCR amplification. Enterobacterial repetitive intergenic consensus (ERIC) PCR was performed to investigate epidemiological relationships among bla_CTX-M-9 gene-carrying E. cloacae isolates.

Results: Antimicrobial resistance rates of E. cloacae isolates (n=148) to ceftazidime, cefotaxime, and aztreonam were 50.0%, 29.6%, and 48.0%, respectively. Among 50 E. cloacae isolates intermediate or resistant to more than one expanded-spectrum β-lactam agent, 41 (27.7%) showed positive results in DDST; of these 41 isolates, 1 was found to carry bla_TEM-52 gene, 16 carried bla_SHV-12 gene, 4 bla_CTX-M-9 gene, and 19 both bla_SHV-12 and bla_CTX-M-9 genes. The 23 E. cloacae isolates carrying bla_CTX-M-9 gene showed 9 different profiles by ERIC PCR.

Conclusion: ESBL-producing E. cloacae was not uncommon in a university hospital in Busan, Korea. The commonest types of ESBLs produced by E. cloacae isolates were SHV-12 and CTX-M9. CTX-M-9 ESBL-producing E. cloacae isolates showed diverse ERIC-PCR profiles, indicating that they were not originated from a common source. (Korean J Clin Microbiol 2005;8(1):1-9)