Background:Extended-spectrum β-lactamase (ESBL) producing Escherichia coli and Klebsiella spp. isolates are clinically resistant to all the β-lactams except carapenems and cephamycins. This study was to determine the prevalence of ESBL producing E. coli and Klebsiella spp. and the rates and trends of resistance to extended-spectrum β-lactams and other antimicrobial agents in ESBL producing E. coli and Klebsiella spp.. 

Methods:During the periods of 2002, a total 2,551 clinical isolates of E. coli & Klebsiella spp. were collected from patients of the Samsung medical center, Seoul, Korea. Antimicrobial susceptibility test and determination of ESBL production were performed by Vitek GNS-433 card. 

Results:151/1,594 (9.5%) of E. coli isolates, 128/896 (14.3%) of K. pneumoniaeisolates and 11/61 (18.0%) of K. oxytica were ESBL producing strains. Resistance to cefoxitin and cefepime were 2.4% and 13.4% in ESBL producing isolates. Imipenem had excellent activity against E .coli and Klebsiella spp. (100% susceptible). 

Conclusion: In this study, ESBL-producing E. coli and Klebsiella spp were more resistant to β-lactams including cefepime than ESBL non-producing E. coli and Klebsiella spp.. ESBL producing E. coli and Klebsiella spp. showed a high level of co-resistance with aminoglycosides and fluoroquinolones. Imipenem showed the highest level of activity against E. coli and Klebsiella spp.. (Korean J Clin Microbiol 2003;6(1):47-51)