Background : The aim of this study was to survey the nation wide susceptibilities of Esherichia coli and Klebsiella pneumoniae against cefotaxime and to determine the prevalence of CTX-M-type extended-spectrum β-lactamases(ESBLs).

Methods : During the period of April to June, 2002, E. coli and K. pneumoniae isolates were collected from 13 hospitals. Antimicrobial susceptibilities to cefotaxime were tested by the disk diffusion method. ESBL production was determined by double disk synergy test. Cefotaxime-resistance of the ESBL-producers was transferred to azide-resistant E. coli J53 by conjugation. MICs of β-lactam antibiotics were determined by agar dilution method. Searches for bla_CTX-M genes were performed by PCR amplication. pIs of β-lactamases were determined by isoelectric focusing.

Results : Ten percents of E. coli and 35 percents of K. pneumoniae isolates among 260 strains of each were intermediate or resistant to cefotaxime. Twenty-three isolates of E. coli and 78 K. pneumoniae isolates showed positive results in the double disk synergy test. One isolate of E. coli and 2 K. pneumoniae isolates harbored bla_CTX-M-3 gene, 2 E. coli isolates harbored bla_CTX-M-15 gene, and 2 E. coli and 2 K. pneumoniae isolates harbored bla_CTX-M-14 gene.

Conclusion : E. coli and K. pneumoniae isolates producing CTX-M-type ESBLs are not uncommon in Korean hospitals. The spread of CTX-M-type ESBL genes could compromise the future usefulness of 3rd generation cephalosporins and aztreonam for the treatment of E. coli and K. pneumoniae infections. (Korean J Clin Microbiol 2004;7(1):48-54)