RESUMO
BACKGROUND: The aim of this study was to survey the nationwide susceptibilities of E. coli and K. pneumoniae against third generation cephalosporins and aztreonam in order to determine the prevalence of extended-spectrum beta-lactamase (ESBL)-producers and to characterize genotypes of ESBLs. METHODS: A total of 6, 567 E. coli and 2, 652 K. pneumoniae non-duplicate strains were isolated from 13 hospitals in April to June 2002. Antimicrobial susceptibilities were tested by the disk diffusion method. Twenty isolates of E. coli and 20 K. pneumoniae were collected from each hospital. ESBL production was determined by a double-disk synergy test. The ceftazidime-resistance of the ESBL-producers was transferred to azide-resistant E. coli J53 by conjugation. MICs of beta-lactam antibiotics to transconjugants were determined by the agar dilution method. Searches for blaTEM , blaSHV , blaCTX-M and blaCMY genes in transconjugants were performed by PCR amplification. RESULTS: Eighty-nine percents of E. coli and 71% of K. pneumoniae isolates were susceptible to ceftazidime. Nine percents of E. coli (23/249) and 30% (78/260) of K. pneumoniae isolates showed positive results in the double-disk synergy test. Ceftazidime-resistance of 13 (57%) E. coli and 42 (53%) K. pneumoniae isolates were transferred to E. coli J53 by conjugation. Among 55 transconjugants, 46 strains were resistant to ceftazidime, while only 16 strains were resistant to cefotaxime. Twelve transconjugants were also resistant to cefoxitin and cefotetan. Banding patterns of PCR amplification showed that the blaTEM , blaSHV , blaCTX-M and blaCMY genes were harboured by 44, 39, 4 and 5 transconjugants, respectively. CONCLUSIONS: E. coli and K. pneumoniae isolates producing TEM-, SHV-type, or CTX-M-type ESBLs are wide spread in Korean hospitals. The spread of ESBL genes could compromise the future usefulness of 3rd generation cephalosporins and aztreonam for the treatment of E. coli and K. pneumoniae infections.