Prevalence and antimicrobial resistance patterns of extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae isolated from blood cultures in an Istanbul University Hospital.

Between January 2001 and September 2006, a total of 459 Escherichia coli and 226 Klebsiella pneumoniae strains were isolated from blood samples of patients with bacteremia who were hospitalized at the Istanbul University Cerrahpasa Medical Faculty. Blood cultures were analyzed with the Bactec 9120 system (Becton Dickinson, USA). Antimicrobic resistance of the E. coli or K. pneumoniae strains was determined by the disk diffusion method according to the Clinical and Laboratory Standards Institute criteria. Extended spectrum beta-lactamase (ESBL) production was examined with the double-disk synergy test. The percentage of ESBL was 40% (182/459) for E. coli and 49% (111/226) for K. pneumoniae. ESBL-producing E. coli and K. pneumoniae were highly resistant to trimethoprim/sulfamethoxazole (60 and 40.5%), amoxicillin/clavulanic acid (56.5 and 48.6%), ciprofloxacin (57.6 and 35%) and gentamicin (38 and 40.5%), respectively; however, lower resistance rates were found for amikacin (19.7 and 16%) and piperacillin/tazobactam (29.6 and 24%). None of the strains were resistant to imipenem. Our data indicated that prevalence of ESBL-producing E. coli and K. pneumoniae strains isolated from blood cultures is high and antimicrobial resistance increases. Considerable effort should be made to decrease the ESBL-positive organisms.