Between January 2001 and February 2009, total of 706 E. coli and 382 K. 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 were determined by the disk diff usion method according to the Clinical and Laboratory Standards Institute (CLSI) criteria. ESBL production was examined with double-disk synergy test. Th e rate of ESBL-production was 38.5% (272/706) for E. coli and 44% (168/382) for K. pneumoniae. Th e antimicrobial resistance rates of ESBL-producing E. coli and K. pneumoniae strains were significantly higher than non ESBL-producing bacteria. Th e resistance percentages of ESBL positive E. coli and K. pneumoniae strains were as follows: for trimethoprim/sulfamethoxazole, 61% and 41%; for amoxicillin/clavulanic acid, 57% and 46%; for ciprofl oxacin, 59% and 33%; for gentamicin, 40% and 37%; for amikacin, 21% and 17%; for piperacillin/tazobactam, 29% and 26% respectively. None of the strains were resistant to imipenem.

Our data indicated that both in the number and resistance rate to antibiotics of ESBL-producing E. coli and K. pneumoniae strains gradually increase