The aim of this study was to detect the presence of extended spectrum beta-lactamase (ESBL) in clinical isolates of Escherichia coli and Klebsiella sp. and to determine in vitro antibiotic resistance of these strains. A total of 78 E.coli and 40 Klebsiella sp. strains isolated from urine, blood, bronchoalveolar lavage, tracheal aspirate, abscess, cerebrospinal fluid and throat swab samples, and identified by conventional methods were included in the study. ESBL activity was screened with double disk synergy test. Antibiotic susceptibilities of the clinical isolates were determined by disc diffusion method using CLSI (Clinical and Laboratory Standards Institute) guidelines. ESBL production was found positive in 25 (32.1%) E.coli and 18 (45%) Klebsiella isolates. The resistance rates of ESBL producing E.coli and Klebsiella strains were as 76% and 5.6% for ciprofloxacin, 68% and 55.6% for trimethoprim/sulfamethoxazole, 64% and 77.8% for gentamicin, 28% and 50% for piperacillin/tazobactam, 0% and 5.6% for cefoxitin, respectively. In ESBL negative isolates of E.coli and Klebsiella sp. these rates were found as follows; 58.5% and 63.6% for amoxicillin/clavulanate, 54.7% and 40.9% for trimethoprim/sulfamethoxazole, 41.5% and 54.5% for piperacillin/tazobactam, 35.8% and 4.5% for ciprofloxacin, 18.9% and 45.5% for gentamicin, 15.1% and 50% for cefotaxime, 13.2% and 36.4% for ceftazidime, 13.2% and 54.5% for aztreonam, 11.3% and 50% for ceftriaxone, 7.5% and 4.5% for cefoxitin, respectively. While all isolates were susceptible to meropenem, cefoxitin was the second most effective antibiotic. It was concluded that ESBL determination should be added to routine antibiotic suspectibility testing in members of Enterobacteriaceae isolates in order to prevent the selection of resistant bacteria and treatment failure.
