Extended-spectrum beta lactamases (ESBLs) are responsible for resistance to cephalosporins (ceftazidime, ceftriaxone, and cefotaxime) and aztreonam in gram-negative bacilli. ESBL producing Klebsiella bacteria are a major problem for clinicians, ESBLs increase are cause of failure in treatment particularly paediatric patients and also in medical and surgical units. In this research ESBL was investigated by combined disc method. In this research, 128 clinical isolates of Klebsiella ssp. were collected from different microbiology laboratories in Ankara. All isolates were identified with classical methods and API 20E. According to the results of identification, 103 K. pneumoniae, 25 K. oxytoca were obtained. ESBL has been detected 59,37% in Klebsiella bacteria by the combined disk method.

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