| Summary: | Abstract Background and objectives: Beta-lactamase enzymes are the most causes of resistance to antibiotics among gram-negative bacteria. Nowadays, Infections due to ESBLs are being increased throughout the world and is considered as a new burden to the health systems. This study aimed at determining the sensitivity pattern of E.coli isolates to beta-lactam antibiotics, and investigating the presence of blaCTX-M, blaTEM, and blaSHV genes in the urine samples. . Material and Methods: In this study, 244 E.coli isolates were screened in 2009-2010. The antibiotic susceptibility of E. coli isolates were determined by disc-diffusion method. Antimicrobial agents tested were cefoxatime, ceftazidime, imipenem, nalidixic acid, and ciprofloxacin. The combined disc test was used to confirm the results. The results were compared to the Clinical and Laboratory Standards Institute (CLSI) and ESBL positive isolates were further investigated for the presence of blaCTX-M, blaTEM, and blaSHV genes by PCR. Results: Of 244 E. coli isolates, 116 (47.1%) are resistant to Ceftazidime, and 96 (39.2%) to cefoxatime. Also, 109 (44.3%) isolates are ESBL positive. blaCTX-M, blaTEM, and blaSHV genes are found among 95 (87.1%), 75 (68.8%), and 77 (70.6%) ESBL positive isolates, respectively. Forty (36.6%) isolates have all three genes, while 68 (62.3%) include blaTEM and blaSHV genes. Moreover, 61 (55.9%) isolates carry blaCTX-M and blaTEM genes, and 54(49.5%) have blactx-M and blashv. Conclusion: Regarding the high frequency of resistance to the third generation cephalosporin antibiotics, precise antibiogram testing is highly recommended before any antibiotic prescription in cases of infections with ESBL producing microorganisms. Key words: ESBL Escherichia coli blaCTX-M blaTEM blaSHV.
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