The Survey of Genes Encoding Beta-Lactamases, in Escherichia Coli Resistant to Beta-Lactam and Non-Beta-Lactam Antibiotics

Objective(s) Resistance to the new generation of cephalosporins which is mediated by Extended-Spectrum beta-lactamases (ESBLs) has been found among Escherichia coli isolates throughout the world. These resistance genes and their producers, the micro-organisms carrying beta-lactamases, are responsible for serious clinical and therapeutic problems among inpatients and it is necessary to pay more attention to detection of ESBLs producing organisms. Materiasl and Methods Collectively 260 isolates of E. coli were obtained from 6 hospitals in Tehran (Iran) during April-2006 to April-2007. The antibiotic susceptibility patterns of isolates were determined by disk diffusion method. phenotypic confirmatory test (PCT) was carried out for screening of ESBLs. Microbroth dilution assay was used to determine the minimum inhibitory concentration (MIC) of ceftazidime. Isolates showing MIC≥2 µg/ml were subjected to polymerase chain reaction (PCR) targeting blaTEM, blaSHV, blaCTX and blaPER genes. Results The PCT showed that 48.08 % of isolates are ESBL producers (125 of 260). The majority of cefotaxim