Fereshteh Shahcheraghi - Department of Microbiology, Pasteur Institute of Iran, Tehran, Ira
Siavash Nasiri - Department of Microbiology, Pasteur Institute of Iran, Tehran, Ira
Hanieh Noveiri - Department of Microbiology, Pasteur Institute of Iran, Tehran, Ira

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 ۲۶۰ isolates of E. coli were obtained from ۶ hospitals in Tehran (Iran) during April-۲۰۰۶ to April-۲۰۰۷. 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>۲ pg/ml were subjected to polymerase chain reaction (PCR) targeting blaTEM, blaSHV, blaCTX and blaPER genes. Results The PCT showed that ۴۸.۰۸% of isolates are ESBL producers (۱۲۵ of ۲۶۰). The majority of cefotaxime resistant (۹۰.۸%) and ceftazidime resistant (۹۲.۵%) isolates were ESBL producers. The obtained results by PCR revealed that ۵.۷۷% (n=۱۵ of ۲۶۰) and ۲۴.۲۳ (n=۶۳) of isolates can produce SHV and TEM type enzymes respectively. blaCTX was detected in ۲۰.۳۸% of isolates (n=۵۳) and none of them could produce blaPER type beta-lactamases. Conclusion The results of our study showed that the ESBL genes have high prevalence among clinical isolates of E. coli. Such high dissemination of ESBLs is a serious problem for public health and therefore, it's necessary to seek a program for monitoring ESBLs in hospitals.

Antibiotic resistance, Escherichia coli, Extended-spectrum beta-lactamases