en Anti-microbial agents, resistance and treatment protocols Anti-microbial agents, resistance and treatment protocols Original article Original article <p dir="ltr"><strong>Introduction:</strong> Extended spectrum beta-lactamase (ESBL) producing <em>Escherichia coli</em> generate a major problem for clinical therapeutics and epidemiological study. The incidence of ESBL producing strains among clinical isolates has been steadily increasing during the past few years, and remains an important cause of failure of therapy with cephalosporins. The aim of this study was to determine the antimicrobial susceptibility pattern and prevalence of ESBLs in <em>E. coli</em> isolates taken from different clinical specimens by phenotypic and genotypic techniques. <strong>Methods:</strong> In this descriptive study, a total of 100 <em>E. coli</em> isolates collected from different clinical specimens were used. The antibiotic resistance pattern to twelve antimicrobial agents was determined by disk diffusion method. The ESBLs producing strains were confirmed by double-disk-diffusion test, and the <em>CTX-M, TEM</em>, <em>SHV</em>, and <em>OXA </em>were detected by PCR. <strong>Results: </strong>The prevalence of ESBL producing <em>E. coli</em> was 56%. The results show that 95% of ESBL producing <em>E. coli</em> isolates tested were resistant to ceftriaxone and cefotaxime, 93% for ceftazidime, 86% for azithromycin, 79% for cefazolin and 43% to imipenem. Among the ESBL producing <em>E. coli</em>, 48%, 30% and 11% were positive for <em>CTX-M</em>, <em>TEM</em> and <em>SHV</em> genes, respectively. <em>OXA</em> was not found in all isolates.<strong> Conclusion:</strong> ESBL producing isolates of <em>E. coli</em> have been increasingly recognized and there is a need to carefully formulate therapeutic strategies to control infections in teaching Hospitals. The high percentage of drug resistance in ESBL producing <em>E. coli</em> suggests that routine detection of ESBL is required by reliable laboratory methods.</p> Escherichia coli, Multi-drug resistance, Extended spectrum beta-lactamase, PCR 153 158 http://jommid.pasteur.ac.ir/browse.php?a_code=A-10-84-1&slc_lang=en&sid=1 Vahideh Kadaei ali_nike23@yahoo.com No Department of biology, Faculty of Basic Science, University of Zabol, Zabol, Iran Ahmad Rashki ah_rashki@usal.es Yes Departments of Physiopathology, Faculty of Veterinary Medicine, University of Zabol, Zabol, Iran