en تخصصي Special Original article Original article <div style="text-align: justify;"><span style="font-family:times new roman;"><strong>Background:</strong> The antibiotic resistance is considered as one of the biggest public health concerns in most countries. The aim of this study was to determine antibiotic resistance pattern of <em>Escherichia coli</em> isolated from chickens with colibacillosis in Yazd, Iran.<br> <strong>Methods:</strong> A total of 200 carcasses of Ross chickens with colibacillosis were collected from farms located around Yazd, central Iran. After </span><span style="font-family:times new roman;">autopsy</span><span style="font-family:times new roman;">, specimens were collected from </span><span style="font-family:times new roman;">air bags</span><span style="font-family:times new roman;"> of carcasses using sterile swaps and transferred immediately to the laboratory. After microbiological culture, the isolates were confirmed by the conventional Polymerase Chain Reaction (PCR) assay. Antimicrobial susceptibility of <em>E. coli</em> isolates </span><span style="font-family:times new roman;">were</span><span style="font-family:times new roman;"> determined by disk diffusion method.<br> <strong>Results:</strong> Out of 200 specimens, 100 (50%) <em>E. coli</em> isolates were identified and confirmed by PCR method. The results of antimicrobial susceptibility tests showed the highest resistance against nalidixic acid (100%), enrofloxacin (87%), ciprofloxacin (86%), and erythromycin (82%), respectively. Also, the highest susceptibility was seen for colistin (100%), meropenem (94%), and gentamicin (93%), respectively.<br> <strong>Conclusion:</strong> In this study, multidrug resistance was observed in avian pathogenic <em>E. coli</em> isolates that represents the heavy usage of these drugs in poultry flocks in Yazd, central Iran. Improper or overuse of antibiotics </span><span style="font-family:times new roman;">usage</span><span style="font-family:times new roman;"> for treatment of the poultry diseases could play an important role in spreading of the antimicrobial resistance genes among pathogenic bacteria from human and animals especially through </span><span style="font-family:times new roman;">food</span><span style="font-family:times new roman;"> chain.</span></div> Escherichia coli, Drug Resistance, Microbial, Poultry, Iran 74 78 http://jfqhc.ssu.ac.ir/browse.php?a_code=A-10-47-2&slc_lang=en&sid=1 M. Bakhshi No Department of Microbiology, Faculty of Medicine, Shahid Sadoughi University of Medical Sciences, Yazd, Iran M. Fatahi Bafghi No Department of Microbiology, Faculty of Medicine, Shahid Sadoughi University of Medical Sciences, Yazd, Iran A. Astani No Department of Microbiology, Faculty of Medicine, Shahid Sadoughi University of Medical Sciences, Yazd, Iran V.R. Ranjbar No Poultry Diseases Clinic, Yazd, Iran H. Zandi hengameh_zandi@yahoo.com Yes Department of Microbiology, Faculty of Medicine, Shahid Sadoughi University of Medical Sciences, Yazd, Iran M. Vakili No Department of Public Health, Faculty of Medicine, Shahid Sadoughi University of Medical Sciences, Yazd, Iran