Introduction: Colibasilosis is a common disease in broiler breeding units that has caused many losses due to bacterial resistance and excessive use of drugs over many years. Colibasilosis occurs in all species of domestic birds and at different ages, but the infection in birds is more common in adults than in adults and occurs more often between the ages of 4 and 9 weeks. Methods: In this study, four birds were sampled from four different poultry farms in Ilam province. From each poultry farm (15 days, 25 days, 35 days and 45 days), samples were taken from the entrance, water, donut and from each of the three cultivars, a total of 192 cultivations were performed and 72 isolates of E. coli were obtained from fecal samples of poultry. The antibiotic susceptibility testing was determined according to the CLSI guidelines based on the gel release method and the presence of Bla, tem, blactxm1, blacmy1, and cfosA3 genes in E. coli samples isolated from poultry stool by PCR method and the antibiotic susceptibility pattern of these strains was determined. Results and Conclusion: The results of antibiotic susceptibility test showed that the least and highest resistance was respectively cefazolin (77.2%) and ampicillin (83.33%) respectively. Twenty-five strains (34.77%) had blatem gene, 16 (22.20%) strains had the bla ctxm-1 gene, 13 (18.10%) had bla cmy-1 gene and 18 (25%) strains had cfosA3 gene. The result of this research shows that the incidence of the frequency of these gene has been increased during the time.
