Objectives: Escherichia coli (E. coli) is one of the most important causes of bacterial infections in broiler flocks and is also one of the most important causes of diarrhea and infant mortality in all animals. In this respect, enterotoxin-producing isolates of this bacterium are particularly important among diarrheagenic E. coli. This study was carried out with the aim of genetic analysis of different enterotoxins and determination of antibiotic resistance pattern, as well as evaluation of virulence factors in E. coli isolates from broiler chickens samples in Ilam province. Materials & Methods: In this study, a total of 275 nasal and cloacal samples from 20 different poultry farms in Ilam province, in Southwest of Iran were taken. The isolates were identified by specific differential media and standard biochemical tests. Using disk diffusion method, the sensitivity of the isolates to different antibiotics was determined, phenotypically. Tetracycline and erythromycin resistant strains were further confirmed by PCR amplification of tetS and ermB genes, respectively. The presence of heat-stable enterotoxin (ST)a- and STb, EAST-1 and LT-encoding genes among E. coli strains was performed by PCR assays. Results & Conclusions: The PCR results showed that out of 69 isolated E. coli isolates, 19 isolates (27.53%) harbored astA gene (encoding EAST-1), four isolates (5.79%) possessed the LT gene, and two isolates (2.89%) harbored both genes. None of the isolates were positive for STa or STb genes. Based on the results of disk diffusion test, the highest level of resistance was to tetracycline (n= 60, ~87.0%) and erythromycin (n=57, 82.6%), respectively. All the tetracycline-resistant E. coli isolates except one (59/60, 98.3%) carried tetS gene and all the erythromycin-resistant isolates were positive for ermB gene. Our study showed that colonization of broiler chickens with toxin-producing E. coli resistant to tetracycline and erythromycin is remarkably prevalent in Ilam province and can be a potential threat to human health and public health through chickens’ meat consumption.
