Avian colibacillosis is responsible for mortality, and economic loss in the poultry industry, worldwide. Avian Pathogenic Escherichia coli (APEC) is the main causative agent of colibacillosis. The pathogenicity of APEC is associated with virulence factors encoded by virulence-associated genes (VAG). APEC virulence factors are involved in colonization, adhesion, iron acquisition, invasion, toxin production, and survival of E. coli against host defenses. Considering the importance of poultry industry in Iran, and the important role of E. coli in avian colibacillosis in the broiler farms, the objective of this study was to investigates the presence of new types of VAGs in APEC and Avian Faecal Escherichia coli (AFEC) isolates from broilers with suspected colibacillosis and healthy broilers, respectively. Among APEC strains, the predominant VAG was iutA (97%), followed by fimC (87%), iss ( 84%), sitA (82%), chuA (79%), cvaA/B (54%), hylA (42%), yjaA (41%), stx2 (6%) and, stx1 (4%), whereas in AFEC strains, the prevalent VAG was fimC (95%), followed by iss ( 93%), sitA(87%), iutA (79%), chuA (77%), yjaA (52%), cvaA/B (27%), hylA (12%), stx2 (2%) and, stx1 (0%). The present study results indicates that prevalence of iutA, hylA, and cvaA/B VAGs in APEC strains significantly higher than AFEC strains.Therfore these VAGs could be use as candidates for predicting the pathogenicity of avian E. coli strains and these genes could be used for future vaccine design against avian colibacillosis.
