Background: Avian Colibacillosis is a complex syndrome that causes great economic loss in the poultry industry. Avian Pathogenic Escherichia coli (APEC) is the most considered aetiological agent of avian Colibacillosis. The pathogenisity of APEC associated with serogroups, and virulence factors coded by virulence associated genes (VAG). Virulence factors are involved in colonization, adhesion, invasion, and survivial of E.coli against host defenses. Among these factors, the fimC (fimberiae mannose-binding type1), cvaA/B (Colicin V A/B), iutA (aerobactinsiderophore receptor), Iss (Increased serum survival) and SitA (a bacterial iron transporter) genes have important roles in the APEC pathogenesis. Objectives: The aim of this study was to determine the virulence genotype of Avian E. coli, isolated from suspected broiler to colibacillosis in broiler farms in the Hamedan, West of Iran. Methods: The present study was carried out on E.coli strains (n=100), isolated from visceral organs of diseased and dead poultry suspected to colibacillosis from different broiler flocks. The presence of five VAG in APEC’s including FimC, cvaA/B, iutA, Iss and, SitA were investigated using multiplex PCR. Results: The multiplex PCR analysis showed that the iutA, fimC, Iss, SitA and cvaA/B virulence associated genes had detection rates of 97%, 85%, 84%, 82%, and 52% respectively. Thirty-three of 100 isolates (33%) harbored five VAG which are known as APEC, and one isolate contains only one VAG.
