Avian pathogenic Escherichia coli (APEC) shares some virulence attributes with strains of E. coli that cause extraintestinal infections in humans. The APEC is considered a possible cause for a zoonosis. The objective of this work was to determine the prevalence of twelve genes that are associated with virulence in a group of APEC isolates, as well as to identify the phylogenetic groups to which they belong. According to the results, one of these isolates harbors 91.6% of the virulence genes and

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... most of the isolates have 7 or 8 of such twelve genes. The genes feoB and iss had the highest prevalence, with 95.6%. Genes associated to the acquisition of iron were present in more than 60% of the APEC isolates, while those of the ibeA invasin and vat toxin were detected with the lowest prevalence. A great genetic diversity was observed on the APEC isolates, which suggest that bacterial systems for iron acquisition, and those related to bacterial resistance to the host's defense mechanisms are fundamental virulence factors in these bacteria. On the other hand, the rest of the virulence genes provide valuable information for the development of vaccines against avian colibacillosis. It was also determined that a high percentage of APEC belongs to the phylogenetic group B1, from which mainly commensal and pathogenic E. coli strains derive.