Virulence-Associated Genes Of Avian Pathogenic E. Coli Isolated From Chickens With Colibacillosis In Enugu State, Nigeria

Background: Strains of Escherichia coli that cause diseases in chickens are collectively known as avian pathogenic E. coli (APEC) and are one of the most reported poultry diseases associated with morbidity, mortality, reduced egg hatchability and condemnation of carcasses at processing. Their pathogenesis and virulence properties are mediated by several genes responsible for adherence to the respiratory tract, resistance to the host immunological defenses, multiplication under iron-restricted conditions and production of cytotoxic effects. The objective of this study was to ascertain the virulence associated genes in the APEC strains from chickens in Enugu State, Nigeria. Methods & Materials: Dead and moribund chickens submitted to the Necropsy Unit of the Department of Veterinary Pathology and Microbiology, University of Nigeria, Nsukka from various farms across Enugu State between January 2011 and December 2013 were sampled for the study. Liver, heart, spleen and oviduct samples from 182 chickens diagnosed of colibacillosis were collected and processed for isolation and identification of APEC strains following standard bacteriological procedures. Virulence genes were detected using multiplex polymerase chain reaction on isolated APEC strains targeting 12 virulence genes (FimH, pap, felA, sfa, fac, csgA, tsh, cvaC, kpsII, iss, iutA, and cnf). Data generated were analyzed by Chi square and correlation coefficient tests using Graph Pad Prism 5. Significance was accepted at 5% probability level. Results: Avian pathogenic E. coli strains were isolated from 52 of the 182 chickens examined. Out of the 12 virulence genes investigated, 9 (FimH, pap, felA, csgA, tsh, cvaC, kpsII, iss and iutA) were detected, with FimH gene being the most prevalent. The virulence genes occurred in various combinations, with fimH-csgA-iss being the most predominant. No significant association (P > 0.05) was found between the virulence genes and the chicken type and source of isolation. Conclusion: The distributions of virulence genes were similar to other extraintestinal or commensal E. coli from humans and other animals suggesting a zoonotic potential. The different pattern of a subset of putative genes implies divergent mechanisms of infection, and control could be challenging.