Development of a live attenuated vaccine against Escherichia coli respiratory infection in broiler chickens

by Peighambari, Seyed Mostafa

DEVELOPMENT OF A LIVE ATTENUATED VACCINE AGAINST ESCHEAUCHLA COLI RESPIRATORY INFECTION IN BROILER CHICICENS Seyed Mostafâ Peighambari University of Guelph, 1998 Advisor: Professor C. L. Gyles The purposes of this snidy were to construct vaccine organisms by creating Acya Acrp mutations in two virulent avian Escherichia coli strains; develop an aerosol challenge model of avian colibaciliosis; and evaluate the safety. immunogenicity and efficacy of the mutant organisms as vaccines. Deletions of the cya and crp genes of two virulent avian E. coli (078 and 02) were made by Pl phage transduction of the genes with TnlO inserted in them and subsequent selection for tetracycline-sensitive colonies. The Acyn and Acya Acrp denvatives had the predicted phenotype and did not revert. The mutants were assessed for attenuation in day-old chickens inoculated subcutaneously and in 9day-old chickens inoculated by the intratracheal route. Following subcutaneous challenge, the percentages of chicks that died were 100, 60, and 0, respectively, for the parent, Acya, and Acya Actp 078 strains. and 100, 70, and 20, respectively , for the 02 strains. htratracheal challenge of chickens resulted in percentages of maximum lesion scores that were 51, 15 and 9% for the parent, Acya. and Acya Acrp 078 strains, respectively, and 98,3 1 and 11 % for the corresponding 02 strains. A challenge model consisting of intranasal administrationof ùifectious bronchitis virus 4 days before exposure of chickens to an aerosol of the 02 or 078 strain of E.coli was developed. Chickens that were 24 days old when they were challengeci with E.coli had low or no mortality, airsacculitis in 50 to 80% of the group, and pencarditis or perihepatitis in O to 29% of the group. Chickens that were vaccinated by spray with the 02 or 078 vaccine organism at 14 days of age, or with the 02 organism at 10 and 14 days of age remaineci healthy but did not develop significant serum or respiratory mucosal antibody responses. Following challenge with the homologous organism 10 days afier vaccination, chickens vaccinated with the 02 strain had significantly lower airsac lesion scores compared with unvaccinated controls. It is concluded that the mutant E. coli are attenuated, safe, and stable, and that the 02 mutant employed as a vaccine administered by spray induced moderate protection against aùsacculitis. To my family, whose encouragement and patience made it possible to complete my program of study and research