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

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Peighambari, Seyed Mostafa

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University of Guelph

Abstract

The purposes of this study were to construct vaccine organisms by creating [Delta]'cya' [Delta]'crp' mutations in two virulent avian 'Escherichia coli' strains; develop an aerosol challenge model of avian colibacillosis; 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' (O78 and O2) were made by P1 phage transduction of the genes with Tn'10' inserted in them and subsequent selection for tetracycline-sensitive colonies. The [Delta]'cya' and [Delta]' cya' [Delta]'crp' derivatives had the predicted phenotype and did not revert. The mutants were assessed for attenuation in day-old chickens inoculated subcutaneously and in 9-day-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, [Delta]'cya', and [Delta]'cya' [Delta]'crp' O78 strains, and 100, 70, and 20, respectively, for the O2 strains. Intratracheal challenge of chickens resulted in percentages of maximum lesion scores that were 51, 15 and 9% for the parent, [Delta]'cya', and [Delta]' cya' [Delta]'crp' O78 strains, respectively, and 98, 31 and 11% for the corresponding O2 strains. A challenge model consisting of intranasal administration of infectious bronchitis virus 4 days before exposure of chickens to an aerosol of the O2 or O78 strain of 'E. coli' was developed. Chickens that were 24 days old when they were challenged with 'E. coli' had low or no mortality, airsacculitis in 50 to 80% of the group, and pericarditis or perihepatitis in 0 to 29% of the group. Chickens that were vaccinated by spray with the O2 or O78 vaccine organism at 14 days of age, or with the O2 organism at 10 and 14 days of age remained healthy but did not develop significant serum or respiratory mucosal antibody responses. Following challenge with the homologous organism 10 days after vaccination, chickens vaccinated with the O2 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 O2 mutant employed as a vaccine administered by spray induced moderate protection against airsacculitis.

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Escherichia coli, respiratory infectin, broiler chickens, live attenuated vaccine, Avian colibacillosis

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