Expression of Escherichia coli Antigens in Salmonella typhimurium as a Vaccine to Prevent Airsacculitis in Chickens

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Abstract
Avian pathogenic Escherichia coli strains are associated with a variety of extraintestinal poultry diseases, including airsacculitis, colisepticemia, and cellulitis. A number of E. coli serotypes are associated with these diseases, although the most prevalent serotype is O78. Fimbrial proteins expressed by these strains appear to be important virulence factors, including type 1 fimbriae, P fimbriae, and curli. We have been working to develop an effective vaccine to protect chickens against these diseases. We have previously shown that an attenuated Salmonella typhimurium strain expressing O78 lipopolysaccharide provides protection against challenge with an O78 avian pathogenic E. coli strain. In this work, we have constructed an attenuated S. typhimurium that expresses both the O78 lipopolysaccharide and E. coli-derived type 1 fimbriae. In these studies, chickens were vaccinated at day of hatch and again at 2 wk of age. Birds were challenged at 4 wk of age. We found that the vaccine candidate provided significant protection against airsacculitis as compared to untreated controls or birds vaccinated with an attenuated S. typhimurium that did not express any E. coli antigens. In a separate experiment, challenged vaccinates showed significant weight gain compared to challenged nonvaccinates. We were not able to demonstrate protection against E. coli O1 or O2 serotype challenge, nor against challenge with wild-type S. typhimurium.