Abstract
Avian pathogenic Escherichia coli (APEC) causes extraintestinal infections in poultry. Vaccines targeting APEC in chickens have been partially successful, but many lack heterologous protection. Recombinant attenuated Salmonella vaccine (RASV) strains can induce broad immunity against Salmonella and be modified to deliver E. coli antigens. Along with vaccine characteristics, understanding the host response is crucial for developing improved vaccines. The objectives of this study were to evaluate host responses to vaccination with an RASV producing E. coli common pilus (ECP) and assess protection against APEC infection in chickens. Four-day-old White Leghorn chickens were unvaccinated or orally vaccinated and boosted 2 weeks later with RASV χ8025(pYA3337), RASV χ8025(pYA4428) carrying ecp operon genes, or a combination of χ8025(pYA3337) and χ8025(pYA4428) (Combo). To assess host responses, serum IgY and intestinal IgA antibody titers were measured, and spleen samples (n = 4/group) were collected from unvaccinated and Combo vaccinated 4-week-old chickens for RNA-seq. Vaccine protection potential against Salmonella and APEC was evaluated in vitro using bacterial inhibition assays. Five-week-old chickens were challenged via air sac with either an APEC O2 or O78 strain. E. coli was enumerated from internal organs, and gross colibacillosis lesions were scored at necropsy. RASV immunized chickens elicited anti-E. coli antibodies. The spleen transcriptome revealed that 93% (89/96) of differentially expressed genes (DEG) were more highly expressed in Combo vaccinated compared to unvaccinated chickens, with signal as the most significantly impacted category. RNA-seq analysis also revealed altered cellular and metabolic processes, response to stimulus after vaccination, and immune system processes. Six DEG including genes linked to transcription regulation, actin cytoskeleton, and signaling were highly positively correlated with antibody levels. Samples from RASV immunized chickens showed protection potential against Salmonella strains using in vitro assays, but a variable response was found for APEC strains. After APEC challenges, significant differences were not detected for bacterial loads or gross lesions scores, but χ8025(pYA3337) immunized and χ8025(pYA4428) immunized chickens had significantly fewer number of APEC-O2-positive samples than unvaccinated chickens. This study shows that RASVs can prime the immune system for APEC infection, and is a first step toward developing improved therapeutics for APEC infections in chickens.
Highlights
Avian pathogenic Escherichia coli (APEC) is a subset of extraintestinal pathogenic E. coli (ExPEC) that commonly causes respiratory and systemic infections in poultry
Chicken responses to recombinant attenuated Salmonella vaccine strain (RASV) strains were assessed phenotypically and genotypically; broad protection potential to Salmonella and APEC serotypes were tested in vitro and protection against APEC infection was tested in vivo
The RASV strain χ8025 was selected to deliver E. coli common pilus (ECP) because it has attenuating mutations of the avirulent Megan Vac 1 vaccine licensed in the United States for reduction of Salmonella in poultry and does not promote a Salmonella carrier state [37]
Summary
Avian pathogenic Escherichia coli (APEC) is a subset of extraintestinal pathogenic E. coli (ExPEC) that commonly causes respiratory and systemic infections in poultry. Humans can acquire APEC through direct contact with animals or contaminated poultry meat and eggs, and these organisms have the potential to cause severe ExPEC-associated human infections [2, 5,6,7,8]. Chickens acquire APEC through a respiratory route of infection, leading to septicemia, fibrinous lesions of internal organs, and death. APEC strains cause local infections in poultry, including cellulitis, salpingitis, and synovitis [1, 10]. APEC-infected chickens result in economic losses to the poultry industry because of lost production time, containment, carcass condemnations, and mortality. A prevention strategy to control disease would have the potential for significant benefits for poultry and producers
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
