Host response and prevention of avian pathogenic Escherichia coli following vaccination with an attenuated Salmonella expressing E. coli common pilus in chickens

Avian pathogenic Escherichia coli (APEC) is a subset of extraintestinal pathogenic E. coli that causes detrimental losses to the poultry industry. Vaccines to reduce APEC in chickens have been partially successful, but many lack protection against multiple serotypes of APEC. Recombinant attenuated Salmonella vaccine (RASV) strains have been used to induce immunity against Salmonella in production chickens and can be modified to deliver foreign antigens as well. This study evaluated the transcriptome of chicken spleens and assessed prevention of APEC infection following vaccination with RASV strains, including a RASV carrying an E. coli antigen. Four-day-old White Leghorn chicks were orally vaccinated with RASV c8025(pYA3337) carrying an empty plasmid, c8025(pYA4428) carrying genes for E. coli common pilus (ECP), a combination of RASVs c8025(pYA3337) and c8025(pYA4428), or PBS (unvaccinated). To assess the host response to vaccination, antibody titers were measured by ELISA and spleen samples (n = 5) were collected from combination vaccinated and unvaccinated groups of four-week-old chickens for RNA sequencing. Five-week old chickens were challenged via air sac with APEC strains APEC-O2 and c7122 (O78). Blood was obtained 24 hours post-challenge, heart, liver, lung, and spleen were collected 48 hours post-challenge for enumeration of E. coli, and gross colibacillosis lesions were scored at necropsy. Chickens vaccinated with RASV strains elicited anti-E. coli EcpA, as well as cross reactive anti-E. coli IutA and IroN IgY antibodies. IgA results. In some organs, bacterial loads and lesions scores were numerically reduced, but no significant differences were detected for vaccinated compared to unvaccinated chickens. Transcriptome results. This data indicates that RASVs could be used to stimulate the immune system and is an initial step toward developing improved therapeutics to combat APEC infections in chickens. Overall design: Chickens were evaluated for the spleen transciptomic response to vaccination with either PBS (non-vaccinated) or RASV chi8025(pYA4428) carrying genes for E. coli common pilus (ECP) (vaccinated). Four spleens from each non-vaccinated and vaccinated chickens were used for library construction and sequenced on the HiSeq 3000. Differential