Evaluation of Two Recombinant Protein-Based Vaccine Regimens against : Impact on Protection, Humoral Immune Responses and Gut Microbiota in Broilers.

infections in humans are traced mainly to poultry products. While vaccinating poultry against could reduce the incidence of human infections, no vaccine is yet available on the market. In our previous study using a plasmid DNA prime/recombinant protein boost vaccine regimen, vaccine candidate YP437 induced partial protective immune responses against in broilers. In order to optimise vaccine efficacy, the vaccination protocol was modified using a protein prime/protein boost regimen with a different number of boosters. Broilers were given two or four intramuscular protein vaccinations (with the YP437 vaccine antigen) before an oral challenge by during a 42-day trial. The caecal load, specific systemic and mucosal antibody levels and caecal microbiota in the vaccinated groups were compared with their respective placebo groups and a challenge group ( infection only). Specific humoral immune responses were induced, but no reduction in caecal load was observed in any of the groups ( > 0.05). Microbiota beta diversity analysis revealed that the bacterial composition of the groups was significantly different ( ≤ 0.001), but that vaccination did not alter the relative abundance of the main bacterial taxa residing in the caeca. The candidate vaccine was ineffective in inducing a humoral immune response and therefore did not provide protection against spp. infection in broilers. More studies are required to find new candidates.