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

Simple Summary: Campylobacter is the most common cause of human bacterial gastroenteritis, and poultry products are the main source of exposure. To reduce human campylobacteriosis, it is necessary to reduce the contamination level of Campylobacter in live poultry. Vaccination could be a solution, but no vaccines for Campylobacter are available to date. In our previous study, a vaccine candidate induced partial protection against Campylobacter in broilers. The objective of the present study was to evaluate whether a protein-based vaccine inoculated at two different frequencies (two or four times) would help to improve the protective immune response during a 42-day trial in broilers orally infected by the bacterium. A specific antibody response was observed regardless of the frequency of inoculation. Moreover, microbiota analysis revealed that significant differences were observed between the groups, but that vaccination did not alter the relative abundance of the main bacterial taxa residing in the caeca. No reduction in Campylobacter caecal load was observed regardless of the vaccine regimen tested. Additional studies testing other vaccine candidates are needed to develop an effective vaccine against Campylobacter in broilers. Campylobacter infections in humans are traced mainly to poultry products. While vaccinating poultry against Campylobacter 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 Campylobacter 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 C. jejuni during a 42-day trial. The caecal Campylobacter 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 (Campylobacter infection only). Specific humoral immune responses were induced, but no reduction in Campylobacter caecal load was observed in any of the groups (p > 0.05). Microbiota beta diversity analysis revealed that the bacterial composition of the groups was significantly different (p ≤ 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 Campylobacter spp. infection in broilers. More studies are required to find new candidates. [ABSTRACT FROM AUTHOR]