Oral vaccination of young broilers with a live <italic>Salmonella</italic> Typhimurium vaccine reduces caecal and internal organ colonization following a <italic>Salmonella</italic> Infantis challenge in a seeder-bird model.

Poultry products are an important source of foodborne <italic>Salmonella</italic> infections in humans. Amongst these, the prevalence of <italic>S.</italic> Infantis is rising. In this study, the protection efficacy of an authorized live-attenuated <italic>S.</italic> Typhimurium vaccine against <italic>S.</italic> Infantis, was examined using a seeder-bird model in broilers. Vaccinated birds displayed a significantly lower colonization of <italic>S.</italic> Infantis bacteria in the caeca compared to the non-vaccinated counterparts (<italic>P</italic> = 0.017), with no significant differences observed in the spleen among the groups, three days post-infection. Thirty-two days post-infection, the disparity in average <italic>S.</italic> Infantis concentration between all-vaccinated and non-vaccinated birds was significant in both caeca (<italic>P</italic> = 0.0003) and spleen (<italic>P</italic> = 0.0002). Interestingly, a third group, consisting of seeder birds that were not vaccinated but housed with vaccinated penmates, exhibited significantly lower <italic>S</italic>. Infantis levels in both caeca (<italic>P</italic> = 0.0014) and spleen (<italic>P</italic> < 0.0001) compared to the non-vaccinated group. These findings underscore the potential of a live-attenuated <italic>S.</italic> Typhimurium vaccine administered to 2-day-old chicks in conferring protection against <italic>S.</italic> Infantis in broilers up to slaughter age. [ABSTRACT FROM AUTHOR]