This study evaluated the impact of vaccine diluents (peptone or water) on the protective effects of Salmonella Typhimurium (S. Typhimurium) vaccine. Vaccinated broilers were challenged with different doses of wild-type S. Typhimurium through dust. At the time of cull, vaccine load was highest in caeca and lowest in spleen. Wild-type S. Typhimurium was detectable after 24 hrs only in the vaccinated birds challenged with 108 CFU and positive control. S. Typhimurium load was lower in the organs of the groups challenged with 104 and 106 compared to the 108 CFU group. The caecal microbiota alpha diversity of the vaccinated or vaccinated and challenged chickens differed from the positive and negative control groups. Beta diversity of the positive control clustered separately from all other treatment groups, showing that vaccine caused minimal changes in gut microbiota structure. The vaccinated and/or wild-type challenged chickens showed significantly higher abundance of Anaerostignum, Lachnoclostridium, Intestinimonas, Colidextribacter, Monoglobus, Acetanaerobacterium and Subdoligranulum. Outcomes from this study demonstrate that the vaccine effectively protected broiler chickens from S. Typhimurium infection and helped maintain a more stable gut microbiota structure, reducing the impact of S. Typhimurium on gut health. Vaccine diluent did not affect gut microbiota composition.
Keywords: Salmonella Typhimurium; Vaxsafe® ST; broiler chickens; dose of infection; gut microbiota; microbial diversity; poultry production; salmonellosis; vaccine diluent.