Evaluation of a modified live Salmonella typhimurium vaccination efficacy against Salmonella enterica serovar Infantis in broiler chickens at processing age

Summary: Salmonella is an important foodborne pathogen, recognized globally, which can be introduced to humans through poultry products. Producers of poultry meat and eggs mitigate this threat through several means including vaccination. Salmonella Infantis has received recent attention due to outbreaks and contamination of processing facilities. Three floor pen experiments evaluated the efficacy of a modified live Salmonella typhimurium vaccine against Salmonella Infantis. In all experiments, chicks were vaccinated at placement and revaccinated on day 14. The first 2 experiments evaluated ceca enumeration and internal organ prevalence in broilers with and without vaccination at different Salmonella Infantis doses (106 and 109). In the third experiment, some broilers in each pen received 1.0 mL of 1.0 × 108 CFU/bird of Salmonella Infantis in a horizontal exposure model. Liver or spleen, ceca, and feathers on rinse samples were collected at processing. The challenge dose administered in experiment 1 (106) did not effectively colonize internal organs, while the 109 dose in experiment 2 overwhelmed defenses. In experiment 3, ceca prevalence and enumeration as well as feathers on bird rinse enumeration were not different between vaccinated and unvaccinated broilers (P > 0.05). Salmonella prevalence in liver or spleen was lower in the vaccinated group (83.3%) compared to the control group (96.3%) (P < 0.05). Liver or spleen enumeration (log10most probable number/g) was lower in vaccinated broilers compared to the unvaccinated control, 1.93 and 2.91, respectively (P < 0.05). The modified live vaccine promoted broiler resistance to Salmonella Infantis colonization in internal organs; however, this protection is not complete and requires additional measures to alleviate the risk of Salmonella.