Abstract
BACKGROUND: Salmonella Typhimurium poses a substantial health risk to both humans and animals. This study evaluated the potential of using the Salmonella Typhimurium ΔsptP mutant as a live-attenuated vaccine candidate by constructing it through homologous recombination and assessing its key biological properties, including growth characteristics, immunogenicity, and protective efficacy. METHODS: We generated the ΔsptP mutant through targeted gene deletion, ensuring the preservation of the bacterial strain's growth and stability. In vitro and in vivo assays were performed to compare the invasive capabilities between the mutant and the wild-type strains. Specifically, we examined the invasion into RAW264.7 murine macrophages and mice. Furthermore, the virulence of the mutant was evaluated by determining the median lethal dose (LD(50)). To evaluate immunogenicity and protection, mice were immunized with 2 × 10(4) CFUs of the ΔsptP mutant, followed by a booster immunization, and then challenged with a virulent strain. RESULTS: The ΔsptP mutant exhibited no significant changes in growth characteristics or genetic stability compared to the wild-type strain. However, it demonstrated a significantly diminished capacity for invasion in both murine macrophages and mice. The LD(50) for the mutant was 39.92-fold higher than that of the wild-type, indicating a marked reduction in virulence. Mice immunized with the ΔsptP mutant and administered a booster immunization exhibited 87.5% protection against challenge with a virulent strain, as compared to the PBS control group. Moreover, the mutant induced IgG antibody levels comparable to those induced by the wild-type strain. CONCLUSIONS: The ΔsptP mutant of Salmonella Typhimurium exhibits markedly reduced virulence while retaining robust immunogenicity and protective efficacy. These findings suggest that the ΔsptP mutant is a promising candidate for a live-attenuated vaccine, potentially providing an effective strategy to prevent Salmonella Typhimurium infections.