Inhibition of the Type III Secretion System of Salmonella Enterica Serovar Typhimurium and Alleviation Pathogenicity Via Treatment with Xanthotoxol.

Antibiotic resistance among bacterial pathogens increasingly undermines the efficacy of conventional therapies, creating an urgent need for alternative strategies that disarm pathogens without imposing strong selective pressure. The Type III secretion system (T3SS) of Salmonella is a syringe‑like protein injection apparatus that translocates bacterial effector proteins into host cells and is essential for epithelial invasion and early stages of pathogenesis. Here, we report that the natural furanocoumarin Xanthotoxol (Xan) inhibits SPI‑1 T3SS function in Salmonella enterica serovar Typhimurium (S. Typhimurium) and protects against infection in vitro and in vivo. Mechanistically, we found that Xan downregulates transcription of key SPI‑1 regulatory genes (hilD, hilC, rtsA and hilA), reduces expression and secretion of SPI‑1 effectors (SipA, SipB, SipC), and blocks effector translocation into host cells. Functionally, Xan selectively reduced S. Typhimurium invasion of epithelial cells without affecting bacterial growth or adhesion. In a streptomycin‑pretreated murine enteritis model, oral Xan treatment decreased bacterial loads in liver and spleen, reduced pro‑inflammatory cytokine levels (TNF‑α, IL‑1β, IL‑6) in cecal homogenates, and ameliorated intestinal and systemic histopathology. Together, these results indicate that Xan is an effective T3SS inhibitor and a promising anti‑virulence candidate that may complement or reduce reliance on traditional antibiotics.