Antioxidant and anti-inflammatory mechanisms of yak-derived Bacillus subtilis against Salmonella Derby–induced enteritis in mice

Salmonella enterica subsp. enterica serovar Derby (S. Derby) is a common non-typhoidal Salmonella serovar. It mainly targets the intestinal epithelium, where it colonizes and invades host tissue, leading to intestinal injury that is largely driven by inflammation and oxidative stress. With the restricted use of antibiotics in animal husbandry, effective and sustainable probiotic-based strategies are increasingly needed. This study investigated the protective effects and underlying mechanisms of yak-derived Bacillus subtilis against S. Derby–induced enteritis in a murine model. Kunming mice were randomly divided into five groups: Control (PBS for days 1–16), Bacillus subtilis (BS) (BS for days 1–16), Infection (PBS for days 1–7 + S. Derby challenge on day 8 + PBS for days 9–16), Treatment (PBS for days 1–7 + challenge on day 8 + BS for days 9–16), and Prevention (BS for days 1–7 + challenge on day 8 + PBS for days 9–16). BS administration alone did not induce adverse effects and showed outcomes comparable to those of the control group. Compared with the infection group, mice in the control and BS groups exhibited significantly higher final body weight (p < 0.05) and enhanced antioxidant capacity, as reflected by increased total antioxidant capacity (T-AOC) and catalase (CAT) activities (p < 0.05), while glutathione (GSH) levels were markedly elevated (p < 0.01). Histopathological analysis revealed severe ileal mucosal damage in infected mice, whereas BS supplementation was associated with better-preserved intestinal morphology and reduced mucosal injury. In addition, BS administration significantly upregulated the expression of tight junction proteins ZO-1 and occludin (p < 0.05). Quantitative PCR analysis further showed that BS supplementation significantly downregulated the expression of key genes in the TLR4/MyD88/NF-κB signaling pathway, including Tlr4, MyD88, and p65 (p < 0.05 or p < 0.01). Consistently,Western blot analysis showed reduced phosphorylation levels of p65 and IκBα in BS-treated mice. These findings suggest that yak-derived Bacillus subtilis may help mitigate Salmonella Derby–induced intestinal dysfunction by enhancing antioxidant defense, preserving intestinal barrier integrity, and modulating TLR4/NF-κB–mediated inflammatory signaling. These findings are consistent with the potential of this yak-derived B. subtilis strain as a probiotic candidate; however, validation in ruminant-relevant models and in yaks is needed before practical application.