Probiotic potential of Bacillus isolated from horses and its therapeutic effect against DSS-induced colitis in mice

The superior biological characteristics of probiotics and their therapeutic applicability in the treatment of specific disorders have been proved by accumulating evidence. Although horses are susceptible to colitis due to their unique intestinal anatomy, there are few studies on probiotics for them. Therefore, this study was conducted to isolate probiotics from healthy horses and evaluate their probiotic characteristics. Specifically, Bacillus licheniformis W1.1, Bacillus pumilus W2.4, Bacillus pumilus Y4.2, Bacillus subtilis Y4.3, Bacillus safensis L6.2, and Bacillus megaterium L7.1 were isolated and identified from the horses. Besides, their probiotic capability and antioxidant capability were also examined. The results demonstrated that Y4.3 and L7.1 exhibited increased hydrophobicity, autoagglutination, and adherence to Caco-2 cells, exceeding 40% and 60%, respectively. The 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging rate of Y4.3 and L7.1 was higher than 80%. Additionally, six Bacillus strains were found to be susceptible to standard antibiotics and they were not hemolytic, proving the safety of this bacterium. After Bacillus sp. was applied to colitis mice, the disease activity index (DAI) score decreased, and the colon was extended notably ( P < 0.05). A significant reduction in pathological histological scores ( P < 0.01), a significant rise in the antioxidant index SOD, and a significant decrease in MDA and MPO ( P < 0.000 1) were observed in the dextran sulfate sodium (DSS)+Y4.3 and DSS+L7.1 groups. Moreover, this bacterium was validated to have the capacity to hinder the progression of UC by targeting the NLRP3 and NF-κB pathways. In conclusion, all six Bacillus strains isolated from horses exhibited probiotic potential. Among these strains, Y4.3 and L7.1 exerted strong effects on resisting UC in mice, suggesting a viable treatment strategy for this disease.