Bacillus subtilis THC1I restores intestinal barrier integrity and gut microbiota balance in antibiotic-associated diarrhea mice

Antibiotic-associated diarrhea (AAD) is a frequent and debilitating complication of antibiotic therapy, often stemming from severe disruption of the gut microbiota. This dysbiosis compromises the intestinal barrier, leading to increased permeability and inflammation. While various probiotic strains have shown promise in mitigating AAD, the specific therapeutic potential of the novel strain Bacillus subtilis THC1I in restoring gut health and barrier function had not been previously investigated.

Fifty mice were randomized into five groups (n=10 each) to assess Bacillus subtilis THC1I's effects on AAD. AAD was induced using gentamycin sulfate and cefradine for five consecutive days. Treatment groups received B. subtilis THC1I spore suspension at 0.82 × 10⁹ or 1.64 × 10⁹ CFU/kg/day. Control groups included a healthy control, an AAD model group, and a positive control receiving Enterogermina® (B. clausii). Outcomes included clinical signs, hematological and biochemical parameters, colonic macroscopic and histopathological indices, inflammatory cytokines, and gut microbiota analysis via 16S rRNA sequencing.

Treatment with Bacillus subtilis THC1I significantly improved clinical symptoms, including body weight, water intake, fecal scores, and fecal water content. The probiotic restored electrolyte balance (sodium and potassium), reduced white blood cell counts, and decreased relative colon weight and inflammation scores. Histopathological analysis confirmed restored epithelial architecture and increased goblet cell density in treated mice. Pro-inflammatory cytokines, specifically TNF-α and IL-1β, were significantly reduced. B. subtilis THC1I partially improved microbial diversity, as indicated by the Shannon index, and profoundly modulated microbiota composition. > It notably decreased pathogenic bacteria from the Proteobacteria phylum (e.g., Escherichia-Shigella, Klebsiella, Salmonella) and Firmicutes phylum (Clostridioides), while promoting beneficial bacteria such as Bacteroides, Muribaculaceae (from Bacteroidota), Lachnospiraceae, and Lactobacillus (from Firmicutes). The probiotic also modulated the dysbiotic overgrowth of the commensal Blautia.