The impact of Bacillus subtilis on gut health of poultry

SUMMARYIt is essential to understand how natural feed additives, as alternatives to antibiotic use, can modulate the immune system and intestinal microbiota to regulate intestinal disorders and improve gut health. Probiotics are among the biological products that may serve as alternatives to synthetic additives in the modern era, as they meet food safety and eco-friendly standards. Bacillus subtilis has been shown to improve gut health in poultry. Dietary supplementation with B. subtilis can modulate the gut microbiome, reduce intestinal inflammation, and boost intestinal barrier function. The inclusion of B. subtilis in poultry feed has been shown to increase the abundance of lactobacilli and Bifidobacterium (by 6.83% and 3.80%, respectively) and reduced the abundance of harmful bacteria, including E. coli, Salmonella, and Clostridium, by 8.9%, 19.8%, and 31.77%, respectively, according to the reviewed studies. Supplementation with B. subtilis positively affected intestinal villus morphology. The improvement rates observed in previous studies following treatment with certain B. subtilis strains were 11.06% in the duodenum, 26.25% in the jejunum, and 19.92% in the ileum compared to the control group. B. subtilis spores can increase cytokine levels in the gut, such as interferon-γ and interleukin-1β, and release antimicrobial peptides that exhibit cytotoxicity towards bacterial pathogens. Feeding B. subtilis also upregulated gene expression of tight junction proteins, including claudin, occludin, and junctional adhesion molecule 2. Diets containing specific B. subtilis strains positively influenced the antioxidant system and digestive enzymes in poultry. This review article presents the most recent research investigating the beneficial effects of B. subtilis on the gastrointestinal tract integrity of poultry.