Fig. 1
From: Mechanisms of probiotic Bacillus against enteric bacterial infections
Probiotic Bacillus employ multifactorial competition mechanism to restrict the expansion of pathogens through four pathways. (1) Bacillus adapt itself in suitable niche against niche-occupying competitors. It approaches the intestinal mucous layer and competitively binds to intestinal epithelial cells and mucous layer components via surface proteins. Thus, the effect of niche occupation by Bacillus expels harmful bacteria from the host intestinal epithelial barrier and reduces pathogen invasion. (2) Competitive utilization of nutrients for Bacillus growth. Bacillus secrete various enzymes to rapidly exploit both the macronutrients and micronutrients in gut environment, resulting in limited availability of nutrition to pathogenic bacteria. (3) Bacillus produce an arsenal of antibacterial metabolites that directly inhibit the growth of pathogens. The metabolites included lipopeptides, bacteriocins, polyketides, and SCFAs are effective against the expansion and invasion of pathogens. (4) Bacillus can consume excess oxygen from gut lumen and host circulation for maintaining the intestinal environment in a state of hypoxia, which drive a dominance of bacteria such as lactate acid bacteria that use fermentation for energy production