Bacillus species, particularly in mixed probiotic formulations (e.g., Bacillus subtilis, Bacillus clausii), have been studied for their potential role in the management of enteritis, especially antibiotic-associated diarrhea and infectious diarrhea. Several randomized controlled trials and clinical studies have demonstrated that Bacillus clausii, for example, can reduce the duration and severity of diarrhea in children with acute enteritis. The mechanism is thought to involve competitive inhibition of pathogens, production of antimicrobial compounds, immunomodulation, and restoration of normal gut flora.

A 2017 meta-analysis (Lai et al., 2017) found that Bacillus clausii was effective in reducing the duration of diarrhea in pediatric patients. Additionally, some studies support the use of Bacillus subtilis in improving gut barrier function and modulating inflammation in animal models of enteritis. While the bulk of evidence is in pediatric populations and for mild to moderate enteritis, results are promising and have led to regulatory approval for the use of certain Bacillus strains as probiotics in some countries.

However, while there is moderate-quality evidence supporting efficacy, more large-scale, high-quality human trials are needed to establish standardized protocols and to confirm long-term safety and effectiveness. Thus, the evidence is rated as moderate (3/5).