Bacillus species, particularly Bacillus coagulans and Bacillus subtilis, are sometimes used as probiotics to support gut and oral health. Their application for thrush (oral candidiasis) is based on their ability to produce antimicrobial compounds and modulate the microbiome. Several in vitro studies have demonstrated that certain Bacillus strains can inhibit the growth of Candida albicans, the primary causative agent of thrush, by producing lipopeptides and other antifungal substances.

However, clinical evidence in humans is limited. There are a few small studies and case reports suggesting that Bacillus-based probiotics may reduce fungal colonization or symptoms when used as adjuncts to standard antifungal therapies, but large randomized controlled trials are lacking. Most research supporting the use of Bacillus for thrush is preclinical or extrapolated from probiotic studies on other bacterial genera (such as Lactobacillus or Saccharomyces). The evidence base is therefore modest (rated 2/5), indicating some scientific rationale and preliminary data, but not robust clinical validation.

In summary, Bacillus probiotics are being investigated for their antifungal properties, but routine use for thrush is not yet strongly supported by high-quality clinical evidence.