In Vitro Analysis of an Alkalihalobacillus clausii Spore-Based Probiotic Formulation Clarifies the Mechanisms Underlying Its Beneficial Properties

Probiotics are microorganisms with recognized beneficial properties that are used to improve host health. In particular, probiotics administered as spores, such as those belonging to the genera Bacillus and Alkalihalobacillus, are attracting great interest due to their high tolerance to gastrointestinal conditions. This in vitro study aimed to assess the probiotic attributes potentially contributing to the in vivo beneficial effects of a commercial spore-based probiotic formulation composed of four Alkalihalobacillus clausii strains. The tolerance and survival of the spores from the formulation in simulated gastrointestinal fluids, as well as their germination rate and adhesion to mucins, were analyzed. Furthermore, metabolic properties of spore-derived vegetative cells were assessed, including lactose degradation and biosynthesis of antioxidant enzymes (catalase and superoxide dismutase), group B vitamins (B2, B8, B9, and B12), short-chain fatty acids (acetate, propionate, and butyrate), and D-lactate. A. clausii spores were shown to survive in artificial gastric juice, adhere to mucins and germinate in vitro, and replicate in simulated intestinal fluid, suggesting their potential resilience in the gastrointestinal tract, where they can exert beneficial effects after germination. A. clausii was also able to produce beneficial enzymes and metabolites, including β-galactosidase, catalase, superoxide dismutase, group B vitamins, and short-chain fatty acids, but it was unable to produce D-lactic acid. Our findings highlight the probiotic properties and potential of such A. clausii strains in both their spore and vegetative forms, reinforcing the clinical relevance of this multi-strain spore-based formulation for enhancing intestinal health.