Yeast-Derived Postbiotics as Emerging Candidates Against Enteric Bacterial Pathogens: Immunomodulatory and Antimicrobial Mechanisms Explored In Vitro

Among the many concerns surrounding global health, antimicrobial resistance (AMR) is widely recognized as a major threat, especially critical within livestock production, where restrictions on antibiotic use demand effective preventive alternatives. The documented health benefits and structural stability have positioned yeast-derived postbiotics as an attractive alternative, but research has largely focused on Saccharomyces cerevisiae, leaving non-Saccharomyces yeast species underexplored. To this end, in this study nine non-conventional yeast strains were selected and subjected to different thermal and chemical inactivation methods to determine the most suitable conditions for postbiotic obtention. Based on their physicochemical characterization and scalability potential, heat-treated postbiotics were selected for subsequent in vitro evaluation. Immunomodulatory assays demonstrated that heat-inactivated postbiotics from the different yeast strains were internalized by macrophages and induced dose-and-species-dependent expression of maturation markers CD40 and CD86, as well as TNF-α production, eliciting a proinflammatory response in vitro. Moreover, among all the species evaluated in this work, Rhodotorula mucilaginosa and Wickerhamomyces anomalus stood out for their ability to significantly reduce the adhesion of the enteropathogen enterotoxigenic Escherichia coli (ETEC) to intestinal cells in vitro. These results highlight the species-dependent immunomodulatory and anti-infective properties of selected yeast-derived postbiotics.