Saccharomyces, particularly Saccharomyces boulardii, is used as a probiotic adjunct during or after antibiotic therapy, rather than as a direct alternative to antibiotics. Clinical evidence supports its use in reducing the risk of antibiotic-associated diarrhea (AAD), including cases caused by Clostridioides difficile, by modulating the gut microbiota and enhancing mucosal immunity. Several randomized controlled trials and meta-analyses have demonstrated that S. boulardii supplementation can significantly lower the incidence of AAD in both adults and children. The mechanism is thought to involve inhibition of pathogen adhesion, restoration of the gut microbial balance, and modulation of the host immune response.

However, Saccharomyces species are not true alternatives to antibiotics for treating bacterial infections. They do not possess bactericidal or bacteriostatic properties against pathogenic bacteria. Instead, their role is supportive, aiming to maintain gut health and prevent complications from antibiotic use. There is no credible evidence supporting the use of unspecified Saccharomyces species as stand-alone replacements for antibiotics in the treatment of infections. Therefore, while the use of Saccharomyces is scientifically validated for managing antibiotic side effects, it is not justified as an alternative to antibiotics for treating infections themselves.