Probiotics for Human Health: Mechanisms, Clinical Evidence, Risks, and Next-Generation Microbial Therapeutics

Probiotics are widely used live microbial supplements intended to promote human health, yet their clinical benefits remain inconsistent and often strain-specific. Most currently available probiotics are derived from Lactobacillus , Bifidobacterium , and Saccharomyces species originally isolated from fermented foods or human microbiota. Preclinical studies suggest that these organisms may influence host physiology through several mechanisms, including antimicrobial activity, toxin inhibition, strengthening of intestinal barrier function, modulation of immune responses, and signaling along the gut–brain axis. However, translation of these mechanisms into consistent clinical benefit has been limited by heterogeneity in probiotic strains, dosing, and study design. Emerging evidence also highlights potential unintended consequences of probiotic use, including rare infections in vulnerable patients, alterations of microbiome recovery after antibiotics, and possible interactions with host metabolism or medications. Recent advances in microbiome research have supported the development of next-generation probiotics and engineered microbial therapeutics, representing a shift toward more targeted and mechanistically informed live microbial therapies.