Intestinal Lactobacillus: Origins, colonization factors, diversity, and health associations.

Genus Lactobacillus is one of the most widely acknowledged probiotics, already detectable in maternal breast milk and in maternal and infant feces. Its gut colonization is governed by host genetics, diet, drugs, and other environmental pressures. Accumulating evidences links the relative abundance or specific species of this genus to health outcomes spanning infancy to adulthood. Exhibiting extensive species-level and phylogenetic diversity, Lactobacilli possess typical probiotic characteristics including modulate the gut microbiota, production beneficial metabolites, and anti-inflammatory, immunomodulatory, and antioxidant effects. This review aims to systematically examine: (1) the origin and colonization dynamics of Lactobacillus in the human gut; (2) host and environmental factors influencing its establishment; (3) its relationship with health and disease; (4) its diversity across populations; and (5) its probiotic properties and clinical applications. We integrate recent findings on how maternal inheritance, host factors, and environmental pressures shape Lactobacillus ecological dynamics across the human lifespan, providing a comprehensive resource for understanding this key beneficial genus and guiding future research and probiotic interventions.