The Oral-Gut Axis: Bidirectional Interactions Between Microbiome and Diseases

Increased colonization of typically oral microorganisms is frequently observed in the gut mucosa or lumen of individuals with gastrointestinal disorders, including patients with inflammatory bowel disease and colorectal cancer. Accumulating clinical and experimental evidence indicates that this phenomenon, known as "gut oralization," plays an important role in the pathogenesis of these diseases. Although several physiological barriers normally restrict the translocation and ectopic colonization of microorganisms from the oral cavity to the gut, certain oral pathobionts-often enriched in individuals with oral diseases such as periodontitis-have evolved specialized strategies to overcome these defenses. This review examines the bidirectional interactions through which bacterial traits, including unique adhesion systems and metabolic adaptations, support colonization and expansion within the gastrointestinal tract, as well as how disease-associated alterations in the gut environment and increased host vulnerability facilitate ectopic colonization by bacteria of oral origin. By integrating clinical and mechanistic evidence, this review highlights the potential of targeting the oral-gut microbial axis as a therapeutic approach for preventing and treating chronic gastrointestinal disorders.