Microbial crosstalk along the oral–gut axis: organ-specific oncogenic adaptations of Porphyromonas gingivalis and Fusobacterium nucleatum

The oral-gut microbiota axis is increasingly recognized as a critical bridge linking local infection to systemic diseases. Growing evidence demonstrates that oral microbes not only enter the gut via saliva, bloodstream, and direct migration but also successfully colonize under specific microenvironmental conditions, reshaping the local microbial ecosystem. Periodontal pathogens such as P. gingivalis and F. nucleatum drive gastrointestinal tumorigenesis through chronic inflammation, metabolite production, and signaling pathway reprogramming. Moreover, oral-gut microbial interactions reveal cancer-specific risk patterns, with distinct roles in esophageal, gastric, colorectal, and pancreatic cancers. This review not only highlights the key mechanisms by which oral microbes promote tumor development but also emphasizes their clinical potential as diagnostic biomarkers and therapeutic targets, offering novel directions for translational research on the oral-gut axis.