Oral-gut strain sharing after Roux-en-Y gastric bypass: A canonical oral microbiome signature in the gut linked to hepatic and glycemic remodeling.

Roux-en-Y gastric bypass (RYGB) induces durable weight loss and metabolic improvement, but the role of oral microbiota in shaping postsurgical gut ecology and metabolic outcomes is unclear. We examined whether RYGB promotes transfer and expansion of oral strains in the distal gut and how these relate to hepatic and glycemic health. In 25 patients from a longitudinal RYGB cohort, paired oral and fecal samples were collected before and 12 months after surgery. We examined the presence, abundance, and structure of cohort-specific canonical oral strains in the gut, and assessed α/β-diversity, cross-site correlations, and clinical associations using univariate tests and linear models. Machine-learning models evaluated the prognostic value of oral canonical strains for hepatic and glycemic outcomes. Oral taxon richness increased after RYGB, while Shannon diversity and individual signatures remained stable. In the gut, canonical oral strains expanded: shared oral-gut strains and their summed abundance rose significantly, converging into a reproducible post-RYGB niche. Abundance and fold change of oral-canonical strains associated with FIB-4, ASAT and fasting glucose, and predictive models suggested a prognostic signal for fasting glucose, TBF% and HbA1c. RYGB is associated with reproducible, strain-level enrichment of oral microbiota in the gut, with links to hepatic and glycemic outcomes.