Characteristics of the Tongue Coating Microbiome and Its Subtype Differences in Patients with Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is associated with microbial dysbiosis, yet subtype-specific alterations in the tongue-coating microbiome remain insufficiently characterized. In this cross-sectional study, tongue-coating samples from 158 participants (94 healthy controls [HC], 19 ulcerative colitis [UC] patients, and 45 Crohn’s disease [CD] patients) were analyzed by 16S rRNA gene amplicon sequencing. We compared alpha and beta diversity, taxonomic composition, differential taxa, exploratory random-forest feature rankings, and SPIEC-EASI co-occurrence networks. Species richness did not differ significantly among groups, whereas Shannon and Simpson indices were lower in UC than in HC and CD. Bray–Curtis and Jaccard ordinations showed significant but partially overlapping community differences among the three groups. UC was characterized by enrichment of Proteobacteria, Neisseria, and Porphyromonass (p < 0.001), whereas CD showed higher relative abundances of Prevotella, Veillonella, Leptotrichia, and TM7x. Random forest and LEfSe analyses yielded concordant candidate discriminative taxa, but no independent validation cohort was available. Network analysis suggested group-specific co-occurrence patterns, with results interpreted as statistical associations rather than direct microbial interactions. These findings support the presence of subtype-associated tongue-coating dysbiosis in IBD and identify candidate taxa for future validation.