Oral microbiota alterations in radiographic axial spondyloarthritis

Objective To investigate alterations in the oral microbiome of patients with radiographic axial spondyloarthritis (r-axSpA), to identify microbial taxa associated with disease status and structural progression, and to explore potential links between oral microbiota composition and systemic immunological profiles. Methods An observational cross-sectional study was conducted including 57 radiographic axial spondyloarthritis patients and 41 healthy controls. Oral samples were analyzed using 16S rRNA gene sequencing; amplicon sequence variants (ASVs) were generated using LotuS2/DADA2 and taxonomically annotated with SILVA, Greengenes, and HITdb. Alpha and beta diversity were assessed using ACE, Pielou indexes, and UniFrac distances with PERMANOVA and ANOSIM. Differential abundance was determined via LEfSe (LDA > 2, p  < 0.05). Associations between microbial taxa, disease activity, structural damage, and immunological markers were evaluated using linear modeling and Spearman correlation analysis. Results R-axSpA patients showed alterations in oral microbiome composition compared with controls, although alpha diversity remained largely comparable. Actinobacteria, Spirochaetes, and Synergistetes tended to be enriched in r-axSpA patients, mainly driven by an increased abundance of Actinomyces and Selenomonas. Several key periodontal pathogens, including Porphyromonas gingivalis and Actinomyces species, were more abundant in the r-axSpA group. Within the r-axSpA group, the abundance of Porphyromonas and Saccharimonadaceae showed associations with the severity of sacroiliitis and ankylosis. These taxa also exhibited positive correlations with systemic pro-inflammatory cytokines (such as IL-17), which may suggest a possible link between oral dysbiosis and enhanced Th17-driven inflammation in r-axSpA. Conclusion Patients may exhibit a distinct proinflammatory oral microbiome profile, with increased representation of Actinomyces and Porphyromonas species. Certain microbial taxa, including members of Porphyromonadaceae and Patescibacteria, have been reported to correlate with cytokines implicated in the immunopathogenesis of radiographic axial spondyloarthritis. These observations suggest that oral dysbiosis could play a role in the maintenance or modulation of systemic inflammation in r-axSpA, and that the oral microbiome might serve as a potential source of biomarkers or a target for future therapeutic strategies.