The sociobiome–oral microbiome mediates dental caries among Indigenous Australians

Background: The sociobiome refers to the social and socioeconomic conditions that shape human microbial communities, linking structural inequities to biological changes in the microbiome. The aim of this study was to examine how individual and neighbourhood socioeconomic status (SES) are associated with the oral microbiota and dental caries in Indigenous Australian adults. Methods: This cross-sectional study involved 100 Indigenous Australian participants aged ≥ 18 years and was embedded within a decolonising, community−based participatory research framework. Demographic, socioeconomic, and oral health behaviour data were collected, followed by a dental examination and collection of saliva and plaque samples. The samples were analysed using 16S rRNA amplicon sequencing, and alpha and beta diversity, redundancy analysis, and differential abundance analysis were conducted. Mediation models were used to examine associations between income (Healthcare card ownership), education (≤ secondary), the oral microbiome, and dental caries. Results: The microbiome analyses showed saliva had higher alpha diversity (p < 0.01), and beta diversity was significantly different between saliva and plaque (adonis p < 0.001). In saliva, alpha diversity was lower with advancing age, secondary education, income, Healthcare card ownership, and dental caries presence. Beta diversity in saliva microbiome composition showed a stronger association with SES than plaque, with income source (R²=3.8%, p < 0.01), education (R²=2.0%, p < 0.01), and dental caries (R²=2.2%, p < 0.01). Differential abundance analysis showed that the Rikenellaceae RC9 gut group, F0058, Fillifactor, and Treponema were elevated in the low-SES and caries groups. Mediation analysis showed that 75% of the impact of low income on caries was mediated via microbiome shifts, compared with 21% for education, highlighting the strong role of oral microbiome alterations in SES-driven caries risk. Conclusion: Socioeconomic disadvantage is associated with variations in the oral microbiome, and these microbial patterns may explain the link between lower income and dental health caries. Saliva may serve as a sensitive biomarker of socioeconomic gradients in oral health. These findings support integrated approaches that address structural determinants of disadvantage alongside microbiome-informed preventive strategies when tackling oral health inequities in Indigenous populations.