Oral mycobiome composition and fungi-bacteria associations in children and young adults with type 1 diabetes

Background: Oral mycobiome in children and young adults with type 1 diabetes (T1D) remains poorly characterized. Objective: We investigated oral fungal community structure and its associations with bacterial communities and immune mediators in individuals with established T1D compared with healthy controls (HC). Design: Oral fungal and bacterial communities were characterized in 68 participants with T1D and 69 HC by ITS and 16S rRNA gene sequencing, alongside multiplex assessment of soluble immune factors. Sequencing data were processed with QIIME 2, immune factors with BioPlex Manager and statistical analyzes with R v.4.3.3. Results: Fungal alpha and beta diversity did not differ significantly between groups. However, several taxa were differentially abundant or prevalent in T1D, including Fusarium, Hanseniaspora, Meyerozyma, Cyberlindnera jadinii, Candida albicans, C. dubliniensis and Malassezia globosa. No significant differences emerged by HbA1c category (<7% vs. ≥7%) within T1D. Notably, Cystobasidium/C. slooffiae and Trichoderma, detected exclusively in T1D, showed stronger positive associations with MCP-1/MCAF and IP-10, respectively, than in HC, while several fungal genera were inversely associated with distinct bacterial taxa. Conclusions: These findings indicate that T1D is associated with selective, taxon-specific oral mycobiome alterations rather than generalized dysbiosis. The observed fungal-immune and fungal-–bacterial links suggest biological relevance, warranting longitudinal and functional investigation.