Oral bacterial diversity is inversely correlated with mucosal inflammation

Objective: We investigated the relationship amongst the oral mucosal bacterial community, clinical severity and inflammatory markers in the two most common immune-mediated oral mucosal diseases, namely recurrent aphthous stomatitis (RAS) and oral lichen planus (LP). Methods: Patients with RAS (n = 15) and LP (n = 18) and healthy controls (n = 13) were recruited using criteria to reduce the effect of factors that influence the microbiota structure independently of oral mucosal disease. Clinical severity was quantified using validated scoring methods. DNA was extracted from oral mucosal swabs for 16S rRNA gene high-throughput sequencing. Salivary cytokines were measured using cytometric bead assays. Correlation studies were conducted amongst microbial diversity, clinical scores and cytokine concentrations. Results: We observed a significant reduction of bacterial diversity in LP and RAS patients compared to controls (p =.021 and.044, respectively). Reduced bacterial diversity in LP and RAS correlated with increased clinical scores of the two conditions (⍴ = −0.551 to −0.714). A negative correlation was observed between microbial diversity and salivary interferon-γ, interleukin-17A and interleukin-1β (⍴ = −0.325 to −0.449). Conclusions: This study reports reduced oral microbial diversity in the context of increased mucosal inflammation and supports the role for microbial diversity as a marker or contributor to oral mucosal inflammatory disease activity and development.