Distinguishing the signals of gingivitis and periodontitis in supragingival plaque: a cross-sectional cohort study in Malawi

Periodontal disease ranges from gingival inflammation (gingivitis) to the inflammation and loss of tooth-supporting tissues (periodontitis). The bacterial composition of supragingival plaque across a range of periodontal severities has not previously been explored with high-throughput sequencing. Furthermore, quantitative modelling of bacterial abundances in supragingival plaque as a function of both gingivitis and periodontitis has not previously been attempted. We assessed a cross-sectional cohort of 962 Malawian women for periodontal disease and used 16S rRNA gene amplicon sequencing (V5-V7 region) to characterise the bacterial composition of supragingival plaque samples. Associations between bacterial relative abundances and gingivitis/periodontitis were investigated by using negative binomial models, adjusting for epidemiological factors. We also examined bacterial co-occurrence networks to assess community structure. The main differences in supragingival plaque composition were associated more with gingivitis than periodontitis, including higher bacterial diversity and greater abundance of particular species. However, even after controlling for gingivitis, the presence of subgingival periodontitis was associated with an altered supragingival plaque. A small number of species were associated with periodontitis but not gingivitis, including members of Prevotella, Treponema, and Selemonas, supporting a more complex disease model than linear progression following on from gingivitis. Co-occurrence networks of periodontitis-associated taxa clustered according to periodontitis across all gingivitis severities. Species including Filifactor alocis and Fusobacterium nucleatum were central to this network, supporting their role in co-aggregation of periodontal biofilms during disease progression. Our findings confirm that periodontitis cannot be considered simply an advanced stage of gingivitis, even when only considering supragingival plaque.