Saccharibacteria (TM7) in saliva and subgingival microbiome as a predictor for gingivitis in individuals with type2 diabetes evaluated by qPCR

Oral samples are widely used for studying oral microbiome in health and diseases. In this study, saliva and subgingival biofilm (SGB) samples obtained from patients with type2 diabetes (T2DM), without periodontitis (G1 group), with gingivitis (G2 group), and periodontitis (G3 group), were used to compare the abundance of Saccharibacteria (TM7), its host's bacteria (Schaalia odontolytica), periodontopathogen (Represented by Fusobacterium nucleatum), and nitrate-reducing bacteria (represented by Rothia mucilaginosa). The gingival crevicular fluid were also used to analyze the transcription levels of interleukin-6 (IL-6) and C-reactive protein (CRP). Healthy individuals' oral samples served as a control, and the targeted bacteria and inflammatory indicators were detected and measured using real-time PCR. The results showed that in either sample, the abundance of TM7 and other targeted bacteria showed a similar profile. Notably, within participants with T2DM, the abundance of TM7 was similar in G1 and G2 groups, but significantly decreased in G3 group. With the exception of the SGB of the G3 group, the relationship between TM7 and its bacterial host was strongly positive across all evaluated samples. Furthermore, CRP had higher transcription levels than IL-6 across the entire group. Despite the fact that the G3 group showed an adverse relationship between TM7 and CRP, patients with T2DM generally showed a positive correlation between TM7 and IL-6/CRP, which was verified by a receiver operating curve.