Study on the relationship between the structure of bacterial flora on the tongue and types of tongue coating in patients with type 2 diabetes mellitus

Objective: To analyze the characteristics of bacterial flora on the tongue and types of tongue coating between healthy individuals and patients with type 2 diabetes mellitus (T2DM) via detecting 16S rDNA of oral tongue coating microbial group. Methods: A total of 42 patients with T2DM were recruited, including 6 with thin white coating, 9 with mirror-like coating, 27 with yellow thick coating (YTC), and 28 healthy individuals. The V4 region of 16S rDNA from the tongue coating microbiota was sequenced using the Linux ubuntu sequencing platform, and the structure of bacterial flora in the tongue was analyzed. Treeplot construction, principal coordinates analysis, redundancy analysis, and linear discriminant analysis were conducted using R software to analyze the differences of bacterial flora in the tongue coating in each group. Results: A total of 8131 different operational taxonomic units (OTUs) were obtained via sequencing, of which 719 OTU samples showed significant differences (P 0.05). Comparing OTUs with the 16S rDNA database of known species and annotation of parallel species revealed 16 species with differences at the phylum level, 31 at the class level, 54 at the order level, 88 at the family level, and 161 at the genus level. The dominant bacteria found in patients with T2DM included Lactobacillus, Streptophyta, Chloroplast, Cyanobacteria-Chloroplast, and Bifidobacteriaceae, etc. Dominant bacteria in the control group belonged to Pasteurellales, Pasteurellaceae, Leptotrichiaceae, Lachnoanaerobaculum, and Ignavibacteria among other bacterial families. All samples were clustered into three groups, each group characterized by dominant bacteria. The order of dominant bacteria in group 1 were Prevotella Neisseria Veillonella Streptococcus Fusobacterium Leptotrichia and so on. The order of dominant bacteria of group 2 were Neisseria Prevotella Fusobacterium Streptococcus porphyromonas and so on. The dominant bacteria of group 3 were Prevotella Fusobacterium Streptococcus Neisseria Leptotrichia Rothia Veillonella porphyromonas f_Pasteurellaceae Capnocytophaga Actinomyces Alloprevotella and so on. Single factor risk estimation: with group 1 used as the reference (OR = 1), the risk of carrying group 2 and group 3 microflora with T2DM increased (OR values were 4.77 and 7.78, respectively). The proportion of group 1 microflora in the control group (25.9%) was higher than that in the T2DM group (5.4%) (χ2 = 3.873, P = 0.049). Compared with group 1 and group 2, group 3 had a significantly dominant microflora structure in YTC group (χ2 = 7.120, P = 0.008). RDA analysis indicated that Neisseria, Fusobacterium, and Prevotella were associated with HbA1c values 10 mmol/L, whereas Rothia, Streptococcus, and Veillonella were more correlated with HbA1c ≤ 10 mmol/L. Conclusion: The incidence of T2DM is related to the imbalance of oral microflora in the human body. The tongue coating flora structure may influence the formation of different tongue coating types in this metabolic condition. Additionally, flora structures of Prevotella, Neisseria, and Fusobacterium were associated with elevated HbA1c.