Variations in Saliva Microbiome Associated With Obesity

Objectives: Obesity is a growing global health problem and often associated with various diseases. Numerous researches have shown that gut microbiome contributes to weight gain. Current observations have found the correlations between stool and saliva microbiome community in systemic conditions such as diabetes, colorectal cancer and rheumatoid arthritis. This study sets out to reveal variations of saliva microbiome in obese individuals.
Methods: Whole unstimulated saliva samples(n=62) were collected from obese people (O, n=33, BMI≥30 kg/m²) and normal-weight people (N, n=29, 20>BMI≥18 kg/m²), stored (-80°C), extracted DNA and amplificated PCR. 16S rRNA gene-based sequencing technique (V3-V4 region; Illumina MiSeq) were used to analyze the microbial characteristics. Further data processing and microbiome analyses were conducted in QIIME.
Results: A total of 3916 operational taxonomic units (OTUs) were generated from 62 saliva samples. The alpha diversity indices (Chao1, Shannon index, observed OTUs and Phylogenetic diversity) were calculated, which showed a decrease in microbial richness and diversity in O. A significant shift in bacterial community compositions were found using unweight UniFrac distances and visualized via principal coordinate analysis. Relative abundance of Bacteroidetes was significantly increased with a concurrent decrease in Proteobacteria in the saliva microbiome of O. The dominant genera, Prevotella and Haemophilus, were found to contribute heavily to dysbiosis observed in the saliva microbiome. Proportions of Prevotella (phy. Bact.) was significantly higher in O compared with N (O=11.2%, N=7.4%, P < 0.05), while proportions of Haemophilus (phy. Prot.) was significantly lower (O=8.8%, N=12.6%, P < 0.01). The co-occurrence networks of saliva communities between the two groups also performed in distinct patterns. At the functional level, obese-associated pathways were identified, the relative abundance of which was significantly altered in the two groups.
Conclusions: Microbial differences were found in O vs N saliva samples. Our data demonstrate that dysbiosis of saliva microbiome is associated with obesity. Further studies of metagenomics need to be carried out to explore the correlation between stool and saliva microbiome community in obese individuals.