The Oral Microbiome in Periodontal Health

Abstract

The estimation of oral microbiome (OM) taxonomic composition in periodontally healthy individuals can often be biased because the clinically periodontally healthy subjects for evaluation can already experience dysbiosis. Usually, they are included just based on the absence of clinical signs of periodontitis. Additionally, the age of subjects is used to be higher to correspond well with tested groups of patients with chronic periodontitis, a disorder typically associated with aging. However, the dysbiosis of the OM precedes the clinical signs of the disease by many months or even years. The absence of periodontal pockets thus does not necessarily mean also good periodontal health and the obtained image of "healthy OM" can be distorted.To overcome this bias, we taxonomically characterized the OM in almost a hundred young students of dentistry with precise oral hygiene and no signs of periodontal disease. We compared the results with the OM composition of older periodontally healthy individuals and also a group of patients with severe periodontitis (aggressive periodontitis according to former classification system). The clustering analysis revealed not only two compact clearly separated clusters corresponding to each state of health, but also a group of samples forming an overlap between both well-pronounced states. Additionally, in the cluster of periodontally healthy samples, few outliers with atypical OM and two major stomatotypes could be distinguished, differing in the prevalence and relative abundance of two main bacterial genera: Streptococcus and Veillonella. We hypothesize that the two stomatotypes could represent the microbial succession from periodontal health to starting dysbiosis. The old and young periodontally healthy subjects do not cluster separately but a trend of the OM in older subjects to periodontitis is visible. Several bacterial genera were identified to be typically more abundant in older periodontally healthy subjects.

Keywords: aging; core microbiome; oral microbiome; periodontal health; periodontitis; stomatotype; taxonomic composition.

Figure 1

Weighted Jaccard Similarity clustering analysis of all OM samples. Weighted Jaccard similarity index 0.3. The red-colored spots correspond to patients with AP, HY samples are green and HO samples are yellow. The transient area is delimited with the gray dashed line.

Figure 2

The distribution of the relative abundances of selected taxa in relation to the age of probands and their state of health. (A) Taxa prevailing in periodontitis, (B) Taxa prevailing in HY, (C) Taxon prevailing in HO. The area of box plots with oral taxa dominant in patients with AP is highlighted in red, HY in green and one boxplot related to taxon most abundant in the HO group is highlighted in yellow. CT stands for combined taxon (See Supplementary Table 3 ).

Figure 3

PCA analysis of all OM samples. Red triangles represent AP samples, green spots HY, and yellow squares represent the HO samples. The inner panel shows the contribution of selected oral taxa to the distribution. The determining taxa for each quadrant are highlighted in colors (green for periodontal health and red for periodontitis), CT8 P. pasteri/catoniae determining the transient state is highlighted by a bigger font. CT stands for combined taxon (See Supplementary Table 3 ).

Figure 4

Hierarchical clustering of all OM samples based on the Bray-Curtis similarity indexes. AP samples are marked red, HO black, and HY green. The upper measure indicates the Bray-curtis value. The determining taxa for each cluster are listed. CT stands for combined taxon (See Supplementary Table 3 ).