Subgingival microbiota in health compared to periodontitis and the influence of smoking

Abstract

The etiology of periodontitis has traditionally been associated to a consortium of three bacterial species-the so-called "red-complex" of periodontal disease-which has been the target for most diagnostic and therapeutic strategies. However, other species have also been found to correlate with disease severity. In addition, the influence of smoking on periodontal microbiota is poorly understood. In the current manuscript, the composition of the subgingival microbiota in healthy individuals vs. patients with chronic periodontitis has been investigated using 16S pyrosequencing and the influence of smoking on periodontal composition has been examined. Subgingival bacterial communities were sampled from 82 patients: 22 non-smoking healthy controls, 28 non-smoking periodontal patients, and 32 smoking periodontal patients. Bacterial diversity was higher in periodontal patients than in healthy subjects, which could be interpreted as the consequence of a nutritionally richer environment or a reduced immune competence. Periodontal patients showed a significantly higher prevalence/relative abundance of "established" periopathogens but also other taxa whose role is not well-established and that should be targets for future research. These include Anaeroglobus, Bulleidia, Desulfobulbus, Filifactor, Mogibacterium, Phocaeicola, Schwartzia or TM7. The microbial community of smoking-associated periodontitis is less diverse and distinct from that of non-smokers, indicating that smoking has an influence on periodontal ecology. Interestingly, the high sequencing coverage allowed the detection at low proportions of periodontal pathogens in all healthy individuals, indicating that chronic periodontitis cannot be strictly considered an infectious disease but the outcome of a polymicrobial dysbiosis, where changes in the proportions of microbial consortia trigger the inflammatory and tissue-degradation responses of the host.

Keywords: 16S ribosomal RNA; chronic periodontitis; dental plaque; microbiome; oral health; smoking.

Figure 1

Bacterial diversity and community structure. (A) Rarefaction curves of all the subgingival samples by study group. The horizontal axis shows the number of sequences obtained by pyrosequencing the 16S gene. The vertical axis shows the number of operational taxonomic units (OTUs) at a level of 97% intersequence similarity, representing an approximation to the number of species for the sequencing effort employed. (B) Principal Coordinates Analysis (PCoA) of all 82 subgingival samples according to bacterial composition, including NS-Control (blue dots), NS-Perio (red), and S-Perio (green); PCoAs were performed with weighted UniFrac analysis with clustering at 97% sequence identity.

Figure 2

Prevalence of patients being positive for different genera, which presented statistically significant differences between three study groups. (A) Genera shown by alphabetical order: A–H. (B) Genus shown by alphabetical order: K–T.

Figure 3

Percentages of taxa by genera, which presented statistically significant differences were detected between three study groups. (A) Percentages above 3% at least one study group. (B) Percentages below 3% in all study groups.

Figure 4

Relationships between percentages of more significant genera (present in ≥50% of patients), represented as a percentage of the total, and values of clinical parameters. (A,B) Probing pocket depth of sampled sites (mm). (C,D) Bleeding on probing of sampled sites (percentage). A mean percentage of taxa by genus was calculated for each PPD and BOP range.