Fretibacterium sp. human oral taxon 360 is a novel biomarker for periodontitis screening in the Japanese population

Abstract

Background: Periodontitis is a common inflammatory disease, leading to bone destruction and tooth loss. Screening for periodontitis is important in preventing the progress of this disease. Various types of bacteria have been examined as potential screening targets, but only culturable pathogenic bacteria have been considered candidates. Recently, the various uncultivable bacteria have been identified in microbiome studies, but the value of these bacteria in periodontitis screening remains unknown.

Objectives: The aim of this study was to evaluate the diagnostic use of uncultivable bacteria Fretibacterium sp. HOT 360 and TM7 sp. HOT 356 for periodontitis screening in the Japanese population.

Material and methods: Stimulated saliva samples were collected from 217 participants (periodontitis group, n = 157; healthy group, n = 60). The two uncultivable bacterial species selected were: Fretibacterium sp. human oral taxon 360 (Fretibacterium sp. HOT 360) and TM7 sp. human oral taxon 356 (TM7 sp. HOT 356). The levels of these two bacterial species were compared with those of Porphyromonas gingivalis (P. gingivalis), a keystone pathogen in periodontitis. These three species of bacteria were then quantified using qualitative real-time polymerase chain reaction (qPCR) with specific primers and Taqman probes. Statistical analysis was performed by SPSS 20.0 software. P value was statistically significant at .05.

Results: The populations of uncultivable bacterial species TM7 sp. HOT 356 and Fretibacterium sp. HOT 360 were significantly higher in periodontitis group than in healthy group. Only Fretibacterium sp. HOT 360 showed a significantly positive correlation with such periodontal parameters as probing pocket depth (PPD) and bleeding on probing (BOP).

Conclusion: These findings indicate that uncultivable bacteria Fretibacterium sp. HOT 360 can be used as a saliva-based diagnostic bacterial biomarker for periodontitis screening.

Fig 1. Bacterial load in healthy participants and those with periodontitis.

Box plot graphs show the levels of periodontopathogens evaluated in this study. The copy numbers of P. gingivalis (a.), Fretibacterium sp. HOT 360 (b.) and TM7 sp. HOT 356 (c.) were significantly higher in participants with chronic periodontitis than in healthy participants. *P < 0.05.

Fig 2. Bar graphs of bacterial loads and percentage of ≥4 mm groups.

The abundance of ≥ 4 mm PPD, as log of rDNA (y-axis), were evaluated with respect to ranges showing 10 percent (x-axis). For non-parametric data, graphs are shown using mean and 95% confident interval of the mean (a to c). For non-parametric data, graphs are shown using median and 95% confident interval of the median (d to g). Significant differences were observed between the groups; data are demonstrated in S1 Table. The abundance of Fretibacterium sp. HOT 360 (b) and combination of bacterial groups with Fretibacterium sp. HOT 360 (d, f, and g) increased with increasing percentage of ≥ 4 mm PPD.

Fig 3. Bar graphs of bacterial loads and percentage of BOP.

The bacteria were categorized according to Offenbacher’s classification. The percentage of BOP reflected the inflammatory status. The acceptable BOP, which could indicate an inflammatory lesion, was over 10%. Bar graphs show the abundance of bacterial species as log of rDNA (y-axis) with respect to 10 percent increases in BOP (x-axis). Parametric data are presented as mean and 95% confident interval of the mean (a to c). Non-parametric data are shown using median and 95% confident interval of the median (d to g). Results indicate significant differences between the groups. Data are demonstrated in S2 Table. The copy numbers of Fretibacterium sp. HOT 360 (b) were related to the percentage of BOP.