PCR Assay for Quantitative Detection of Porphyromonas gingivalis in Children

Objectives: Porphyromonas gingivalis is a major periodontal pathogen in destructive periodontal disease. The aim of the present study was to measure relative quantification of P. gingivalis in dental plaque from Japanese children, by using a TaqMan PCR method, and then compared with the periodontal status.

Methods: Dental plaque specimens were obtained from 5 children with healthy gingiva, 14 with gingivitis, and 10 with periodontitis (all aged 3 to 16 years old). Previously we confirmed them harboring P. gingivalis in their oral cavities by a conventional PCR method. A quantitative PCR assay was performed to detect the relative quantification of the target bacterium. The standard curve for organism was plotted for primer-probe set by using critical threshold cycle (Ct) value.

Results: The number of target gene copies for P. gingivalis in dental plaque was determined as follows: Log₁₀(cells) = 37.11 - 3.10 x Ct, R² = 0.948 (P<0.01). The percent distribution of P. gingivalis was 0.01, 0.36, and 1.04 for subjects with healthy gingiva, gingivitis, and periodontitis, respectively. P. gingivalis was more prevalent in those with periodontitis than in those with healthy gingiva (P<0.05, Scheffé's multiple comparison test). Conclusions: Our results suggest that the number of P. gingivalis is highly associated with periodontal disease in children.