Prevalence and quantification of the uncommon Archaea phylotype Thermoplasmata in chronic periodontitis

Chronic periodontitis is a chronic inflammatory disease of the periodontal tissues and is caused by invasion of certain types of bacteria and Archaea, with Methanobrevibacter oralis as the predominant archaeon. In this study, we investigated the prevalence and quantity of the newly discovered Archaea phylotype Thermoplasmata in patients with chronic periodontitis.

Subgingival plaque samples were obtained from 49 patients with chronic periodontitis and 45 periodontally healthy subjects. Qualitative analyses of Archaea and class Thermoplasmata were carried out by amplification of 16S rRNA genes in DNA extracts from plaque samples, and all the samples were quantitatively analyzed by real-time polymerase chain reaction (PCR).

The prevalence of Archaea in patients with chronic periodontitis was 69.4% according to the conventional PCR results, but was 87.8% according to real-time PCR. In the control group, three samples were detected as positive, but none of these were confirmed in qualitative analyses. The prevalence of class Thermoplasmata was 18.4% by nested PCR and 24.5% by quantitative PCR in the chronic periodontitis group. The prevalence of Thermoplasmata was significantly lower than that of total Archaea. The relative abundances of Archaea and Thermoplasmata varied among samples. Thermoplasmata were not the predominant archaeons in the subgingival dental plaque. Among the clinical parameters of patients with periodontitis, probing depth was positively associated with Archaea detection.

The existence of Archaea was correlated closely with the presence of chronic periodontitis. Thermoplasmata represented a minor archaeon in periodontal infection.