Periodontitis Associated Occult Bacteraemia Detected by 16S rRNA Gene Sequencing

Bacteraemia associated with chronic periodontitis is implicated in a variety of systemic disorders. Objective: To determine, using molecular techniques, the clonal relationship between the bacterial profiles in blood, tongue (dorsum) and the periodontal niche in patients with severe periodontitis. Methods: Venous blood was collected prior to periodontal examination, followed by tongue brushings and subgingival plaque. Extracted DNA from each sample was screened for the presence of bacterial 16S rRNA genes using PCR, which were then cloned and sequenced according to established protocols. Sequence identities were established by querying against GenBank database. Clonality of the bacterial profiles recovered from blood was evaluated by comparison with profiles from oral niches, and greater than 99% sequence similarity was considered as belonging to members of the same clone. Results: Five subjects with periodontitis and 5 healthy controls were studied. All the subjects in the periodontitis group had evidence of bacteraemia with positive 16S bands, while none of the healthy subjects were positive. Sequences of blood isolates predominantly belonged to the genus Streptococcus and demonstrated almost identical clonality with those derived from subgingival plaque. Similar clonalities were also observed with Dialister and Brevibacterium species. Profiles of the subgingival niche showed more diverse clonality than those from the tongue dorsum, both in healthy and periodontitis subjects. Conclusions: Bacterial profiles in bacteraemias can be derived, independently of standard culture procedures, using 16S rRNA sequence based approaches. Spontaneous bacteraemic episodes may occur in subjects with periodontitis even in the absence of mechanical manipulation of the oral cavity. The most likely origin of the blood borne bacteria either in health or disease is the periodontal niche rather than the tongue dorsum. Our data imply that chronic periodontitis may create occult bacteraemias possibly harmful for general health. (Supported by a grant from SRT of The University of Hong Kong)