'Synergistetes' in Periodontal Health and Disease

Introduction: Members of the phylum ‘Synergistetes' have been frequently detected in the human oral cavity at sites of dental disease, but almost never in health. Only two oral ‘Synergistetes' taxa are currently cultivable.

Objectives: To develop culture-independent techniques: to investigate the diversity and distribution of ‘Synergistetes' in the oral cavity; to establish whether ‘Synergistetes' taxa are more strongly associated with periodontitis than health; and to visualise unculturable ‘Synergistetes' in situ.

Methods: Sixty samples collected from five chronic periodontitis cases and five matched periodontally-healthy controls included saliva, swabs from cheek mucosa and dorsum of tongue, and supra- and sub-gingival plaque from healthy and ‘diseased' sites (cases only). ‘Synergistetes' present were identified by: PCR amplification of 16S rDNA using a phylum-specific primer pair (27F/806R), cloning to purify the mixed amplicons and sequencing of 45 clones/sample. Subgingival plaque from deep pockets in six additional subjects with periodontitis was analysed using fluorescent in-situ hybridisation (FISH) with fluorochrome-labelled probes specifically targeting rRNA of unculturable oral ‘Synergistetes'.

Results: Phylogenetic analysis of 1664 clones sequenced revealed twelve ‘Synergistetes' taxa (five novel). ‘Synergistetes' were detected in nine of ten subjects. Subgingival plaque, the habitat most frequently colonised (8/10), had the most taxon-rich ‘Synergistetes' population. One of the five taxa exclusive to the cases, ‘Synergistetes' 4Div2, was found in significantly more cases than controls (p=0.048) and made up a greater proportion of the clones from subgingival plaque at diseased sites (cases) than at healthy sites in cases (p=0.019) or controls (p=0.019). FISH analysis of subgingival plaque provided the first visualisation of unculturable oral ‘Synergistetes'. These taxa (curved rods, 3-7΅m long) were present in all six subjects, comprising up to 10% of the total plaque bacteria.

Conclusion: The human oral cavity harbours a diverse population of ‘Synergistetes'. ‘Synergistetes' 4Div2 is strongly associated with periodontitis and may have a pathogenic role.