Treponeme major surface protein (msp) genotypes associated with periodontitis

Abstract

Objective: Studies have consistently linked oral treponeme (spirochete) bacteria, especially Treponema denticola, with periodontal disease. Oral treponemes possess a cell surface-exposed major surface protein (Msp), which is strongly-implicated in their pathogenic capabilities. Our objective was to survey and compare treponeme mspgene sequences present within subjects with periodontitis, versus periodontitis-free controls. Method: A consensus PCR-based strategy was used to sequence the msp gene, or ca. 450-900bp msp gene fragments from a diverse selection of phylogroup 1 and 2 oral treponeme strains (n=22); including: T. denticola, Treponema putidum, Treponema medium and ‘Treponema vincentii’. Pooled (multi-site) subgingival plaque samples were collected from periodontitis (n=10) and periodontitis-free individuals, whose periodontal health status had been clinically-evaluated. Msp gene fragments were PCR-amplified from purified subgingival plaque DNA, TOPO-cloned and sequenced (ca. 30 clones) for each subject. Strain and clinical mspgene sequences were analyzed using various computational and statistical methods.

Result: Msp gene sequences in T. denticola strains formed three main phylogenetic lineages, whilst two clades were identified in ‘T. vincentii’ and T. medium strains. 626 clinical msp sequences were determined, assigned to 21 msp genotypes (95% identity cut-off). The T. denticola ATCC 35405 msp genotype was the most prevalent and had the highest clonal abundance in both subject groups. Various taxonomy and phylogeny-based statistical clustering approaches all clearly indicated that periodontitis and periodontitis-free subjects contained highly-distinct communities of treponeme msp genotypes (p values <0.005). The clonal abundance of two msp genotypes; one corresponding to T. denticolaOTK and another corresponding to an as-yet uncultivated phylogroup 1 treponeme, were associated with periodontitis (p<0.05).

Conclusion: Individual subjects typically contain multiple treponeme msp genotypes (i.e. multiple phylogroup 1 and 2 treponeme lineages) in their oral cavity. Specific msp genotypes have differing statistical associations with periodontal health status.