Objective: Porphyromonas gingivalis (Pg) is a major etiological agent of periodontitis. Prior studies have shown differences in virulence among strains of Pg. pg0717 was identified in W83, a "virulent" strain, but not in ATCC 33277, a "less-virulent" strain. This suggests pg0717 contributes to virulent phenotypes of Pg strains. A prior clinical study suggests pg0717 is associated with increasing periodontitis severity. This investigation was performed to determine the association of the presence of pg0717 with periodontitis severity and correlation with virulent phenotypes of laboratory strains of Pg.
Methods: Whole-genome sequencing of laboratory strains (A7A1-28, A7436, AJW4, FDC381) of Pg was performed. Sequences of W83, ATCC 33277, TDC60 and W50 are publicly available. Bioinformatics analysis of sequenced strains was performed. Plaque or gingival crevicular fluid was harvested from 34 healthy controls and 39 aggressive periodontitis patients at the University of Florida College of Dentistry, Forsyth Dental Institute and Ege University using IRB-approved protocols, then phenol-chloroform extracted to isolate genomic DNA (gDNA). PCR with pg0717-specific primers was performed on gDNA from clinical samples, then analyzed via gel electrophoresis. pg0717 presence was examined for association with clinical measures of periodontitis.
Results: Putative proteins identical to the W83 pg0717 sequence were identified in A7436 and W50. In contrast, elongated pg0717-like proteins were found in A7A1-28 and TDC60, truncated pg0717-like proteins were found in FDC381 and ATCC 33277, and AJW4 lacked a pg0717-like protein. PCR analyses of aggressive periodontitis samples indicated greater than 40% of diseased patients harbored pg0717-positive strains of Pg; these patients displayed greater pocket depth and clinical attachment loss, and more frequent bleeding-on-probing, than patients lacking pg0717-positive Pg.
Conclusions: pg0717-like proteins are found in many strains, but variable truncation suggests loss of function in several strains. Clinical data associate intact pg0717 with more severe periodontitis, suggesting its potential use as a diagnostic tool.