Objectives: The aims of this study were to investigate the phenotypic and genotypic characteristics of invasive P.gingivalis.
Method: P. gingivalis NCTC 11834 and W50 cells were assessed for their invasion of H357 oral keratinocytes (EC). Cy-dye-labelled cDNA of those bacteria that invaded and those that did not was hybridized on P.gingivalis genome microarrays (TIGR). Selected genes were checked for expression by RT-PCR, normalising to 16SrRNA. Isolates were compared by RFLP analysis and arg-gingipain activity (Bapna).
Results: P.gingivalis cells that had invaded one set of ECs invaded a second set with higher efficiency, suggesting selection of an invasive phenotype. 6/60 colonies from a primary culture also showed increased EC invasion. This invasive type showed low arg-gingipain activity. Invasive and poorly invasive phenotypes had the same RFLP pattern. Gene array analysis showed 104 genes were up-regulated and 51 genes were down-regulated in the invasive phenotype (p<0.05). The arg-gingipain gene (rgpB) was down regulated in the invasive type while haemagglutinin (hagE), iron regulated (hmuY) and oxidative stress genes (sodB, oxyR) were amongst those up-regulated. Semi-quantitative RT-PCR largely confirmed these findings.
Conclusion: Phenotypes with different invasive capability are detectable in cultures of P.gingivalis and these differ at the transcriptome level. These phenotypes may represent phase switching, which in vivo could provide the organism with a mechanism for persistence at a subgingival site.