Effect of Environmental pH on Bacterial Adhesion to Human Gingival Epithelium and Fimbrial Protein Synthesis of Porphyromonas gingivalis

Since pH in the human gingival crevice ranges from below 7.0 in healthy subjects to over 8.0 in periodontal disease, we investigated the effect of environmental pH on bacterial adhesion to human gingiva cells and on fimbrial protein synthesis by Porphyromonas gingivals 381. P. gingivalis cells were cultured in 30 mM HEPES-buffered culture medium at various pH ranges (6.0-8.5). Human gingival carcinoma cell line Ca 9-22 was cultured on microculture plates, and adherence was detected by using [3H] -labeled P. gingivalis. P. gingivalis growth was dependent on pH in the pH 6.0 to pH 7.0, but was inhibited in the pH 7.5 to 8.5 range. Stable adhesion of P. gingivalis to Ca 9-22 cells was observed at pH levels between 6.5 and 8.0, with maximum adhesion obtained at pH 7.5. This adherence was blocked by anti-P. gingivalis fimbriae monoclonal antibody (EF 3-11). The highest fimbrial protein synthesis was observed at pH 7.5. These results indicate that environmental pH regulates P. gingivalis growth and adhesion to host cells and fimbriae expression. They also suggest that the pH of the periodontal pocket rises during the host inflammatory response and that fimbriae synthesis increase markedly, possibly enabling it to evade host defenses by invasion of P. gingivalis to gingival cells.