Comparison of Fluorescence Microscopy and Culture Assays to Quantitate Adhesion of Porphyromonas gingivalis to Mono‐ and Multi‐Layered Pocket Epithelium Cultures

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Abstract
Background: The present study compared 2 different methods (direct versus indirect evaluation) for the quantification of the adhesion of Porphyromonas gingivalis strains to in vitro cultured monolayers of pocket epithelium. Methods: The indirect culture viability assay (calculation of colony forming units) was compared to a direct microscopic evaluation using a novel fluorescent stain. The fluorescent kit was found to stain both bacteria and epithelial cells and enabled a differentiation between dead and living cells. Results: Comparing the visual to the culture data, a high and significant correlation was found (Pearson's correlation = 0.75; P P P. gingivalis strains (Pg 4 and Pg 5) were applied, Pg 4 showed a significantly lower adhesion capacity. This intra‐strain variability was observed by the culture assay (2.3 x 106 versus 7.8 x 106 ± 2.7 x 106; P P P. gingivalis strains. However, interstrain differences in adhesion capacity were evident for both tissues. Conclusions: This study highlights the reproducibility of a direct microscopic evaluation of bacterial adhesion to in vitro cultured epithelial cells, and suggests both intrastrain (P. gingivalis) and inter‐cell (live versus dead) variation in adhesion capacity. Studies are needed to determine the extent to which P. gingivalis strain variation is reflected in variation of other strains in humans. J Periodontol 1999;70:618‐625.