Adherence of Streptococcus sanguis to hydroxyapatite coated with lysozyme and lysozyme-supplemented saliva

Abstract

The adherence of [3H]thymidine-labeled Streptococcus sanguis strains to bare hydroxyapatite and to hydroxyapatite coated with a range of concentrations of lysozyme, poly-L-lysine, poly-L-glutamic acid, whole saliva supernatant, and combinations of some of the above was studied. Adherence of several strains of S. sanguis to bare hydroxyapatite and saliva-coated hydroxyapatite was compared. Saliva present as a pellicle on the hydroxyapatite inhibited adherence of some strains (903, M-5, 73X11) and stimulated that of others (S35, B-4, 66X49). Strains 903 and S35 were chosen for further study. Adherence of both strains was stimulated up to fivefold by the presence of adsorbed lysozyme or poly-L-lysine on the hydroxyapatite, whereas poly-L-glutamic acid inhibited adherence (80 to 95%). Adherence of strain S35 to hydroxyapatite coated with combinations of saliva and (i) lysozyme, (ii) poly-L-lysine, or (iii) poly-L-glutamic acid was unaffected compared with adherence to hydroxyapatite coated with saliva alone. In contrast, adherence of strain 903 to hydroxyapatite coated with combinations of saliva and either lysozyme or poly-L-lysine was inhibited up to ca. 90% compared with hydroxyapatite coated with saliva alone. Strain 903 was also unaffected by combinations of poly-L-glutamic acid and saliva on the hydroxyapatite. Adherent cells of both strains were completely (greater than 90%) eluted with high-ionic-strength buffer from either bare hydroxyapatite or hydroxyapatite coated with lysozyme alone. Adherent cells of strain S35 were only poorly eluted (25%) from hydroxyapatite coated with either saliva alone or saliva and lysozyme. Strain 903 elution from hydroxyapatite coated with either saliva alone or saliva and lysozyme was essentially complete. These observations were taken to indicate that the two test strains adhered to saliva-coated hydroxyapatite by different mechanisms. Protein-coated hydroxyapatite was shown not to be saturated under the conditions described here. Examination by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the variously supplemented salivary pellicles formed on the hydroxyapatite demonstrated that major changes in salivary protein composition did not occur when lysozyme, poly-L-lysine, or poly-L-glutamic acid was used to supplement saliva. Lysozyme-dependent aggregation of strain 903 was shown not to occur under the conditions of our experiments. We suggest that the basis for stimulation of adherence to hydroxyapatite coated only with lysozyme is an increase in the cationic surface area available for electrostatic adherence of the microorganisms.(ABSTRACT TRUNCATED AT 400 WORDS)