A Comparison of the Adhesion Profiles and Cell Surface Characteristics ofStreptococcus mitiswith those of Other Members of theStreptococcus sanguisGroup

Abstract

A collection of 12 strains of Streptococcus mitis were tested for their in vitro adhesion profiles and compared to those of other strains within the Streptococcus sanguis group (SSG). The S. mitis isolates from saliva and the strains isolated from plaque gave significantly greater cell surface hydrophobicities ( P < 0.01) than isolates from other sites. The saliva isolates were generally not aggregated by saliva wherea s S. sanguis I and II strains gave aggregation values over a wide range. Strains from all species gave a wide range of values for adhesion to saliva-coated hydroxyapatite (SHA), but isolates from dental plaque adhered significantly ( P < 0.01) better to SHA than other isolates. The adhesion to SHA was not related to cell surface hydrophobicity or salivary aggregation. Strain pairs were allowed to interact with each other in the SHA adhesion assay. Homologous pairings usually gave reduced adhesion as did some non-homologous pairings, possibly as the result of occupying similar salivary receptors. Occasionally non-homologous pairings increased the adhesion of one member suggesting that certain SSG strains can modify the salivary pellicle to facilitate the adhesion of other SSG strains. Most strains were poor adherers to buccal epithelial cells (BEC), although S. sanguis I strains were more adhesive ( P < 0.025) than other species/biotypes. Serological tests on SSG strains for surface antigens showed 12 per cent reactivity with antisera to lipoteichoic acid and 40 per cent reactivity with antisera to protein P1; in neither case was there a correlation with adhesion to SHA or BEC or aggregation by saliva. Strains of S. mitis were more likely to coaggregate with veillonella than with actinomyces strains, whereas strains of S. sanguis tended to coaggregate with representatives of both genera. Keywords: Adhesion; Saliva; Streptococcus mitis ; Streptococcus sanguis ; Surface antigens; Coaggregation; Hydrophobicity.