The role of hydrophobicity in Streptococcus sanguis and Streptococcus salivarius adhesion to salivary fraction-coated hydroxyapatite

Abstract

The influence of salivary components on the adhesion of Streptococcus sanguis (NCTC 7863 and B43) and S. salivarius (NCTC 8618 and A24) to an in vitro model of the tooth, hydroxyapatite (HA), was investigated. Salivary fractions containing high and low molecular weight components (FI and FIII respectively) were prepared by gel filtration, with subfractions of FIII: FIII(a), FIII(b), FIII(c) and FIII(d), obtained by anion exchange chromatography. The chemical and hydrophobic nature of the derived fractions was determined. In addition, the relative surface hydrophobicity of the bacterial strains was measured. From the adherence data and the information relating to the physical and chemical characteristics of the fractions and bacteria, elucidation of possible mechanisms involved in streptococcal adhesion to the saliva-treated HA was undertaken. Hydrophobic interactions appeared to play an important role in the adhesion of bacteria pretreated with fractions of a hydrophobic nature, such as FIII(a), as correlation between the hydrophobicity of the bacteria and adherence was reported. However the influence of hydrophobic interactions on bacterial adhesion decreased when relatively hydrophilic fractions were used to coat the HA surface. The use of type strains and clinical isolates of S. sanguis and S. salivarius indicated differences in the mechanisms by which the bacteria adhere to salivary fraction-coated HA. Treatment of HA with low molecular weight components, in particular those present in FIII(c), significantly increased adhesion of S. sanguis B43 ( P < 0.05). S. salivarius A24 adherence to FIII-coated HA was also enhanced ( P < 0.05). However, while adherence of S. sanguis B43 to FI-coated HA was enhanced, the attachment of S. salivarius A24 to HA treated with the high molecular weight components was inhibited. These findings may indicate that the presence of high molecular weight salivary components in the acquired enamel pellicle results in selective bacterial adhesion at the tooth surface.