Effect of pH and some reagents on the sucrose-independent non-specific sorption of the oral bacterium Streptococcus mutans to glass

Abstract

The effect of hydrogen-ion concentration on the sucrose-independent attachment of various strains of Streptococcus mutans to glass was studied using overlapping phosphate and acetate buffers through a pH range of 4.0 to 8.0 at a constant molarity. Some strains of the same serotype showed nearly identical patterns of adhesion with respect to pH, and all strains of serotype a, d and g behaved similarly, showing increased sorption at low pH only. Studies with serotype g cells demonstrated that increased sorption at low pH was not a result of changes in the ionic strength of the buffer. Metal chloride salts increased adhesion at some concentrations. Cyclohexyl isocyanide, EDTA, Tween 80, and saccharides had varied effects on several strains of serotype b and g cells at pH 4.6. Pre-treatment of serotype b and g cells with proteolytic enzymes or 2-mercaptoethanol usually resulted in reduced adhesion at pH 4.6; pre-treatment with dextranase had no effect or increased adhesion. The results suggest that the pH-sensitive adhesin is a protein, and that low pH increases adhesion either by increasing hydrogen bonding between the adhesin and the substrate or by altering the conformation of the adhesin. Contraction of the diffuse double layer is also important in explaining how adhesion is increased at low pH.