Interaction of streptococcal aggregating factors with thiol- and disulphide-reactive compounds

Abstract

The saliva-dependent aggregation of two strains of Streptococcus sanguis is interfered with by reagents that react with sulphydryl or disulphide groups. Iodoacetamide, p-chloromercuribenzoate, ferricyanide, dithiothreitol, glutathione and thiodiglycol reduce aggregating activity significantly, although thiocyanate is without effect. lodoacetamide and cysteine exhibit maximal inhibition at about 2 mM. Experiments show that the inhibitory effect is due to an interaction with the salivary aggregating factor and not with the cells. The effect of iodoacetamide on the factor is irreversible, but cells that are already aggregated by saliva become dissociated following addition of the reagent. The aggregation of Streptococcus mitis strain 26 is not affected by iodoacetamide or ferricyanide but is inhibited by cysteine. The conclusion is made that thiol groups and disulphide linkages play a vital role in maintaining functional ability of the salivary aggregating factors. The differences in response between the sanguis and mitis factors reflect the basic structural dissimilarities of the molecules. Our findings also suggest that sulphur-containing products of metabolism that occur in the oral cavity may participate in the control of bacterial adhesion and colonization.