Aggregation of Streptococcus sanguis biotypes I and II by parotid saliva: a comparison between peritrichously fibrillar and tufted strains.

Twelve strains of Streptococcus sanguis biotype I and seven strains of Streptococcus sanguis biotype II carrying either peritrichous fibrils or tufts of fibrils, were examined for their susceptibility to aggregation by parotid saliva. Salivary aggregation was evaluated using a spectrophotometric measurement of sedimentation to assess clump size. A clear distinction emerged between structural sub-groups. Irrespective of biotype, strains carrying peritrichous fibrils aggregated strongly whilst tufted strains were little affected. The one strain with peritrichous fimbriae as well as fibrils, was not aggregated by saliva. Pre-treatment of two peritrichously fibrillar strains with parotid saliva reduced their ability to adhere to parotid saliva-coated hydroxyapatite, whereas adhesion of two tufted strains was not inhibited. Inhibition of adhesion may have been due to steric hindrance, but blocking of bacterial adhesins by saliva components could not be discounted.