Surface properties of Streptococcus sanguis FW213 mutants nonadherent to saliva-coated hydroxyapatite

Seventeen mutants of Streptococcus sanguis FW213 nonadherent to saliva-coated spheroidal hydroxyapatite were isolated after mutagenesis with ethyl methanesulfonate, nitrosoguanidine, nitrous acid, hydroxylamine, or 2-aminopurine. Enrichment for nonadherent mutants was accomplished by successive adsorptions of the adherent strains to saliva-coated hydroxyapatite. After enrichment, variant colonial morphology on tryptic agar was used as a screening technique for selection of nonadherent mutants, with loss of colonial opacity frequently associated with loss of adherence ability. These mutants were further characterized for additional surface properties, including twitching motility, saliva-induced aggregation, coaggregation with Actinomyces species, surface hydrophobicity, and presence of fimbriae. Results from these assays indicated that the nonadherent mutants fell into six phenotypic groups. A correlation between the loss of adherence ability, a decrease in cell fimbriation, and a decrease in surface hydrophobicity is apparent.