A comparison of the adhesive properties and surface ultrastructure of the fibrillar Streptococcus sanguis 12 and an adhesion deficient non‐fibrillar mutant 12 na

Abstract

Streptococcus sanguis 12 and a naturally occurring mutant, 12 na, were screened for their ultrastructure and adhesive properties in vitro. Negative staining showed that Strep. sanguis 12 carried three types of surface structure. The majority of cells carried long fibrils that in different batches ranged in length from 80 to 207 nm, and shorter fibrils which were 51.0 +/- 15.7 nm long. Both types of fibrils were primarily located at the poles of the cells. Occasionally cells were seen that carried fimbriae, which are structurally distinct from fibrils, and were 3-4 nm wide and less than 1.0 micron long. Strain 12 na carried no detectable surface structures. Ruthenium red staining revealed that both strains carried a loose, amorphous, extracellular polysaccharide layer attached to the cell wall. Streptococcus sanguis 12 na was 83% less adhesive than strain 12 in a saliva-coated hydroxyapatite assay, and 50% less adhesive in a buccal epithelial cell adhesion assay. In contrast, strain 12 na was more sensitive to aggregation by parotid saliva than strain 12, and both strains were equally aggregated by whole saliva. The cell surface hydrophobicity of the two strains was similar. Extraction of surface proteins by sodium lauroyl-sarcosinate followed by sodium dodecylsulphate polyacrylamide gel electrophoresis demonstrated that Strep. sanguis 12 expressed more high mol.wt proteins on its surface than strain 12 na. Using immunogold labelling, the fibrils of strain 12 labelled well with antiserum directed against the long fibrils, but so did the cell surfaces of both Strep. sanguis 12 and 12 na. High molecular weight proteins and cell surface fibrils may be associated with adhesion in this strain.