Surface ultrastructure of some oral bacteria.

Adhesion of Streptococcus sanguis, Fusobacterium nucleatum and an Actinomyces sp. to enamel and epon and their interspecies cohesion was studied with scanning and transmission electron microscopy. For adhesion studies enamel or epon was coated with salivary macromolecules and then cells of S. sanguis and in some experiments also with F. nucleatum or Actinomyces sp. Cells of S. sanguis were seen scattered over the surface of a thin "pellicle" that was heavily stained, and F. nucleatum and Actinomyces sp. adhered to S. sanguis or directly to the "pellicle". For studies of cohesion S. sanguis was brought to cohere with F. nucleatum or Actinomyces sp. and then processed for transmission electron microscopy. The morphology of the cell surface structures involved was studied in negatively stained preparations or in thin sections of material treated with ruthenium red or poststained with uranyl and lead salts, phosphotungstic acid or periodic acid-thiocarbohydrazide-osmium tetroxide. S. sanguis demonstrated a fuzzy coat of fimbriae that seemed to unfold in areas of contact with other cells, while cells of F. nucleatum had 6-10 polar pilus-like fimbriae, which appeared to be instrumental in cohesion, as did a dense coat of long, slender fimbriae that covered cells of Actinomyces sp.