Proportional Distribution and Relative Adherence of Streptococcus miteor (mitis) on Various Surfaces in the Human Oral Cavity

A group of streptococci possessing the characteristics of Streptococcus miteor (S. mitis) was found to predominate on nonkeratinized human oral mucosa. These organisms averaged from 76 to 89% of the total flora cultivable on anaerobically incubated blood agar plates from cheek, lip, and ventral tongue surfaces. They averaged 34, 40, and 18% of the streptococci in dental plaque, in saliva, and on the tongue dorsum, respectively. Their ability to adhere to oral surfaces was studied by introducing mixtures of streptomycin-resistant strains of S. miteor, S. salivarius, and S. mutans into the mouths of volunteers. Samples of oral surfaces taken 1 hr later indicated S. miteor adhered far better than the other streptococci to buccal mucosa and to teeth, but S. salivarius showed a higher affinity to the tongue dorsum. Glucose-grown cells of S. mutans adhered feebly to all oral surfaces studied and were rapidly cleared from the mouth. Cells of S. miteor and S. salivarius present naturally in saliva adhered to cleaned teeth comparable to in vitro cultivated strains. Electron microscopy of cells of S. miteor attached to buccal epithelial cells obtained from germfree rats indicated that the organisms possessed a fibrillar “fuzzy” coat which appeared to mediate their attachment to the epithelial cell membrane. This “fuzzy” coat was removed by treatment with trypsin, and it appears to be similar to that previously observed on cells of S. pyogenes and S. salivarius.