CHARACTERIZATION OF SMOOTH AND ROUGH MORPHOTYPES OF PEPTOSTREPTOCOCCUS-MICROS

Isolation of the smooth (Sm) morphotype of Peptostreptococcus micros, a suspected oral pathogen, is sometimes accompanied by isolation of a rough (Rg) morphotype of P, micros, The Rg type readily changes to a S m-like variant (Rg(Sm)) in broth culture. Sm and Rg isolates and Rg(Sm ) variants were compared to determine whether these three types are th e result of phase variation, The Rg(Sm) variants resembled the Sm morp hotype in colony morphology; furthermore, the Sm type and the Rg(Sm) t ype did not have the fibrillar surface structures characteristic of th e Rg type, and the Sm and Rg(Sm) types were more hydrophobic than the Rg type. However, when we compared the sodium dodecyl sulfate-polyacry lamide gel electrophoresis patterns of whole-cell proteins, serotyping data, pyrolysis mass spectrometry data, 16S ribosomal DNA sequences, and hemolytic activities, the Rg(Sm) variants and the Rg isolates were very similar and were clearly distinct from the Sm isolates, These re sults suggest that the Rg and Rg(Sm) types form a cluster distinct fro m the Sm type and thus provide evidence that P, micros can be differen tiated into two groups, one consisting of the Sm type and the other co nsisting of the Rg and Rg(Sm) types.