• Streptococcus sanguis;
  • colony morphology variation;
  • transformation;
  • hemagglutination;
  • polar fimbriation

Strains of Streptococcus sanguis expressing spreading zones around the colonies and competence in genetic transformation, were subcultivated in the laboratory, and in three strains a variation to non-spreading colony morphology on human blood agar plates was observed. These variants were isolated and compared with the original strains by genetic transformation, hemagglutination and electron microscopy.

In genetic transformation with streptomycin resistance as genetic marker, the non-spreading variants showed a decrease to 1/50 or less of the transformation frequencies compared to the wild types. Hemagglutination of guinea-pig erythrocytes is a common characteristic of S.sanguis strains, but the non-spreading variants did not hemagglutinate. In electron microscopy studies the wild-type strains of S.sanguis, but not the non-spreading variants, presented long, polar fimbriae. One of the non-spreading variants had short, peritrichous fimbriae. The co-variation in surface-spreading, competence in genetic transformation, hemagglutination and polar fimbriation is discussed.