Haemagglutinating activities of oral strains of Streptococcus milleri group

Of a total 148 strains of Streptococcus milleri group, 66 agglutinated sheep erythrocytes. The haemagglutinating strains were confined to serotypes g, h, i, j or were untypeable, and had no Lancefield group antigens (A to G and K), all of which have been shown to belong to Streptococcus intermedius. Cell surface hydrophobicity did not significantly differ even between the agglutinating and non-agglutinating S. intermedius strains. The haemagglutinating activity of strain 0813-1 (serotype i) was partially sensitive to heat (100 degrees C, 30 min) or trypsin (1 mg/ml, 30 min) treatment, but completely lost after the heat and subsequent trypsin treatments. Only L-arginine, L-lysine (100 mM), mucin, and fetuin (1 mg/ml) partially inhibited the haemagglutination with native bacterial cells but completely inhibited that with heated cells, whereas none was inhibitory in the reaction with trypsin-treated cells. The results suggest that at least two haemagglutinins are involved in the agglutination of the S. intermedius strain and that the heat-stable but trypsin-sensitive haemagglutinin recognizes the receptors on the erythrocyte surface which contain L-arginine and L-lysine at the reactive site.