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Strains of oral Streptococcus milleri group were compared with the type strains of Streptococcus anginosus, S. intermedius, and S. constellatus by DNA-DNA hybridization at 60 degrees C. Of the 29 strains tested, twelve, twelve, and two strains were closely related to S. anginosus ATCC 33397T, S. intermedius ATCC 27335T, and S. constellatus ATCC 27823T, respectively. Generally, the strains classified in the S. anginosus group in DNA homology were non-beta-haemolytic and belonged to API S. milleri II and biotype I (lactose fermenting), whereas the strains of S. constellatus group were beta-haemolytic and belonged to API S. milleri I and biotype II (lactose non-fermenting). The strains of the S. intermedius group were all non-beta-haemolytic and belonged to API S. milleri II and mostly biotype II (lactose fermenting). Furthermore, all except one strain of the S. anginosus group were Lancefield group A/serotype a (A/a), ungroupable/serotype b (-/b), C/c, -/d, -/e, F/f or G/k, whereas those of the S. constellatus group were F/-. The strains of the S. intermedius group were -/g, -/h, -/i, -/j, or -/-.

Of the 29 'Streptococcus milleri' strains tested, all thirteen Streptococcus intermedius (DNA homology group 2) strains but none of the thirteen Streptococcus anginosus (group 1) strains produced beta-N-acetylglucosaminidase, beta-N-acetylgalactosaminidase, alpha-N-acetylneuraminidase, beta-galactosidase, alpha-glucosidase, and hyaluronidase. The three Streptococcus constellatus (group 3) strains produced only the latter two. Glycosidase production divided 274 clinical isolates into 103 S. anginosus, 101 S. intermedius, and 70 S. constellatus strains. Generally, strains of S. anginosus and S. intermedius were non-beta-haemolytic. API II and biotype Ia (lactose positive), but the former contained almost all API III strains and belonged to Lancefield group A/serotype a (A/a), -/b, C/c, -/d, -/e, F/f or G/k, and the latter included most of biotype IId (lactose negative) and serovar -/g, -/h, -/i or -/j. S constellatus strains were beta-, alpha- or gamma-haemolytic, of API I or II but mostly biotype Ib (lactose negative), and of F/- or -/b. S. intermedius was a major member of the oral isolates. Non-oral isolates were virtually all S. anginosus (mainly urogenital isolates) or S. constellatus (the other systemic isolates).

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.