Physiological Characteristics and Deoxyribonucleic Acid Relatedness of Streptococcus intermedius Strains

Fifteen strains of Streptococcus intermedius and three mannitol-fermenting S. intermedius-like isolates from urine were studied by the S1 nuclease DNA homology assay and two physiological characterization methods. Three distinct homology groups (I, II, and III) were found. The three mannitol-fermenting S. intermedius-like strains and 2 of the 15 strains of S. intermedius did not fall within these groups. Each of the distinct homology groups could be distinguished by physiological testing. Homology group I strains were bile esculin positive (BE+), starch negative (Sta−), non-CO2 dependent, and melibiose negative (mel−); homology group II strains were BE−, Sta−, CO2 dependent, and mel−; homology group III strains were BE−, Sta+, non-CO2 dependent, and mel+. The two nonhomologous S. intermedius strains and three S. intermedius-like isolates from were phenotypically distinct from those in homology groups I through III. Characterization by the Rapid Strep system (Analytab Products, Plainview, N.Y.) identified homology groups I and II as either “S. milleri” I or II and homology group III strains as S. sanguis I or II. One nonhomologous S. intermedius strain was identified as S. sanguis I, and the other “S. milleri” I and the S. intermedius-like mannitol-fermenting strains were identified as S. milleri III by this method. We conclude that homology groups I, II, and III and the S. intermedius-like isolates from urine may represent separate taxa, but we do not make such a proposal on the basis of our limited data.