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The usefulness and reliability of partial sequence analysis of the manganese-dependent superoxide dismutase gene (sodA), autolysin (lytA) gene amplification and species-specific PCR based on the D-alanine:D-alanine ligase (ddl) gene for differentiating each member of the mitis group of the genus Streptococcus was investigated. On the phylogenetic tree based on sodA partial sequences (366 bp) from 96 strains, including all species currently within the mitis group isolated in different geographic areas (mainly Japan and the UK), eight well separated clusters were generated corresponding to recognized species, and all strains fell into those clusters to which they had also been assigned by DNA–DNA hybridization. The Streptococcus pneumoniae sub-cluster was located within the Streptococcus mitis cluster, but the sodA gene of S. pneumoniae was very conserved and therefore could be separated from all other species examined. Furthermore, the lytA gene amplification approach could also be used to differentiate S. pneumoniae from other species. The species-specific amplification product of the ddl gene was successfully detected in Streptococcus sanguinis and Streptococcus gordonii, but failed to be detected in some strains of Streptococcus oralis including the type strain and S. mitis. We conclude that the partial sequence analysis of the sodA gene could be applied globally as a reliable and easy method for the accurate identification of all species currently within the mitis group.

Streptococcus anginosus is one of the three species currently included in the “anginosus group” of oral or viridans streptococci. In this study 21 strains of S. anginosus were examined in order to determine whether this species, as currently defined, is sufficiently heterogeneous to warrant further subdivision. Phenotypic strain characterization was carried out by performing biochemical tests with a commercial system (Rapid ID32 STREP kit; bioMerieux), by performing tests to determine hyaluronidase production, hemolysis on blood agar, and gliding motility on chocolate agar, by determining Lancefield groups, and by comparing whole-cell polypeptide patterns obtained by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Variations in genotype were determined by studying 16S-23S rRNA intergenic spacer size polymorphisms by PCR amplification, by ribotyping, and by performing DNA-DNA base pairing studies. S. anginosus was found to be heterogeneous at both the species and intraspecies (subspecies) levels. Beta-hemolytic Lancefield group C strains that did not produce hyaluronidase formed a DNA homology group that was separate from the majority of the S. anginosus strains; the members of this group produced a 380-bp intergenic spacer PCR product, exhibited distinct ribotypes, produced an atypical SDS-PAGE pattern, and represented a previously undescribed species in the anginosus group. Two other strains (ATCC 9895 and 1007-77) remained ungrouped as determined by DNA-DNA hybridization and thus represented additional centers of variation at the species level. Hyaluronidase-producing, beta-hemolytic, Lancefield group C strains produced the same atypical SDS-PAGE pattern as beta-hemolytic Lancefield group C strains that did not produce hyaluronidase but differed from the latter organisms by producing a 600-bp intergenic spacer PCR product. In addition, both DNA homology data and ribotyping data suggested that these strains comprise a subspecies of S. anginosus. With the notable exception of the beta-hemolytic Lancefield group C strains that did not produce hyaluronidase, strains ATCC 9895 and 1007-77, and the beta-hemolytic Lancefield group C hyaluronidase-producing strains mentioned above, the strains studied formed a closely related group within which some additional genotypic and phenotypic heterogeneity was observed. The latter group included both strains that fermented mannitol and strains that did not ferment mannitol, as well as strains that exhibited so-called gliding motility. Although no clear-cut division of these organisms was possible, our results indicate that strain NCTC 10713 may not be the most suitable type strain for S. anginosus. We concluded that S. anginosus strains exhibit sufficient heterogeneity to warrant division at both the species and subspecies levels, although insufficient numbers of strains belonging to the putative new taxa have been characterized to allow formal taxonomic proposals to be made.

The 16S-23S rRNA intergenic spacer has been suggested as a suitable region of the bacterial genome from which to derive useful taxonomic information, particularly with regard to identification at the species level. To investigate this approach as an aid to the identification of the three species comprising the ‘Streptococcus milleri group’ (SMG), the spacers of isolates of Streptococcus intermedius, Streptococcus anginosus and Streptococcus constellatus were amplified by PCR and length polymorphisms determined by agarose gel electrophoresis. Phenotypically atypical isolates which had been identified presumptively as belonging to these three species were also included. Spacers from two representatives of each spacer length found within the three SMG species were sequenced. 16S-23S rRNA intergenic spacer length polymorphisms allowed discrimination between S. anginosus (350 bp or 450 bp amplification product) and S. constellatus (380 bp amplification product), species that are difficult to differentiate phenotypically. S. intermedius (330 bp or 450 bp amplification product) and S. anginosus (350 bp or 450 bp amplification product) were not reliably distinguished by this method but are phenotypically distinct. Sequencing data demonstrated that the spacers had a central region of highly variable length flanked by conserved regions which included a single tRNAAla gene. Polymorphism in the length of the 16S-23S spacer determined by PCR provides a rapid and useful adjunct to strain identification for S. anginosus and S. constellatus, which are not readily differentiated phenotypically.

Summary Clinical strains presumptively identified as Streptococcus milleri (60), and blind coded collection strains (21) were characterised in conventional tests and pyrolysis mass spectrometry. Comparison of the clusters found by these two approaches revealed five clearly distinct centres of variation. Three corresponded to the DNA homology groups suggested by Whiley and Hardie (1989) as representing the species S. anginosus, S. intermedius and S. constellatus; a fourth comprised three Lancefield group C β-haemolytic strains; the fifth may represent a biotype of S. anginosus. The characteristics of the latter group are described.

Strains currently classified as Streptococcus anginosus include strains previously identified as Streptococcus constellatus (Prevot 1924) Holdeman and Moore 1974, Streptococcus intermedius (Prevot 1925), and "Streptococcus milleri" (Guthof 1956) because these specific epithets were argued to be later synonyms of Streptococcus anginosus (Andrewes and Horder 1906) Smith and Sherman 1938 by Coykendall et al. (Int. J. Syst. Bacteriol. 37:222-228, 1987). However, recent data from DNA-DNA hybridization experiments, whole-cell-derived polypeptide patterns determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and data from phenotypic testing have demonstrated that Streptococcus anginosus strains represent three readily identifiable taxa to which the previously assigned type strains of Streptococcus constellatus (strain NCDO 2226 [= ATCC 27823], Streptococcus intermedius (strain NCDO 2227 [= ATCC 27335], and Streptococcus anginosus (strain NCTC 10713 [= ATCC 33397] have been shown to belong. Therefore, we propose recognition of Streptococcus constellatus (emend.) (type strain NCDO 2226 [= ATCC 27823]), Streptococcus intermedius (emend.) (type strain NCDO 2227 [= ATCC 27335]), and Streptococcus anginosus (emend.) (type strain NCTC 10713 [= ATCC 33397]) as distinct species and propose an emended description of each of these taxa.

Strains of streptococci originally isolated from the dental plaque of monkeys (Macaca fascicularis) and designated as Streptococcus mutans serotype h were compared with the other species of the mutans streptococcus group. Despite the close resemblance noted previously between these strains and Streptococcus sobrinus, closer examination revealed several important differences. Strains of serotype h ferment mannitol but not sorbitol, melibiose, inulin, or raffinose, do not produce hydrogen peroxide, and are unable to grow in the presence of bacitracin at 2 units per ml. They exhibit a distinct polypeptide pattern by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and possess several antigens absent from S. sobrinus as revealed by Western blotting (immunoblotting). Virtually identical polar lipid patterns were observed by two-dimensional thin-layer chromatography for both serotype h strains and S. sobrinus, although on the basis of long-chain fatty acid analysis by capillary gas-liquid chromatography, the former could be distinguished by the presence of a peak tentatively identified as cyclopropane acid (cis-9, 10-methyleneoctadecanoate (ΔC 19:0). Deoxyribonucleic acid (DNA)-DNA hybridization studies by both the S1 nuclease and renaturation rate methods showed that serotype h strains differ from S. mutans, S. sobrinus, Streptococcus cricetus, Streptococcus rattus, Streptococcus ferus, and Streptococcus macacae. On the basis of these data, we believe that S. mutans serotype h strains represent a distinct species for which the name Streptococcus downei is proposed. The DNA base composition is 41 to 42 moles percent guanine plus cytosine. The type strain is strain MFe28 (NCTC 11391T), which is cariogenic in monoassociated germfree rats.