Proposal to Elevate the Subspecies of Streptococcus mutans to Species Status, Based on Their Molecular Composition

Abstract

It is proposed to confer species rank to the genetically distinct streptococci that have been considered subspecies of Streptococcus mutans Clarke: S . mutans subsp. rattus Coykendall, S. mutans subsp. cricetus Coykendall, and S . mutans subsp. sobrinus Coykendall. S , mutans is defined to exclude phenotypically similar bacteria that have deoxyribonucleic acid (DNA) guanine plup Oytosine contents appreciably different from 36 to 38 mol% and/or that do not demonstrate DNA base-sequence homology with the type strain. Streptococci that resemble S. mutans but that are quite disparate in molecular constitution are here regarded as comprising four new species: S. rattus (Coykendall) Deoxyribonucleic acid (DNA) hybridization differences in lactate dehydrogenases among (32) and the analysis of enzymes by serological three of the genospecies in respect to the enand electrophoretic methods have provided new zyme's kinetic response to pyruvate (5). He also approaches to bacterial taxonomy and fostered demonstrated electrophoretic differences in a molecular concept of species (27, 34). Thus, mannitol-and sorbitol-1-phosphate dehydroone may now define a species as a bacterium genases (4). Using serological methods, London that has a unique overall sequence of nucleo-found that aldolases of "S. mutans" were hetertide bases in its chromosome and a complement ogeneous and concluded that "S. mutans" inof enzymes characteristic of that species. Put cluded "divergent groups" of organisms (26). simply, we expect members of a species to not Heterogeneity has also been observed in polyonly "look alike" and "act alike," but also to be saccharide-synthesizing enzymes (7, 28) and in constructed of, and controlled by, molecules invertase (J. M. Tamer et al., J. Dent. Res., vol that are alike. Thus, members of a species 54, special issue A; Abstr. 53rd Gen. Session should be molecularly homologous. Bacteria Inter. Assoc. Dent. Res., 1975). S. mutans genthat are molecularly disparate should not be ospecies correlate well with the serological called by the same species name. groups described by Bratthall (2). Additional Some organisms reported to resemble Strep-serogroups found by Perch et al. (30) seem to tococcus mutans Clarke 1924 (8) are phenotypi-represent variants within the genospecies (12). cally quite similar (6,16,17,30) but are molecu-Differences have been observed in cell wall carlarly heterogeneous. Analysis of their DNA bohydrates among some genospecies (24), and base-sequence similarities has shown the exist-some morphological differences have been reence of four genetic groups (ll), which we call ported (13). "genospecies," a term introduced by Ravin (31).It is clear that "S. mutans" is actually a DNA from strains within each genospecies hy-group of streptococci, but, because of the overall bridized almost completely, but DNA from biochemical similarity of all S. mutans strains, strains of different genospecies hybridized it was proposed to conserve the nomenspecies poorly (10,ll). Furthermore, intergroup hybrid "Streptoc...

Emended description of Streptococcus ferus isolated from pigs and rats

“…Table 1 summarizes the characteristics that can be used for the differentiation of the species from phylogenetically related species. It should be noted that the tests indicated in the original description of S. ferus (Coykendall, 1977) and in related papers (Freedman et al, 1982;Coykendall, 1983) as well as in reviews (Hardie & Whiley, 1995) cannot be used. Notably, failure to produce acid from raffinose, as described by Coykendall (1977Coykendall ( , 1983, is not a distinguishing characteristic, because the test was found to be positive for all strains from pigs.…”

“…Streptococcus sobrinus is also a colonizer of the human mouth and can be very cariogenic (Coykendall, 1983). Streptococcus downei and Streptococcus macacae were isolated from the dental plaque of monkeys (Coykendall, 1977;Beighton et al, 1984).…”

Comparative Studies on the Protein Profiles and Hydrophobicity of Strains of Streptococcus mutans Serotype c

“…The extent of genetic diversity in oral streptococci has led to those previously identified as Streptococcus mutans being reclassified into five species under the general name of mutans streptococci, with S. mutans strains now having a more restricted range of characteristics (Coykendall, 1977(Coykendall, , 1983. Strains representative of the four species that are human commensals are also readily distinguishable on the basis of their extracellular protein profiles, with lesser differences between the protein profiles of strains from the different serotypes of S. mutans (c, e andf) and Streptococcus sobrinus ( d and g ) (Hardy et al, 1986).…”

Streptococcus mutans Serotype b Strain (St. rattus, Coykendall): First Isolation in Japan from Human Dental Plaque

“…1). Although it has been proposed to regroup the members of the mutans group of streptococci into five species (10,11) and three of them appear in the Approved Lists of Bacterial Names (32), the mutans members have traditionally been divided into eight different serotypes, a through h, on the basis of serological reactions (1, 3,4,20). The predominant method of serotyping used in these studies was a precipitation reaction between an antigen extracted from cells of a particular serotype strain and an antiserum adsorbed with strains of other serotypes.…”