This review traces the history of the human, nonhemolytic, or viridans, streptococci and describes improvements in their taxonomy wrought by study of their biochemical profiles and analysis of their nucleic acids. The goal was to define species on the basis of genetic relationships and to describe these species by their phenotypic characteristics so that they can be easily identified. This method has resulted in the division of some species. Streptococcus mutans has been divided into four species, two of which are common in humans. Three more mutans group species are indigenous to animals. Conversely, S. constellatus, S. intermedius, and "S. milleri" have been combined under S. anginosus. S. mitis (or "S. mitior") can be well-defined and includes S. sanguis II. There is genetic heterogeneity within S. sanguis, but the species is usually easy to identify. There is also some heterogeneity in S. bovis, but most human isolates are genetically related. Discussions of the taxonomy of these species are accompanied by descriptions of the characteristics by which these streptococci can be identified. Among these species are potential pathogens which should be suspected in cases of endocarditis and purulent infections of liver, brain, and other tissues.

Classification and identification of the viridans streptococci.

In two preliminary publications (Loewe, Plummer, Niven, and Sherman, 1946; Niven and White, 1946) a report has been presented outlining the identities of various streptococcus cultures isolated from a large number of cases of subacute bacterial endocarditis. One of the largest groups recorded appeared to represent a hitherto unrecognized variety, or species. This streptococcus, which was recovered from approximately one-third of the patients afflicted with bacterial endocarditis, has several unique physiological characteristics which afford a relatively simple and accurate means for identification. Furthermore, all the strains which have been studied thus far have fallen into one of two serological types. For the sake of convenience this streptococcus is referred to as \"Streptococcus s.b.e.\" The successful use of penicillin-anticoagulant therapy for subacute bacterial endocarditis by Loewe (1945a, 1945b) has recently received wide attention. For the first time a large proportion of the patients suffering from this disease are being cured. As reported by Loewe, a majority of the cases which do not respond to the treatment are ones from which Streptococcus s.b.e. have been recovered. The purpose of the present publication is to describe in detail the physiological characteristics of Streptococcus s.b.e.

Streptococcus S.B.E.: A Streptococcus Associated with Subacute Bacterial Endocarditis.

Streptococcus sanguis on media containing 3% sucrose gives rise to characteristic hard cohesive colonies (designated Spp+). Populations of Spp+ bacteria (strain Challis) on sucrose media switch to a soft noncohesive phenotype (designated Spp-) at a frequency of 10(-4) to 10(-3). Spp- bacteria switch back to Spp+ bacteria at a similar frequency. Successive rounds of Spp variation were observed. The Spp phenotypic switch was associated with changes in extracellular glucosyltransferase activity. Images

Spontaneous switching of the sucrose-promoted colony phenotype in Streptococcus sanguis.

Summary
The commensal oral microbial flora has evolved with the human host to support colonization of the various intraoral sites without triggering a significant immune response. In exchange, the commensal microbes provide critical protection against invading pathogens. The intrinsic ability of the oral flora to create a symbiotic microbial community with the host can be disturbed, selecting for the overgrowth of a dysbiotic community that can result in dental diseases, such as caries and periodontitis. Although the mechanisms of molecular pathogenesis in oral diseases are well characterized, much less is known about the molecular mechanisms used by the commensal flora to maintain oral health. Here we focus on the commensal species Streptococcus sanguinis, which is found in abundance in the early oral biofilm and is strongly correlated with oral health. Streptococcus sanguinis exhibits a variety of features that make it ideally suited as a model organism to explore the molecular basis for commensalism. As such, this review will describe our current mechanistic understanding of S. sanguinis commensalism and speculate upon its molecular traits that may be exploitable to maintain or restore oral health under conditions that would otherwise lead to disease.

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The road less traveled - defining molecular commensalism with Streptococcus sanguinis.

Summary: DNA was isolated from 19 strains and substrains of Streptococcus sanguis and analysed for guanine plus cytosine (GC) contents and base sequence homologies. Three groups could be discerned: group 1 strains had 40·8 to 42·8 mol% GC; group 2, 42·7 to 44·0 mol% GC; group 3, 43·8 to 46·4 mol% GC. DNA homologies between groups 1 and 3 were 40 to 60% at 67°C and 40% at 72°C. The homologies of group 2 towards groups 1 and 3 were much lower. Strains in groups 1 and 3 hydrolysed arginine and aesculin and fermented inulin; group 2 strains did not. Groups 1 and 3 could be considered subspecies of S. sanguis. Group 2 should not be considered S. sanguis.

DNA base sequence homologies among strains of Streptococcus sanguis.

The identity of 113 cultures of streptococci recovered from cases of subacute bacterial endocarditis has been reported recently (Niven and White, 1946). Of this number, 42 seemed to represent a hitherto unrecognized variety, or species, which has been tentatively labeled Streptococcus s.b.e. In contrast with other streptococci associated with endocarditis those cases caused by Streptococcus s.b.e. respond sluggishly, or not at all, to Loewe's penicillin-anticoagulant therapy (Loewe, 1945a, 1945b; Loewe, Plummer, Niven, and Sherman, 1946). Since prompt identification of Streptococcus s.b.e. may be a lifesaving measure, adequate methods for accomplishing this would be desirable. A detailed description of this streptococcus is to be given in a forthcoming publication. In the present report a unique physiological characteristic of Streptococcus s.b.e. will be described, namely, the ability to synthesize a polysaccharide from sucrose in broth culture.

Z. Kiziuta

Papers

Synthesis of a Polysaccharide from Sucrose by Streptococcus S.B.E.