SUMMARY: Eighteen cariogenic streptococcal strains identified as members of (Clarke, 1924) were compared on the basis of biochemical tests, mannitol-i-phosphate dehydrogenases, DNA base compositions and DNA base sequence homologies. Some slight biochemical differences were found which correlated with the large differences in DNA base composition and sequence heterology which exist among these strains. All strains could be assigned to one of four groups based on these biochemical and genetic differences. Furthermore, these four groups correlated with four serological groups described by Bratthall (1970). It is proposed to divide into four subspecies: subsp. , the type subspecies, has a guanine-cytosine (G-C) of 36 to 38 mol % and belongs to Bratthall serological group subsp. subsp. nov. has 41 to 43 mol % G-C, belongs to Bratthall group , and can be distinguished from the other subspecies by its production of ammonia from arginine; subsp. subsp. nov. has 42 to 44 mol % G-C, belongs to Bratthall group a, and can be distinguished by its lack of growth in air: subsp. subsp. nov. has 44 to 46 mol % G-C, belongs to Bratthall group , and can be distinguished by its failure to ferment raffinose.


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