Abstract
Deoxyribonucleic acid (DNA) homology was used to examine genetic relatedness among 25 yellow-pigmented strains of group D streptococci and to clarify the possible genetic relatedness of these strains to Streptococcus faecium and Streptococcus faecalis. In all cases, the DNA of the yellow-pigmented strains hybridized with the DNA of S. faecium and S. faecalis at a level of less than 25%. Based on median thermal dissociation temperatures (Tm's) and hybridization tests, the yellow-pigmented strains were divided into two groups (I and II). DNAs of strains in group I had relatively low Tm’s and did not exhibit significant homology with DNA of the herein designated type strain (ATCC 25788) of S. faecium subsp. casseliflavus. The DNAs of group II strains, on the other hand, exhibited high Tm’s and had a high degree of homology with the DNA of the type strain of the above-mentioned subspecies. Three physiological traits were found to be peculiar to group II organisms: ability to grow in the presence of 6.5% sodium chloride, inability to ferment sorbitol, and inability to decarboxylate tyrosine. It is proposed that the group II strains constitute a separate and distinct species. Because the strains presently placed in this species include the type strain of S. faecium subsp. casseliflavus Mundt and Graham, the name of this species, according to the rules of the Bacteriological Code, is Streptococcus casseliflavus (Mundt and Graham) comb. nov.
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