The degree of homology between group D ( and ) and group N () streptococci was assessed by deoxyribonucleic acid (DNA)-DNA hybridization. Interspecific DNA duplexes between and exhibited high levels (>75%) of formation at 60 and 70 C, and low levels (<10%) of DNA duplex formation were observed between group D and group N organisms at 60 and 70 C. Thermal stability studies indicated less than 2% unpaired bases in these duplexes. Atypical strains which have characteristics of both group D and group N streptococci were included in an attempt to identify them with established species. The results indicate that DNA-DNA hybridization studies may be useful in placing atypical strains in a particular species if screening of physiologic properties is used to separate these strains into groups resembling , and Results obtained with an authentic strain of subsp. Mundt and Graham indicate that this organism deserves the subspecific designation.


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