The genetic relationships among 33 streptococci that were identified as or and were isolated from humans were determined by deoxyribonucleic acid-deoxyribonucleic acid hybridization on membrane filters. The phenotypic characteristics of these bacteria were determined by their action on 20 substrates in a commercially prepared system, as well as by colony morphology and conventional tests. The strains were biochemically heterogeneous but genetically homogeneous. Although there were some phenotypic similarities between and , these two species were genetically distinct. Within there was genetic heterogeneity. Typical strains ( biotype I) were genetically homologous with some, but not all, of the variant strains ( biotype II). Other biotype II strains formed a separate genetic group, the members of which were biochemically somewhat different from other biotype II strains.


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