Physiological Characteristics and Deoxyribonucleic Acid Relatedness of Human Isolates of Streptococcus bovis and Streptococcus bovis (var.)

Abstract

The current classification of S. bovis is problematic. Many bovine strains, including the type strain, are not typical of S. bovis strains derived from humans, especially in physiologic characteristics. A number of strains physiologically resembling some S. intermedius (MG) strains carry the group D antigen and have been classified as S. bovis (var.) strains. In this work, one compared the physiologic characteristics and DNA relatedness of human strains of S. bovis and S. bovis (var.), the bovine type strain and selected bile-tolerant, esculin-hydrolyzing strains of viridans streptococci. The results indicate a lack of relationship between strains derived from humans and the bovine S. bovis type strain. Although, like the classic S. bovis strains of human origin, the bovine type strain was able to hydrolyze starch, it differed from human S. bovis strains in that it failed to form acid from mannitol and melibiose. The S. bovis (var.) strains did not hydrolyze starch or form acid from mannitol. They were distinguished from the bile-tolerant, esculin-hydrolyzing S. intermedius (MG) strains by their inability to decarboxylate arginine, their ability to form acid from melibiose, and their production of the Lancefield group D antigen. All S. bovis strains of human origin, including the S. bovis (var.) strains, formed a single DNA homology group distinct from the bovine type strain. None of the S. bovis strains were homologous to the S. intermedius (MG) or S. salivarius strains studied. S. bovis (var.) forms a subspecies of strains of human origin and S. bovis strains derived from humans should be removed from the S. bovis taxon.