Physiological classification of oral viridans streptococci.

The human mouth harbors large numbers of a variety of greening streptococci. For many years the classification and nomenclature of these organisms have been confused, but recent studies have clarified the situation considerably. Five distinct species can be distinguished among the oral streptococci S mutans, S sanguis, S mitior, S milleri, and S salivarius, and these may be identified using a simple scheme consisting of seven physiological tests. Further subdivisions within these species may be achieved using serological methods. A small number of oral streptococci remain which cannot easily be identified with existing schemes. These may represent additional species that, as yet, have not been adequately described. There seems little justification for continuing the practive of calling all alpha-hemolytic streptococci simple "Streptococcus viridans".