Streptococcus salivarius and Other Non-hemolytic Streptococci of the Human Throat.

The non-hemolytic streptococci of the human throat form, simultaneously, one of the oldest and least known groups of the genus. These familiar but illdefined organisms are usually referred to as the "salivarius group," as "Streptococcus viridars" and "indifferent streptococci" according to the degree of greening produced in blood agar, or simply as the "mouth streptococcus." In their early classical work Andrewes and Horder (1906) applied the names of Streptococcus salivarius and Streptococcus mitis to these organisms, Streptococcus salivarius being marked by its ability to curdle milk, usuaUy to reduce neutral red, and frequently by the fermentation of raffinose and inulin, whereas these properties were usually lacked by Streptococcus mitis. The distinction was therefore a statistical one without a sharp boundary and they suggested that Streptococcus mitis might be considered only as a "variant by defect" of Streptococcus salivarius. Although Andrewes and Horder were inclined to consider Streptococcus salivarius "in its most typical form" as a distinct entity, in many cultures its separation rested only on the "tenuous milk reaction." Safford, Sherman and Hodge (1937) carried the description of Streptococcus salivarius much further, showing that the typical cultures formed a very homogeneous group marked by the fermentation of raffinose and inulin, little or no greening in blood agar, vigorous acid production as shown by final pH values of 4.4 to 4.0 in glucose broth and the prompt coagulation of milk, together with many other correlating characteristics. However, as they did not feel justified in drawing the line rigidly on the basis of inulin fermentation, there was a gradual gradation from what they considered the "typical" Streptococcus salivarius through the entire group; the differentiation therefore remaining a statistical one without a sharp boundary line. In such compilations as that by Sherman (1937), in which all of the non-hemolytic streptococci of the human throat are considered as Streptococcus salivarius, the resulting "species" is a poorly defined and somewhat heterogeneous group. Oerskov (1930) and Oerskov and Poulsen (1931) reported that certain nonhemolytic streptococci, when grown on sucrose or raffinose agar, produce a polysaccharide which results in the formation of large mucoid colonies, a property long known to be possessed by the heterofermentative streptococcal organisms of the genus Leuconostoc or Betacoccus. As they did not establish the homofermentative nature of their organisms, and as isolations were made from milk and animal sources as well as the human throat, it is probable that the doubt concerning the nature of the organisms dealt with prevented a proper appreciation of Oerskov's important discovery. The heterofermentative beta-