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 ill-defined organisms are usually referred to as the "salivarius group, " as "Strepto-coccus viridars " and "indifferent streptococci " according to the degree of green-ing 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, Strepto-coccus 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 con-sider 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 homo-geneous 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 sali-varius through the entire group; the differentiation therefore remaining a sta-tistical 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.