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

Abstract

A collection of 331 cultures representing the predominating non-hemolytic streptococci of the human throat was studied in detail; 184 strains were identified as Str. salivarius, and the remaining 147 as members of the Str. mitis group. Str. salivarius appears to be a remarkably homogeneous and clearly defined species, especially marked by its ability to synthesize large amts. of polysaccharide from sucrose, to ferment both raffinose and inulin, its inability to produce marked greening in blood agar, and many other correlating and apparently constant characteristics. About 40% of the strains of Str. salivarius belong to one serological type (Type I). There is at least 1 other serological type which includes a fairly large proportion of the strains of this species, and an unknown number of other types. The so-called "Streptococcus cardio-arthritidis" was physiologically and serologically identified as Str. salivarius. By the use of a nutrient agar containing sucrose (5%) and Na azide (0.02%), which has both selective and differential values for this purpose, it was shown that Str. salivarius commonly occurs in large numbers in the human intestine. Str. salivarius was isolated from the fecal samples of 15 of the 18 persons examined, the numbers of this organism ranging from 1,200 to 129,000,000 per gram. The organisms identified as Str. mitis form a rather heterogeneous and perhaps complex group, givirig diverse tests in many of the reactions studied. The group has, however, a considerable degree of homogeneity and can be readily differentiated, not only from Str. salivarius, but from several other spp. of viridans streptococci. Lactose-non-fermenting, non-hemolytic streptococci from the human throat are generally considered to be Str. equinus. Of 21 such strains studied, 16 proved to be Str. salivarius, whereas the other 5 were identified as members of the Str. mitis group. 8 strains of lactose-non-fermenting organisms from the human genito-urinary tract, which had been reported as Str. equinus, were found to be Group B streptococci.