A Serological Classification of Viridans Streptococci with Special Reference to Those Isolated from Subacute Bacterial Endocarditis

A total of 108 strains of viridans streptococci from subacute bacterial endocarditis, and 99 strains from human throats and extracted teeth have been studied, and approximately two-thirds of all the strains so far have been differentiated into a number of serological groups. The similarity between strains from these sources is evident from the fact that approximately 50 per cent of the reacting strains from each source fall into two groups I and II, and that three groups I, II, and IV, contain streptococci from both sources in approximately the same distribution. Fifteen vaginal strains of viridians streptococci failed, with the exception of one strain, to react with groups I-IV of the endocarditis serums. More than three-fourths of the strains from both sources were Streptococcus salivarius as determined by Sherman's criteria. However, no correlation between the biochemical and serological classification could be made. It may be concluded that the viridans streptococci are amenable to classification by serological methods. The results so far obtained do not indicate a serological difference between strains of viridans streptococci isolated from subacute bacterial endocarditis, and those isolated from human throats and extracted teeth. The greater definitive value of serological methods in the identification of a particular strain is indicated.