STUDIES ON HEMOLYTIC STREPTOCOCCI VI. THE EPIDEMICUS GRouP

In an earlier paper (1935) it was shown that, in hemolytic streptococci of Lancefield's group A which ferment lactose and salicin but not mannitol, there is some correlation between resist-ance to phage C/594 and ability to produce epidemics of septic sore throat. The present communication reports further studies on this resistant group of strains, as compared with the group of strains differentiated from it only by sensitivity to phage C/594, designated as Streptococcus pyogenes in the second paper of this series. The group of resistant strains will here be designated the epi-demicus group, deferring the description of the species Strepto-coccus epidemicus until further studies have determined more clearly whether or not certain strains which differ more or less from the type strain should be included in the species. Defi-nitely, however, the type strain of S. epidemicus must be the strain known in the literature as X40, isolated by Davis and Rosenow in 1912 from the spleen of a fatal human case during the Chicago epidemic of septic sore throat. Davis gave it the species name epidemicus. It is maintained in the American Type Culture Collection and designated as S. epidemicus No. 624 in the catalog. Our number is 890. Essential characters are as follows: It belongs to Lancefield's group A, ferments lactose and salicin but not mannitol, resists phage C/594, and belongs to Griffith's type 13. Eighteen of Griffith's 30 serologic type strains were found to belong to Lancefield's group A and to produce the specified fer