Transformation of Hemolytic Streptococci,∗

Abstract

Two methods of typing hemolytic streptococci have been suggested by recent investigators: (a) the Lancefield method 1 based on the existence of at least 5 antigenically distinct type-specific “carbohydrates” in different human, veterinary and environmental strains, and (b) the Tillett-Garner-Madison technic, 2 based on the presence of at least 3 different type-specific fibrinolyses. Both methods assume that the selected diagnostic character is genetically stable.

To test this assumed stability an attempt was made to transform a typical antihuman fibrinolytic strain of S. hemolyticus into a non-fibrinolytic strain of apparent veterinary origin. The strain selected for this attempt was originally isolated by Lancefield from a case of scarlet fever. The strain (C203) is specifically lytic for human fibrin and contains only one type-specific carbohydrate.

To make the proposed transformation, 4 rabbits were injected intraperitoneally with doses varying from 2 to 20 cc. of a 24-hour beef-heart-infusion broth culture. Three days later, the rabbit receiving 20 cc. was in a moribund condition. Blood was withdrawn by cardiac puncture and plated out on 2% rabbit-blood beef-heart-infusion agar. A single typical hemolytic colony on this plate, was used for the production of the broth culture for inoculation of the second group of 4 rabbits. This process was repeated for 22 successful animal passages.

Three times, during the 18 months this work was in progress, the virulence of the strain increased to approximately 700 times that of the original broth culture. In each case, however, the acquired virulence was almost completely lost before the next animal passage.

At varying stages of the transformation the recovered hemolytic colony was retitrated for the 5 Lancefield type-specific carbohydrates and for the Tillett-Garner antihuman fibrinolytic enzyme. Typical data thus obtained are recorded in Table I.