Specificity of Toxin of a Non-Hemolytic Variant of a Scarlet Fever Streptococcus

Abstract

A strain of hemolytic streptococcus, No. 1452, isolated by Jones and Little 1 from the infected udder of a cow the milk of which had caused an epidemic of scarlet fever was sent to us about 3 years ago. On receipt, this streptococcus formed large mucoid colonies resembling Str. epidemicus on ascites blood agar and capsules were demonstrable in India ink preparations. The toxin of this strain corresponded to the specific toxin of the streptococcus of scarlet fever and not to the toxin of septic sore throat. 2

The culture had been kept in the refrigerator on 0.5% blood infusion agar slants. At one transplanting it was noted that the strain had lost its hemolytic and mucoid characteristics; the colonies had become small and biconvex and produced green pigment on ascites blood agar. Stained organisms showed rather short chains of Gram positive cocci, typical of streptococci.

A single mouse passage was made and from the heart's blood 2 types of colony were grown; one, green pigment-producing and nonhemolytic like the parent variant and the other identical with the original hemolytic capsule-producing, mucoid colony-forming organism. In an hemolysin test in blood broth the green producing streptococcus completely failed to lyse the blood cells.

A toxin was prepared from bacteria from each type of colony in meat infusion broth (pH 7.4, 1% peptone, 1% NaCl) by incubating 7 days at 35°C. A 1:1000 dilution of the toxin of the non-hemoly-tic variant in physiologic saline and a 1:1500 dilution of the toxin of the hemolytic strain gave skin reactions practically equivalent in size and intensity to those produced by the Dick skin test toxin. Generally, however, the toxin of the hemolytic strain produced a slightly larger reaction. Intradermal skin tests with 0.1 cc. of each of the diluted toxins and 0.1 cc. of Dick skin test toxin as control were made on 10 previously determined Dick positive subjects, 6 adults and 4 children. All gave red areas from 1.5 to 2 cm. in diameter with both toxins.

These subjects were then immunized with 5 doses of the Dick toxin. Six weeks after the last dose identical skin tests were made. Nine out of 10 were negative to all 3 toxins. One child remained positive to the Dick skin test toxin and the toxin of the hemolytic strain in a dilution of 1:1000. There was no skin reaction to the toxin of the non-hemolytic variant in a dilution of 1:1000. Five additional Dick positive subjects who had given positive reactions to our toxins both in a dilution of 1:1000, after similar immunization gave negative skin tests to the toxin of the non-hemolytic variant 1:1000 and the toxin of the hemolytic strain 1:1500.