Variation in the group-specific carbohydrate of group C hemolytic Streptococci.

Certain strains of Group C hemolytic streptococci, termed Group C-intermediate, contain a group-specific carbohydrate antigen which gives a precipitin cross-reaction with A-variant antiserum. The carbohydrate antigens of these strains have a rhamnose:hexosamine ratio ranging from 2.4 to 2.6 whereas the ratio of typical Group C strains varies between 1.1 and 1.7. N-acetylgalactosamine, the major hexosamine in all of these strains is the principle determinant of Group C specificity. The high concentration of rhamnose in the C-intermediate carbohydrate suggests that a portion of the rhamnose oligosaccharide side chains are devoid of terminal N-acetylgalactosamine and thus react with Group A-variant antiserum. This view is supported by the fact that the induced variant enzyme, which destroys A-variant carbohydrate reactivity with the liberation of rhamnose oligosaccharides, has a similar action upon the Group C-intermediate carbohydrate. C-intermediate carbohydrate, after treatment with variant enzyme which removed approximately 25 per cent of the rhamnose, does not react with A-variant antisera.