Morphological and immunological characteristics of Streptococcus pyogenes, group A, type 50.

Streptococcus pyogenes, group A, type 50, in contrast to other group A streptococci, causes spontaneous disease in mice thereby providing a suitable experimental model for the study of human streptococcosis. Type 50 possesses various peculiar morphological and immunobiological characteristics and under certain conditions forms and extremely thick non-antigenic capsule which seems to interfere with the binding of antibody. This interference is most likely responsible for the difficulties in detecting type 50 streptococci in the tissues of infected mice by immunofluorescent staining. Whereas the surface components (hyaluronic acid, M-antigen) of the type 50 Streptococcus exhibit several uncommon features, the more deeply located cell wall antigens, like peptidoglycan and C-carbohydrate, do not differ in either their chemical constituents or their serological reactions from the comparable components of other group A streptococci.