The Relative Importance of the Capsule and the M-Antigen in Determining Colony Form of Group a Streptococci

Evidence is presented showing that the surface configuration of Group A streptococcal colonies depends largely on whether or not the cocci form a capsule. Strains which form capsules during growth on agar produce mucoid or matt colonies. Strains that do not form capsules during growth on agar produce glossy colonies. Whether or not M antigen is formed by the growing cocci appears to have no direct effect on surface configuration of the colony, although there is an indirect and partial association between M production and the mucoid-matt variant state and between M deficiency and the glossy variant state.