FALSE statement about the Streptococcus is:: (A) M protein is responsible for production of mucoid colonies, (B) M protein is the major surface protein of group A streptococci, (C) Mucoid colonies are virulent, (D) Endotoxin causes rash of scarlet fever
Answer is A. Strains with well marked capsules produce mucoid colonies. Streptococcus pyogenes can be typed based on surface proteins to M,T,R. M protein is most impoant of these. It act as a virulence factor by inhibiting phagocytosis. It is antigenic and antibody to this promotes phagocytosis of coccus. M protein is heat labile and acid stable but susceptible to tryptic digestion. Also know: Pyrogenic exotoxins (erythrogenic, dick, scarlatinal toxin) -dick test is used to identify children susceptible to scarlet fever, a type of acute pharyngitis with erythematous rash. The M protein itself is a fibrillar coiled-coil molecule with structural homology to myosin. Its carboxy terminus is rooted in the peptidoglycan of the cell wall, and the amino-terminal regions extend out from the surface. The specificity of the multiple serotypes of M protein is determined by variations in the amino sequence of the amino-terminal poion of the molecule. Antigenicity and functions differ in domains of the molecule. There are more than 80 M protein serotypes present. Ref: Ray C.G., Ryan K.J. (2010). Chapter 25. Streptococci and Enterococci. In C.G. Ray, K.J. Ryan (Eds), Sherris Medical Microbiology, 5e.