All are true about streptococcus except -

Ans. is 'a' i.e., M protein is responsible for the production of mucoid colonies M. protein M. protein is cell wall protein. M. protein acts as the major virulence factor. It acts by inhibiting phagocytosis. Antibody to M protein is protective. Other two cell wall proteins such as T & R protein have no virulence. Capsule Capsule is composed of hyaluronic acid. Capsule also helps in virulence by inhibiting phagocytosis. Group 'A' streptococcus (strep. pyogenes) elaborates a polysaccharide capsule composed of hyaluronic acid. This production of large amounts of hyaluronic acid capsule results in characteristic mucoid appearance of bacterial colonies. So, strains with well marked capsules produce mucoid colonies capsule is responsible for the production of mucoid colonies (not M protein). So, mucoid colonies are virulent because of capsule which impas virulence to the organism. Hair like pili Umbria) project through the capsule. The pili consist paly of M protein and are covered with lipoteichoic acid which is impoant in the attachment of streptococci to epithelial cells. About other options c & d Option c ? Virulent strains, on fresh isolation from lesions, produce a matt (finely granular) colony, while avirulent strains form 'glossy' colonies. Strains with well marked capsules produce mucoid colonies, corresponding in virulence to the matt type.