<prompt> True about streptococcus pyogenes are all except -Causes only localized infectionRheumatic fever is non-supporative complicationsErythrogenic toxin causes scarlet feverGlomerulonephritis is due to antigenic crossreactivity  <response>: Ans. is 6a i.e., Causes only localized infectiono Streptococcal diseases can be braodly classified into three groups1 Suppurative infections These are otitis media, sore throat, mastoiditis, pneumonia, abscesses, erysipelas, impetigo non-bullous impetigo or impetigo contagiosum, cellulitis, necrotizing fascitis, puerperal sepsis and bacteremia.o Sore throat is the most common streptococcal disease. The M protein types of a S. pyogenes most commonly associated with skin infection impetigo are different from those causing resporatory infection Pharyngitis.2 Toxin mediated These are scarlet fever and toxic shock syndrome. Scarlet fever is caused by erythrogenic toxin. Toxic shock syndrome TST is due to pyrogenic exotoxin A erythrogenic toxin produced by strains M type-1 and -3 of strep, pyogenes. These strains are also called as Flesh eating bacteria.3 Non-suppurative complications immune mediated These are rheumatic fever and glomerulonephritis. Rheumatic fever follows streptococcal throat infection hut not skin infection, whereas glomerulonephritis can occur after throat or skin infections. These non-supporative complications are due to antigenic cross-reactivity of streptococcal antigenic component with human tissues. This antigen cross reactivity is resoponsible for the production of cross reacting antibodies, i.e. antibodies are formed against streptococcal antigens but they damage host tissue antigens because of similarity between streptococcal antigens and human tissue antigens - antigenic cross reactivity. 