Group A streptococci is best siagnosed by:

Ans. (b) i.e. Bacitracin sensitivity "Species identification of Pyogenic streptococci is based largely on serological detection of group antigen by immune precipitation or co-agglutination techniques". An additional test that is useful in the presumptive identification of Str. pyogenes (Group A Streptococci) is bactracin sensitivity test. In contrast to most of other streptococci, Str. pyogenes is uniformly sensitive and large inhibition zones are formed around bacitracin discs on blood agar. Str. agulactiae, the other pyogenic streptococci is identified presumptively by the CAMP reaction.