<prompt> A person from village is complaining of development of pustules. Extract from pus has shown gram positive cocci, showing hemolysis, catalase ve, identified as a group of streptococci. Following test is used :Bacitracin sensitivityNovobiocin sensitivityOptochin sensitivityNone of the above  <response>: Sensitivity to bacitracin is employed as a convenient method for differentiating Str. pyogenes from other hemolytic streptococci.Pustule A vesicle filled with leukocyte. MC cause is virus. MC bacterial cause is Strep. pyogenes.Remember :Str. pyogenes is the etiologic agent in most of the streptococcal skin infection.Vancomycin is the drug of choice.Optochin senstivity and bile solubility is used to differentiate pneumococci from Strep. viridans group. 