A child had pustular lesion on leg. On gram staining gram positive cocci are seen. To establish the diagnosis of Group A streptococcal erythroderma, the test used is?

Streptococcal erythroderma is caused by streptococcus pyogenes. Sensitivity to bacitracin is employed as a convenient method for differentiating str.pyogenes from other hemolytic streptococci. Pustule: A vesicle filled with leukocyte. Most common cause is virus. Most common bacterial cause is str.pyogenes. Str.pyogenes is the etiological agent in most of streptococcal skin infection. Vancomycin is the drug of choice. Ref: Ananthanarayan 7th Ed Page 205