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 :
“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.
Bacitracin sensitivity
Novobiocin sensitivity
Optochin sensitivity
None of the above