A child presents with infective skin lesion of the leg. A culture was done which showed gram+ve cocci in chains which were hemolytic colonies. The test to confirm the organism is: (A) Bile solubility, (B) Optochin sensitivity, (C) Bacitracin sensitivity, (D) Catalase positive
Answer is C. The culture is suggestive of infection with Streptococcus pyogenes which is gram-positive, occurring in chains and beta-hemolytic. A convenient method for the identification of Streptococcus pyogenes is based on Maxted's observation that they are more sensitive to bacitracin than other streptococci. Bacitracin sensitivity test: A filter paper disc of 0.04U is applied on the surface of an inoculated blood agar. After incubation, a wide zone of inhibition is seen with Streptococcus pyogenes and not with other streptococci. Reference: Textbook of Microbiology; Anathanarayan and paniker's; 10th edition; Page no: 217