A child has infectious skin lesions on the leg. A culture reveals gram-positive cocci arranged in chains with hemolytic colonies. Which test is most appropriate to accurately identify this organism?

Explanation

The presence of gram-positive cocci in chains with hemolytic colonies suggests a streptococcal species. Bacitracin sensitivity is the preferred test to differentiate Streptococcus pyogenes (which is bacitracin sensitive) from other beta-hemolytic streptococci. Bile solubility and optochin sensitivity are used for identifying Streptococcus pneumoniae, while catalase and coagulase tests help differentiate staphylococci.