Impetigo

A 17-year-old young man presents to his primary care physician for evaluation of lesions on the abdomen. The lesions were fluid-filled sacs that eventually burst, leaving behind yellow, crusted areas of inflammation. The patient is otherwise healthy and does not take any medications. Temperature is 37.7°C (99.9°F), blood pressure is 112/73 mmHg, and pulse is 68/min. Physical examination is notable for the following finding:



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Which of the following pathogenic factors is most likely responsible for this patient’s clinical presentation?