Cellulitis

A 36-year-old man presents to the emergency department for evaluation of a rash on the right forearm. The patient was recently admitted to the hospital for pain-control in the setting of nephrolithiasis. He recalls, “After I left, I was feeling fine, then the next day my arm started hurting, and I noticed a red rash near the site where I had my IV.” He is otherwise healthy and does not take any medications daily. Temperature is 38.0°C (100.4°F), pulse is 110/min, respirations are 14/min, and blood pressure is 119/77 mmHg. Physical examination demonstrates a well demarcated erythematous, warm, and painful rash over the anterior aspect of the right forearm without fluctuance. Infection with which of the following organisms is most likely responsible for this patient’s cutaneous findings?