PLE-3263

35/F presents with a 1-week history of fever, chills, and left ankle pain. The patient is a known IV drug abuser. On PE, vital signs are as follows: BP 110/60, HR 108, RR 18, T 40C. Auscultation reveals a grade 2/4 holosystolic murmur best heard at the right upper sternal border. The left ankle is visibly swollen and warm. Which of the following describes the most likely etiologic agent?