1. Presented by Nicolas Giraldo-Castillo, MD, PhD, and reviewed by Patricia Simner, MSc, PhD.

An adult patient with a past medical history of chronic heart disease, atrial fibrillation, and poor dentition presented to the ED with a three-day history of fever, chills, body aches, and fatigue. On review of systems, they also reported occasional nausea and vomiting, but no respiratory, urinary, or gastrointestinal symptoms. Current medications included warfarin, aspirin, furosemide, and metoprolol. On admission, the patient was febrile (temperature: 39.4 ?C), but the other vital signs were within normal limits. The CBC showed normal WBC, with relative neutrophilia (82%), mild anemia (Hb 10), and thrombocytopenia (PLT 81). Imaging studies included a CT scan with contrast that showed an acute pulmonary embolus involving the left main pulmonary artery, and an echocardiogram that showed a mobile echodensity on the tricuspid valve (1.1 x 0.5cm) associated with increased stenosis. The lower extremity ultrasound was negative for thrombus.
Three consecutive blood cultures showed the following organism in the aerobic bottles after 24 hours:

This organism grew on blood and chocolate agar, but did not grow on MacConkey agar nor Columbia CNA.
Which organism is most likely causing the patient's symptoms?