A 25-year-old male presented to the emergency department complaining of fever associated with shortness of breath for 3 days. He is an active smoker with occasional use of IV heroin. Temperature is 39.8C. Cardiac auscultation revealed pan systemic murmur at apex with radiation to the axilla. Lung auscultation is clear. Echocardiogram showed moderate mitral valve regurgitation with vegetation/abscess. What is the most frequent etiologic organism for this patient acute condition?