Which among the following is the most common cause of acute infective endocarditis?

Streptococci and staphylococci are the cause of greater than 80% of infective endocarditis (IE) cases in which a responsible organism is identified. Streptococcal species were historically the most common group of pathogens, but S. aureus as the most frequently isolated microbial agent worldwide. Viridans group streptococci, or alpha-hemolytic streptococci, are a frequent cause of community-acquired native valve endocarditis (NVE). Ref: O'Gara P.T., Haldar S.M. (2011). Chapter 86. Infective Endocarditis. In V. Fuster, R.A. Walsh, R.A. Harrington (Eds), Hurst's The Hea, 13e.