A 67-year-old man with alcoholism has fever, chills, cough, and pleurisy pain. His sputum is a dark brown color, and upon cultivation on blood agar produces alpha hemolytic colonies, composed of gram-positive, optochin-positive cocci. The microbes are which of the following?
E. faecalis
N. meningitidis
S. aureus
S. pneumoniae
S. pyogenes