Gram-positive cocci in pairs, alpha-hemolytic, optochin susceptible, bile soluble. Which organism is this?

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Differentiating alpha-hemolytic, optochin-sensitive, bile-soluble streptococci helps identify Streptococcus pneumoniae. This organism appears as Gram-positive cocci in pairs (diplococci) and produces alpha-hemolysis, a greenish zone on blood agar from partial hemolysis. The combination of being inhibited by optochin and dissolving in bile is distinctive: optochin sensitivity distinguishes it from other alpha-hemolytic streptococci that are optochin resistant, and bile solubility further sets it apart because S. pneumoniae dissolves in bile due to its autolytic enzymes, whereas viridans streptococci do not. Together these traits point to Streptococcus pneumoniae, the encapsulated diplococcus associated with pneumonia, otitis media, and meningitis.