Which description best characterizes Streptococcus pneumoniae on Gram stain and lab features?

Which description best characterizes Streptococcus pneumoniae on Gram stain and lab features?

• A. Gram-positive cocci in chains; beta-hemolysis; optochin resistant
• B. Gram-positive diplococci; alpha-hemolysis; optochin sensitive
• C. Gram-negative diplococci; nonhemolytic; optochin sensitive
• D. Gram-positive cocci in clusters; gamma-hemolysis; optochin resistant

Answer: (B)

Identifying Streptococcus pneumoniae hinges on its Gram stain appearance and lab profile. It is Gram-positive and tends to present as lancet-shaped cocci arranged primarily in pairs (diplococci). On blood agar, it typically shows alpha-hemolysis, giving a greenish hue around colonies. A key distinguishing test is sensitivity to optochin; S. pneumoniae is inhibited by optochin, unlike many other streptococci such as viridans streptococci, which are resistant. So the combination of Gram-positive diplococci, alpha-hemolysis, and optochin sensitivity best fits Streptococcus pneumoniae. The other descriptions describe different organisms (for example, Gram-positive cocci in chains with beta-hemolysis or Gram-negative diplococci) and do not match this organism’s characteristic profile.

Identifying Streptococcus pneumoniae hinges on its Gram stain appearance and lab profile. It is Gram-positive and tends to present as lancet-shaped cocci arranged primarily in pairs (diplococci). On blood agar, it typically shows alpha-hemolysis, giving a greenish hue around colonies. A key distinguishing test is sensitivity to optochin; S. pneumoniae is inhibited by optochin, unlike many other streptococci such as viridans streptococci, which are resistant. So the combination of Gram-positive diplococci, alpha-hemolysis, and optochin sensitivity best fits Streptococcus pneumoniae. The other descriptions describe different organisms (for example, Gram-positive cocci in chains with beta-hemolysis or Gram-negative diplococci) and do not match this organism’s characteristic profile.