Which organism is the most common cause of community-acquired pneumonia and is described as Gram-positive diplococci?

Which organism is the most common cause of community-acquired pneumonia and is described as Gram-positive diplococci?

• A. Streptococcus pneumoniae
• B. Haemophilus influenzae
• C. Mycoplasma pneumoniae
• D. Staphylococcus aureus

Answer: (A)

The main idea is recognizing the organism most commonly responsible for community-acquired pneumonia and its characteristic Gram stain appearance. Streptococcus pneumoniae is the leading cause of CAP in adults, and it appears as Gram-positive lancet-shaped diplococci. It is an encapsulated organism, a feature that helps it resist phagocytosis and is targeted by vaccines. On culture, it typically shows alpha-hemolysis on blood agar and is optochin sensitive and bile soluble, which helps distinguish it from other bacteria. By contrast, Haemophilus influenzae is a Gram-negative coccobacillus, Mycoplasma pneumoniae lacks a typical cell wall and does not appear as Gram-positive diplococci, and Staphylococcus aureus is Gram-positive cocci in clusters and is less commonly the culprit in typical community-acquired pneumonia. Therefore, the description fits Streptococcus pneumoniae.

The main idea is recognizing the organism most commonly responsible for community-acquired pneumonia and its characteristic Gram stain appearance. Streptococcus pneumoniae is the leading cause of CAP in adults, and it appears as Gram-positive lancet-shaped diplococci. It is an encapsulated organism, a feature that helps it resist phagocytosis and is targeted by vaccines. On culture, it typically shows alpha-hemolysis on blood agar and is optochin sensitive and bile soluble, which helps distinguish it from other bacteria. By contrast, Haemophilus influenzae is a Gram-negative coccobacillus, Mycoplasma pneumoniae lacks a typical cell wall and does not appear as Gram-positive diplococci, and Staphylococcus aureus is Gram-positive cocci in clusters and is less commonly the culprit in typical community-acquired pneumonia. Therefore, the description fits Streptococcus pneumoniae.