Most common cause of bacterial pneumonia, meningitis, and otitis media?

• A. Staph aureus
• B. Streptococcus pyogenes
• C. Streptococcus pneumoniae
• D. Staph epidermidis

Answer: (C)

This is about the pathogen most likely to cause the three infections together: Streptococcus pneumoniae. Its ability to colonize the nasopharynx and then invade sterile sites makes it a leading cause of several common bacterial infections. The pneumococcus has a polysaccharide capsule that helps it resist being eaten by immune cells, which enables it to spread from the upper airway to the lungs, meninges, and middle ear. As a result, it is the most frequent bacterial cause of community-acquired pneumonia, a major cause of bacterial meningitis in both adults and children, and the leading cause of acute otitis media in children. In the lab, it’s a Gram-positive, lancet-shaped diplococcus that is encapsulated and typically optochin sensitive and bile soluble, which helps distinguish it from other bacteria. While Staph aureus, Strep pyogenes, and Staph epidermidis can cause some of these infections in particular settings, they do not have the same overall prominence across all three conditions.