skip to main content

Pneumococcal capsule virulence — MRCPCH TAS MCQ

Instant feedback + full explanation. One question, done properly.

ModerateMicrobiologyPneumococcal capsule virulenceMRCPCH TAS

A 3-year-old with pneumonia has blood cultures growing alpha-haemolytic diplococci that are optochin sensitive. Which virulence factor most helps the organism evade phagocytosis?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: A — Polysaccharide capsule

Streptococcus pneumoniae uses its polysaccharide capsule to resist phagocytosis, and conjugate vaccines target capsular antigens. Protein A is a Staphylococcus aureus virulence factor. The pearl is that impaired splenic function increases risk from encapsulated organisms.

Reference: Nelson Textbook of Pediatrics; UKHSA Green Book; RCPCH Theory examination syllabi