Microbial diagnostics · USMLE Step 1

A CSF sample from a meningitis patient shows many PMNs but no organisms on Gram stain. Which test is most helpful for rapid diagnosis?

  1. Culture on chocolate agar
  2. Latex agglutination test
  3. PCR for bacterial pathogens
  4. India ink stain preparation
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Correct answer: PCR for bacterial pathogens

PCR can detect bacterial DNA even when Gram stain is negative. It is rapid and highly sensitive for meningitis pathogens.

Difficulty: Medium Question 4 of 20

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