Microbial diagnostics · USMLE Step 1

A stool sample from a child with bloody diarrhea is tested for Shiga toxin. Which method is most appropriate?

  1. Latex agglutination test
  2. Stool culture on MacConkey agar
  3. PCR for Shiga toxin genes
  4. Catalase test
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Correct answer: PCR for Shiga toxin genes

PCR rapidly detects Shiga toxin genes and is highly sensitive. Culture alone may not identify toxin-producing strains.

Difficulty: Medium Question 13 of 20

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