Microbial diagnostics · USMLE Step 1

A patient with suspected diphtheria undergoes laboratory evaluation. Which test confirms toxigenicity?

  1. PCR for Corynebacterium diphtheriae
  2. Culture on tellurite agar
  3. Elek test
  4. Catalase test
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Correct answer: Elek test

The Elek test detects diphtheria toxin production. Culture alone cannot determine toxigenicity.

Difficulty: Medium Question 17 of 20

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