Microbial diagnostics · USMLE Step 1

A fungal infection is suspected in a patient with chronic cough and cavitary lung lesions. What diagnostic test best identifies fungal cell wall components?

  1. Galactomannan assay
  2. Bacterial Gram stain
  3. Catalase enzyme test
  4. Tzanck smear cytology
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Correct answer: Galactomannan assay

Galactomannan assay detects Aspergillus cell wall components. It aids in diagnosing invasive aspergillosis.

Difficulty: Medium Question 7 of 20

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