Sep 10 • Multiple choice answers
🧪 Answer Reveal: Recall Question
Question:
A branching Gram-positive rod is recovered from an immunocompromised patient.
The organism is aerobic and partially acid-fast.
Which organism is MOST likely?
✅ Correct Answer: B) Nocardia
🧠 Explanation:
The key clues point directly to Nocardia:
✔ Branching, filamentous Gram-positive rods
✔ Aerobic
✔ Partially/weakly acid-fast
✔ Often associated with infections in immunocompromised patients
Nocordia contains mycolic acids in its cell wall, which gives it its characteristic partial acid-fastness. A modified acid-fast stain can be used to demonstrate this.
🔬 Why not the other options?
A) Actinomyces ❌
• Also forms branching Gram-positive filaments
• But is anaerobic and not acid-fast
C) Listeria ❌
• Small Gram-positive rod
• Known for tumbling motility and cold enrichment
D) Corynebacterium ❌
• Club-shaped Gram-positive rods
• Often arranged in “Chinese letters”
• C. diphtheriae is associated with metachromatic granules
💡 Quick Recall Tip:
The big Nocardia combination:
🌬️ Aerobic
🌿 Branching filaments
🔴 Partially acid-fast
= NOCARDIA
🔥 High-Yield Comparison:
Nocardia → Aerobic + partially acid-fast
Actinomyces → Anaerobic + non-acid-fast
If an exam gives you branching Gram-positive rods, check those TWO clues next! 👀
👇 Did you get it right before the reveal? Drop a 🧫 below!
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🧪 Answer Reveal: Recall Question
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