Bacterial infections: Mycobacterium marinum: practice question

A Dermatology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Dermatology · Bacterial infections: Mycobacterium marinum

Sample item

An aquarium cleaner has a violaceous nodule on the hand that gradually spreads up the arm in a line of nodules. Biopsy culture grows organisms at 30 degrees C. What is the most likely organism?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. Mycobacterium marinum

M. marinum grows best at 28 to 32 degrees C and causes fish-tank granuloma, which may show sporotrichoid spread. Treatment is a combination such as clarithromycin with ethambutol, or doxycycline.

Option by option

  • A. Mycobacterium leprae

    M. leprae cannot be cultured on artificial media.

  • B. Mycobacterium marinum (correct)

    Correct. Water exposure and lower-temperature growth indicate M. marinum.

  • C. Nocardia brasiliensis

    Nocardia has a different exposure history and is acid-fast branching, but not typically fish-tank related.

  • D. Sporothrix schenckii

    Sporothrix also produces sporotrichoid spread but follows plant thorn injury and is a fungus.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Dermatology question

What is the answer to this Dermatology question?

The best answer is B, Mycobacterium marinum. M.

Why is "Mycobacterium leprae" not the answer?

M. leprae cannot be cultured on artificial media.

Why is "Nocardia brasiliensis" not the answer?

Nocardia has a different exposure history and is acid-fast branching, but not typically fish-tank related.

Why is "Sporothrix schenckii" not the answer?

Sporothrix also produces sporotrichoid spread but follows plant thorn injury and is a fungus.

What concept does this question test?

It tests Bacterial infections: Mycobacterium marinum in Dermatology. marinum grows best at 28 to 32 degrees C and causes fish-tank granuloma, which may show sporotrichoid spread. Treatment is a combination such as clarithromycin with ethambutol, or doxycycline.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Bacterial infections: Mycobacterium marinum?

Learn each condition by its primary lesion, site and signature sign. Then use the flashcards and the other Dermatology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.