Bacteriology: mycobacteria: practice question

A Microbiology 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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Microbiology · Bacteriology: mycobacteria

Sample item

A man with advanced HIV and a CD4 count of 30 cells/mm3 has fever, night sweats, weight loss and anaemia. Blood culture grows acid-fast bacilli after several weeks. Which organism is the most likely cause, and how is it treated?

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

The answer and the reasoning

D. Mycobacterium avium complex, treated with a macrolide plus ethambutol

Disseminated Mycobacterium avium complex infection occurs in advanced HIV, usually with CD4 below 50 cells/mm3, and is diagnosed by mycobacterial blood culture. Treatment is a macrolide (clarithromycin or azithromycin) plus ethambutol, with antiretroviral therapy to restore immunity.

Option by option

  • A. Mycobacterium tuberculosis, treated with isoniazid alone

    Tuberculosis is common in HIV, but isoniazid alone would never be used to treat active disease, and this picture at CD4 below 50 favours MAC.

  • B. Mycobacterium marinum, treated with doxycycline

    M. marinum causes skin infection after exposure to fish tanks.

  • C. Mycobacterium leprae, treated with dapsone

    M. leprae cannot be cultured and does not cause this syndrome.

  • D. Mycobacterium avium complex, treated with a macrolide plus ethambutol (correct)

    Correct. M. avium complex is a typical pathogen at very low CD4 counts, and a macrolide with ethambutol is the standard treatment.

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 Microbiology question

What is the answer to this Microbiology question?

The best answer is D, Mycobacterium avium complex, treated with a macrolide plus ethambutol. Disseminated Mycobacterium avium complex infection occurs in advanced HIV, usually with CD4 below 50 cells/mm3, and is diagnosed by mycobacterial blood culture.

Why is "Mycobacterium tuberculosis, treated with isoniazid alone" not the answer?

Tuberculosis is common in HIV, but isoniazid alone would never be used to treat active disease, and this picture at CD4 below 50 favours MAC.

Why is "Mycobacterium marinum, treated with doxycycline" not the answer?

M. marinum causes skin infection after exposure to fish tanks.

Why is "Mycobacterium leprae, treated with dapsone" not the answer?

M. leprae cannot be cultured and does not cause this syndrome.

What concept does this question test?

It tests Bacteriology: mycobacteria in Microbiology. Treatment is a macrolide (clarithromycin or azithromycin) plus ethambutol, with antiretroviral therapy to restore immunity.

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 Bacteriology: mycobacteria?

Make a one-line identity card for each organism: shape and stain, defining test, toxin, disease and drug. Then use the flashcards and the other Microbiology 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.