Bacteriology: Mycobacterium ulcerans: 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.

Try it

Microbiology · Bacteriology: Mycobacterium ulcerans

Sample item

A child from a swampy region of West Africa has a painless, large skin ulcer with undermined edges and little fever. Acid-fast bacilli are seen in the smear. Which factor accounts for the extensive tissue necrosis?

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

The answer and the reasoning

A. Mycolactone, a lipid toxin with cytotoxic and immunosuppressive activity

Buruli ulcer is caused by Mycobacterium ulcerans, which produces the polyketide toxin mycolactone, causing necrosis of skin and subcutaneous fat and local immunosuppression, so the ulcer is painless. The organism grows best at 30 to 33 degrees Celsius, explaining the skin predilection. Treatment is with rifampicin plus clarithromycin or streptomycin.

Option by option

  • A. Mycolactone, a lipid toxin with cytotoxic and immunosuppressive activity (correct)

    Correct. Mycolactone explains the painless necrotic ulcer with undermined edges.

  • B. Cord factor causing granuloma formation

    Cord factor is associated with Mycobacterium tuberculosis virulence, not this toxin-mediated necrosis.

  • C. Exotoxin A inhibiting elongation factor 2

    Exotoxin A is produced by Pseudomonas aeruginosa.

  • D. Pore-forming leukocidin

    Leukocidin is produced by some Staphylococcus aureus strains.

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.

More Microbiology questions

Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is A, Mycolactone, a lipid toxin with cytotoxic and immunosuppressive activity. Buruli ulcer is caused by Mycobacterium ulcerans, which produces the polyketide toxin mycolactone, causing necrosis of skin and subcutaneous fat and local immunosuppression, so the ulcer is painless.

Why is "Cord factor causing granuloma formation" not the answer?

Cord factor is associated with Mycobacterium tuberculosis virulence, not this toxin-mediated necrosis.

Why is "Exotoxin A inhibiting elongation factor 2" not the answer?

Exotoxin A is produced by Pseudomonas aeruginosa.

Why is "Pore-forming leukocidin" not the answer?

Leukocidin is produced by some Staphylococcus aureus strains.

What concept does this question test?

It tests Bacteriology: Mycobacterium ulcerans in Microbiology. The organism grows best at 30 to 33 degrees Celsius, explaining the skin predilection. Treatment is with rifampicin plus clarithromycin or streptomycin.

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: Mycobacterium ulcerans?

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.