Bacteriology: ecthyma gangrenosum: 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: ecthyma gangrenosum

Sample item

A neutropenic patient on chemotherapy develops painless dark necrotic skin lesions with a surrounding erythematous rim. Blood cultures grow an oxidase-positive Gram-negative bacillus. What is the likely organism?

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

The answer and the reasoning

D. Pseudomonas aeruginosa

Ecthyma gangrenosum is a vasculitic skin lesion from Pseudomonas bacteraemia in neutropenic hosts. E. coli is oxidase negative, group A streptococcus is a Gram-positive coccus, and Acinetobacter is oxidase negative.

Option by option

  • A. Acinetobacter baumannii

    Acinetobacter is oxidase negative.

  • B. Streptococcus pyogenes

    S. pyogenes is a Gram-positive coccus.

  • C. Escherichia coli

    E. coli is oxidase negative and does not typically cause this lesion.

  • D. Pseudomonas aeruginosa (correct)

    Correct. Ecthyma gangrenosum with an oxidase-positive bacillus points to Pseudomonas.

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 D, Pseudomonas aeruginosa. Ecthyma gangrenosum is a vasculitic skin lesion from Pseudomonas bacteraemia in neutropenic hosts.

Why is "Acinetobacter baumannii" not the answer?

Acinetobacter is oxidase negative.

Why is "Streptococcus pyogenes" not the answer?

S. pyogenes is a Gram-positive coccus.

Why is "Escherichia coli" not the answer?

E. coli is oxidase negative and does not typically cause this lesion.

What concept does this question test?

It tests Bacteriology: ecthyma gangrenosum in Microbiology. E. coli is oxidase negative, group A streptococcus is a Gram-positive coccus, and Acinetobacter is oxidase negative.

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: ecthyma gangrenosum?

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.