Bacteriology: spontaneous gas gangrene: 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: spontaneous gas gangrene

Sample item

A 66-year-old man with no history of trauma has sudden severe thigh pain, crepitus and rapidly spreading myonecrosis. Blood culture grows an aerotolerant Gram-positive spore-forming bacillus. Which organism and underlying condition should be sought?

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

The answer and the reasoning

A. Clostridium septicum; occult colonic carcinoma

Spontaneous, non-traumatic gas gangrene is typically caused by Clostridium septicum, which is more aerotolerant than other clostridia and enters from a bowel lesion. Colorectal cancer or neutropenia should be looked for in every such patient.

Option by option

  • A. Clostridium septicum; occult colonic carcinoma (correct)

    Correct. C. septicum causes spontaneous gas gangrene and is linked with colonic malignancy.

  • B. Clostridium tetani; deep puncture wound

    C. tetani produces tetanospasmin and spastic paralysis, not myonecrosis.

  • C. Clostridium sordellii; recent medical abortion

    C. sordellii is linked with toxic shock after childbirth or abortion, with little local pus.

  • D. Clostridium perfringens; crush injury to the limb

    C. perfringens usually causes traumatic gas gangrene after contaminated or crush wounds.

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 A, Clostridium septicum; occult colonic carcinoma. Spontaneous, non-traumatic gas gangrene is typically caused by Clostridium septicum, which is more aerotolerant than other clostridia and enters from a bowel lesion.

Why is "Clostridium tetani; deep puncture wound" not the answer?

C. tetani produces tetanospasmin and spastic paralysis, not myonecrosis.

Why is "Clostridium sordellii; recent medical abortion" not the answer?

C. sordellii is linked with toxic shock after childbirth or abortion, with little local pus.

Why is "Clostridium perfringens; crush injury to the limb" not the answer?

C. perfringens usually causes traumatic gas gangrene after contaminated or crush wounds.

What concept does this question test?

It tests Bacteriology: spontaneous gas gangrene in Microbiology. Colorectal cancer or neutropenia should be looked for in every such patient.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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: spontaneous gas gangrene?

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.