Bacteriology: Erysipelothrix rhusiopathiae: 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: Erysipelothrix rhusiopathiae

Sample item

A fishmonger has a well-demarcated violaceous, painful swelling of the finger after a fish bone puncture, with little suppuration and no fever. Culture grows a thin Gram-positive bacillus that is catalase negative and produces H2S in triple sugar iron agar. Which organism is it?

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

The answer and the reasoning

D. Erysipelothrix rhusiopathiae

Erysipelothrix rhusiopathiae causes erysipeloid, a localised cellulitis of the hand in people who handle fish, meat or poultry. It is a catalase-negative Gram-positive bacillus and one of the few that produce H2S, and penicillin is effective.

Option by option

  • A. Listeria monocytogenes

    Listeria is catalase positive, shows tumbling motility and does not cause erysipeloid.

  • B. Streptococcus pyogenes

    S. pyogenes is a Gram-positive coccus and not a bacillus.

  • C. Mycobacterium marinum

    M. marinum is acid-fast and produces slowly progressing nodules after aquarium exposure.

  • D. Erysipelothrix rhusiopathiae (correct)

    Correct. A catalase-negative H2S-producing Gram-positive bacillus after handling fish is Erysipelothrix.

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, Erysipelothrix rhusiopathiae. Erysipelothrix rhusiopathiae causes erysipeloid, a localised cellulitis of the hand in people who handle fish, meat or poultry.

Why is "Listeria monocytogenes" not the answer?

Listeria is catalase positive, shows tumbling motility and does not cause erysipeloid.

Why is "Streptococcus pyogenes" not the answer?

S. pyogenes is a Gram-positive coccus and not a bacillus.

Why is "Mycobacterium marinum" not the answer?

M. marinum is acid-fast and produces slowly progressing nodules after aquarium exposure.

What concept does this question test?

It tests Bacteriology: Erysipelothrix rhusiopathiae in Microbiology. It is a catalase-negative Gram-positive bacillus and one of the few that produce H2S, and penicillin is effective.

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: Erysipelothrix rhusiopathiae?

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.