Bacteriology: erythrasma: 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: erythrasma

Sample item

A diabetic man has well-demarcated, dry, red-brown patches in both groins and axillae. Under Wood's lamp they fluoresce coral red, and a KOH mount shows no fungal elements. Which organism is responsible?

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

The answer and the reasoning

A. Corynebacterium minutissimum

Erythrasma is a superficial skin-fold infection by Corynebacterium minutissimum, whose porphyrins give coral-red fluorescence under Wood's lamp. It responds to erythromycin and topical antibacterials.

Option by option

  • A. Corynebacterium minutissimum (correct)

    Correct. Coral-red fluorescence with negative KOH identifies this diphtheroid.

  • B. Microsporum canis

    Microsporum canis causes tinea capitis with green fluorescence of hair.

  • C. Trichophyton rubrum

    Trichophyton rubrum causes tinea cruris with a positive KOH mount and no coral-red fluorescence.

  • D. Malassezia furfur

    Malassezia causes pityriasis versicolor, with a positive KOH mount showing yeast and short hyphae.

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, Corynebacterium minutissimum. Erythrasma is a superficial skin-fold infection by Corynebacterium minutissimum, whose porphyrins give coral-red fluorescence under Wood's lamp.

Why is "Microsporum canis" not the answer?

Microsporum canis causes tinea capitis with green fluorescence of hair.

Why is "Trichophyton rubrum" not the answer?

Trichophyton rubrum causes tinea cruris with a positive KOH mount and no coral-red fluorescence.

Why is "Malassezia furfur" not the answer?

Malassezia causes pityriasis versicolor, with a positive KOH mount showing yeast and short hyphae.

What concept does this question test?

It tests Bacteriology: erythrasma in Microbiology. It responds to erythromycin and topical antibacterials.

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: erythrasma?

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.