Mycology: dermatophyte identification: 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 · Mycology: dermatophyte identification

Sample item

A culture from a patient with tinea corporis grows a powdery colony with numerous round microconidia in grape-like clusters and spiral hyphae. Urease is positive and the in vitro hair perforation test is positive. Which species is most likely?

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

The answer and the reasoning

D. Trichophyton mentagrophytes

Trichophyton mentagrophytes forms clusters of round microconidia, spiral hyphae, a positive urease test and a positive hair perforation test. Trichophyton rubrum, in contrast, usually has a red reverse pigment, few microconidia and a negative hair perforation test. Microsporum species form spindle-shaped macroconidia, and Epidermophyton has club-shaped macroconidia.

Option by option

  • A. Epidermophyton floccosum

    Epidermophyton produces club-shaped macroconidia with no microconidia.

  • B. Trichophyton rubrum

    T. rubrum typically has red pigment and a negative hair perforation test.

  • C. Microsporum audouinii

    Microsporum species produce spindle-shaped macroconidia and do not infect nails.

  • D. Trichophyton mentagrophytes (correct)

    Grape-like microconidia with spiral hyphae and positive hair perforation identify T. mentagrophytes.

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, Trichophyton mentagrophytes. Trichophyton mentagrophytes forms clusters of round microconidia, spiral hyphae, a positive urease test and a positive hair perforation test.

Why is "Epidermophyton floccosum" not the answer?

Epidermophyton produces club-shaped macroconidia with no microconidia.

Why is "Trichophyton rubrum" not the answer?

T. rubrum typically has red pigment and a negative hair perforation test.

Why is "Microsporum audouinii" not the answer?

Microsporum species produce spindle-shaped macroconidia and do not infect nails.

What concept does this question test?

It tests Mycology: dermatophyte identification in Microbiology. Trichophyton rubrum, in contrast, usually has a red reverse pigment, few microconidia and a negative hair perforation test. Microsporum species form spindle-shaped macroconidia, and Epidermophyton has club-shaped macroconidia.

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 Mycology: dermatophyte identification?

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.