Clinical microbiology and hospital infection control: cefoxitin disc: 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 · Clinical microbiology and hospital infection control: cefoxitin disc

Sample item

A laboratory wants to detect methicillin resistance in a Staphylococcus aureus isolate using disc diffusion. Which disc is used as the preferred surrogate marker?

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

The answer and the reasoning

C. Cefoxitin

Cefoxitin is a better inducer of mecA expression than oxacillin, so cefoxitin disc diffusion reliably detects mecA-mediated methicillin resistance. Vancomycin susceptibility needs MIC methods, and penicillin and gentamicin do not indicate methicillin resistance.

Option by option

  • A. Gentamicin

    Gentamicin resistance is unrelated to mecA.

  • B. Penicillin

    Penicillin resistance is mediated by penicillinase and does not define MRSA.

  • C. Cefoxitin (correct)

    Correct. Cefoxitin disc is the surrogate for mecA.

  • D. Vancomycin

    Vancomycin is tested by MIC because disc diffusion is unreliable.

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 C, Cefoxitin. Cefoxitin is a better inducer of mecA expression than oxacillin, so cefoxitin disc diffusion reliably detects mecA-mediated methicillin resistance.

Why is "Gentamicin" not the answer?

Gentamicin resistance is unrelated to mecA.

Why is "Penicillin" not the answer?

Penicillin resistance is mediated by penicillinase and does not define MRSA.

Why is "Vancomycin" not the answer?

Vancomycin is tested by MIC because disc diffusion is unreliable.

What concept does this question test?

It tests Clinical microbiology and hospital infection control: cefoxitin disc in Microbiology. Vancomycin susceptibility needs MIC methods, and penicillin and gentamicin do not indicate methicillin resistance.

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 Clinical microbiology and hospital infection control: cefoxitin disc?

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.