Antimicrobial resistance: vancomycin-resistant enterococci: 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 · Antimicrobial resistance: vancomycin-resistant enterococci

Sample item

Enterococcus faecium from a dialysis patient's blood shows a vancomycin MIC above 256 mg/L and is also resistant to teicoplanin. Which gene and mechanism explain this phenotype?

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

The answer and the reasoning

C. vanA, with replacement of D-Ala-D-Ala by D-Ala-D-Lac in the peptidoglycan precursor

In vanA-type resistance, a ligase produces D-Ala-D-Lac instead of D-Ala-D-Ala, which lowers vancomycin binding about 1000-fold. It confers high-level resistance to both vancomycin and teicoplanin and is carried on a transposon, usually in Enterococcus faecium. Linezolid or daptomycin is used for treatment.

Option by option

  • A. mecA, with an altered penicillin-binding protein

    mecA gives methicillin resistance in staphylococci and does not affect vancomycin.

  • B. vanC, with D-Ala-D-Ser causing high-level resistance to both drugs

    vanC gives low-level intrinsic vancomycin resistance in species such as Enterococcus gallinarum, with teicoplanin remaining susceptible.

  • C. vanA, with replacement of D-Ala-D-Ala by D-Ala-D-Lac in the peptidoglycan precursor (correct)

    The vanA cluster alters the precursor terminus and causes resistance to both glycopeptides.

  • D. vanB, with D-Ala-D-Lac and preserved teicoplanin susceptibility

    vanB also uses D-Ala-D-Lac, but teicoplanin remains active, which does not match this isolate.

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, vanA, with replacement of D-Ala-D-Ala by D-Ala-D-Lac in the peptidoglycan precursor. In vanA-type resistance, a ligase produces D-Ala-D-Lac instead of D-Ala-D-Ala, which lowers vancomycin binding about 1000-fold.

Why is "mecA, with an altered penicillin-binding protein" not the answer?

mecA gives methicillin resistance in staphylococci and does not affect vancomycin.

Why is "vanC, with D-Ala-D-Ser causing high-level resistance to both drugs" not the answer?

vanC gives low-level intrinsic vancomycin resistance in species such as Enterococcus gallinarum, with teicoplanin remaining susceptible.

Why is "vanB, with D-Ala-D-Lac and preserved teicoplanin susceptibility" not the answer?

vanB also uses D-Ala-D-Lac, but teicoplanin remains active, which does not match this isolate.

What concept does this question test?

It tests Antimicrobial resistance: vancomycin-resistant enterococci in Microbiology. It confers high-level resistance to both vancomycin and teicoplanin and is carried on a transposon, usually in Enterococcus faecium. Linezolid or daptomycin is used for treatment.

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 Antimicrobial resistance: vancomycin-resistant enterococci?

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.