Parasitology: chloroquine resistance mechanism: 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 · Parasitology: chloroquine resistance mechanism

Sample item

Chloroquine-resistant Plasmodium falciparum accumulates much less drug in its digestive vacuole than sensitive strains. Which change mainly explains this?

AIncreased dihydrofolate reductase production by the parasiteBMutant PfCRT transporter that pumps the drug outCFaster haemozoin crystal growth that traps the drugDAltered cytochrome b drug-binding site in the mitochondrion

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

The answer and the reasoning

B. Mutant PfCRT transporter that pumps the drug out

Chloroquine concentrates in the parasite food vacuole and blocks haem polymerisation. Resistant parasites carry mutant PfCRT, which effluxes the drug from the vacuole so it no longer reaches toxic concentrations.

Option by option

A. Increased dihydrofolate reductase production by the parasite
Extra dihydrofolate reductase relates to antifolate resistance, not chloroquine.
B. Mutant PfCRT transporter that pumps the drug out (correct)
Correct. Mutant PfCRT-mediated efflux lowers vacuolar chloroquine.
C. Faster haemozoin crystal growth that traps the drug
Enhanced haemozoin formation would remove toxic haem, but the main resistance mechanism is drug efflux.
D. Altered cytochrome b drug-binding site in the mitochondrion
Cytochrome b changes relate to atovaquone resistance.

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.

Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is B, Mutant PfCRT transporter that pumps the drug out. Chloroquine concentrates in the parasite food vacuole and blocks haem polymerisation.

Why is "Increased dihydrofolate reductase production by the parasite" not the answer?

Extra dihydrofolate reductase relates to antifolate resistance, not chloroquine.

Why is "Faster haemozoin crystal growth that traps the drug" not the answer?

Enhanced haemozoin formation would remove toxic haem, but the main resistance mechanism is drug efflux.

Why is "Altered cytochrome b drug-binding site in the mitochondrion" not the answer?

Cytochrome b changes relate to atovaquone resistance.

What concept does this question test?

It tests Parasitology: chloroquine resistance mechanism in Microbiology. Resistant parasites carry mutant PfCRT, which effluxes the drug from the vacuole so it no longer reaches toxic concentrations.

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 Parasitology: chloroquine resistance mechanism?

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.