Parasitology: Entamoeba histolytica 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 · Parasitology: Entamoeba histolytica identification

Sample item

An asymptomatic food handler has stool microscopy showing cysts with four nuclei and chromatoidal bars, consistent with the Entamoeba histolytica complex. Which investigation best confirms whether the pathogenic species is present?

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

The answer and the reasoning

B. Stool antigen detection or PCR specific for E. histolytica

E. histolytica, E. dispar and E. moshkovskii have morphologically identical cysts and trophozoites, and only E. histolytica is pathogenic. Species-specific stool antigen tests or PCR distinguish them. Nuclear count and size cannot separate them, and serology in an endemic area may reflect past infection.

Option by option

  • A. Counting nuclei in the cysts after iodine staining

    Four nuclei are seen in all three species and so cannot separate them.

  • B. Stool antigen detection or PCR specific for E. histolytica (correct)

    Species-specific antigen or DNA detection separates the pathogen from look-alikes.

  • C. Measuring cyst diameter with a calibrated eyepiece

    Cyst size overlaps between these species and does not give a reliable answer.

  • D. Serum amoebic antibody titre

    Serum antibodies may reflect past exposure in endemic areas and are not a test of intestinal carriage.

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 B, Stool antigen detection or PCR specific for E. histolytica. E.

Why is "Counting nuclei in the cysts after iodine staining" not the answer?

Four nuclei are seen in all three species and so cannot separate them.

Why is "Measuring cyst diameter with a calibrated eyepiece" not the answer?

Cyst size overlaps between these species and does not give a reliable answer.

Why is "Serum amoebic antibody titre" not the answer?

Serum antibodies may reflect past exposure in endemic areas and are not a test of intestinal carriage.

What concept does this question test?

It tests Parasitology: Entamoeba histolytica identification in Microbiology. histolytica, E. dispar and E. moshkovskii have morphologically identical cysts and trophozoites, and only E. histolytica is pathogenic. Species-specific stool antigen tests or PCR distinguish them. Nuclear count and size cannot separate them, and serology in an endemic area may reflect past infection.

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: Entamoeba histolytica 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.