Immunology: Ascoli thermoprecipitation: 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 · Immunology: Ascoli thermoprecipitation

Sample item

A suspect dried animal hide is boiled in saline and the clear extract is layered over a specific anthrax antiserum in a narrow tube. A white ring appears at the interface within minutes. Which test is this?

AAscoli thermoprecipitin testBElek gel testCNagler reactionDSchick test

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

The answer and the reasoning

A. Ascoli thermoprecipitin test

The Ascoli test is a ring test in which heat-stable anthrax antigen in extracts of hides, tissues or wool reacts with antiserum, producing a ring at the junction. It is useful when the specimen is putrefied or heavily contaminated, and live bacilli can no longer be cultured. The Elek test checks toxigenicity of diphtheria bacilli.

Option by option

A. Ascoli thermoprecipitin test (correct)
Correct. Heat-stable antigen extracted from the hide forms a ring with antiserum.
B. Elek gel test
The Elek gel precipitation test detects toxin production by Corynebacterium diphtheriae in agar.
C. Nagler reaction
The Nagler reaction detects lecithinase of Clostridium perfringens on egg yolk agar.
D. Schick test
The Schick test is an intradermal toxin test for susceptibility to diphtheria.

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 A, Ascoli thermoprecipitin test. The Ascoli test is a ring test in which heat-stable anthrax antigen in extracts of hides, tissues or wool reacts with antiserum, producing a ring at the junction.

Why is "Elek gel test" not the answer?

The Elek gel precipitation test detects toxin production by Corynebacterium diphtheriae in agar.

Why is "Nagler reaction" not the answer?

The Nagler reaction detects lecithinase of Clostridium perfringens on egg yolk agar.

Why is "Schick test" not the answer?

The Schick test is an intradermal toxin test for susceptibility to diphtheria.

What concept does this question test?

It tests Immunology: Ascoli thermoprecipitation in Microbiology. It is useful when the specimen is putrefied or heavily contaminated, and live bacilli can no longer be cultured. The Elek test checks toxigenicity of diphtheria bacilli.

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 Immunology: Ascoli thermoprecipitation?

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.