Culture media: 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 · Culture media

Sample item

Which medium is used to grow Corynebacterium diphtheriae?

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

The answer and the reasoning

C. Loeffler's serum slope

Loeffler's serum slope promotes rapid growth of C. diphtheriae and its characteristic metachromatic granules. Tellurite media such as Tinsdale are selective. MacConkey differentiates lactose fermenters, Lowenstein–Jensen grows mycobacteria and Thayer–Martin grows Neisseria.

Option by option

  • A. Thayer–Martin medium

    Thayer–Martin medium is selective for pathogenic Neisseria.

  • B. MacConkey agar

    MacConkey agar is selective for gram-negative bacilli and differentiates lactose fermenters.

  • C. Loeffler's serum slope (correct)

    Correct. It is the classical enrichment medium for diphtheria bacilli.

  • D. Lowenstein–Jensen medium

    Lowenstein–Jensen medium is for Mycobacterium tuberculosis.

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, Loeffler's serum slope. Loeffler's serum slope promotes rapid growth of C.

Why is "Thayer–Martin medium" not the answer?

Thayer–Martin medium is selective for pathogenic Neisseria.

Why is "MacConkey agar" not the answer?

MacConkey agar is selective for gram-negative bacilli and differentiates lactose fermenters.

Why is "Lowenstein–Jensen medium" not the answer?

Lowenstein–Jensen medium is for Mycobacterium tuberculosis.

What concept does this question test?

It tests Culture media in Microbiology. diphtheriae and its characteristic metachromatic granules. Tellurite media such as Tinsdale are selective. MacConkey differentiates lactose fermenters, Lowenstein–Jensen grows mycobacteria and Thayer–Martin grows Neisseria.

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 Culture media?

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.