Laboratory diagnosis: MALDI-TOF: 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 · Laboratory diagnosis: MALDI-TOF

Sample item

A laboratory identifies bacterial colonies within minutes using MALDI-TOF mass spectrometry. What does the instrument actually measure?

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

The answer and the reasoning

D. Mass-to-charge spectra of ionised proteins, mostly ribosomal, compared with a reference database

A colony is mixed with a matrix and ionised with a laser. The time of flight of the ions gives a protein fingerprint, chiefly of ribosomal proteins, that is matched against a library. It is fast and cheap per isolate, but routine use does not detect resistance mechanisms.

Option by option

  • A. The pattern of carbon source utilisation

    Carbon source utilisation is the basis of biochemical panel systems.

  • B. Agglutination of colonies with specific antisera

    Agglutination with antisera is a serological method and is not used in MALDI-TOF.

  • C. The sequence of the 16S rRNA gene amplified by PCR

    16S sequencing is a molecular method that takes hours, not a mass spectrometric one.

  • D. Mass-to-charge spectra of ionised proteins, mostly ribosomal, compared with a reference database (correct)

    Correct. The protein spectrum is matched to a reference database.

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 D, Mass-to-charge spectra of ionised proteins, mostly ribosomal, compared with a reference database. A colony is mixed with a matrix and ionised with a laser.

Why is "The pattern of carbon source utilisation" not the answer?

Carbon source utilisation is the basis of biochemical panel systems.

Why is "Agglutination of colonies with specific antisera" not the answer?

Agglutination with antisera is a serological method and is not used in MALDI-TOF.

Why is "The sequence of the 16S rRNA gene amplified by PCR" not the answer?

16S sequencing is a molecular method that takes hours, not a mass spectrometric one.

What concept does this question test?

It tests Laboratory diagnosis: MALDI-TOF in Microbiology. The time of flight of the ions gives a protein fingerprint, chiefly of ribosomal proteins, that is matched against a library. It is fast and cheap per isolate, but routine use does not detect resistance mechanisms.

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 Laboratory diagnosis: MALDI-TOF?

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.