General microbiology: sterilisation: 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 · General microbiology: sterilisation

Sample item

A hospital needs to sterilise a heat-labile, moisture-sensitive fibreoptic endoscope accessory between cases without leaving toxic residues. Which method is most suitable?

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

The answer and the reasoning

B. Hydrogen peroxide gas plasma at low temperature

Low-temperature hydrogen peroxide gas plasma sterilises heat- and moisture-sensitive instruments in under an hour and leaves only water and oxygen as by-products. It cannot be used for liquids, powders or cellulose materials. Steam and dry heat damage delicate devices, and boiling does not kill spores.

Option by option

  • A. Boiling in water for 20 minutes

    Boiling is only disinfection; it does not destroy bacterial spores.

  • B. Hydrogen peroxide gas plasma at low temperature (correct)

    Correct. The plasma process works near 50 degrees Celsius and leaves no toxic residue.

  • C. Hot air oven at 160 degrees Celsius for 2 hours

    Dry heat at 160 degrees Celsius would melt or distort the device components.

  • D. Autoclaving at 121 degrees Celsius for 15 minutes

    Moist heat at 121 degrees Celsius would damage the optics, adhesives and plastics.

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, Hydrogen peroxide gas plasma at low temperature. Low-temperature hydrogen peroxide gas plasma sterilises heat- and moisture-sensitive instruments in under an hour and leaves only water and oxygen as by-products.

Why is "Boiling in water for 20 minutes" not the answer?

Boiling is only disinfection; it does not destroy bacterial spores.

Why is "Hot air oven at 160 degrees Celsius for 2 hours" not the answer?

Dry heat at 160 degrees Celsius would melt or distort the device components.

Why is "Autoclaving at 121 degrees Celsius for 15 minutes" not the answer?

Moist heat at 121 degrees Celsius would damage the optics, adhesives and plastics.

What concept does this question test?

It tests General microbiology: sterilisation in Microbiology. It cannot be used for liquids, powders or cellulose materials. Steam and dry heat damage delicate devices, and boiling does not kill spores.

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 General microbiology: sterilisation?

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.