Sterilisation: biological indicator for dry heat: 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 · Sterilisation: biological indicator for dry heat

Sample item

A laboratory sterilises glass syringes and heat-stable powders in a hot air oven at 160 degrees C for 2 hours. Which spore preparation is placed in the load as the biological indicator?

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

The answer and the reasoning

A. Bacillus atrophaeus spores

Dry heat sterilisation is monitored with spores of Bacillus atrophaeus (Bacillus subtilis var. niger), which are very resistant to dry heat. Each sterilisation method has its own indicator organism chosen for its resistance to that agent.

Option by option

  • A. Bacillus atrophaeus spores (correct)

    Correct. B. atrophaeus spores resist dry heat and are the standard indicator for hot air ovens and ethylene oxide.

  • B. Geobacillus stearothermophilus spores

    Geobacillus stearothermophilus spores are the indicator for moist heat in autoclaves.

  • C. Deinococcus radiodurans cells

    Deinococcus radiodurans is radiation-resistant but is not a spore-forming dry heat indicator.

  • D. Bacillus pumilus spores

    Bacillus pumilus spores are used to monitor ionising radiation sterilisation.

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 A, Bacillus atrophaeus spores. Dry heat sterilisation is monitored with spores of Bacillus atrophaeus (Bacillus subtilis var.

Why is "Geobacillus stearothermophilus spores" not the answer?

Geobacillus stearothermophilus spores are the indicator for moist heat in autoclaves.

Why is "Deinococcus radiodurans cells" not the answer?

Deinococcus radiodurans is radiation-resistant but is not a spore-forming dry heat indicator.

Why is "Bacillus pumilus spores" not the answer?

Bacillus pumilus spores are used to monitor ionising radiation sterilisation.

What concept does this question test?

It tests Sterilisation: biological indicator for dry heat in Microbiology. niger), which are very resistant to dry heat. Each sterilisation method has its own indicator organism chosen for its resistance to that agent.

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 Sterilisation: biological indicator for dry heat?

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.