Autoclave Biological Indicators — MFDS Part 1 MCQ
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Correct answer: C — Spores of Geobacillus stearothermophilus
The correct answer is C. Geobacillus stearothermophilus spores are the specified biological challenge for steam sterilisation because of their resistance to moist heat. Biological indicators assess whether test microorganisms survive the process, but UK guidance states that they should not be used for routine monitoring of steam sterilisers; exceptional use should follow advice from a microbiologist with decontamination expertise. Routine assurance instead relies on validated cycle parameters, automatic control tests and the applicable steam-penetration tests. Bacillus atrophaeus is the most plausible distractor because its spores are used principally to challenge dry-heat and certain chemical processes, not wet-heat steam sterilisation. The other listed spore-forming organisms are not the specified reference biological indicators for this purpose.
Reference: NHS England, Health Technical Memorandum 01-01: Management and decontamination of surgical instruments, Part C: Steam sterilization, sections 2.100–2.103, 2016. https://www.england.nhs.uk/wp-content/uploads/2021/05/HTM0101PartC.pdf