Autoclave sterilization fails in a central sterile services unit. Biological indicators (Geobacillus stearothermophilus spore strips) placed inside the load show growth after incubation. Which parameter most likely failed?
- A Insufficient ethylene oxide exposure time
- B The autoclave UV lamp failed, reducing bactericidal activity
- C pH of steam condensate was above 7.0, neutralising sterilisation
- D Temperature did not reach 121°C, or exposure time was less than 15 minutes, or steam failed to penetrate the load — most commonly air pockets preventing steam contact ✓
Explanation
Geobacillus stearothermophilus spores are the biological indicator for moist heat (autoclave) sterilisation because they are among the most heat-resistant organisms, destroyed only at 121°C for 15 minutes (gravity displacement) or 134°C for 3 minutes (pre-vacuum). If spore strips show growth, it indicates the load was not adequately sterilised, most commonly due to: failure to reach 121°C, insufficient time, or — very commonly — air pockets preventing steam from contacting all surfaces (indicating a faulty air removal cycle or overloaded autoclave). Ethylene oxide is a cold sterilant, unrelated to autoclaving. Autoclaves do not use UV lamps. pH of condensate is irrelevant to steam sterilisation efficacy.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.