For monitoring the efficacy of an autoclave (steam sterilization), which biological indicator is used, and what is its specific endpoint test?
- A Bacillus atrophaeus spores — used for dry heat sterilization monitoring, not autoclaving
- B Geobacillus stearothermophilus spores — positive (yellow/turbid) broth after incubation indicates sterilization failure ✓
- C Clostridium sporogenes spores — anaerobic indicator that changes colour in aerobic conditions
- D Aspergillus niger spores — fungal indicator most resistant to steam
Explanation
The biological indicator for autoclave (moist heat/steam sterilization) is Geobacillus stearothermophilus (formerly Bacillus stearothermophilus) spores; the standard run is 121°C for 15 minutes (gravity cycle) or 132°C for 4 minutes (pre-vacuum). After autoclaving, the indicator strip is incubated at 56°C for 24–48 hours; if the pH indicator in the broth remains purple (no acid production, no growth), sterilization was successful. Yellow/turbid broth indicates surviving spores and sterilization failure. Bacillus atrophaeus is used for ethylene oxide and dry heat monitoring.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.