A biological sterilization indicator used to test autoclave efficiency is which organism?

A biological sterilization indicator used to test autoclave efficiency is which organism?

• A. Virus
• B. Bacillus thuringiensis
• C. Clostridium botulinum
• D. Bacillus stearothermophilus

Answer: (D)

Biological indicators for autoclave validation rely on an organism that is unusually hard to kill by the sterilization method, so you can trust the cycle’s effectiveness if it kills it. For steam autoclaves, spores of Bacillus stearothermophilus are the standard choice because they form heat-resistant spores that withstand moist heat at high temperatures. If the cycle is properly run, these spores are killed; after processing, the indicator is incubated to check for any growth—no growth means the autoclave achieved the needed sterilization. Other options aren’t suitable: a virus doesn’t provide a reliable, safe benchmark for this purpose; Bacillus thuringiensis is used for pest control, not as a resistance standard; and Clostridium botulinum is dangerous and not used as a sterilization indicator.