Which Bacillus species is commonly used as a biological indicator for autoclave validation?

Which Bacillus species is commonly used as a biological indicator for autoclave validation?

• A. Bacillus megaterium
• B. Bacillus cereus
• C. Bacillus stearothermophilus
• D. Bacillus subtilis

Answer: (C)

Biological indicators for autoclave validation use spores that are very resistant to moist heat. Bacillus stearothermophilus is the standard choice because its spores withstand steam much more than the other Bacillus species listed, providing a stringent test of the cycle. If this indicator is inactivated, you can be confident the autoclave achieved the necessary conditions throughout the load; if it grows, the cycle didn’t meet requirements. The other species have spores that are not as reliably heat-resistant for steam validation, so they’re not as appropriate for this purpose.

Biological indicators for autoclave validation use spores that are very resistant to moist heat. Bacillus stearothermophilus is the standard choice because its spores withstand steam much more than the other Bacillus species listed, providing a stringent test of the cycle. If this indicator is inactivated, you can be confident the autoclave achieved the necessary conditions throughout the load; if it grows, the cycle didn’t meet requirements. The other species have spores that are not as reliably heat-resistant for steam validation, so they’re not as appropriate for this purpose.