This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
Bacteria used to check the working efficiency of an autoclave is: 
Select and explain. 
A. Bacillus stearothermophilus, B. Bacillus subtilis, C. Campylobacter, D. Bacillus tardinicus
A: Bacillus stearothermophilus
Answer: A: Bacillus stearothermophilus 
Explanation: There are three indicators that may be used to detect the efficacy of the autoclave process: 

Physical: Pressure and temperature recording devices.
Chemical: Indicators that change color after being exposed to specific temperatures, such as temperature-sensitive tape. The color change upon exposure to the given temperature.
Biological: Bacillus stearothermophilus spores are used, due to its resistance to heat, for the testing that measures the biological performance of the autoclave process.