Bacteria used to check the working efficiency of an autoclave is:
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.
Bacillus stearothermophilus
Bacillus subtilis
Campylobacter
Bacillus tardinicus
Bacillus stearothermophilus