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