This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: general microbiology, Subject name: Microbiology
The indicator used in the autoclave is? 
Select and explain. 
A. Clostridium tetani, B. Bacillus stereothermophilus, C. Bacillus pumilis, D. Bacillus subtilis Var Niger
B: Bacillus stereothermophilus
Answer: B: Bacillus stereothermophilus 
Explanation: Sterilization control: for determining the efficacy of moist heat sterilization, spores of Bacillus stearothermophilus are used as the test organism. This is a thermophilic organism with an optimum growth temperature of 55-60oC and its spores require exposure of 12 minutes at 121oC to be killed REF:Ananthanarayan & Panicker's Textbook of Microbiology 8th edition pg no:34