Microbiology Bacillus used to test efficacy of Sterilisation by Autoclave is? A Bacillus subtilis. B Bacillus pumilis. C Bacillus stearothermophilus D Coxiella burnetti. 💡 Explanation Bacillus used to test efficacy of Sterilisation by Autoclave is? ✓ Correct Answer: C. Bacillus stearothermophilus