What is the target organism used in biological indicators for steam sterilization?

The target organism used in biological indicators for steam sterilization is Bacillus stearothermophilus. This bacterium is used because its spores exhibit a high resistance to saturated steam sterilization. This means they require higher temperatures and longer exposure times to be killed compared to most other microorganisms. If Bacillus stearothermophilus spores are inactivated during a steam sterilization cycle, it is a reliable indication that the cycle was effective in killing other, less resistant microorganisms that may be present on medical devices or other items being sterilized. Therefore, the use of Bacillus stearothermophilus spores provides a safety margin, ensuring that the sterilization process is capable of achieving a high level of sterility assurance.