Which microorganism is used in biological indicators?

Biological indicators commonly use the microorganism Geobacillus stearothermophilus. This bacterium is highly resistant to heat and serves as a reliable test organism for validating sterilization processes, particularly in steam sterilization. Its spores are used to confirm that sterilization conditions have been effectively met. When subjected to proper sterilization, the spores should be killed, indicating the process's efficacy.