Certified Nurses Operating Room (CNOR) Practice Exam

Which organism is used as a biological indicator for sterilization effectiveness?

1. Escherichia coli

2. Geobacillus Stearothermophilus

3. Staphylococcus epidermidis

4. Bacillus cereus

The correct answer is: Geobacillus Stearothermophilus

Geobacillus stearothermophilus is the organism used as a biological indicator for sterilization effectiveness, particularly for steam and ethylene oxide sterilization processes. This bacterium forms heat-resistant spores, which makes it an ideal candidate for testing sterilization methods. Once subjected to sterilization, if the spores of Geobacillus stearothermophilus are killed, it indicates that the sterilization process was successful and effective at the temperatures and conditions required. This organism is specifically chosen due to its resilience and the fact that its spores survive normal environmental conditions. If these spores can be cultured and demonstrate growth after a sterilization cycle, it signifies that the sterilization may not have been effective. Therefore, Geobacillus stearothermophilus serves as a reliable measure of how well the sterilization process is working, ensuring patient safety in medical and surgical settings.