The CBIC Certified Infection Control Exam Study Guide (6th edition) clearly states that steam sterilization (moist heat sterilization) must be validated using biological indicators containing Geobacillus stearothermophilus spores. This organism is selected because its spores are highly resistant to moist heat, making them an ideal challenge organism for assessing the effectiveness of steam sterilization processes.

Biological indicators are used to confirm that sterilization conditions—such as temperature, pressure, and exposure time—are sufficient to achieve microbial inactivation. Geobacillus stearothermophilus thrives at high temperatures and demonstrates strong resistance to steam, so if these spores are destroyed, it provides high confidence that other less-resistant microorganisms, including bacteria, viruses, and fungi, have also been eliminated.

The other options are incorrect for steam sterilization validation. Staphylococcus aureus is a vegetative bacterium and is far less resistant than bacterial spores. Bacillus anthracis is not used as a biological indicator due to safety concerns and lack of standardization. Bacillus atrophaeus is used as the biological indicator for dry heat and ethylene oxide sterilization, not steam.

Understanding which biological indicators correspond to specific sterilization modalities is a high-yield topic on the CIC® exam and is essential for ensuring compliance with evidence-based sterilization and disinfection standards.

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