Medical Device Reprocessing Association of Ontario (MDRAO) Practice Exam

Which biological indicator is used for ETO sterilization?

1. Geobacillus stearothermophilus

2. Bacillus atropheus

3. Clostridium tetani

4. Bacillus subtilis

The correct answer is: Bacillus atropheus

The biological indicator used for Ethylene Oxide (ETO) sterilization is Bacillus atropheus. This organism is particularly chosen because it is a spore-forming bacterium that is more resistant to ETO exposure than many pathogenic microorganisms. The use of spores allows for a reliable means of determining whether the sterilization process was effective. After the ETO sterilization cycle, the biological indicator is incubated to check for growth. The absence of growth confirms that the ETO process was sufficient to kill the spores, thus validating the sterilization. In contrast, while Geobacillus stearothermophilus is commonly used as a biological indicator for steam sterilization processes, and Bacillus subtilis may also be used for testing various sterilization methods, neither of these is suitable for ETO. Clostridium tetani, although a spore-forming bacterium, is not used in this context due to its pathogenic nature and the specific properties required for ETO biological indicators. Thus, Bacillus atropheus remains the standard for ETO sterilization validation.