Biological indicators for monitoring an autoclave or unsaturated chemical vapor unit contain spores of?

The correct answer is that biological indicators for monitoring an autoclave or unsaturated chemical vapor unit contain spores of Geobacillus stearothermophilus. This organism is particularly suited for this purpose due to its spores' high resistance to heat and its ability to survive the sterilization process. The presence of these spores makes them an ideal indicator for assessing the efficacy of sterilization methods, as successful sterilization will result in the inactivation of these spores.

In the context of steam sterilization, Geobacillus stearothermophilus is commonly used because it is a thermophilic bacterium that can withstand higher temperatures than many other bacterial spores, making it a reliable test for autoclave performance. If the autoclave fails to reach the necessary sterilization conditions, these spores can survive and indicate a failure in the sterilization process.

The other bacteria mentioned in the options do not serve the same purpose in monitoring sterilization processes. Bacillus subtilis, while also a spore-forming organism, is typically used in different sterilization validations and does not have the same thermal resistance as Geobacillus stearothermophilus. Clostridium perfringens and Staphylococcus aureus are not suitable