Which bacterium is commonly used as an indicator for sterilization in an autoclave?

Bacillus sternothermophilus is commonly utilized as an indicator organism for sterilization processes in autoclaves due to its high resistance to heat and other sterilization methods. This bacterium is capable of withstanding extreme temperatures and conditions that are typically used during autoclaving, making it an excellent test organism to validate the effectiveness of sterilization.

When autoclaving, the objective is to destroy all microorganisms, including spores, which are particularly resistant forms of bacteria. Bacillus sternothermophilus spores serve as a benchmark; if these spores are killed during the autoclave cycle, it indicates that the conditions were sufficient to eliminate a broad spectrum of bacteria. The use of a known concentration, such as 10^6 spores, provides a reliable standard for ensuring the thoroughness of the sterilization process.

In contrast, the other bacteria listed do not meet the criteria as effectively as Bacillus sternothermophilus for use in sterilization indicators. While Bacillus anthracis is a pathogenic organism and not typically used for this purpose, Bacillus cereus and Bacillus subtilis have certain properties that are less optimal for indicating autoclave efficacy compared to Bacillus sternothermophilus.