Why are highly resistant bacterial spores used in biological indicators?

Highly resistant bacterial spores are used in biological indicators primarily because they withstand harsh conditions. These spores are notably resilient to extreme temperatures, desiccation, and various chemicals, which makes them an ideal choice for testing the effectiveness of sterilization processes. When subjected to sterilization methods such as steam under pressure or ethylene oxide gas, the survival or death of these spores allows practitioners to evaluate whether the sterilization conditions were sufficient to eliminate all microbial threats.

The robustness of these spores, such as those from the genera Bacillus or Clostridium, means that if they survive a sterilization cycle, it indicates a potential failure in the sterilization process, thereby serving as a reliable indicator of sterility. Their ability to endure challenging environments is a critical factor that underlines their role in ensuring that sterilization methods are effective.