What is the difference between a Biological Indicator (BI) and a Chemical Indicator (CI) in steam sterilization?

Biological Indicators (BIs) and Chemical Indicators (CIs) are both used to monitor steam sterilization processes, but they differ significantly in what they measure and how they indicate sterilization effectiveness. A Chemical Indicator (CI) is a device that uses a chemical reaction to assess the presence of specific physical conditions, such as temperature, time, and the presence of steam. They provide a visual indication that certain sterilization parameters have been met, typically through a color change. However, CIs do not directly measure microbial inactivation. A Biological Indicator (BI), on the other hand, contains a known population of highly resistant microorganisms, typically Bacillus stearothermophilus spores for steam sterilization. After the sterilization cycle, the BI is incubated to determine if any of the spores survived the process. If no spores survive, it indicates that the sterilization process was effective in killing microorganisms. BIs provide a direct measure of sterilization effectiveness by assessing microbial inactivation, while CIs only indicate that certain physical parameters were met. CIs are used for routine monitoring of each sterilization cycle, while BIs are used for periodic validation and to confirm the effectiveness of the sterilization process in killing microorganisms.