Why do we use BI’s (Biological Indicators?)

Various methods are used to monitor the efficacy of a sterilization process. This would include physical monitoring, chemical indicators (CI) and the use of biological indicators (BI).

In CSSD we should read the sterilization process print out in order to verify that the parameters of the sterilization cycle were met. Chemical indicators will verify that one or more conditions needed for sterilization (for example time, steam and temperature) have been achieved within a specific instrument set.

Biological indicators however verify that the conditions at a point in the load where the BI was placed were adequate or sufficient to kill the population of micro-organisms contained in the BI. Therefore BI’s demonstrate the lethality of the sterilization process.

Self-contained BI consists of spores on a carrier and incubation media (food source for the spores).  BI’s provide the only direct way to measure how lethal a sterilization process was. BI’s are placed in a fully loaded sterilizer and processed with the load. After sterilization the BI is crushed in order to mix the spores and the incubation media and incubated at the temperature and for the time period recommended by the manufacturer. If the spores were killed in the sterilization process the media will not change colour, and the load can be passed.

AAMI 2010. Comprehensive guide to steam sterilization and sterility assurance in health care facilities. ST79.

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