Biological Indicators(BI) are the standard preparation containing spores of selected micro-organisms having known stable high resistance to one or more sterilization process. Use of BI has been recommended by British Pharmacopeia 1988 and by National Drug Control Authorities to monitor the efficacy of the radiation sterilization process as part of process control though the products are released on the basis of chemical dosimetric measurements.
The use of Biological Indicators (BI’s) for validation and process monitoring, or the use of sterility testing for release of product, are not recommended practice for radiation sterilization.
There are many organisms that have been found to have a higher resistance to radiation than the typical biological indicator of spores of Bacillus pumilus. These organisms can naturally have a higher resistance to radiation, or when irradiated under certain circumstances (for example, anaerobic conditions, encapsulation) can become more resistant to radiation. A listing of the resistances of many organism can be found in Block (1983). In addition, industrial experience has indicated that the radiation resistance of products with naturally occurring bioburden exceeds the resistance of the spores of Bacillus pumilus in many instances. Therefore, unless the resistance of the product is proven to be less than the resistance of the BI’s, the use of BI’s is not recommended for validation or process monitoring.