USP Chapter <71> Sterility Test states that prior to conducting a sterility test on a sterilized product, its level of bacteriostatic and fungistatic activity should be determined, that is the degree of inhibition to microbial growth that may be caused by substances in or on the product. Bacteriostasis/Fungistasis (B/F) should be evaluated following the first sterilization or aseptic manufacturing of all new products prior to sterility testing or when significant product or manufacturing changes occur. The testing is designed to evaluate B/F activity and to validate the chosen sterility test method.
Based on the media type to be used in the Sterility Test, low numbers (<100 CFU) of selected bacteria and fungi challenge organisms as specified in the USP, are added to containers with the test article present to demonstrate that they can be detected in the presence of the test article.
For samples sterility tested by the membrane filtration method, test samples are filtered through a 0.45 µm membrane filter and rinsed with a sterile diluent. The rinse is then inoculated with the chosen organisms and the membrane filters are aseptically added to the appropriate media.
For samples sterility tested by the direct transfer method, test samples are aseptically transferred into a volume of media sufficient to cover the sample, the containers are then inoculated with the chosen organisms. The volume of media utilized in the B/F testing must be the same amount utilized for routine sterility testing procedures.
The B/F validation will demonstrate reproducibility of the method to reliably recover representative microorganisms. If growth is inhibited, a documented investigation must be initiated and modifications such as increased dilution, additional membrane filter washes or addition of inactivating agents should be implemented to the test method to optimize recovery.
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