by Bryan Brezoff, ID’s Section Leader, BS, SM RM(NRCM) & Jacob Lee, B&F Study Director, BS, RM(NRCM)
Most people are aware of the need to meet the USP<71> standard test of sterility, but they are quite often less aware of the included B&F requirement—B&F meaning Bacteriostasis and Fungistasis (also referred to as method suitability or sterility validation). Manufacturers need to be aware of this test to ensure their products meet the sterility validation requirements.
In simple terms, the B&F validation tests to see if the device itself has any inherent qualities that will inhibit the growth bacteria or fungi. The device is typically placed into a liquid media and inoculated with microorganisms (six samples are needed for this test to be conducted with six different known microorganisms). The product passes the test if organisms grow within the media indicating that the device itself does not inhibit or kill microorganisms. If no microorganisms grow then the B&F test fails, and this can invalidate a test of sterility.
This validation is a precautionary test that ensures there are no false-negatives in the test of sterility. If there is a failure of the B&F test then other test methods should be considered to ensure that microbial growth is possible. Products that are coated with or contain an antibiotic are usually the culprits. In these cases a neutralizer solution needs to be added that can remove or supress the inhibitory effects of any potential antimicrobial. Neutralizing these effects will ensure that microorganisms, if present, have the opportunity to grow and therefore will not affect the outcome of any test of sterility.
We recommend performing a yearly B&F on already validated product as a way to check that your process over that time has not changed in a way that would affect sterility results. A new B&F is required for any new product or any product that has undergone changes in the way that product is manufactured (new process, equipment, etc).