Sterility Assurance Testing

Sterility Testing – Bacteriostasis – Fungistasis – Bioburden Testing

Keeping medical devices safe requires effective sterilization procedures. Sterilization of medical devices and ensuring that biological products are not contaminated with harmful agents requires stringent testing procedures to isolate and identify any contaminants if they exist. The FDA has established some of the requirements for an acceptable sterility assurance program. A sterile material is by definition free from viable organisms. There are two commonly used types of sterility methods:

Direct inoculation of final product into two different types of media followed by incubation at two different temperatures for 14 days. Turbidity in the media would be indicative of the presence of a contaminant and that contaminant must be identified. If the test shows no turbidity in either medium, it needs to be confirmed by bacteriostasis/ fungistasis testing. A negative control is also included in the assay to ensure the validity of the test.

Membrane filtration of the product through a pre-rinsed sterile size exclusion filter capable of retaining bacteria and fungi followed by dividing the filter into two parts and inoculating each one of them into a different medium. The inoculated media is monitored over a 14 day period for turbidity. If turbidity develops, the organism must be isolated and identified. Test articles that are sterile must be tested for bacteriostasis/fungistasis. A negative control is also included in the assay to ensure the validity of the test.

Membrane filtration of the product through a pre-rinsed sterile size exclusion filter capable of retaining bacteria and fungi followed by dividing the filter into two parts and inoculating each one of them into a different medium. The inoculated media is monitored over a 14 day period for turbidity. If turbidity develops, the organism must be isolated and identified. Test articles that are sterile must be tested for bacteriostasis/fungistasis. A negative control is also included in the assay to ensure the validity of the test.

The United States Pharmacopeia and 21 CFR 610.12 recommend using two media for both the direct inoculation and membrane filtration methods. In both cases, the test article or membrane is incubated for 14 days in the two different test media at two different temperatures.

Sterility Assurance & Bacteriostasis/Fungistasis Testing

In order to prevent the occurrence of false negative results in Sterility tests due to the presence of inhibitors in the test article that would inhibit microbial growth, it is essential to perform a periodic Bacteriostasis/Fungistasis test. The test involves the use of 6 organisms of different classes of bacterial and mold to ensure that the presence of the presence of the test article in the same medium with the indicator organisms does not prevent or inhibit growth of those organisms.