Sterility Testing

MDS offers biosafety (sterility) testing of biologics, and Pharmacopeial Sterility of biologics and biopharmaceuticals following USP, JP, EP, ICH Section 21 of the Code of Federal Regulations (CFR), International and FDA Points to Consider (PTC) documents. The outline below represents existing regulations and current industry practice. Exceptions may exist depending on the product and process from which it was generated.

Sterility Testing Methods

Direct Inoculation (Immersion)

In the Direct Inoculation (the immersion) method the test articles are inoculated directly into tubes or bottles that contain an appropriate medium and are incubated for a period of 14 days.

The advantages of the direct inoculation method are: 1) provides a means of sterility testing for materials that cannot be easily filtered. 2) consumes less product volume during the conduct of the bacteriostasis and fungistasis (B&F) testing
The disadvantage of this method is volume constraint. Also, inherently bacteriostatic or fungistatic components cannot be removed or adequately neutralized.

Membrane Filtration and Direct Transfer

The membrane filtration method requires the test article to first pass through a size exclusion membrane capable of retaining microorganisms. An appropriate amount of rinse fluid is then passed through the filter before transferring the membrane into the test medium. The pharmacopeias and 21 CFR 610.12 recommend using two media for both the immersion and membrane filtration methods. In both test methods the test article or membrane is incubated for 14 days in the test media. The majority of biological samples will be tested using the immersion method. However, for test articles with large volumes in which the entire contents must be tested or if there is a substance within the test article that is known or determined to be bacteriostatic or fungistatic (e.g., cell culture containing methotrexate), the membrane filtration method may be required.

The advantage of the membrane filtration method is that: 1) can accommodate large volume samples (up to 500 ml); 2) if the test article contains substances that inhibit the growth of microorganisms, rinsing the filter membrane with a suitable rinse agent can remove all or most of these inhibitory substances
The disadvantage of this method is that it can consume a large volume of final product during B&F testing, especially in the case of final container testing

MDS offers custom protocols for direct transfer method. Typically, the direct transfer method is used for solid dose forms, medical devices, ointments, and creams. For test articles produced by nonaseptic manufacturing processes, a bioburden (or microbial limits) assay should be performed.

Bacteriostasis/Fungistasis (B&F) contamination

This testing is commonly referred sterility test validation, qualification or verification. It is important to determine if the test article that will be tested for sterility contains elements that will interfere with the growth of microorganisms within the growth media used for the assay. In this test, low numbers of microorganisms are added to a media volume containing the test material to confirm that the test material does not interfere with the organism’s growth.

The B&F test is typically required only once for a given sample type, provided that no additional changes to the product, formulation or manufacturing process occurred. However, suitability testing could be
performed on a periodic basis to confirm that no significant changes have occurred to the product or process that may affect the sterility assay results.

A Contract Research Organization

Flow Cytometry

Sterility Testing