5.1 This test method is designed to assess the retentivity of a sterilizing filter under standard challenge conditions.

5.1.1 A challenge of 10⁷ bacteria per cm² of effective filtration area is selected to provide a high degree of assurance that the filter will be challenged uniformly across the membrane surface to assure it will quantitatively retain large numbers of organisms. The model challenge organism, B. diminuta, is widely considered to be a small bacterium and is recognized as an industry standard for qualifying sterilizing filters. Other species may represent a worst-case test in terms of ability to penetrate a filter. This test does not provide assurance that filters can completely retain such bacteria.

5.1.2 The analytical procedure utilized in this test method provides a method to assign a numerical value to the filtration efficiency of the filter being evaluated under standard filtration conditions. For the purpose of product sterility assurance, additional process-specific studies should be performed.

1.1 This test method determines the bacterial retention characteristics of membrane filters for liquid filtration using Brevundimonas diminuta as the challenge organism. This test method may be employed to evaluate any membrane filter system used for liquid sterilization.

1.2 This test method is not intended to be used in performance of product- and process-specific validation of the bacterial retention characteristics of membrane filters to be used in pharmaceutical or biopharmaceutical sterilizing filtration, or both. Process- and product-specific bacterial retention validation should be carried out using the intended product manufacturing process parameters and the product solution or surrogate as the carrier fluid.

1.3 The values stated in SI units are to be regarded as standard.

1.3.1 Exception—The inch-pound values given for units of pressure are to be regarded as standard; SI unit conversions are shown in parentheses.

1.4 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.