Filter Integrity Testing

Bacterial Filter Integrity

Filters are tested for their ability to retain bacteria that have a diameter equal to or slightly larger than the pore size of the filter being tested. Filters are challenged with ≥ 1.0 x 107 cfu/cm2  of the effective filtration area at a specified pressure. The filtrate obtained from the challenge is filtered through an appropriate assay filter which is plated onto agar. After incubation, the assay filters are observed for the presence of the challenge organism.  Acceptable performance of the filters is demonstrated by the membrane retaining the entire bacterial challenge of ≥ 1.0 x 107 cfu/cm2 of the filter area. Bubble points are performed on hydrophilic and hydrophobic filters. A test used to indicate maximum pore size of a filter. Used to test the integrity of filters with a specific, validated, pressure values, wetting liquids and temperatures for a specific pore size. Notes: currently test 0.1, 0.22 and 0.45µm filters – hydrophobic and hydrophobic capsules and membranes.

 

Bacterial Filter Retention Studies

These studies test the ability of a filter to retain bacteria after being exposed to product during process conditions.  A smaller filter made from the same material as the process filter can be used.  Three different lots of test filters are exposed to product at specific pressure, temperature, flow rate and membrane fluid contact time. The product is recirculated through the test filters per the process conditions. After re-circulation, the filters are challenged with a bacterial challenge of ≥ 1.0 x107 cfu/cm2 of the effective filtration area. Viability study results determine whether the bacterial challenge is performed in the test product or in a surrogate fluid. The filtrate obtained from the challenge is filtered through an appropriate assay filter which is plated onto agar. After incubation, the assay filters are observed for the presence of the challenge organism.  Acceptable performance of the filters is demonstrated by the membrane retaining the entire bacterial challenge of ≥ 1.0 x107 cfu/cm2 of the filter area.