Membrane filters challenge testing

Fevy, R.V. The effect of pH, viscosity, and additives on the bacterial retention of membrane filters challenged with pseudomonas diminuta. In Fluid Filtration Liquid American Society for Testing and Materials (ASTM) Washington, DC, 1987 Vol. II. 

Verification of the microbial retention efficiency of the membrane filters may be undertaken using either Hquid or aerosol challenge tests. A Hquid challenge test is more stringent. Furthermore, this test can provide retention information for process conditions such as extreme moisture after sterilization or air entrained with water drops. A Hquid challenge is performed using a protocol similar to that described for Hquid filtration. 

Assay at 5, 10, and 15 min intervals. Perform the entire operation in a laminar-flow hood. At the conclusion of each challenge time interval, pass the contents of each tube through a separate membrane filter unit. Wash each membrane with 3 X 100 ml portions of neutralizer solution. Remove each membrane from its filter unit and place face up on the surface of appropriate poured agar plate. Positive controls must be tested last. 

Figure 7.8 Correlation of P. diminuta microbial challenge and bubble point test data for a series of related membranes [6]. Reprinted from T.J. Leahy and M.J. Sullivan, Validation of Bacterial Retention Capabilities of Membrane Filters, Pharm. Technol. 2, 65 (1978) with permission from Pharmaceutical Technology, Eugene, OR...

ENM filters with antimicrobial functionality have also attracted growing attention. Zhang and co-workers prepared PAN ENMs with fiber diameters of 450 nm and treated the ENMs in hydroxylamine aqueous solution to introduce -C(NH2) = N-OH groups, which were used for coordination with Ag+ ions to form silver nanoparticles. Then, the functionalized membranes were challenged by antimicrobial tests against Staphylococcus aureus and Escherichia coli. The results indicated that the new membranes became antimicrobial without distinguishable morphological variations [87]. 

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