Sterilizing filtration is the process of removing all microorganisms excluding viruses from the solution, without adversely affecting the product quality. It is suitable sterilization method (aseptic process) for heat sensitive drug products . 1. Porcelain filter cartridges- Discontinued 2. Asbestos cellulose layers- - Discontinued 3. Membrane filters Pseudomonas diminuta (currently reclassified as Brevundimonas diminuta)= 0.3x0.6-0.8 µm registered with American Type Culture Collection ATCC No.: 19146. Use of this organism leads to several advantage - 1. Non-pathogenic to human. 2. Can be consistently cultured under controlled condition to to yield very small , mono-dispersed cells with narrow size distribution. 3. A process stream isolate, it is therefore a realistic potential problem organism. The disadvantages of B. diminuta are- 1. Not viable in many pharmaceutical formulations. 2. May not be the smallest bacterium potentially encountere d in all formulations, ...