RT Journal Article SR Electronic T1 Method for Qualifying Microbial Removal Performance of 0.1 Micron Rated Filters Part I: Characterization of Water Isolates for Potential Use as Standard Challenge Organisms to Qualify 0.1 Micron Rated Filters JF PDA Journal of Pharmaceutical Science and Technology JO PDA J Pharm Sci Technol FD Parenteral Drug Association (PDA) SP 346 OP 372 VO 55 IS 6 A1 Sundaram, Srikanth A1 Eisenhuth, Jean A1 Howard, Glenn A1 Brandwein, Harvey YR 2001 UL http://journal.pda.org/content/55/6/346.abstract AB Although 0.1 μm rated filters intended for pharmaceutical sterilization applications have been commercially available for at least 15 years, there is no industry-wide standard for qualifying the microbial removal performance of these filters. In this article, we report on the bacterial challenge methodology used to screen four bacterial species for potential utility as a standard challenge organism to qualify 0.1 μm rated filters. These isolates were, in their natural state, demonstrated to penetrate 0.2/0.22 μm rated filters in prior studies. In the screening challenges described in this study, three out of these four candidates tested demonstrated consistent penetration of one 0.22 μm rated filter type tested (when cultured in a low nutrient medium under standard laboratory conditions). These included 6204-22 (FAME ID Acidovorax avenae citrulli), 6266-15 (FAME ID Comamonas acidovorans), and 6266-34 (FAME ID Hydrogenophaga pseudoflava). Of these, H. pseudoflava (6266-34) was chosen for additional experiments with other 0.2 μm rated filter membranes. In total, seventeen 0.2 and 0.22 μm rated filter discs, spanning five different “sterilizing grade” filter types from three different filter manufacturers were tested. H. pseudoflava penetration was observed for every filter tested. Under the same challenge conditions, H. pseudoflava was consistently retained by a 0.1 μm rated hydrophilic PVDF (polyvinylidenefluoride) filter with a specified high titer reduction claim for Acholeplasma laidlawii. In order to ensure selection of the most stable penetrative phenotype (i.e., select for non-revertants), H. pseudoflava was subjected to three rounds of “filter cloning,” and these results are described herein. The advantages of using H. pseudoflava for qualifying the microbial removal performance of 0.1 μm rated filters are also discussed.