Application of membrane filtration for removal of diminutive bioburden organisms in pharmaceutical products and processes

In this report, we present results of a recent investigation in our laboratories demonstrated the effect of process conditions and/or drug product composition on the ability of 0.2 micron and 0.22 micron sterilizing grade filters to fully retain Ralstonia (formerly Burkholderia, formerly Pseudomonas) pickettii. R. pickettii is a opportunistic pathogen widely distributed in nature as well as clinical specimens and there have been several reports of nosocomial infections due to intrinsic manufacture-related R. pickettii contamination in filter-sterilized parenteral fluids. This study documents the penetration of 0.2 micron nylon 66 and 0.22 micron modified PVDF sterilizing grade filters by R. pickettii (grown and challenged) in a drug solution under conditions that simulated a pharmaceutical filling operation. Penetration was not observed for every filter disc tested, and this may be explained, in part, by the stochastic nature (i.e., governed by the rules of probability) of the retention mechanisms involved. Scanning electron microscopy revealed significant changes in the microorganism's size and morphology as a result of exposure to the drug solution; these changes are consistent with those reported for bacteria subjected to nutrient deprivation. The SEM analyses of R. pickettii challenge suspensions in the drug solution showed that the average cell length decreased from 1.25 +/- 0.27 microns to 0.84 +/- 0.17 micron between zero and 24 hours. In addition, significant changes were observed in the size (length) distributions, with approximately 35% of the cells at 24 hours being smaller than any cell observed at the start of the challenge. These data suggest that the significant reduction in bioburden size and morphology that occurred as a result of exposure to the drug solution may play a role in the reduced ability of the 0.2 micron and 0.22 micron filters tested in this study to retain these organisms. Under the same test conditions where penetration of 0.2/0.22 micron filters was observed, 0.1 micron rated membrane filters qualified with both B. diminuta and Acholeplasma laidlawii mycoplasma consistently provided sterile effluent. Bacterial penetration of 0.2 (or 0.22) micron sterilizing grade filters was not observed under identical test conditions with either R. pickettii in a standardized solution (saline lactose broth) routinely used in challenge testing filters, or with the standard test organism, B. diminuta, in the drug solution. This study thus supports the renewed emphasis on both product- and process specific validation as well as routine bioburden monitoring expressed by regulatory agencies, and the use of enhanced bacterial removal efficiency 0.1 micron rated filters to provide enhanced sterility assurance in pharmaceutical processes.