Sorption of bacterial endotoxin and retention of bacteria by positively charged membrane filters.

Positively charged membrane filters (Pall, Posidyne) were studied for their ability to retain both bacterial endotoxins and bacteria. Filters (0.2 microns pore size) were challenged with high (up to 5* 10(5) EU) levels of bacterial endotoxin. When the endotoxin was dispersed in water, a more than 10,000 fold reduction of the endotoxin was obtained, whereas the reduction was only a factor 20 when Ringer's solution was used to disperse the endotoxin. Retention of bacteria was dependent on the type of organism, the pore size of the filter and the suspending liquid. Although filters with pore sizes > 0.2 microns were not suitable to be used as a final filter in an aseptic production process, a very reduction in the number of bacteria could be obtained. Possible applications for these filters in the production of sterile pharmaceuticals are discussed.