RT Journal Article SR Electronic T1 Retention of Water-Borne Bacteria by Membrane Filters Part II: Scanning Electron Microscopy (SEM) and Fatty Acid Methyl Ester (FAME) Characterization of Bacterial Species Recovered Downstream of 0.2/0.22 Micron Rated Filters JF PDA Journal of Pharmaceutical Science and Technology JO PDA J Pharm Sci Technol FD Parenteral Drug Association (PDA) SP 87 OP 113 VO 55 IS 2 A1 Sundaram, Srikanth A1 Mallick, Scott A1 Eisenhuth, Jean A1 Howard, Glenn A1 Brandwein, Harvey YR 2001 UL http://journal.pda.org/content/55/2/87.abstract AB The results of scanning electron microscopic (SEM) and fatty acid methyl ester (FAME) characterization of the bacterial species shown to penetrate conventional 0.2/0.22 μm rated “sterilizing grade” filters are presented. SEM data suggest that retention of bacteria by these filters appears to be strongly influenced by the morphology, and especially the width of bacteria and less so by length. When the bacterial cell width is small, less than 0.3 μm or so, the cell length does not appear to limit the ability to penetrate 0.2/0.22 μm rated filters. As the bacterial width increases, there is also a strong, almost exponential, decrease in the allowable length for penetration, with most penetrative cells tending to be coccoid beyond a width of 0.5 μm. Significant percentages of the bacteria (40-50%) that were observed downstream of these filters were larger than B. diminuta, the standard organism used to qualify 0.2/0.22 μm rated filters. The average sizes of natural waterborne bacteria that penetrated the filters tested were 20-40% larger in width, and 40-70% larger in length, compared to B. diminuta. These results indicate that size exclusion is not the sole mechanism governing bacterial retention. All isolates identified via FAME analyses were common environmental or ubiquitous organisms, and some, such as Acidovorax sp. and Hydrogenophaga pseudoflava, have also been isolated from pharmaceutical water systems. Most of the bacteria recovered downstream of 0.2/0.22 μm rated filters were gram negative, oxidase positive, motile, nonfermentors.