Articles
RSSDiminutive Bacteria Implications For Sterile Filtration
August 23, 2004
Diminutive bacteria were obtained by filtering tap water through 0.45µm filter discs. The mixed population of bacteria obtained in the filtrate was repeatedly grown and filtered through 0.45µm filter discs. One of the species isolated was of special interest, as it was found to consistently penetrate 0.2µm filter discs. This bacterium, although not yet fully classified, has been identified as a Pseudomonas species and will be referred to a Pseudomonas sp. in this publication. A culture technique was developed that provided:
Summary
In the 1960s, sterilizing filters used for liquids were based on 0.45µm membranes, but when penetration by Brevundimonas
(Pseudomonas) diminuta was reported, 0.2µm /0.22µm was adopted as the new standard. It is now recognized that bacteria
smaller than B. diminuta exist. Furthermore, occasional filter penetration has been reported for certain product and process
conditions. Filter validation has therefore become more complex because of the need to simulate the process during
challenge testing.
A diminutive pseudomonas species has been isolated and cultured successfully to allow detailed filter penetration studies to be performed. Consistent penetration of 0.2µm and 0.22µm filters has been shown in challenge tests of 60 - 90 minutes. Full retention was obtained with 0.1µm filters. The recent availability of high flow and high efficiency 0.1µm filters can provide enhanced sterility assurance and may help to simplify the problem of validating sterile filtration processes.
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