What is sterile filtration and when is a filter truly sterile?
Sterile filtration is the removal of microorganisms from a liquid or gas without compromising the quality of the product. This form of filtration is particularly essential in the pharmaceutical and biotechnological industries, where safety and product quality are regulated by law.
When membrane filters were first introduced in the 1960s, filters with a pore size of 0.45 µm were considered so-called sterilizing grade filters. It later became clear, however, that this assumption was not entirely correct. Dr. Frances Bowman of the US FDA demonstrated that certain microorganisms were still able to pass through a 0.45 µm filter.
This insight led to stricter requirements for sterile filtration and ultimately to the development of a standardized test method: ASTM F838.
When may a filter be considered sterile?
A filter may only be designated as a sterilizing filter (0.2 µm) when it:
- effectively retains at least 10⁷ CFU of Brevundimonas diminuta (ATCC 19146) per cm² of effective filter area, and
- has been demonstrably tested in accordance with ASTM F838
Sterile filtration is therefore not merely a matter of pore size, but above all of proven performance under defined test conditions.
A 0.45 µm filter can remove particles and some microorganisms but does not provide full microbiological assurance. Only 0.2 µm filters validated according to ASTM F838 are suitable for sterile filtration.
Research by the US FDA demonstrated that certain microorganisms can pass through a 0.45 µm filter. For this reason, this pore size is no longer considered sterilizing grade within GMP environments.
ASTM F838 is a standardized test method used to demonstrate whether a filter is suitable for sterile filtration. The test measures a filter’s bacterial retention using Brevundimonas diminuta under defined conditions.
Brevundimonas diminuta is a very small and motile microorganism and is therefore used as a worst-case test organism. If a filter effectively retains this bacterium, it is considered suitable for sterile applications.
No. Pore size alone is not sufficient. A filter must also be demonstrably tested according to a recognized standard, such as ASTM F838. Sterile filtration is about proven performance, not just specifications.
Sterile filtration is essential in industries where product safety is legally regulated, such as the pharmaceutical, biotechnological, veterinary, and medical industries.
Sterile filtration mechanically removes microorganisms from liquids or gases, whereas sterilization (such as heat or steam) inactivates microorganisms. Filtration is often more product-friendly and better controllable.
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Expertise in Sterile Filtration for Regulated Industries
Van Borselen Filters provides in-depth expertise in sterile filtration in accordance with internationally recognized standards, including ASTM F838. We support pharmaceutical and biotechnological manufacturers with reliable filtration solutions where proven performance, validation, and product safety are essential.