We use 0.45 micron filters in sterility testing because they effectively retain microorganisms without compromising their viability, ensuring accurate test results.
Here's a breakdown of why this pore size is preferred:
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Effective Retention: The 0.45 micron pore size is small enough to trap most bacteria and fungi present in a sample, preventing them from passing through the filter.
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Viability Preservation: According to a provided reference, "the filter paper and applied vacuum will allow microorganisms to be easily retained and will have no effect on the viability of the microorganisms involved in the test." This is crucial because the sterility test relies on the ability of any retained microorganisms to grow and be detected.
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Comparison to 0.22 micron filters: The same reference contrasts this with 0.22 micron filters, stating that "the stringent pore size and applied vacuum cause damage to the microbial cell." Damaging the cells can lead to false negatives in sterility testing, as the damaged microorganisms may not be able to grow and indicate contamination.
In essence, 0.45 micron filters provide the optimal balance between retaining microorganisms and maintaining their viability, which is essential for the reliability of sterility testing.
