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Tests for Sterility

Products that are labeled sterile are expected to be free of microbial contamination. Some times testing is performed to ensure that these products are stored in such a manner as to remain contamination-free over their entire shelf life. Drug and biologics manufacturers must test each batch or lot in order to validate their claims.

  1. Membrane Filtration Method

    • Pharmaceutical products are usually tested using the membrane filtration method. This test requires that the small membrane paper used to filter the rinse liquid after immersion be segmented and then transferred to the medium for testing. The preferred medium for this method is fluid thioglycollate medium, which supports the growth of aerobic and anaerobic microorganisms. Aerobic organisms are those that can survive and grow in an oxygenated environment, while anaerobic usually cannot. This test requires many manipulations and the product must be incubated for 14 days. The testing takes place in a closed system which minimizes the risk for extrinsic contamination from material coming from the outside.

    Product Flush Sterility Testing Method

    • Medical devices with hollow tubes, such as infusion and transfusion equipment, are easier tested with this method. The procedure recommended is to place the sample device into bacteriological growth mediums used specifically for devices with lumens, which are hollow tubular structures. This method is used to monitor for bacterial growth within small, narrow devices. It requires a 14 day incubation period. Each sample is checked for the presence of any bacteria and numbers found are recorded by a microbiologist.

    Direct Innoculation Method

    • With this testing method, articles are inoculated directly into a tube or bottle with the appropriate medium. They are then incubated for several days. This method is easier to test materials because it can handle larger samples and provides a an easier means of testing trickier materials. This test is used to confirm the ability of microorganisms to grow in a medium that has been set up for testing.

    Methlyene Blue Dye Test Method

    • Medical packages labeled sterile must be tested for package integrity. The U.S. Department of Health and Human Services recommends an immersion test, in which a sealed sample package is fully submerged in a blue dye mixture and then inspected to make certain that the dye did not enter the package and that sterility is maintained.

    Radiation Testing Method

    • Gamma ray radiation testing is useful for testing sterility of single- use disposable medical supplies, such as needles and syringes. With this method, the product being sterilized is passed beneath an electron beam where it absorbs the energy from the electrons. This process alters chemical and biological bonds and destroys the reproductive cells of any microorganisms present.

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