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Microbiological testing for wet wipes
Greetings all,
I was hoping someone might be able to shed some light on how wet wipe products are tested for micro. When testing the finished wipe, is the same amount of inoculant used as would be used in a sample of pure wipe solution (or any other formulation for that matter)?I have read that wet wipes are notoriously difficult to preserve. Does anyone know why this is? -
1 Reply
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Hi Bati,
Preservative challenge tests for wipes are definitely more challenging than similar tests for liquid products. Most of the large companies that make wet wipes have developed customized challenge test protocols, but they usually go something like this:
The company delivers several sets of wet wipes to the lab in sealed baggies, having same wipe/liquid ratio that will be used in the final packaging. Then the lab inoculates stacks of wipes separately for each microorganism and contact time, typically by inserting a micropipette tip into the middle of the stack (in between wipes) and delivering the inoculum.
Then the lab counts the initial microbial population and eventually the final microbial population by transferring the wipes to a large volume of neutralizing solution, such as 100 ml of D/E broth, mixing thoroughly to remove microbes from the wipes, then counting the number of surviving microbes in the fluid and back-calculating to CFU/wipe.
One of the things that makes wet wipes more difficult to preserve is cellulose-based substrates, which are great food for fungi and wipe/liquid interactions which sometimes reduce levels of free, available preservative in the liquid over time (presumably by weak binding of the preservative to the substrate, which takes the preservative out of the picture as far as germs are concerned).
Let me know if you have any more questions.
- Ben
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