Microbial challenge testing on cosmetic dry product formulation are performed by using in-house methods. I had performed challenge testing on cosmetic dry powder product formulations by using spray inoculums that consisted of Ps. aeruginosa, S. aureus, Candida ablicans, Penicillium species and Aspergillus brasiliensis as the challenge test organisms based upon the typical contaminants that you would find during consumer usage. The number of sprays was determined to be equivalent to 0.1 ml inoculum for 20 grams of powder for each challenge test organism that resulted in an initial theoretical inoculum level of 10e5 CFU/gram. You are correct that cosmetic dry product formulations have water activity levels below 0.6. At these water activity levels, contaminating organisms during consumer usage will not proliferate, but they can survive in these product formulations at high levels during usage. It is not uncommon to find dry powder product formulations to be contaminated during consumer usage with high levels of Gram-positive cocci, yeast and mold isolates. In some of these dry powder product formulations, they will often contain binders that are able to absorb water or humidity from the environment to allow organisms to survive and proliferate by having a presence of a source of water. In addition, you will often have consumers wet the doe foot foam applicators with water to remove additional powder from the powder godlets for application of the powder onto the face or eye-area. By doing this, there is introduction of water into the formulation. By each of these occurrences, mold would often proliferate in these product formulations. If you had unpreserved dry powder product formulations, it was not uncommon to have product compliants of mold growth occurring in these product formulation that were present in the marketplace. Because of this reason, preservatives such as Sodium methylparaben and Sodium ethyylparaben were included as ingredients in these formulations due to their water solubility. I have also seen people use methylparaben and ethylparaben as the preservatives in these product formulations. This microbial challenge work was done during the development stage only and not during real-time stability studies. I agree that microbial challenge testing of these dry powder product formulations is not widespread and the knowledge in how to conduct this type of microbial challenge testing on this type of product formulation is not widespread in the industry or understood. In regards to your question of how accurate was this testing, it was found to be very accurate and compliants due to mold growth in these types of product formulations went away after the inclusion of preservatives had been done and the formulations had been found to adequately preserved during the development stage by doing microbial challenge testing on them. By responding with my answers here to your inquiry, I know that alot of people are going to disagree with me about conducting microbial challenge testing on these formulations, but it was easier to perform this testing and not to deal with a for cause FDA inspection for product contamination in the marketplace and a possible product recall.
Donald J. English Microbiological Quality Consulting LLC
Florham Park, New Jersey 07932
Sent from my iPhone
> On Nov 7, 2018, at 9:23 AM, Caron Ockerman <[log in to unmask]> wrote:
> To all,
> I am not aware of any validated method accepted by industry to test AET on dried products. It is my understanding that dried products do not require AET because the water activity is so low. I think I know of one cosmetic company that performed their own validation using spray inoculation, but other than that company, I have heard little on how to perform this testing. I do not have the microbiological testing book from the PCPC, but even in the limited conversations I have had with them, AET isn't required on powder products.
> I guess my question is: has anyone performed this? How did you do it? How accurate were the results? Many thanks for your input!
> Kind Regards,
> Caron Ockerman | Microbiology Lab Manager
> Elba Laboratories | 1925 W. Maple Rd. | Troy, MI 48084
> Phone: 248.288.6098 | http://elba-labs.com<http://elba-labs.com/>
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