Strategies for the Microbiological Testing of Cosmetic Gels

Background: Official methods for the microbiological testing of cosmetics are available; evidence is required for the suitability of procedure employed particularly while dealing with thick or viscous preparations such as gel formulations.

Aim: To illustrate the inherent problems that exist in conventional methodologies used for the microbiological testing of cosmetic gels and to recommend new strategies which could yield more consistent results.

Place and Duration of Study: The work was carried out at the quality control laboratories in Jordan Medical Solutions Manufacturing Company over a period of 4 months

Methodology: A carbomer based hair styling gel formulation and a cell suspension of Pseudomonas aeruginosa ATCC 9027 were prepared following standard procedures. Homogeneous dispersion of the prepared microbial challenge into the gel was achieved by two approaches. The first depended on inoculating the gel preparation prior to the addition of alkali while the second relied on breaking down the gel matrix by acidification of the original gel to pH 4 in order to allow the release of contaminants from the gel matrix. The traditional pour plate technique on 1 ml sample was used for microbial count.

Results: The percentage coefficient variation (PCV) in bacterial count recovered from the gel using the traditional approach was 30.58% whereas; when the proposed strategies were employed the PCV was 7.15%. The smaller the PCV, the better is the precision and repeatability of the assay.

Conclusion: Strategies presented herein are more suitable for the microbiological testing of cosmetic gels than the known routine methods.