The Comparison of microbial challenge and In-use test method on Preservative Efficacy Testing in Skincare Products
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Presented by: Isty Adhitya Purwasena
Introduction: Many skincare products formulations were mostly susceptible to microbial growth due to their high water content and nature of ingredients. Preservatives are usually added to avoid the growth of microbial contaminants in skincare products. Preservation efficacy testing (PET) is carried out to demonstrate the efficacy of the antimicrobial activity used in the products during the normal condition of storage and use. One of the most commonly used methods on PET is the microbial challenge test based on the Ph. Eur. (European Pharmacopoeia). The acceptance criteria of passed A in Ph. Eur. usually considered as the only safe and determined as adequate concentration for the product. On the other hand, the criteria of passed B or even failed which contained a lower concentration of preservatives might still be effective to prevent the growth of microbial contaminant during the in-use test. This study aims to confirm the adequate concentration of preservatives in the skincare product resulting from PET by comparing microbial challenge test and in-use test method. This confirmation is necessary to ensure the concentration of optimum preservatives in the skincare products resulting in a more cost-effective and safe product.
Methods: Four types of skincare products consisting of day cream, face mask, gel, and face mist were tested in this study. The preservatives contained in each formula of this skincare were varied from standard concentration (normally applied by the industry), lower and minimum coded as 01,02 and 03 respectively. The products of day cream, face mask, and gel was packaged in tube and pot while face mist was in a spray bottle. PET was performed based on Ph. Eur. using the following microbial test Escherichia coli ATCC 8739, Staphylococcus aureus ATCC 6538, Pseudomonas aeruginosa ATCC 9027, Candida albicans ATCC 10231, and Aspergillus niger ATCC 16404. The acceptance criteria were then determined based on three groups: passed-A (recommended efficacy), passed-B (minimal efficacy), and C (failed). The skincare products were distributed to 90 volunteers to be applied regularly in their hand palms for 8 weeks during the in-use testing program. Each returned skincare product was microbiologically examined and classified into three groups that meet the acceptance criteria for the in-use test: Well-preserved, Marginally-preserved and Failed. The isolated microbes obtained from the returned products were then microscopically analyzed.
Results and discussion: The Day cream resulted in passed-A for 01 preservative variation while passed-B for variations 02 and 03. However, its in-use test shows that all preservative variations have similar results. Their tube packaging products were predicted to be marginally preserved while pot packaging product was classified as failed or poorly preserved against microbial contamination. The microbial challenge test of face mask product showed that the variation 01 and 02 were passed A while passed B for variation 03. These products were marginally preserved in pot packaging and well preserved in tube packaging except one product was categorized as failed due to Gram negative bacteria being detected at variation 03. The gel product showed the result of Passed B in variation 01 and failed in the other variation on the microbial challenge test. Hence the result of the in-use test showed that this product was predicted as marginally preserved both in pot and tube packaging. The last product is face mist that showed passed A for variation 01 and passed B for the others while its in-use test showed that all of the product variations were marginally preserved. This result suggests that pass B or even failed criteria with a lower concentration of preservative could be considered as adequate preservative since their performance on in-use test showed that the product could avoid the growth of microbial contaminant. In addition, 21 types of microbial isolates were obtained from in-use tests consisting of bacteria, molds, and yeast. The most common contaminants found in all types of skincare products are generally identified as cocci/staphylococci cells.
Conclusion: The acceptance criteria of Passed B based on Ph. Eur. microbial challenge test could be considered as adequate preservative since it gives an almost similar result with Passed A criteria during the in-use test. This result indicates that a lower concentration of preservatives could be applied in the skincare resulting in a more economically and relatively safe product.
Methods: Four types of skincare products consisting of day cream, face mask, gel, and face mist were tested in this study. The preservatives contained in each formula of this skincare were varied from standard concentration (normally applied by the industry), lower and minimum coded as 01,02 and 03 respectively. The products of day cream, face mask, and gel was packaged in tube and pot while face mist was in a spray bottle. PET was performed based on Ph. Eur. using the following microbial test Escherichia coli ATCC 8739, Staphylococcus aureus ATCC 6538, Pseudomonas aeruginosa ATCC 9027, Candida albicans ATCC 10231, and Aspergillus niger ATCC 16404. The acceptance criteria were then determined based on three groups: passed-A (recommended efficacy), passed-B (minimal efficacy), and C (failed). The skincare products were distributed to 90 volunteers to be applied regularly in their hand palms for 8 weeks during the in-use testing program. Each returned skincare product was microbiologically examined and classified into three groups that meet the acceptance criteria for the in-use test: Well-preserved, Marginally-preserved and Failed. The isolated microbes obtained from the returned products were then microscopically analyzed.
Results and discussion: The Day cream resulted in passed-A for 01 preservative variation while passed-B for variations 02 and 03. However, its in-use test shows that all preservative variations have similar results. Their tube packaging products were predicted to be marginally preserved while pot packaging product was classified as failed or poorly preserved against microbial contamination. The microbial challenge test of face mask product showed that the variation 01 and 02 were passed A while passed B for variation 03. These products were marginally preserved in pot packaging and well preserved in tube packaging except one product was categorized as failed due to Gram negative bacteria being detected at variation 03. The gel product showed the result of Passed B in variation 01 and failed in the other variation on the microbial challenge test. Hence the result of the in-use test showed that this product was predicted as marginally preserved both in pot and tube packaging. The last product is face mist that showed passed A for variation 01 and passed B for the others while its in-use test showed that all of the product variations were marginally preserved. This result suggests that pass B or even failed criteria with a lower concentration of preservative could be considered as adequate preservative since their performance on in-use test showed that the product could avoid the growth of microbial contaminant. In addition, 21 types of microbial isolates were obtained from in-use tests consisting of bacteria, molds, and yeast. The most common contaminants found in all types of skincare products are generally identified as cocci/staphylococci cells.
Conclusion: The acceptance criteria of Passed B based on Ph. Eur. microbial challenge test could be considered as adequate preservative since it gives an almost similar result with Passed A criteria during the in-use test. This result indicates that a lower concentration of preservatives could be applied in the skincare resulting in a more economically and relatively safe product.