The Antimicrobial Effectiveness Test (AET) is designed to provide a laboratory test that gauges the level of biological activity possessed by the preservative system in a pharmaceutical or cosmetic product. The USP <51> and the BP/EP have specific requirements and different acceptance criteria for each type of pharmaceutical product. When performed according to USP <51>, five indicator organisms are utilized for the purpose of challenging the preservative system in a product. Three of the five USP indicator organisms, Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus, address the growth of bacteria. Candida albicans is the representative yeast, while Aspergillus niger is a mold. Other organisms can be incorporated into the test as customer and product needs dictate.
The AET test is performed by inoculating the product aliquot with a number of organisms between 1 x 10^5 (100,000) to 1 x 10^6 (1,000,000) colony forming units (CFU) per mL of product. At various intervals, depending on the category, the product is tested to determine its ability to control reproduction or destroy the microorganisms. A logarithmic reduction is evaluated at each test interval required for the category.
For testing purposes, the USP has divided test articles into four separate categories:
- Category 1 – Injections, other parenterals including emulsions, otic, sterile nasal products made with aqueous bases or vehicles.
- Category 2 – Topically used products made with aqueous bases or vehicles, non-sterile nasal products, and emulsions, including those applied to mucous membranes.
- Category 3 – Oral products other than antacids made with aqueous bases or vehicles.
- Category 4 – Antacids made with an aqueous base.
AET is typically performed during product development and as part of a stability study, to determine if a preservative system will stand up to the product’s shelf life. The first time a product is tested for Antimicrobial Effectiveness, a validation is necessary to show the microorganisms are able to withstand the formulation. A full validation is performed in three independent studies with each of the studies recovering not less than 70% of the growth inoculum versus the control.
The Cosmetic, Toiletry, and Fragrance Association 2007, “CTFA Microbiology Guidelines”, CTFA M-3 provides methodology for testing cosmetics similar to the USP AET test.
|Assay Description||Service Code||Sample Volume|
|USP Antimicrobial Effectiveness Test||ML42||> 20 mL or g|
|EP Antimicrobial Effectiveness Test||ML43||> 40 mL or g|
|USP and EP Antimicrobial Effectiveness Test combines||ML44||>40 mL or g|
|AET method validation||ML45||> 100 mL or g|