USP <61> – Microbial Enumeration Test

The USP <61> – Microbial Enumerations Test is a product safety test found in Chapter 61 of the United States Pharmacopeia. It is suggested for use by the FDA for pharmaceuticals as well as cosmetics and personal care products to ensure that a product’s preparation complies with pre-set specifications for microbiological quality.

The USP <61> test is similar to an aerobic plate count assay as both tests determine if a product is currently contaminated with bacteria or fungi.

The USP <61> test is a full quantitative analysis of a product to determine the Total Aerobic Microbial Count (TAMC) and Total Yeast and Mold Count (TYMC) present in the sample. It also includes a neutralization and recovery validation using specific microorganisms. This ensures that the methods used to determine the presence of these microorganisms are appropriate for each individual product.

Acceptable Guidelines for Microbial Limits

Cosmetics and personal care products are not expected to be completely free of all microorganisms; however, they must be completely free of high-virulence microbial pathogens, especially in eye-area products, and the total number of microorganisms in the product must be low. Since there are no widely accepted standards for the number of microorganisms, there are some temporary guidelines to follow.

For eye-area and baby products, no more than 100 colony forming units (CFU)/ g or ml of product is considered acceptable. For non-eye-area products, no more than 1000 CFU/ g or ml of product is considered acceptable. If the product is determined to have aerobic microbial counts at or below these levels, further testing under USP <62> – Test for Specified Microorganisms – or an equivalent test may be necessary to determine if those microorganisms are high-virulence pathogens.

Pathogens are opportunistic pathogens whose presence in a cosmetic or personal care product would be of particular concern, especially in eye-area cosmetics, including S. aureusP. aeruginosa, and C. albicans. These three microorganisms along with B. subtilis and A. brasiliensis are used as indicator organisms for the neutralization and recovery validation portion of the test.