USP <61> Test- Microbial Enumeration Test

Cosmetics and personal care products, pharmaceutical and other products which are categorized as non sterile products are not completely free of microorganisms. USP 61 test is carried out to find out if these organisms are present in low or high numbers.

USP 61 Microbial Enumeration Test is carried out on Pharmaceutical products, Cosmetics and personal care products , textile and other miscellaneous products to be checked for their safety before release of the product to the market.

Purpose of USP 61 Microbial Enumeration Test

USP 61 test determines if product is already contaminated or it does not have high number of bacteria, yeast, mold, or fungi in it.

USP 61 Microbial enumeration test is a quantitative test which determines the Total Aerobic Microbial Count (TAMC) and Total Yeast and Mold Count ( TYMC) present in the test product.

If the product is determined to a have low count of bacteria, yeast and mold, it can still be harmful if pathogens are present even though they are very low in number. Therefore, it should also be determined that the product does not have harmful bacteria present. Harmful organisms and pathogens are supposed to be absent in a product .

USP 62 Test For Specified Microorganisms determines whether these pathogens are present or absent.

USP 61 Microbial Enumeration Testing Labs - Microbial Growth Agar Media

USP 61 Microbial Enumeration Test Methods Techniques

Plate Count Test Methods for Microbial Enumeration

• Pour-Plate Method
• Surface-Spread Method

Membrane Filtration Test Method for Microbial Enumeration

Membrane Filtration techniques can only be used for microbial enumeration of the products which can be filtered through a membrane filter.

Interpretation / Analysis of Results for USP <61> Microbial Enumeration Tests

TAMC - Total Aerobic Microbial Count

• Equal to number of cfu found using Soybean-Casein Digest Agar
• If colonies of fungi are apparent, they are counted and included in TAMC

• Equal to number of cfu found using Sabouraud Dextrose Agar
• If colonies of bacteria are apparent, they are counted and included in TYMC

USP 61 Suitability Testing

Antimicrobial or preservatives present in the products can themselves inhibit the microorganisms and could interfere in the detection of the microorganisms present in the test product. Suitabilty test is carried out to assure that any antimicrobial activity of the test agent does not affect the reliability of the USP 61 test to recover the microorganisms that may be present in that product. In Suitability test method, a low number of microorganisms are inoculated into the product and a test method is established to recover the organisms inoculated. USP 61 test method is carried out by using neutralization and dilution techniques, and the product's inhbiting activity is therefore quenched (if present) in order to recover the organisms inoculated in the product. The average microbial counts obtained for the total aerobic count and the total yeast and mold count, must be ≥ 50% and ≤ 200% of those obtained from the positive control inoculum plates. Once the suitability of USP 61 test method is established, All of the products from the same formulation are tested by following that suitability method for that product.

Amount of Sample Required for USP 61 Testing

USP 61 test: 10 grams / mls/ patches

USP 61 Suitability Test: 30 to 40 grams / mls/ patches

Turn Around Time for USP 61 Testing

5 to 7 days

Turn Around Time for USP 61 Suitability Testing

7 to 14 days

Commonly Ordered Other Tests Along USP 61 Test are:

USP 62 Test: Test for Specified Microorganisms which test for presence or absence of Staphylococcus aureus, E.coli, Salmonella, Pseudomonas aeruginosa, Total Gram Negative bacteria, Clostridium and Candida albicans in a product

USP 51: Antimicrobial Preservative Effectiveness Test or Preservative Challenge Test

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More information about this test can be viewed at the following other locations:
-U.S. Pharmacopeia (Chapter <61> PDF)
-The Harmonization of the Microbial Limits Test - Enumeration by Scott Sutton, Ph.D.
-USP Updates <61> and <62> for Microbial Testing of Non-Steriles

• The United States Pharmacopeia (USP) has significantly changed the USP XXXI <61> Microbial Limits Test, updating it and dividing it into two parts