USP <61> Microbial Enumeration Tests
USP <61> Microbiological Examination of Nonsterile Products- 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 that these organisms are present in low number or high number.
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 Test
USP 61 test determines if product is already contaminated or it does not have high number of bacteria, yeast or mold / 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 have low count of bacteria, yeast and mold, it can still be harmful if pathogens are present even though in very low number. Therefore, it should also be determined that the product do not have harmful bacteria present. Harmful organisms or 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
Soybean-Casein Digest Agar- Samples are inoculated onto Soybean-Casein Digest Agar or other suitable growth media for Total Aerobic Microbial Count (TAMC)
Sabouraud Dextrose Agar - Samples are inoculated onto Sabouraud Dextrose Agar for Total Yeast Microbial Count (TYMC)
USP 61 Microbial Enumeration Test Methods Techniques
Plate Count Methods
- Pour-Plate Method
- Surface-Spread Method
Membrane Filtration techniques can only be used for testing 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
TYMC - Total Combined Yeasts and Molds 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 quenched (if present) 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.
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
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