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USP 61

Published: January 30th, 2019

Revised: January 30th, 2019

Microbial Examination of Nonsterile products: Microbial Enumeration Tests

USP Chapter 61 Microbial Examination of Nonsterile products: Microbial Enumeration Tests is a product safety test designed to evaluate the microbial content of nonsterile products such as pharmaceuticals products, cosmetics and personal care. These tests can be performed on finished products, raw materials or environmental swabs.

The USP <61> contains two tests, microbial enumeration and a suitability test:

1. Microbial enumeration

The microbial enumeration 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.

TAMC – Total Aerobic Microbial Count

Samples are plated onto bacterial recovery media such as TSA, followed by 3-5 days of incubation, to recover colonies of organisms that can grow aerobically at 30-35 degrees C. Bacterial colonies, as well as fungal colonies that are recovered from this test are used in a final calculated plate count.

TYMC – Total Yeast and Mold Count

Samples are plated onto fungal recovery media (usually SDA), followed by 5-7 days of incubation, to target fungal colonies (yeasts and molds) that can grow aerobically at ambient temperatures (20-25 degrees C). Fungal colonies as well as bacterial colonies that grow on the plates are used in a final calculated plate count.

Unlike typical environmental monitoring test such as HPC, both bacterial and fungal microorganisms are counted. To determine total bacterial or fungal counts, two separate growth media are used and incubated at temperatures to selectively favour the growth of one type of organism over the other. It is only when these tests are used in combination that we can determine the pass or fail criteria for your product.

2. Suitability Test

This test is a preliminary step required to determine whether product is suitable for USP 61. Since pharmaceuticals products, cosmetics and personal care may contain inhibitors that will negatively bias the results of the test. This test requires bacteria to be spiked with the product in question and then subsequently recovered without being inhibited.

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