Total Aerobic Microbial Count (TAMC) and Total Yeast and Molds Count (TYMC) microbial limits testing is a way of quantitatively measuring the number of viable microorganisms present in a non-sterile product. With these two tests, Nucro-Technics’ microbiology testing lab can enumerate the viable aerobic microorganisms present in pharmaceutical products and raw materials. Performance of these tests is outlined in USP <61>.  This chapter is harmonized with the European Pharmacopoeia (EP 2.6.12), and equivalent chapters in the British Pharmacopoeia (BP), and the Japanese Pharmacopoeia (JP).

The USP <61> procedure specifically focuses on determining the number of colony-forming units (CFUs) of aerobic bacteria and fungi that can grow under non-selective conditions. This testing is essential for:

• Verifying that products meet predetermined specifications
• Monitoring manufacturing processes and environments
• Ensuring product stability throughout shelf life
• Demonstrating compliance with regulatory requirements

Method Suitability Testing: Validating the USP <61> Total Aerobic Microbial Count (TAMC) and Total Yeast and Molds Count (TYMC) Microbial Limits Test for your Product

Method suitability testing is a crucial prerequisite for TAMC and TYMC testing. This validation ensures that the test method can accurately detect microorganisms in the presence of the product being tested. This testing would verify that:

• The product does not have antimicrobial properties that could inhibit microbial growth
• The chosen test method can recover microorganisms in the presence of the product
• Test conditions are appropriate for the specific product characteristics

For Total Aerobic Microbial Counts testing (TAMC), the following organisms are inoculated / evaluated:

• Staphylococcus aureus
• Pseudomonas aeruginosa
• Bacillus subtilis
• Candida albicans
• Aspergillus brasiliensis

For Total Yeast and Molds Count testing (TYMC), the following organisms are inoculated / evaluated:

• Candida albicans
• Aspergillus brasiliensis

When performing the suitability testing within our microbiology testing laboratory, the number of organisms recovered for each test organism is compared to the control. The recovery has to be between 50% and 150% of the inoculated number of test organisms. A successful suitability test will prove that there is no inhibition caused by the sample that is preventing test organisms (if present) from being detected.

How USP <61> Total Aerobic Microbial Count (TAMC) and Total Yeast and Molds Count (TYMC) Microbial Limits Testing is Performed

Routine testing for Total Aerobic Microbial Counts (TAMC) and Total Yeast and Molds Count (TYMC) will be performed in a manner that is reflective of the suitability testing. At a very high level, the following steps are taken for the conduct of a Total Aerobic Microbial Count:

1. Sample Preparation
2. Incorporating the Sample onto a Growth Medium
3. Incubation
4. Enumeration and Reporting

Sample Preparation

For microbial limits testing, preparation of samples within Nucro-Technics’ GMP microbiology testing laboratory is dependent on the type of material being tested. There are a number of approaches that can be followed depending on whether the test article is water-soluble, a non-fatty product that is insoluble in water, a fatty product, or a transdermal patch.

Incorporating the Sample onto a Growth Medium

Once a sample is prepared appropriately within the GMP microbiology testing laboratory, it needs to be transferred to an appropriate growth medium in order to recover the organisms that may be present. There are a few different approaches that can be utilized for microbial limits tests, and one would pick one approach over another as a result of the physical properties of the sample itself. These approaches are the:

• Membrane Filtration Method (for filterable samples);
• Pour Plate Method (for viscous samples, samples with complex matrices, and insoluble samples); and
• Spread Plate Method.

Incubation

After samples have been incorporated onto a growth medium within the GMP microbiology testing lab, they are incubated. For bacteria, this incubation is at 30°C-35°C for 3-5 days. For yeasts and mold (fungi), the incubation is 5-7 days at 20°C-25°C.

Enumeration and Reporting

After incubation, colonies are counted and results are calculated as CFU per gram or CUF per mL of the original sample.

Microbial limits testing is generally a function of batch size. For the purposes of regulatory compliance, to perform a routine test per USP <61>, 10 grams of material is typically needed. There are provisions in place for materials used as active substances and where the sample quantity is limited, or batch size is extremely small. In these cases the amount tested shall be 1% of the batch.

For clients looking for a GMP-compliant microbiology testing laboratory to perform USP <61> Total Aerobic Microbial Count (TAMC) and Total Yeast and Molds Count (TYMC) testing, Nucro-Technics is an excellent choice. With the largest microbiology laboratory in Canada, our organization has been running these tests on a daily basis for more than 50 years and for 500+ clients to help meet the regulatory testing needs of the pharmaceutical and biotech industries.

With the largest microbiology laboratory in Canada, our organization has been performing thousands of microbiological tests to meet the needs of the pharmaceuticals industry since our founding in 1970.