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USP <61>
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Summary
USP <61> test method is used to determine the microbiological quality of nonsterile products by identifying Total Aerobic Microbial Count (TAMC) and Total Yeast and Mold Count (TYMC). The test verifies if microbial levels are under specified acceptance criteria for non – sterile products, ensuring product safety, quality, and compliance with regulatory requirements.
Quick understanding of the test
USP <61> - Microbial Enumeration Test
- For Total Aerobic Microbial Counts testing (TAMC)
- Staphylococcus aureus
- Pseudomonas aeruginosa
- Bacillus subtilis
- Candida albicans
- Aspergillus niger
- For Total Yeast and Molds Count testing (TYMC)
- Candida albicans
- Aspergillus brasiliensis
- Test samples are diluted using suitable buffers.
- Growth promotion tests are performed on the media.
- Test samples suspected to contain antimicrobial agents are subjected to neutralization and then incubated.
- Microbial counts in the sample are assessed using either membrane filtration method or plate count method.
- Negative controls are carried out to ensure there is no external contamination.
- Ensures that non-sterile products are free from harmful microbial contamination.
- USP 61-certified products are more likely to meet the stringent quality requirements for market approval.
Turnaround Time
Results
Passing criteria
- Eye-area and baby products: Maximum of 100 CFU/g or ml is acceptable.
- Other products: Maximum of 1,000 CFU/g or ml is acceptable.
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What is USP Microbial Enumeration Test?
USP <61> is a quantitative microbiological test described in the United States Pharmacopeia for evaluating total aerobic bacteria, yeasts, and molds in non-sterile products including pharmaceuticals, cosmetics and in raw materials. USP 61 is also referred to as the ‘Microbial bioburden test’, ‘Microbial Limits Test’ or ‘Microbial enumeration test.
USP 61 method evaluates Total Aerobic Microbial Count (TAMC) and Total Yeast and Mold Count ( TYMC) of the test sample.
USP <61> is a critical test to ensure compliance with US pharmacopeial standards and is recognized by global regulators. It supports product safety, quality control, and batch release decisions. USP <61> confirms the total microbial count is within limits, but it does not identify the organisms present. USP <62> is then used to determine the presence or absence of specific, objectionable pathogens in non-sterile products.
Products tested under USP testing
USP <61> testing is used for wide range of product, including:
- Cosmetic/ personal care products
- Topical and oral non-sterile pharmaceutical products
- Herbal and botanical formulations
- Nutritional supplements
Total Aerobic Microbial Count (TAMC)
TAMC measures the total number of viable aerobic bacteria present in a product. High TAMC values may indicate poor raw material quality, inadequate hygiene, or ineffective preservation.
Total Yeast and Mold Count (TYMC)
TYMC measures the total number of yeasts and mold present in a sample. Products with high moisture content or plant-based ingredients are susceptible to yeast and mold contamination. High TYMC values are mainly associated with poor storage conditions.
USP Test Methods
USP <61> Microbial Enumeration Test method involves adding a specified quantity of the product to a suitable diluent to prepare a test sample. The sample is then analyzed using one of the standard enumeration methods based on the product type and microbial load.Soybean-Casein Digest Agar/Broth is used to determine the Total Aerobic Microbial Count (TAMC), while Sabouraud Dextrose Agar/Broth is used for the Total Yeast and Mold Count (TYMC).
USP <61> Microbial Enumeration Techniques
Membrane Filtration Method: This method is applicable for filterable samples. filtered.
Plate count Methods: This includes Pour-Plate and Spread Plate methods.It is suitable for viscous samples, samples with complex matrices, and insoluble samples
Mostยญ Probableยญ Number (MPN) Method : It is the least accurate method for microbial counts but most appropriate for certain product groups with very less bioburden.
Suitability Testing & Neutralization
The suitability test in USP <61> verifies whether the microbial enumeration method can accurately detect and recover microorganisms from a non-sterile product. This step is critical because some products contain antimicrobial ingredients that can inhibit microbial growth and result in falsely low counts. In this test, a known number of standard microorganisms is inoculated into the product, while a control sample is prepared using a neutral diluent without the product. Both samples are then processed using the same microbial enumeration method.
If the product inhibits microbial recovery, neutralization is required. Neutralization suppresses the antimicrobial activity of the product, allowing accurate enumeration of viable microorganisms that survive the test process.
Interpretation of USP <61> Microbial Enumeration Test Results
- Total Aerobic Microbial Count (TAMC) is expressed as CFU which is equivalent to the number of colonies on Soybean-Casein Digest Agar. In addition, the presence of fungal colonies on the Soybean-Casein Digest Agar shall also be counted in the TAMC.
- Total Yeast and Mold Count (TYMC) is equivalent to the number of colonies (CFU) found on the Sabouraud Dextrose Agar. Any colonies of bacteria count toward TYMC.
Acceptable guidelines for USP Microbial Enumeration Test
Cosmetics and personal care products are not expected to be completely free of microbes, but they must not contain harmful pathogens. According to FDA BAM Chapter 23, the acceptable limits of microbial count as per USP standards are:
- Eye-area and baby products: Maximum of 100 CFU/g or ml is acceptable.
- Other products: Maximum of 1,000 CFU/g or ml is acceptable.
USP <61> vs USP <62>
Parameter | USP <61> (Microbial Enumeration Tests) | USP <62> (Tests for Specified Microorganisms) |
Purpose | To quantitatively determine total aerobic bacteria (TAMC) and total yeast and mold (TYMC) to assess overall microbial load. | To qualitatively detect the presence or absence of specific objectionable microorganisms that may pose health risks. |
Mandatory Test Microorganisms | Counts all culturable aerobic microbes under test conditions (no defined pathogens list). | Specific pathogens such as Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Salmonella spp., bile-tolerant Gram-negative bacteria, Candida albicans. |
Scope of Products | Non-sterile products pharmaceuticals (oral solids/liquids, creams, ointments), cosmetics and personal cate products | Non-sterile pharmaceuticals, cosmetics, and related products (useful for products with higher risk of contamination). |
Results Interpretation | Quantitative – reported as colony-forming units (CFU) per gram or mL and compared to acceptance limits in USP <1111>. | Qualitative: pass if tested pathogens are absent, fail if any specified microorganism is detected. |
Key Difference | Focuses on how many microbes are present (bioburden level). | Focuses on whether specific harmful microbes are present or absent. |
Importance of USP <61> Microbial Enumeration Test
Non-sterile products such as pharmaceuticals, cosmetics, and personal care items are constantly at a risk of microbial contamination during production, handling, or storage. This risk extends to a wide range of industries including food, beverages, medical devices, and nutritional supplements, where even small microbial imbalances can compromise safety and quality leading to product spoilage, reduced shelf life, and potential health issues. Without consistent microbial monitoring, manufacturers face challenges in maintaining regulatory compliance and protecting consumer health.
The USP 61 Microbial Enumeration Test offers a standardized method to determine the total viable microbial count in non-sterile products and raw materials. It helps detect bacterial and fungal contamination at an early stage, allowing manufacturers to take corrective actions before products are released to market. By routinely implementing USP 61, manufacturers can maintain product integrity and comply with regulatory standards.
Why Choose Our Lab for USP Testing
At MIS, we offer precise and compliant USP 61 testing services.
We also perform USP 60 and USP 62 tests to assess the growth of specific microorganisms in non-sterile products. Our experts understand the clientโs needs and expectations first and take complete responsibility to provide reliable and accurate results.
Request USP Testing
Contact our experts now to discuss your Microbial enumeration test requirements and other related antimicrobial tests.
Frequently Asked Questions
DR. Martinoz Scholtz
Samples are prepared by aseptic dilution in a sterile diluent to provide low-concentration levels for the plating. This is necessary to avoid errors in counting microbial colonies.
USP <61> is a microbiological limit test for non-sterile products. It quantitatively measures viable microorganisms to determine total aerobic microbial count (TAMC) and total yeast and mold count (TYMC) in a sample.
The test ensures that the microbial levels are within the acceptable limits in non-sterile products thus reducing the possible adverse health effects like infections and allergic reactions.
A controlled environment, working with sterile equipment, exercising good laboratory practices, and maintaining strict aseptic conditions can help reduce the possibility of contamination.
Sample ingredients that inhibit microbial growth, such as preservatives or poor sample preparation techniques, can give false positives for a microorganism’s presence.
USP <61> is applied to non-sterile pharmaceuticals, cosmetics, personal care products and other non-sterile materials where microbial limits are relevant, including finished products and raw materials.
If microbial counts exceed acceptance criteria, the batch is rejected or held, leading to an investigation to identify contamination sources and potentially reformulation.
USP <61> quantifies total microorganisms (TAMC & TYMC), whereas USP <62> qualitatively tests for the presence or absence of specified pathogens like E. coli or S. aureus.
USP <61> is mandatory for non-sterile pharmaceuticals where USP standards apply, whereas in cosmetics regulation it is a recognized standard but legal requirements vary by country.
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