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USP <61>
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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
- For products designed for infants, used under the eye area or mucous membranes: <200 CFU/ml or 102 CFU/ml
- For other products: <2000 CFU/ml or 103 CFU/ml
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Abstract
The United States Pharmacopeia (USP) 61 Microbial Enumeration Test is a quality test to check the presence and quantity of micro-organisms 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.’ The test is a standard method used to assess microbial load with potential risks to ensure conformity with regulations. USP 61 test determines Total Aerobic Microbial Count (TAMC) and Total Yeast and Mold Count ( TYMC) present in the test sample.
USP <61> Microbial Enumeration Test Method Explained
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 Method for USP <61> Microbial Enumeration Test
The suitability test in USP <61> checks if the microbial enumeration method can accurately detect and recover microorganisms from a non-sterile product. This is necessary because some products contain antimicrobial agents that inhibit microbial growth, leading to false low counts. In the test, a known number of standard microorganisms are added to the product and a control sample is prepared in a neutral diluent without the product. Both the product sample and the control are processed using the same microbial enumeration method. If the number of recovered microorganisms from the product sample is reduced by a factor greater than 2, it indicates inhibition. In this case, neutralizing agents are added to get valid results.
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.
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.
Conclusion
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.
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.
In case a product fails the test, an investigation is done to identify the source of contamination. The product can either be reformulated or rejected depending on the results obtained.
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 for the determination of the presence of total viable aerobic bacteria and fungi. USP 62 deals with the detection of specific microbiological agents that may be pathogenic.
The recent USP <61> update, approved by the Pharmacopeial Discussion Group (PDG), refines the membrane filtration method suitability criteria. It now requires that the count of each test organism must not differ by more than a factor of 2 from the control value.
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