USP Microbial Examination of Non-Sterile Products

A road map to the world of non-sterile testing regulations

By James E.T. Gebo, technical representative, Laboratory Services, and Kimberly Kitch, laboratory technician, Microtest Laboratories Inc.

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Many products released to the market that are used on a daily basis are not required to be sterile. Examples include over-the-counter medicines, creams and supplements to name a few. The microbial quality of these products is ensured because the manufacturers are required to evaluate the microbial content of each product. To accomplish this, Microbial Examination of Nonsterile Products is performed. This test, formally known as the Microbial Limits Test, determines the bioburden of the product and also if objectionable organisms are present. On May 1, 2009, the harmonized test method became effective, requiring manufacturers to meet the new guidelines set forth in it.

For manufacturers, it is critical to understand how the recent harmonization of the USP, EP and JP requirements affects the processing of raw materials and finished products. It’s also essential for manufacturers to be well aware of the considerations to examine when establishing a microbial limits testing policy.

The harmonization of this test made some major changes to the USP requiring manufacturers to evaluate their testing plan and products in order to meet the newer requirements. One of the major changes was the splitting of the older test, contained in USP <61>, into two tests now contained within USP <61> and <62>. The testing discussed in USP <61>, Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests, covers the examination of a product to determine the microbial content. In contrast, the testing covered in USP <62>, Microbiological Examination of Nonsterile Products: Test for Specified Microorganisms, sets forth the methods used to detect organisms that are considered objectionable. These two tests make up the referee test used to determine if a product meets your established specifications for microbiological quality.

A benefit of the harmonization is that comprehensive single test can be followed to comply with the three pharmacopeias’ regulations. However, to accomplish this task, changes had to be made, which pose some challenges to manufacturers. The biggest change came in the addition of three microorganisms to the previous four that were contained in USP <61>. Tests for bile-tolerant gram-negative bacteria, C. albicans, and Clostridium species were added to the list of specific organisms now contained in USP <62>. The methods used to screen for E. coli and Salmonella sp. were also updated to conform to the other pharmacopeia.

Additionally, negative controls were added to the suitability and growth promotion tests. As a result of these changes, manufacturers will have to evaluate their testing methodologies to ensure they comply with the new guidelines.

A new requirement to confirm any growth detected during the test for specified microorganisms was added. Manufacturers may not have performed identifications before and may not be familiar with which method would be most suitable to use. The compendium does not speak of a specific method to perform these identifications. To help determine which method is best, it is important to understand the rationale for the ID. USP <62> is used to screen for specific organisms, therefore utilization of a technique capable of identification to the species level would be most appropriate. Today’s modernized PCR genetic identification techniques are best suited for this application because of their large libraries and accuracy.

When planning for these changes, one should keep in mind the scheduling implications of meeting the new requirements. Ensuring the test method is compliant with the new USP methods will require re-validation of the E. coli and the Salmonella sp. Additionally, one may need to validate the three organisms that were added to the USP. Performing identifications on growth detected during the <62> test will likely extend the turnaround time for the final results. These are all important factors that need to be considered when planning or evaluating one’s testing schedule.

Scheduling implications are not the only drawback to the harmonization of this test. There are fiscal concerns that arise considering portions of the test will have to be validated and that one may have to perform identifications during the testing. It is also likely that the price of testing may have increased because of the changes that were made during harmonization. These may not have been planned for in an original testing budget, so supplementary funding may be required to cover these costs. 

One final consideration that needs to be addressed is the availability of sample. If established sampling plans are in place, the availability of product may be limited. Due to re-validations being required for some parts of the test, additional sample may be required. This may involve modification of your current sampling plans to ensure that there is sufficient product available for testing.

It is important to ensure that adequate quantities of product are available when you are developing your sampling plan. USP <61> and <62> detail the quantity of sample that is required for each of the tests contained therein. While the minimum quantities are provided in these chapters, it’s best to have some material on hand for any unforeseen circumstances. Table 1 provides a quick reference for the quantities of material that are set forth in the USP chapters. Final sample requirements will ultimately vary based on the number of organisms being screened and whether or not suitability work is required. Also note that there are some special sampling provisions provided in the guidelines that are not included in Table 1.

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