Microbial Limits Test – USP <60>, USP <61> and <62>

The microbial limits test (MLT) procedures described in USP <61> and <62> are performed to determine whether a product complies with compendial specifications for microbial quality, and consists of two parts. The quantitative phase, Microbial Enumeration, determines the total number of aerobic organisms as well as a total yeast and mold count on a product. The qualitative phase of a microbial limits test is known as the Test for Specified Microorganisms. This test is designed to determine the presence or absence of specific objectionable organisms in a product. PBL can also perform suitability and screening for Burkolderia cepacia complex according to the new USP <60>.

Prior to performing MLT testing on a product, the method must be validated to ensure that the product has no microbial inhibitory properties which could result in false negatives. This validation testing is known as the MLT Method Suitability Test. If these antimicrobial properties are present, these can be eliminated by dilution, filtration, neutralization or inactivation before testing the product.

The relevant standards for the Microbial Limits Test have been harmonized for the US, European, British, and Japanese markets. Microbial Limits Tests is typically performed following cGMP and should be conducted by a GMP microbiology laboratory. The MLT tests are usually performed on non-sterile pharmaceutical, healthcare and cosmetic products that can range from raw materials to finished products.

Available Pharmaceutical Microbial Limits Testing Services

  • MLT Method Suitability Test
  • Microbial Enumeration (Total Aerobic Microbial Count and Total Combined Yeasts and Mold Count)
  • Screening Test for Specified Microorganisms:
    • P. aeruginosa
    • E. coli
    • S. aureus
    • Salmonella
    • Bile tolerant gram negative bacteria
    • C. albicans
    • Clostridium
    • B. cepacia complex (Bcc)

Read More About Microbial Limits Testing (MLT)


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