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

The microbial limits test (MLT) procedure 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.

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 produce false negatives. This validation testing is known as the MLT Method Suitability Test.

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.

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

Read More About Microbial Limits Testing (MLT)


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