Microbial Limits Test

Bioburden/Microbial Enumeration Testing (MET) is performed on various pharmaceutical articles including raw materials and finished forms, as well as medical devices and packages, which will be categorized as non-sterile, to determine the microbial load on the products.

Typically, bioburden testing is included with a sterilization program to ensure pre-sterilization microbial load is within the tolerance of the sterilization cycle, to ensure residuals after sterilization are at acceptable levels, and to confirm products are properly sterilized throughout the program.  Bioburden Testing is also used during the release of a product to market to demonstrate that the manufacturing process remains in control. This includes enumeration by total aerobic microbial count and total yeast and mold count, which are used to ensure acceptable levels based on safety and regulatory guidelines.

Regulatory bodies require pharmaceutical and medical device companies to monitor the bioburden load in products used for humans and animals to ensure product safety according to procedures outlined in the following USP guidances: IIII


USP <61>  An enumeration test, sometimes referred to as bioburden, that quantifies microorganisms in non-sterile products or raw materials.  It determines the total aerobic microbial count (TAMC), as well as the total yeast and mold count (TYMC).

USP <62> It tests for the presence or absence of specific organisms in a product, which can include the following: Escherichia coli, Candida albicans, Staphylococcus aureus, Pseudomonas aeruginosa, Salmonella species, Clostridia species and bile tolerant Gram negative bacteria. These tests are conducted using general and selective broth and agar media to amplify specific pathogens or objectionable organisms present in the product and isolate them. Any presumptive positive organisms are typically tested through classical biochemical and culture based techniques, and may be tested by newer methods such as MALDI-TOF or gene sequencing for confirmation.

USP <61> and USP <62>  testing provides harmonization to the European Pharmacopeia methods for testing non-sterile pharmaceuticals. USP requires that prior to routine enumeration testing a method suitability test must be performed. Amount of sample required for each test is typically around 10 grams/mL/patches and for the suitability test is 30 to 40 grams/mL/patches.

MET may include assessment of the physical characteristics and inherent antimicrobial properties of the product in question. We provide guidance to our clients to ensure appropriate testing is conducted on specific products, with many years of experience in the pharmaceutical, cosmetic, and consumer industries, dealing with a diverse and vast list of products and specifications.

During testing of bioburden, we utilizes the following techniques:

Membrane Filtration Method

Standard Plate Count

Pour Plate Method

Most Probable Number

Direct Enrichment

Membrane Filtration Enrichment