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Bioburden is the presence of viable microorganisms on a surface (or complete item), inside a device, or in a portion of liquid, before sterilization. Bioburden can be introduced from the raw materials used in the manufacturing process or through the workforce in the manufacturing environment or during the packaging of end products.  With numerous sources of potential contamination, the bioburden of a product can fluctuate between batches hence routine testing is implemented as a part of quality control.  

Bioburden testing, or total viable count testing, is the measure of microbial contamination levels on or in a product.

Bioburden can be introduced from the raw materials used in the manufacturing process, or be introduced via the workforce or manufacturing environment. With numerous sources of contamination, the bioburden of a product can fluctuate between batches, so regular, routine testing is advisable.

Purpose…
Bioburden testing or Microbial testing is a quality control process that detects and quantifies microbial contamination of a product at different stages of production i.e., from initial manufacturing to final distribution.
The purpose of bioburden testing is to enumerate the quantity of viable microorganisms on a pharmaceutical product, medical device, component, raw material, or package before sterilisation. Bioburden testing is also an important indicator of problems in the production process which could lead to product recalls later.

For a sterilisation process to be effective on a newly manufactured pharmaceutical product or medical device, manufacturers must be aware of the number, properties and characteristics of microorganisms that occur in the products naturally or while going through the production process. This is a crucial step prior to setting sterilisation parameters such as dosing, temperature etc. to ensure that the process is effective and the product safe when used. 

Bioburden test results may be used to:

  • Demonstrate microbial quality control of the manufacturing process through routine monitoring and trending (ISO 11737)
  • Determine radiation dose for terminally sterilized product (ISO 11137)
  • Investigate root cause of contamination excursions from routine production (Alert and Action levels)
  • Test raw and finished product materials for microbiological examination of non-sterile products (USP<61>)
  • Methods for the absence of specified or objectionable microorganisms can be developed. These methods not only give total viable counts, but also identify the presence or absence of specified microorganisms, providing complete, robust test results. (USP<62>, USP<60>)
 
The test is performed by taking replicate samples and submitting them to tests of sterility. The samples are incubated and scored for presence/absence of growth. The number of samples that are positive for growth is used to calculate the bioburden estimate.
 
What is bioburden testing as per USP?
 
USP <61> is often called a “Bioburden” or “Microbial Limits”. This test determines how many microorganisms are present in nonsterile drug products. During a USP <61> test, the drug product is prepared and plated on two types of growth media, Soybean-Casein Digest Agar and Sabouraud Dextrose Agar.
 
What is the CFU limit for bioburden?
Based upon current practice, for aseptically filled products, the UBPS bioburden limit is 10 CFU/100 mL and for terminally sterilized products, this limit is 100 CFU/100 mL.
What is the bioburden limit for FDA?
The EMA guideline further states that a bioburden limit of no more than 10 colony-forming units (CFU) per 100 mL will be considered acceptable in most situations. The EMA guideline also states that a pre-filtration sample volume of less than 100 mL may be tested if justified.
Method…
Membrane Filtration Method for Bioburden Testing
In this method, the sample is passed through a membrane filter with a 0.45 µm pore size. The membrane functions as a barrier and captures microorganisms larger than the membrane pore size. During filtration, a vacuum can be used to speed up the process.

In General Bioburden testing or Microbial testing is a quality control process that detects and quantifies microbial contamination of a product at different stages of production i.e., from initial manufacturing to final distribution. Effective quality control and accurate test results are essential to minimize risks for consumers and are required by regulated production environments. Therefore, bioburden analysis is often included in routine testing to ensure the safety, quality, and regulatory compliance of each manufactured product batch.

Bioburden testing is performed for medical devices, pharmaceuticals, food and beverages, water, packaging, raw materials, human tissue, animal tissue, and cosmetics. When standard methods, as described below are followed, it is important to ensure that the testing method does not introduce bacteria into the test sample or kill bacteria in the test sample.