Bioburden Recovery Efficiency
Updated: Jun 3, 2022
What is Bioburden?
Bioburden is the population of viable microorganisms present on or in a product. The bioburden of a product can come from a few sources such as:
Raw materials
Manufacturing of components
Assembly processes
Manufacturing environment
Assembly/manufacturing aids (e.g. compressed gases, water, lubricants)
Cleaning processes
Packaging of finished products
You can reduce the bioburden levels on your products by controlling the microbial population of these sources.
The determination of bioburden on a medical device is commonly called a bioburden test. A bioburden test usually comprises of a technique to remove the microorganisms from the product followed by a culturing method to count the removed bioburden.
What is Bioburden Recovery Efficiency?
In practice, it is impossible to enumerate every microorganism that is present on a product due to the nature of the product, the extraction method and culturing limitations.
Some method might be more effective at removing the microorganisms but might cause cell death, make them unculturable and thus not enumerable. Whereas some methods might be gentle to the microorganisms but are less effective at removal.
Therefore, care should be taken when choosing the most suitable and effective method to estimate the bioburden of a product.
Since complete removal of bioburden is not possible, bioburden recovery efficiency tests are performed to establish a bioburden correction factor. It is a measure of the ability of a specific method to remove, collect and/or culture microorganisms from a product.
The bioburden correction factor will “correct” the bioburden data so it will “include” or account for microorganisms that are not removed or cultured. Bioburden recovery efficiency tests can also be done to compare the effectiveness between test methods.
What is Bioburden Correction Factor?
The bioburden correction factor is a numerical value applied to the bioburden count which will result in a final bioburden estimation of the product.
When this value is applied, microorganisms not removed from the product or not detected by the culture conditions used will be accounted for.
Bioburden data that have been adjusted using the bioburden correction factor are understood to represent the true bioburden count more accurately; this is called a bioburden estimate.
A bioburden test method for a specified product is not valid until a bioburden correction factor is established and applied.
There are two commonly used methods for bioburden correction factor determination:
Repetitive recovery
Product inoculation
How to Calculate the Bioburden Correction Factor?
Repetitive Recovery
Using this method, a medical device is subjected to a removal/extraction technique repeatedly until a significant reduction in bioburden count is observed. Usually, 5 times repetition is sufficient.
For example, if the bioburden method used to extract the microorganisms is sonication followed by membrane filtration of the eluent, then, the product must go through 5 rounds of sonication and membrane filtration. The membrane filter from each round is cultured and the bioburden population counted.
Below is an example of repetitive recovery data taken from ISO11737-1:2018.
Using average recovery by first treatment, 48.2% and appropriate rounding, the bioburden correction factor (CF) by repetitive recovery is:
Correction Factor, CF = 100/4.82
CF = 2.07
CF = 2.1
Product Inoculation
The product inoculation method uses a suspension of a known number of microorganisms to create an artificial bioburden on a product.
This artificial bioburden is then extracted using the selected method and counted to determine how many of the inoculated microorganisms were recovered. The efficiency of the method to remove the artificial bioburden is determined and a correction factor is established.
As an example, 100 CFU suspension of an aerobic organism is inoculated onto 3 products each and left to dry under laminar airflow conditions.
All 3 products are then subjected to the chosen method to extract the inoculated microorganisms and count them. The correction factor is determined using the average recovery among the 3 products.
Below is an example of repetitive recovery data taken from ISO11737-1:2018.
The mean number of microorganisms removed was 76. Therefore, the bioburden correction factor (CF) for bioburden recovery efficiency, including appropriate rounding is:
Correction Factor, CF = 100/75.7
CF = 1.32
CF = 1.3
Which method to use?
Generally, the repetitive recovery method is most suited for products with a higher bioburden and the inoculated product method is best for products with a lower bioburden.
However, other factors like the nature of the product, the type of material used or the capacity of the laboratory to perform these tests should be considered.
ISO11737-1:2018 has summarized typical product and method characteristics that should be considered when selecting an appropriate bioburden recovery efficiency.
At Sanichem Resources, we are experienced and accredited to perform both repetitive recovery and product inoculation method for bioburden correction factor determination. We welcome any inquiry on these tests and other related topics.