Determining the bioburden of medical devices is one way of checking and evaluating the effectiveness of all production hygiene steps on the end product. The term bioburden refers to the microbial contamination of a medical device before it is sterilized.


The bioburden is the sum of all microorganisms from various sources, including raw materials, component manufacturing, assembly processes, the manufacturing environment, assembly and manufacturing aids, cleaning processes and packaging of the finished product.

It is not possible to give an exact figure for the microbial load, as many factors can influence the determination of the bioburden. In practice, the bioburden is determined according to a defined procedure that includes a characterization of the population in addition to the quantification or estimation of the microorganisms. Due to the wide variety of materials used in the manufacture and construction of medical devices and the associated different surface adhesion of microorganisms, DIN EN ISO 11737-1 presents different process parameters.

The same applies to the huge number of different microorganisms that can occur on medical devices. DIN EN ISO 11737-1 also provides a large selection of appropriate rinsing solutions and culture media, including incubation conditions in various combinations.
The process used at GfPS mbH takes into account the different needs of microorganisms: slow-growing fungi have to be cultivated differently to fast-growing bacteria. Anaerobically growing bacteria are cultivated in the absence of atmospheric oxygen.

The bioburden limits are set by the manufacturer of the products. The mean value and standard deviation per product group are used to help determine the alarm limits. An alarm limit (or action limit) results from the sum of the mean value and twice (or three times) the standard deviation.

Validation of the bioburden method according to DIN EN ISO 11737-1

According to DIN EN ISO 11737-1, the bioburden method must be validated in order to prove the suitability of the test method and to assess the suitability of the technique for sampling the microorganisms.
There are two traditional approaches to validating the efficacy of sampling microorganisms from healthcare products. These approaches are:

  • Determination of the recovery rate by means of repeated recovery: the repeated treatment of a product sample followed by a quantitative assessment of the extent of recovery, with relatively high natural microbial contamination of the product.

Products with moderate to high (e.g. 100 CFU to 1,000 CFU) or high (e.g. B. > 1 000 CFU) Bioburden.

Five non-sterile samples are repeatedly rinsed with the corresponding rinsing solution. A recovery rate can be determined from the ratio between the number of colonies after the first application and the total number of colonies.


  • Determination of the recovery rate using the inoculation method (inoculated product): Product inoculation with a known number of microorganisms, followed by a quantitative assessment of the extent of recovery at a low natural contamination rate of the product.
    Products with a low, e.g. < 100 CFU or very low, e.g. < 10 CFU bioburden.
    For this purpose, five (sterile or slightly contaminated) samples are contaminated with a defined microorganism, e.g. Bacillus atrophaeus spores, and subjected to the selected bioburden process after drying. A recovery rate can be determined from the ratio between the number of spores detached from the product and the total number of spores with which the product was contaminated.

A correction factor is determined from both methods described, which, multiplied by the number of microorganisms from the routine bioburden determinations, gives the estimated values of the actual microbial load.

Validation must be carried out at fixed intervals in accordance with DIN EN ISO 11737-1. The scope is determined by means of a risk assessment.
This may mean that a theoretical consideration is sufficient. Changes to the product, product groups or manufacturing processes must be checked and evaluated.

Determination of the total bacterial count using the MPN method

The MPN method is used to quantitatively determine the concentration of bacteria in a sample. The starting solution or sample is introduced into the nutrient broth at certain dilution levels to ensure the presence or absence of microorganisms.

Neutralization of inhibitory substances MST

This test for the detection of the neutralization of inhibitory or generally antimicrobial properties demonstrates the validity of the method and performance of the routinely determined bioburden.
If the product can be negatively affected due to its physical or chemical properties, a system must be used to neutralize, remove or minimize the effect of any substances released. The effectiveness of such a system must be proven.
Various microorganisms and incubation conditions are examined in order to obtain a meaningful result.

Bioburdening of textiles

Nowadays, modern functional fabrics have to deliver top performance. We check the effectiveness of your products and analyze the relevant hygiene parameters. With the help of advanced textile analytics, we support you in the quality assurance of your production. We determine the bacterial load (bioburden) of textiles with particularly high requirements for sterility.


  • according to DIN EN ISO 11737
  • according to DIN EN 13795
  • according to DIN EN 14065
  • according to FDA
  • BAM Appendix 2
  • according to Ph. Eur. 2.6.12
  • according to USP <61>

We will be happy to assist you with your questions about Bioburden at