Bioburden testing is used for the estimation of the population of microorganisms on the surfaces of medical devices, empty product vials and bulk product by membrane filtration. In the case of medical devices it is an important part of the initial process validation and ongoing process control as set out in various ISO standards.
PRINCIPLE OF TEST:
The population of viable microorganisms (bioburden) in a product or on a product surface is required to monitor a production process, be it for a medicinal product or a medical device. In most cases, with a medicinal product one is examining the product directly, in which case there is a need to make sure there are no antimicrobial properties in the product to affect the results. This is normally done by microorganism spike/recovery experiments. In the case of medical devices there is the possibility that the extraction procedure may not remove all the microorganisms from the device, thereby causing an underestimation of the actual bioburden present. Therefore there is a need to establish a correction factor for the particular device being studied. The methods for establishing the correction factor are discussed below. There are two approaches that can be employed. These are based upon the standard ISO 11737:1.
For medical devices with a predicted natural bioburden, a repetitive treatment is employed. The device is rinsed with diluent and filtered and repeated multiple times until there are no or very few micro organisms recovered. The number of colonies recovered after initial filter of the removal technique is expressed as a fraction of the total number of colonies counted. This fraction is then applied as the correction factor for all further testing of that device by that method. The routine result is then expressed as the bioburden estimate, which represents the detected bioburden count multiplied by the correction factor.
For devices with a predicted low bioburden, an inoculation treatment is employed. The device is artificially inoculated with a known low number of Bacillus subtilus ATCC 11774. The inoculated device is then immersed in diluent, massaged and the rinse filtered. The correction factor is calculated as the proportion of organisms removed compared to the original inoculum applied. The routine result is then expressed as the bioburden estimate, which represents the detected bioburden count multiplied by the correction factor.
Validation: 3 – 5 devices
Bioburden estimate: 1 device