You need a culture-based method to detect viable cells of the production strain. Cultivation-independent methods, such as PCR to detect DNA from the production strain, are not adequate as they are not sensitive enough.
The procedure should enable the recovery of stressed cells. This can be done by using milder and longer incubation conditions. If the strain is known to produce spores, it is particularly important to verify their absence in the product. To prevent the overgrowth of contaminating microbiota, a selective medium may have to be used, but this must not interfere with the growth of the production strain. Care must be taken also to confirm that the product does not prevent the growth of the production strain. The production strain serves as the positive control to prove the validity of the assay.
The absence of the production strain should be demonstrated from at least 9 g or 9 mL of the product without preservatives, taken from at least 3 independent production batches, a total of 9 samples being the minimum. If colonies are found, they are analysed using production strain–specific PCR. If production strain is found in the product, the production process may need to be adjusted.
Biosafe has an optimised method for several types of feed additives, food enzymes and other fermentation products.
Preliminary testing is always carried out to establish proper conditions for the main test.
To minimize the time and effort of testing, Biosafe will ask you for details about the test strain and the sample. All information will be kept strictly confidential. The test strain is destroyed after the project.