The European Pharmacopoeia specifies in the chapters describing the microbiological methods (2.6.12, 2.6.13, and 2.6.31) that the suitability of the test method for detecting microorganisms in the presence of the product must be demonstrated. This proof must be reconfirmed for all changes to the method or the product.

For this purpose, the product is inoculated with suspensions of the organisms mentioned in the aforementioned chapters, treated further as described there, and incubated on the mentioned media under the specified conditions.

In quantitative methods, the number for each reference microorganism may deviate by a maximum factor of 2 from the reference value, which was determined using the same methods in the absence of the product.

In qualitative methods, the growth of the reference microorganisms must be detectable as the result of the test in the absence of the product.

If the suitability of the method cannot be demonstrated using standard procedures, the method must be appropriately adjusted (for example, by higher product dilutions or by using a different diluent or other neutralizing substances).