Sterility testing is an essential step in the production of many pharmaceutical products. By default, it is assumed that each newly produced product is not sterile. The degree of non-sterilityis expressed by the Colony Forming Unit (CFU) value in 100 microliters of volume, which is equal to the number of colonies of a given microorganism that appeared on an agar plate after applying 100 microliters of the test solution on the plate and following by incubating the plate for a certain time. There are many different methods for determining non-sterility, the most popular of which are: 1) ATP fluorescent analysis using Adenylate Kinase amplification (AK method); 2) The method of counting colonies on agar plates (Plate count method), 3) The method of visual determination of the turbidity of the solution (Visual method); and 4) ATP fluorescentanalysis (ATP method). Each of them differs in its sensitivity i.e., by its ability to detect the minimum CFU is otherwise called the Limit of Detection (LOD). The LOD of the method is determined from CFU standards that are produced by the industry, such as Bioball (Biomerieux). Our LOD for the AK method is 0.05 CFU. For the Plate count method LOD=1 CFU, this is the natural reference method. In sensitive ATP and Visual methods have LODs of several hundred CFUs. If the non-sterility of a pharmaceutical product is less than the LOD of the method used, this does not guarantee sterility. The guarantee of sterility is the absence of reproduction of microorganisms in the appropriate nutrient medium.

Keywords: Sterility test, Limit of Detection (LOD)