Interpretation of quantitative microbiological results

The complex nature of the quantitative microbial situation in a substrate s hould be understood as one point in a multidimensional system of co-ordinat es representing the vast variety of microbiological facets - for example ba cterial species, metabolic activity - which add to it. No method is capable of measuring the complete situation of the bacteriological status of a sam ple, and different methods and/or measuring principles can be influenced by different factors to different degrees. This means that the application of different methods does not lead inevitably to identical results. Examples of such influencing factors - bacterial species, bacterial aggregation, hea t inactivation - are given. A general problem of quantitative microbiologic al methods which has to be faced is the fact that calibration in its strict sense is not possible and the figures measured are only defined by the des cription of the method. Despite general limitations the Standard Plate Coun t method is agreed upon as reference/official method and as such serves as an "anchor point" when defining bacteriological quality in the frame of leg islation and many trade agreements and also when defining method related cr iteria in those cases where the reference method is replaced by a routine/a lternative method. The examination of samples reflecting the intended field of application by both methods is the prerequisite for the evaluation of s uch routine methods and for the elaboration of a suitable transformation of routine/alternative values on the scale of the reference method in order t o check whether limits fixed in the dimension of the reference method are m et.