ABSTRACT
Probiotic bacteria, or more specifi cally bacterial strains with probiotic properties, are identifi ed by their specifi c probiotic properties. The latter are the health effects they exert on the human host. These health effects have to be established in double-blind, placebo-controlled clinical studies. It goes without saying that it is not practicable to identify established probiotic bacteria in food or faeces by their health effects, because this would mean that for every strain to be identifi ed a clinical study would have to be carried out. The situation would change, if the bacterial gene products (or gene product, if there is only one) responsible for the probiotic effects, their states of activity and their cellular concentrations necessary to exert the probiotic effects were known. Then, identifi cation of the bacterial species in conjunction with the correctly expressed active gene products would be suffi cient for identifi cation of a probiotic strain. However, as long as a clear correlation between gene products of a specifi c bacterial strain on one hand and manifestation of a health effect on the other hand has not been established, surrogate assays are needed. Such surrogate assays aim at identifying probiotic bacteria by strain-specifi c methods. This is in line with the statement made by FAO/WHO (2006): “Strain typing has to be performed with a reproducible genetic method or using a unique phenotypic trait.”
