**4. Conclusions**

The use of probiotics for the prevention and / or treatment of gastrointestinal disorders have a strong theoretical justification, based on the beneficial functions of the indigenous microbiota, fundamental for maturation and health of the digestive ecosystem. However, a number of issues need to be resolved before general guidelines regarding the use of probiotics can be given. Basic research must provide more detailed data on the mechanisms of probiotic action on the molecular level, after which coordinated rigorously conducted clinical trials must be undertaken to find the probiotic strain and dosage with optimal results for each clinical situation. It is unlikely that one strain or probiotic combination will be sufficient for all purposes. At the moment, the heterogeneity of probiotic clinical trials hampers interpretation – in particular the diversity of probiotic strains, dosing regimens and forms of administration used and the varied patient groups recruited in the available studies makes interpretation difficult. Concluding, more biological and well controlled clinical trials must be carried out for a more precise understanding of both the mechanisms underlying the probiotic action and the complex gastrointestinal ecosystem with which probiotics are expected to interact.
