[Fundamentals of the microbiome]

Until the middle of the 20th century, clinical microbiology was limited to bacterial cultures enabling the detection of pathogenic microorganisms. Knowledge about the mutual relationship between humans and microorganisms has increased slowly. With the introduction of culture-independent analysis methods, comprehensive cataloging of the human microbiome was possible for the first time. Since then, compositional changes in relation to diseases have been studied. The goals of the Human Microbiome Project and MetaHIT include comparative studies of healthy and diseased individuals. Numerous libraries on time- and location-dependent changes of the microbiota composition in human diseases have been created. However, a mathematical correlation does not equal biological or medical relevance. Future research needs to validate the hypotheses generated in these studies in functional experiments and evaluate their true impact on clinical practice.