The 2017-2018 lecture was an important milestone in an extremely dynamic field of microbiology: the microbiota. The aim was an update on key topics: the mechanisms ensuring stability, robustness and resilience of the gut microbiota, as well as the mechanisms underlying its barrier effect against intruding microbes, particularly pathogens; the basis and rationality of symbioses studied in animal model systems, with a particular interest in the role of the microbe/host interaction in the development of the latter, the "symbiosis fables". We investigated the existence of true viral symbioses at the frontiers of latency and their possible role, in particular, in the maturation of the immune system, or even its senescence and the onset of autoimmune diseases. We have also studied ways of moving from correlation to causation in the pathological effects associated with microbiota imbalance (dysbiosis), and have attempted to establish a definition of pathological microbiological signatures and adapt "Koch's postulates revisited" to complex microbial populations. Finally, we looked at the reciprocal developmental influence of various microbiota and the newborn/infant.
Each lecture was complemented by a seminar on a specific topic related to the lecture theme, given by a leading specialist in the field. These seminars not only dealt with the topic in question, but also emphasized the experimental approaches and methodologies used in the laboratory or in the field.