The relationships between a well-balanced gut microbiota (GM), health and animal performance are now well established. The normal development of the GM may favor a ‘barrier effect’ against pathogens. This mechanism take place in adult chickens and mainly relies on the first bacteria colonizing the intestine of chicks. Our recent results have demonstrated the protective activity of adult microbiota inoculated in chick before Salmonella infection. In line with this, the present project aims at an in-depth characterization of the adult microbiota isolated at INRAE, namely the PaFAIM, available in sufficient quantity for repeated experiments and that may be used as starting microbiota in chicks. The PaFAIM is free from pathogen and from any gene of antibioresistance since its initial sampling. In this project, we will assess whether the PaFAIM, used as starting microbiota, may lead to the development of a complex and well-balanced GM with beneficial effects on host immune response, animal performance, and providing a barrier effect against Salmonella caecal colonization as does an adult undefined gut microbiota. This will be achieved through a multidisciplinary approach including multi-omic characterization at the scale of the whole holobiont, and an epidemiologic modelling approach. This project will pave the way for a further development of a simplified, tailored microbiota providing a protective effect against intestinal pathogens and increasing chick robustness.