The gut microbiota, its relationship to the immune system, and possibilities of its modulation.

Research of the gut microbiota allows a better understanding of its composition and function and reveals the links between changes in the composition of bacteria and various intestinal but also systemic diseases. The gut microbiota performs several of important functions in the host body and influences many physiological processes. Gut bacteria synthesize many compounds needed for the proper function of the body (e.g., vitamins, short-chain fatty acids, and amino acids). They help maintain the integrity of the intestinal barrier and protect against pathogens. The gut microbiota plays a crucial role in the development and function of the immune system. Significant changes in the composition of the intestinal microbiota led to a dysbiotic state and the loss of its beneficial functions for humans. The review article summarizes the basic knowledge about the composition and function of the bacterial gut microbiota in healthy people, its role in the development of the immune system, and the mechanisms involved in maintaining homeostasis. It also presents current knowledge about the possibility of targeted modulation of the bacterial gut microbiota and faecal transplantation.