Intestinal microbiome in health and disease: Introduction

At the end of the nineteenth century, Robert Koch and Louis Pasteur developed the concept that transmissible human diseases are caused by microbial infections and, thereby, revolutionized the view of physicians on how to prevent and treat epidemics. More than 100 years later, the next conceptual revolution implies that naturally occurring communities of “commensal” microbes, collectively called microbiome, in and on human body sites affect health and the development of numerous diseases. The intestine provides an explicitly large interface to the environment and is criti- cally involved in immune and metabolic homeostasis, providing the conceptual basis that this spatially adapted communities of microorganisms affects human health. Immune, metabolic, and xenobiotic receptors sense and process microbial signals and thereby contribute to a mutualistic relationship between the microbiome and the host. It seems a plausible hypothesis that the microbiome, considered as the forgotten organ, coevolved with the mammalian host, leading to a symbi- otic interdependence of this metaorganism. Increasing evidence suggests that “unfavor- able or so-called dysbiotic” changes in the gut microbiome lead to a distortion of microbe-host homeostasis and potentially affect disease susceptibility. In this book, we discuss breakthroughs, challenges, and applications of microbiome research at a cutting-edge level.