The Human Microbiome in Health and Disease

At the microscopic scale, the human body becomes a complex ecosystem, harboring hundreds of millions of microorganisms on its surface and in its interior. This diverse and innumerable assemblage of organisms constitutes what is collectively referred to as the human microbiome. Increasingly, research is revealing a profound interrelationship between the health of an individual and the state of their microbiome. As distinct microbial communities can be localized to certain parts of the body, investigations have been launched to survey the significance of the gut, respiratory, reproductive tract, oral, and skin microbiomes. Underpinning this research is the belief that an improved understanding of the human microbiome will allow for the prevention and control of chronic diseases, the remediation of suboptimal health, and a potential revolution in medical technologies. Research into the interactions between the microbiome and health will hopefully lead to the development of microbiome-based medicine, capable of not only treating diseases but preventing them as well. In this chapter we will define, in greater depth, what the human microbiome is, what factors influence its composition, and how it relates to the gut, the immune system, brain development, obesity, and infection. Overall, we explore how something as small as one micron has the power to radically influence health, diet, and lifestyle.