An introduction to microbial dysbiosis

This chapter provides some introductory thoughts on the concept of microbial dysbiosis by addressing three related issues. These issues include what should be regarded as normal in the context of a benign commensal microbiota, what are the characteristics of dysbiosis, and what is the functional importance of dysbiosis. People are well accustomed to the concept that the host-associated microbiota change throughout normal human development. For example, the intestinal microbiota at birth is initially colonized by Enterobacteria. Dysbiosis is now recognized as a definitive change in the microbiota at a given site in the body, crucially accompanied by a breakdown of host-microbial mutualism. Dysbiosis of human-associated microbiota is now thought to be the defining event of multiple inflammatory and systemically driven pathologies. Key features of dysbiosis include a decrease in microbial population diversity, reductions in beneficial microbes and increased levels of pathobionts.