Chapter 4 - Gut Microbiota in Health and Disease

Abstract

Although single pathogens are well-known for causing disease, growing evidence suggests alterations in the structure or function of the human gut microbiota may play a role in the pathogenesis or maintenance of several chronic diseases and other conditions. Normally, the gut immune system functions to maintain homeostasis in the intestinal environment, tolerating commensal gut microbes while protecting against infection by pathogens. Several pathogens, however, are well adapted for causing disease by gaining access to the gut environment. Many of the complex diseases associated with alterations in the gut microbiota are related to inflammation. The list of diseases with a possible connection to gut microbiota includes asthma and allergy, inflammatory bowel disease, metabolic syndrome and obesity, type 2 diabetes, cardiovascular disease, type 1 diabetes, liver disease, necrotizing enterocolitis, irritable bowel syndrome, some cancers, malnutrition, celiac disease, and brain-related conditions (depression, Parkinson's disease, and autism spectrum disorders). While a significant difference in gut microbiota composition associated with disease states may be called a “dysbiosis,” defining a “healthy” microbiota is a challenging task that lies ahead.