Microbial Symbioses with Humans PDF

Microbial Symbioses with Humans All sites on a human that contain microorganisms are part of a microbiome. A microbiome is a functional collection of different microbes in a particular environmental system (e.g., the human microbiome). Microbiota to describe all the microbes in a micr...

Microbial Symbioses with Humans All sites on a human that contain microorganisms are part of a microbiome. A microbiome is a functional collection of different microbes in a particular environmental system (e.g., the human microbiome). Microbiota to describe all the microbes in a microhabitat (e.g., skin microbiota). Different microhabitats support different microbes, so the skin will have very different microbes than the mouth.  I. Structure and Function of the Healthy Adult Human Microbiome 24.1 Overview of the Human Microbiome 24.2 Gastrointestinal Microbiota 24.3 Oral Cavity and Airways 24.4 Urogenital Tracts and Their Microbes 24.5 The Skin and Its Microbes 24.1 Overview of the Human Microbiome There are approximately 1013 microbes in the human microbiome (Figure 24.1) living in complex communities. Figure 24.1 Benefit and complexity of Human Microbiome Future Benefits of Knowing the Human Microbiome – development of biomarkers for predicting predisposition to diseases – designing targeted therapies – personalized drug therapies and probiotics We are at an early stage of studies which reveal that there are complex interactions between host and its microbiota.  Experimental Protocols and Body Target Sites – Most Bacteria cannot be cultured; however, advanced sequencing techniques allow for identification of different microbiota at different body sites. (Figure 24.2) – There have been multiple studies to determine the nature of the normal microbiota. (Table 24.1)  Basic questions about the human microbiome: – Do individuals share a core human microbiome? – Is there a correlation between the composition of microbiota colonizing a body site and host genotype? – Do differences in the human microbiome correlate with differences in human health? – Are differences in the relative abundance of specific bacterial populations important to either health or disease?  24.2 Gastrointestinal Microbiota Humans are monogastric and omnivorous. Microbes in gut affect early development, health, and predisposition to disease. Colonization of gut begins at birth. The human gastrointestinal (GI) tract (Figure 24.3) Consists of stomach, small intestine, and large intestine and comprises 400 m2 of surface area Responsible for digestion of food, absorption of nutrients, and Contains 1013 to 1014 microbial cells; production of nutrients by the indigenous microbial flora. Human digestion tract and functions Figure 24.3  The Stomach and Small Intestine – Microbial populations in different areas of the GI tract are influenced by diet and the physical conditions in the area. – The acidity of the stomach and the duodenum of the small intestine (~pH 2) prevent many organisms from colonizing the GI tract; however, there is a rich microbiome in the healthy stomach. – Firmicutes, Bacteroidetes, and Actinobacteria are common in the gastric fluid, while Firmicutes and Proteobacteria are common in the mucus layer of the stomach. – Helicobacter pylori was discovered in the 1980s and has since been found in ~50 percent of the world’s population. When present, it is found in the gastric mucosa.  Intestinal microorganisms carry out a variety of essential metabolic reactions that produce various compounds. The Large Intestine – The colon is essentially an in vivo fermentation vessel, with the microbiota using nutrients derived from the digestion of food. – Most organisms are restricted to the lumen of the large intestine, while others are in the mucosal layers. (Figure 24.6)