GI Tract Microbiota Characters PDF

GI tract microbiota characters The vast majority (~98 percent) of all human gut phylotypes fall into one of three major bacterial phyla: Firmicutes, Bacteroidetes, and Proteobacteria. – Individuals may have mostly Firmicutes, mostly Bacteriodetes, or a mix of the two. This may regu...

GI tract microbiota characters The vast majority (~98 percent) of all human gut phylotypes fall into one of three major bacterial phyla: Firmicutes, Bacteroidetes, and Proteobacteria. – Individuals may have mostly Firmicutes, mostly Bacteriodetes, or a mix of the two. This may regulate metabolism and the host’s propensity for obesity. – While individuals vary in their gut microbiota, each individual has a relatively stable gut microbiota. – There are three basic enterotypes currently being studied: #1 is enriched in Bacteroides (Bacteroidetes) #2 is enriched in Prevotella (Bacteroidetes) #3 is enriched in Ruminococcus (Firmicutes). Early studies indicate that each enterotype is functionally as well as phylogenetically distinct.  Products of Intestinal Microbiota and “Educating” the Immune System – Many microbial metabolites or transformation products that can be generated in the gut have significant influence on host physiology. (Table 24.2) – vitamin production – modification of steroids – amino acid biosynthesis  important ∅ Table 24.2  The coenzyme vitamin B12 The structure of vitamin B12 A complex of corrin ring and cobalt British biochemist & crystallographer Nobel Prize in Chemistry in 1964 Vitamin B12 is produced by intestinal bacteria. It can also be obtained from dietary meat and the richest natural source is raw liver. Patients may lack intrinsic factor, a glycoprotein essential for vitamin B12 absorption in the gut. Deficiency leads to pernicious anemia. http://www.ssplprints.com/image/93941/vitamin-b12-crystal-structure-model-1957-1959  24.3 Oral Cavity and Airways The oral cavity is a complex, heterogeneous microbial habitat. (Figure 24.7) Saliva contains antimicrobial enzymes (amylase, lipase, lysozyme). But high concentrations of nutrients near surfaces in the mouth promote localized microbial growth. The tooth consists of a mineral matrix (enamel) surrounding living tissue, the dentin, and pulp. (Figure 24.8)  At least 750 species of aerobic and anaerobic microbes, including a minor representation of methanogenic Archaea and yeast, are known to reside in the oral cavity, distributed among teeth, tissue surfaces, and saliva. The most abundant genera in the oral cavity are Firmicutes. The primary colonizers of clean tooth surfaces are species of Streptococcus; obligate anaerobes such as Veillonella and Fusobacterium colonize habitats below the gum line. Those are mostly good ones. Dental plaque is a complex mixed- culture biofilm composed of several different genera of Bacteria and their accumulated products. And it is a breakdown in the generally stable mutualisms of the healthy microbial flora.  Dental Caries and Periodontitis – Cells form a biofilm called dental plaque, which has Streptococcus and other fermenting bacteria. (Figure 24.21) – These fermenters produce acid, which wears down the tooth enamel. – Periodontal disease is thought to contribute to several systemic conditions, including cardiovascular disease and arthritis. Diverse morphology of the 52 organisms present and the slime layer (arrows) on model tooth 때  Airways Microenvironments of the Respiratory Tract (refer to the Medical Microbiology lecture) – Microbes thrive in the upper respiratory tract. Bacteria continually enter the upper respiratory tract from the air during breathing. Most are trapped in the mucus of the nasal and oral passages and expelled with nasal secretions or swallowed and then killed in the stomach. – The lower respiratory tract has no normal microbiota in healthy adults. Ciliated mucosal cells move particles up and out of the lungs.