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Unformatted text preview: Chapter 23- Human Microflora and Nonspecific Host Defenses Human Microflora Humans colonized by many microbes Normal flora Commensal (Mutualistic) organisms Microbe populations change constantly Vary with type of tissue, condition pH, moisture, other microbes present Intestinal flora varies with food eaten Can cause disease if reach abnormal location Normal Human Flora There are billions of microbial cells living in & on the human body Sites where bacteria are normally found: Skin Oral cavity Gastrointestinal tract Respiratory tract Urogenital tract Human Microflora: Skin Skin is difficult to colonize Dry, salty, acidic, protective oils Microbes grow mostly in moist areas underarms genitals, etc Associated with sebaceous (oil) glands & apocrine (sweat) glands (pH 4-6) Factors that affect types of normal flora weather, age, personal hygiene Bacterial species commonly associated with the skin: Most are Gram positive Staphylococcus Gram +, aerobic cocci Propionibacterium Gram +, anaerobic rods Propionibacterium acnes can cause acne Acinetobacter Gram - rods Few G found on skin Human Microflora: Mouth Bacteria in the mouth prior to tooth formation are mainly aerotolerant anaerobes such as Streptococcus & Lactobacillus Acidic glycoproteins in saliva form a layer on teeth providing a firm attachment site for microbes, usually Streptococcus species Extensive growth of these microbes results in thick bacterial layers called dental plaque microflora of dental plaques make acids that decalcify tooth enamel; results in dental caries (tooth decay, cavities) Tooth surfaces in and near the gingival crevice where food particles remain are common sites of tooth decay. Floss!!! Diets high in sucrose are cariogenic cavity causing Lactic acid bacteria Streptococcus mutans produces dextran (polysaccharide used for attachment to tooth surface) only when sucrose is present Diets containing fluoride during formation of tooth enamel make teeth more resistant to tooth decay Incorporation of fluoride into the calcium phosphate crystal matrix increases resistance to decalcification. Normal flora of the gastrointestinal tract Human Microflora: Stomach pH ~2 Only acid-tolerant bacteria can colonize stomach wall ex. Helicobacter pylori (peptic ulcers) Very few bacteria are found in stomach fluids Human Microflora: Small Intestine # of bacteria increases down through small intestine (due to rising pH) Duodenum : few bacteria due to stomach acids; mainly Gram + cocci and bacilli Jejunum : Enterococcus, Lactobacillus Ileum : microbiota reflects that of large intestine; large number of Bacteroides & facultative aerobes like E. coli Human Microflora: Large Intestine Fermentation vessel; many bacteria (more than 300 species), mostly anaerobes Commonly 10^11 bacterial cells/gram of intestinal contents bacterial cells/gram of intestinal contents...
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This note was uploaded on 08/04/2009 for the course BIOL 2051 taught by Professor Brininstool during the Fall '07 term at LSU.
- Fall '07