BIOL_2051_ch23_notes - Chapter 23 Human Microflora and...

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Chapter 23- Human Microflora and Nonspecific Host Defenses Human Microflora Humans colonized by many microbes Normal flora “Commensal” (mutualistic) organism Microbe populations change constantly Vary with type of organism , environmental conditions pH, moisture, other microbes present Intestinal flora varies with food eaten Can cause disease if they reach abnormal location Normal Human Flora There are billions of microbial cells living in and on the human body, 90% microbial vs. 10% human cells 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, and has protective oils (from sweat and oil glands) Microbes grow mostly in moist areas- underarms, genitals, etc. Factors that affect types of normal flora- weather, age, personal hygiene Bacterial species commonly associated with the skin: Most are Gram + Staphylococcus Gram +. aerobic cocci Propionibacterium Gram +, anaerobic rods
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Propionibacterium acnes can cause acne Acinetobacter Gram - rods Few G – bacteria found on skin Human Microflora: Mouth Bacteria in the mouth prior to tooth formation are mainly aerotolerant anaerobes such as 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 carcinogenic-cavity causing Lactic acid bacteria ferment the sucrose to lactic acid, causing decalcification 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
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BIOL_2051_ch23_notes - Chapter 23 Human Microflora and...

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