lecture 1

lecture 1 - Chapter 23- Human Microflora and Nonspecific...

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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 (carnivores have much more bacteroides…varies from week to week, etc. e. coli and bacteroides are always there, just vary in numbers) Can cause disease if reach abnormal location Normal Human Flora There are billions of microbial cells living in and on the human body Sites where bacteria are normally found: Skin Oral cavity Gastrointestinal tract Respiratory tract (certain parts are sterile, like the lungs) Urogenital tract (certain parts are sterile, like the bladder) See Fig 23.1 overview of body, picture of woman Table 23.1 gives prominent bacterial ecosystems of humans (numbers of bacs in high areas…skin, mouth, genitourinary tract, intestine) Human Microflora: Skin Skin is difficult to colonize (harsh environment) Dry, salty, acidic, protective oils Microbes grow mostly in moist areas – underarms, genitals, ( scalp, between your toes) Associated with sebaceous (oil) glands and apocrine (sweat) glands (pH 4-6) Factors that affect types of normal flora- weather, age, personal hygiene (more flora in the summer, young children have a larger variety, how often you wash your hands, when you shower, what soap you use) Bacterial species commonly associated with the skin:
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Most are Gram + Staphylococcus Gram +, aerobic cocci Propionibacterium Gram +, anaerobic rods Propionibacterium acnes can cause acne Another species makes swiss cheese Acinetobacter Gram - rods Few G – bacteria found on the skin Human Microflora: Mouth Bacteria in the mouth prior to tooth formation are mainly aerotolerant anaerobes such as streptococcus and 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 (because you’re literally feeding the bacteria, not because of the sugar’s effects on your teeth themselves) Lactic acid bacteria ferment the sucrose to lactic acid (wears down teeth) (like lactobacillus) Streptococcus mutans produces dextran ( polysaccharide used for attachment to tooth surface) only when sucrose is present (so you eat sugar and then all these other bacs can attach to your teeth because s. mutans is making dextran)
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lecture 1 - Chapter 23- Human Microflora and Nonspecific...

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