207_2009_Lect_26TwentySix

207_2009_Lect_26TwentySix - 11/16/2009 Biology 207, 2009...

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11/16/2009 1 Biology 207, 2009 Lecture twenty-six Wednesday, November 18 Human-microbe interactions Epidemiology Normal bacterial and fungal residents of the human body many species of bacteria and many fungi are normally resident on and in the human body they are found in those regions of the body normally exposed to the environment skin, oral cavity, upper respiratory tract, intestinal tract, urogenital tract yp p p y g these bacteria usually are beneficial; they are important for a normal state of health in the gut tract: vitamin synthesis (thiamine, riboflavin, B 12 ); synthesis of enzymes (breakdown of certain carbohydrates) and solubilization of fats; th ki d i th i t ti d it l t d l h on the skin and in the intestine and urogenital tract and elsewhere: preemption of living space and attachment sites that could be used by pathogens; alteration of physiological conditions (pH, oxygen, etc.) such that growth of pathogens is inhibited. the presence of normal microbial residents of the body serves to block the entry or growth of pathogens Skin microbes resident on the skin mostly are associated with the sweat glands and sebaceous glands of hair follicles; ecretions of these skin glands are Fig. 28.2 s cr t ons of th s s n g an s ar rich in urea, amino acids, salts, lactic acid, lipids; pH 4-6. most resident microbes of the skin are Gram-positive ( Staphylococcus , Corynebacterium , Propionibacterium ) the surface of the skin (upper layer of epidermis) is dry and shed continuously the skin provides a major barrier to invasion of the body by microbes non-specific defense – physical barrier, presence of normal resident microbes, presence fatty acids and lactic acid (low pH) Respiratory tract mucous membranes support the growth of resident microbes upper respiratory tract (sinuses, nasopharynx, pharynx, oral cavity, larynx) Fig. 28.10 - bacteria enter by air, are trapped in the nasal passages and removed in nasal secretions. Resident microbes -- Staphylococcus, Streptococcus , normally present and some are potentially harmful, but usually do not cause illness; other resident microbes and the immune system keep them in check. lower respiratory tract (trachea, bronchi, lungs) - essentially sterile; cilia line the respiratory tract, beating upward, removing particulates and bacteria; mucociliary clearance non-specific defense – mucous (traps microbes), cilia (remove them)
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11/16/2009 2 Oral cavity a complex habitat – mouth, teeth, tongue saliva – water, salts, low levels of carbohydrates, proteins, urea, ammonia, amino acids, vitamins – nutrients for bacteria lysozyme (disrupts peptidoglycan of bacterial cell wall) and lactoperoxidase (generates singlet oxygen) – these enzymes are antibacterial Streptococcus - role in dental carries - single cells attach to tooth surface
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207_2009_Lect_26TwentySix - 11/16/2009 Biology 207, 2009...

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