lecutre 6 - Stanford Microbiology and Immunology 204:...

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Stanford Microbiology and Immunology 204: Innate Immunology Lecture 6 Our Flora We carry 2 kg of microbes in our guts and 200g on our skin. We are an ecosystem, not a sterile object fighting to remain clean. There are many examples of symbiosis where a microbe provides nutrients for a host. In this lecture we will focus on symbiotic relationships in which the parasite plays a role in immune function. Plant endophytes An endophyte is an organism that completes part of its lifecycle within a plant. The alkaloid toxin ergot is produced by endophytes in rye. Ergot toxins are derivatives of lysergic acid, the precursor of LSD. Those who work with horses or cattle may have encountered tall fescue toxicosis, which results when your animal eats grasses infected with the fungus. All plant species examined carry endophytic fungi asymptomatically. Is it simply a commensal? Why is it so common? Tropical tree – Theobroma cacao – chocolate source Plants were grown “germ free tree” from surface sterilized seeds. Some leaves on each plant were treated with endophytes or a control treatment. Leaves on single plants were then challenged with phytophthora (a fungal plant pathogen) and leaf mortality was assayed. Leaf mortality greatly reduced by presence of the fungi. Think about this next time you lather up in your antimicrobial soap I’m not warranting you all stop bathing – but this sterility kick is silly Maybe you are better off with your bacteria. For example: Vaginal pH and native flora “lactobacillus are the Xena warrior princesses of the vagina” Sharon Hillier http://www.nih.gov/news/NIH-Record/02_06_2001/story06.htm Vaginal pH is typically maintained at pH 4-4.5 by lactic acid Bacteria are the likely source for this compound as both D and L forms are present and the humans only make the L form. Normal flora consist largely of lactobacillus species – but not the ones in yogurt. In response to estrogen, glycogen is deposited upon the epithelial surface just prior to ovulation. This is degraded anaerobically by the bacteria to produce lactic acid. Why do our bodies do this? It sounds like the body is feeding its flora.
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Stanford Microbiology and Immunology 204: Innate Immunology Lecture 6 Proof that the low pH comes from lactic acid producing bacteria and not the vaginal epithelia comes from identification of the chemical structure of the lactic
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lecutre 6 - Stanford Microbiology and Immunology 204:...

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