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Lecture40&41 - LECTURES 40& 41 04& 11...

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Unformatted text preview: LECTURES 40 & 41 04 & 11 December 2009 (P. J. Hollenbeck) BIOL 231 Cell Biology of Pathogens Reading (just a bit): pp. 124-25; 223-26 Prob: exam IV 2005, #8 “That’s the problem with Nature. Something’s always stinging you or oozing mucus on you. Let’s go inside and watch TV.”-Calvin & Hobbes I. Pathogens – what are they and how do they invade our bodies? (A) What are they? Pathogens are agents that cause infectious diseases. Human pathogens include: (1) other metazoan organisms, such as Ascaris (a nematode parasite) or Taenia solium (tapeworm, a segmented parasite) (2) Single-celled protozoa, such as Toxoplasma gondii (3) Fungi, such as yeast or Tinea pedis (athlete’s foot) (4) Bacteria (you can probably name a dozen) (5) Viruses (again, you know a lot of these) (6) Prions, such as bovine spongiform encephalitis (“mad cow disease”), we’ll come back to these shortly (B) Most organisms that live in us or on us are NOT pathogens. (1) Your body is comprised of approximately 10 human cells, but your typical, healthy 13 body load of bacteria, fungi and protozoa is approx 10 cells! The vast majority of 14 these live with us and use us for nutrition without adversely affecting our health – indeed, some play a positive role in our own normal body functions, such as digestion. (2) Opportunistic versus dedicated pathogens. Opportunistic pathogens take advantage of wounds in the skin, deficiencies in the immune system, and so on, to enter and thrive in the body. This puts them in a place where they do not normally reside, and can transform them from innocuous – or even helpful – microbes into disease-causing agents.** Dedicated pathogens have evolved highly-specialized mechanisms for breaching organismal, cellular and biochemical defenses. They usually also have the ability to evoke responses from the host that actually enhance pathogen survival. (C) Whether opportunistic or dedicated, pathogens must do the following to survive: (1) Colonize the host organism. Opportunistic pathogens and dedicated pathogens tend to do this in different ways. (2) Find a niche in the host compatible with their nutritional and reproductive needs (3) Avoid or subvert the host’s immune responses to invasion (4) Replicate themselves, using resources of the host-1- (5) Spread to a new host, repeat the process. <Our body has several lines of defense to prevent pathogens from entering in the first place. The epithelial sheets of cells that form our body’s boundary are our first line of defense.> (6) Many of our epithelia, such as lung and GI tract, secrete mucus that serves as a physical barrier and also contains factors such as anti-bacterial peptides. Lung epithelia have cilia that constantly sweep the mucus (and the bacteria trapped in it) out of the airway. The GI tract accomplishes the same thing via peristalsis....
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Lecture40&amp;41 - LECTURES 40& 41 04& 11...

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