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5-Chemical Barriers, 7.pptx

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5-Chemical Barriers, 7.pptx

  1. 1. Biochemical Barriers Mammalian hosts have a chemical arsenal with which to combat the continuous onslaught of microorganisms.
  2. 2. Some of these chemicals (gastric juices, salivary glycoproteins, lysozyme, oleic acid on the skin, urea) have already been discussed with respect to the specific body site(s) they protect.
  3. 3. In addition, blood, lymph, and other body fluids contain a potpourri of defensive chemicals such as bacteriocins, beta-lysin, and other polypeptides.
  4. 4. Bacteriocins As previously noted, the first line of defense against microorganisms is the host’s anatomical barrier, consisting of the skin and mucous membranes.
  5. 5. As previously noted, the first line of defense against microorganisms is the host’s anatomical barrier, consisting of the skin and mucous membranes.
  6. 6. These surfaces are colonized by normal microbiota, which by themselves provide a biological barrier against uncontrolled proliferation of foreign microorganisms.
  7. 7. Many of these normal bacteria synthesize and release plasmid-plasmidencoded toxic proteins (e.g., colicin, staphylococcin) called bacteriocins that are lethal to related species. Bacteriocins may give their producers an adaptive advantage against other bacteria.
  8. 8. Most bacteriocins that have been identified are peptides or proteins and are produced by gram- negative bacteria. (However, recently it has been discovered that some gram-positive bacteria produce bacteriocin-like peptides).
  9. 9. Beta-Lysin and Other Polypeptides Beta-lysin is a cationic polypeptide released from blood platelets; it can kill some gram-positive bacteria by disrupting their plasma membranes.
  10. 10. Inflammation Inflammation [Latin, inflammatio, to set on fire] is an important nonspecific defense reaction to tissue injury, such as that caused by a pathogen or wound.
  11. 11. Acute inflammation is the immediate response of the body to injury or cell death. These signs include redness warmth, pain, swelling, and altered function.
  12. 12. The acute inflammatory response begins when injured tissue cells release chemical signals (inflammatory mediators) that activate the inner lining (endothelium) of nearby capillaries.
  13. 13. The inflammatory mediators that are released by the injured tissue cells also raise the acidity in the surrounding extracellular fluid.
  14. 14. The Complement System Complement was discovered many years ago as a heat-labile component of human blood plasma that augments opsonization of bacteria by antibodies and helps other antibodies kill bacteria.
  15. 15. This activity was said to “complement” the antibacterial activity of antibody; hence, the name complement. It is now known that the complement system is composed of a large number of serum proteins that play a major role in the animal’s defensive immune response.

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