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What Makes A Microorganism Pathogenic

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What Makes A Microorganism Pathogenic

  1. 1. What makes a microorganism pathogenic? Or…… how do bacteria make us ill?
  2. 2. What makes a microorganism pathogenic? <ul><li>Must be capable of living as a parasite in its host’s body. (The bacteria that causes leprosy is an obligate parasite, viruses are obligate parasites). BUT not all parasites are pathogens. </li></ul>
  3. 3. What makes a microorganism pathogenic? <ul><li>A pathogen is a badly adapted parasite whose presence in the host disrupts the normal running of the host’s body and results in an interaction called a disease. </li></ul>
  4. 4. What makes a microorganism pathogenic? <ul><li>What brings about the disruption is either the pathogen’s invasiveness or its toxigenicity or both. </li></ul>
  5. 5. What makes a microorganism pathogenic? <ul><li>Invasiveness </li></ul><ul><li>is the ability of a pathogen to spread through the host’s body from its site of entry, to enter host tissues and to multiply there. This ability depends on two things: </li></ul><ul><li>having a surface structure that protects it from phagocytosis and other host defences e.g. a slime capsule </li></ul><ul><li>being able to secrete enzymes that breakdown connective tissue and intercellular cement enabling the pathogen to invade tissues </li></ul>
  6. 6. What makes a microorganism pathogenic? <ul><li>Highly invasive pathogens include those that cause bubonic plague or anthrax. </li></ul>
  7. 7. What makes a microorganism pathogenic? <ul><li>However, some pathogens show almost no invasiveness at all, e.g. Salmonella enteritidis causes severe food poisoning when taken into the gut but is incapable of spreading from the gut to other parts of the body. </li></ul>
  8. 8. What makes a microorganism pathogenic? <ul><li>Clostridium tetani, the bacteria which causes tetanus is introduced into or cuts or wounds but rarely spreads from that site. </li></ul>
  9. 9. What makes a microorganism pathogenic? <ul><li>Toxigenicity </li></ul><ul><li>Pathogens which are non-invasive cause their disease by their toxigenicity: that is they release chemicals (toxins) which are poisonous to the host. </li></ul>
  10. 10. What makes a microorganism pathogenic? <ul><li>Bacterial toxins can be divided into two distinct types. </li></ul><ul><li>Exotoxins are chemicals (usually proteins) which are secreted by pathogens into their surroundings. They are inactivated by heat. e.g. Clostridium tetani produces and exotoxin which affects the nervous system. </li></ul>
  11. 11. What makes a microorganism pathogenic? <ul><li>Endotoxins are components of the cell wall of all Gram-negative bacteria. </li></ul><ul><li>They are all lipopolysaccharides and are not easily inactivated by heat. </li></ul><ul><li>Endotoxins are not secreted, but are released when bacterial cells break up after death. </li></ul>
  12. 12. What makes a microorganism pathogenic <ul><li>Small amounts of endotoxin lead to fever and activations of the immune system. In larger amounts, endotoxins cause toxic shock which can lead to the collapse of the circulatory system and death. </li></ul>

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