Microbiology Ch 15

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Microbiology Ch 15
2011-04-04 21:28:36
Micro Pathogenicity Microbes

Worksheet questions for Ch 15 on Pathogenicicty.
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  1. Pathogenicity?
    What is virulence?
    • Pathogenicity = to cause disease by overcoming the defences of the host.
    • Virulence = the degree or extent of pathogenicity
  2. 3 portals of entry
    1. Mucous membranes - first line of defense - lungs, GI, GU (STDs) , conjunctiva (gonorrhea, chlamudia)

    2. Skin -first line of defence -largest organ - breaks, ducts in glands, on top of skin

    3. Parentieral - entry other than through the mouth or GI tract - directly deposited into tissue - punctures, bites, cuts
  3. How do microbes enter the host?
    • 1. Portals of entry - mucous membranes, skin, parenteral
    • 2. Preferred portals - most microbes have one preferred entry point - some diseases can only result from one specific one
  4. What factors contribute to pathogenicity?
    • 1. # of microbes - the more microbes that gain entry increases the likelihood of a disease
    • ID 50 = indicator of virulence - dose needed to infect 50% of test population

    LD50 = indicator of lethality - dose needed to kill 50% of test population

    • 2. Adherence - ability of microbes to adhere to tissue
    • a. Microbe ligand binds to host receptor
    • b. biofilms - communities of microbes that cling together and share nutrients - able to resist disinfection - 65% of human infections
  5. How do bacteria penetrate host defenses?
    1. Capsule - outside cell wall -well organized glycocalyx - not slime later - used for attachment & prevention of phagocytosis

    2. Cell Wall components on bacteria - used to attach and prevent phagocytosis - eg, mycolic acid

    3. Enzymes - produced by bacteria - used to wall themselves off, spread more easily, & destroy host IgA (which is designed to block microbes ability to adhere)

    4. Antigenic vatiaiton on bacteria - some can alter their surface Ags to fool host defenses - Influenza mutates it envelope spikes (H1, N1), conjugation plasmid gives new surface Ags

    5. Use of host's cytoskeleton - bacteria use proteins called "invasins" to rearrange the actin filaments of the host cell cytoskeleton - causes membrane ruffling (rearranging of microtubules) - allows bacteria to enter -move around on microtubules & can use gap junctions to move from cell to cell.
  6. How do bacteria damage host cells?
    1. Using hosts nutrients - uses siderophores (proteins) to bind Fe so host can have it for Hgb production

    2. Direct damage - entry→growth→host cell lysis

    • 3. Production of Toxins - Toxins can enter the bloodstream and effect all areas. Two types:
    • a. exotoxin - bacteria makes & releases into BS
    • b. endotoxin - embedded in Gram (-) cell wall - released when the bacteria dies

    4. Induce hypersensitivity immune response

    5. Plasmids - can carry R (resistance) factors or a toxin that determines the bacteria pathogenicity

    6. Lysogeny - insertion of phage into bacteria chromosome = bacteria can make toxin
  7. Toxin
    poisonous substance (protine) that can be produced by some bacteria - adds to pathogenicity - Toxin can travel in the blood or on dead bacteria

    - most toxins damage cell membrane
  8. Toxigenicity
    the ability of a bacteria to make toxin
  9. Toxemia
    toxin in hosts blood
  10. Toxoid
    pieces of heat inactivated toxin used in vaccines - host can make Ags against the toxin
  11. antitoxin
    Abs against a certain toxin (Ag) that inactivates the toxin - used to treat botulism & tetanus
  12. What is a cytokine?
    Cytokins are proteins that regulate immune response and mediate cell-to-cell communication. They are produced by macrophages.
  13. What is lysogeny?
    Lysogeny - insertion of phage into bacteria chromosome = bacteria can make toxin
  14. What is a siderophore?
    • Siderophores are proteins that are released by bacteria.
    • - take Fe from iron transport proteins (transferrin, Hgb) by binding it even more tightly.

    - also one way that bacteria cause damage - taking nutrients from host cells
  15. Difference between exotoxin & endotoxin
    • Exotoxin = gram (+) bacteria (mostly) - toxin is made by the cell and secreted or is released at lysis
    • - protein (enzyme) - soluble in blood - can travel in blood stream
    • - very potent and potetially lethal
    • - destroy host cell membrane components
    • - sometimes host can produce antitoxin (Ab)
    • - usually produced from gene on plasmid

    • Endotoxin - Toxin is inserted on Gram (-) outer cell membrane
    • - lipidpolysaccharides
    • - released only when cell dies (why infection sometimes gets worse when you start antibiotics)
    • - cause macrophages to release large amounts of cytokins (abnormal immune response) which leads to shock
  16. 3 types of exotoxins?
    • 1. AB toxins - most commom exotoxin - enters host cell & inhibits protein synthisis
    • - A= acitve part - does damage- stays in host cell
    • - B= binding part - binds to host cell membrane - after A delivered it releases

    • 2. Membrane-disrupting toxins
    • - lyse host cells by
    • a. making protein channels in plasma membrane
    • - - leukocidins - kill WBC's
    • - - hemolysins - kills RBC's

    b. disrupt host cells phospholipid bilayer

    • 3. Superantigen - super toxins - cause a super out of control immune response -
    • - cause macrophages to release large amounts of cytokins
    • - cytokins cause all Sx = fever, nausea, vomiting, diarrhea, shock, death
  17. How are viruses pathogenic?
    1. They hide inside a cell (obligate intercellular parasites) to reporduce - immune system can detect them

    2. Attack immune cells directly
  18. What are the cytopathic effects of a virus? (how does it cause damage)
    • 1. stop host cell proteinsysthesis
    • 2. causes lysosomal digestive enzymes to be released - cell eats itself
    • 3. damages host cell DNA
    • 4. turns oncogenes on - transformed cells have no contact inhibition → uncomtrolled cell growth == tumor
    • 5. Make surface Ag changes on host cell - host attacks itself (RA)
  19. What are the 5 portals of exit for a microbe?
    Pathogenicity inclused exit from host - to infect another host

    - Most microbes use same entrance & exit ports

    • 1. Respiratory tract - cough, sneeze
    • 2. GI - hand to mouth
    • 3. GU (Genitourinary) - STDs
    • 4. Skin/ open wounds
    • 5. Blood
  20. What is interferon?
    What is an oncogene?
    Interferon - proteins (cytokins) that interfere with viral replication inside a host cell

    Oncogene - mutated from of normal cellular genes - once turned on, it transform the cell and begins rampant replicaiton.