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Survival plot
Kaplan-Meier plot
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Steps involved in bacterial pathogenesis
- Colonization
- migrate
- tissue or cellular destruction
- dissemination
- The cycle repeats with colonization again
- During this process, the bacteria has to evade the host immune system, always happening at every step
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Colonization
- Nonspecific
- Usually mediated by polysaccharides, sugars, Biofilms
- don’t discriminate between surfaces
- Specific
- Pili bind to specific receptors
- Serve as adhesins for binding to certain proteins on the host cell surface
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Tissue destruction:
enzymes that degrade the extracellular matrix: Collagenases, proteases, toxins
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Dissemination
sugar hydrolases: Allow bacteria to escape the biofilm
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Evasion of host response
Half of the genome deals with the host immune system
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Initial hose response
- macrophage phagocytosing the pathogen, forming phagosome, fuses with lysosome
- Lysosome has a damaging environment:
- Low pH
- Superoxide radicals
- lysosomal hydrolases
- Phagocyte also displays things to the rest of the immune system
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evade Initial hose response
- Inhibit fusion of phagosome and lysosome: Legionella, Mycobacterium, Chlamydia
- Resistance to lysosomal enzymes: Salmonella, some strains of Mycobacterium
- Escape the phagosome and get into the cytoplasm, adapt to cytoplasmic replication: Listeria, Rickettsia
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Legionella pneumophila
causes pneumonia, respiratory disease
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Legionella pneumophila
- 1. phagosome
- 2. prevents fusion of lysosome by Mediates the formation of the membrane of the ER around the phagosome, forming a triple-layered membrane
- 3. breaks down ER membrane, products triggers the bacteria to replicate within the single membrane bound structure and produce flagella
- 4. burst from the cell and spread to other cells, dissemination
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Listeria monocytogenes
Causes disease listeriosis
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Listeria monocytogenes
- 1. invades a cell via phagosome
- 2. lyses the phagosome,
- 3. divides in the cytosol
- 4. takes actin filaments, coats itself with this and uses this to push itself out into neighboring cell
- 5. enveloped by two membranes: One from the original cell, and another from the new cell
- 6. the cycle continues
- the mechanism prevents the bacteria from getting into contact with the immune system
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Other mechanism
produce Ig protease to break dowm antibody
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