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Microbial Pathogenesis - Coggle Diagram
Microbial Pathogenesis
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Stages of Pathogenicity
- Exposure/Contact- encounter with a potential pathogen
- Portal of Entry- anatomical site where pathogen enters the host
some pathogens can cross the blood-placental barrier. Ex: Listeria monocytogenes causes foodborne illlness listeriosis or miscarriage; chlamydia or gonorrhea can cause eye infections/blindness
- Adhesion- attachment using adhesion factors Ex: adhesins; biofilm growth (community of bacteria that produce glycocalyx as extrapolymeric substance (EPS)
- Invasion- dissemination into tissues or the body; pathogens can produce exoenzymes or toxins or virulence factors
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one mechanism relies on effector proteins secreted by the pathogen; these trigger entry into the host cell. Ex: Salmonella & Shigella cause membrane ruffling
one mechanism relies on surface proteins expressed on the pathogen that bind to receptors on the host Ex: Yersinia pseudotuberculosis surface protein invasin that binds to beta-1 integrins on the host surface
- Infection- successful multiplication of the pathogen
- Portal of Exit- pathogens leave the body. Ex: coughing/sneezing expels pathogens from respiratory tract
Types of Infection
Local Infection- confined to small area, typically near portal of entry. Ex: boil or abcess by Staphylococcus aureus
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Primary infection makes host susceptible to a secondary infection by another pathogen. Ex: HIV increases risk of other pathogens
Virulence Factors
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virulence factors produced by individual pathogens determine the extent & severity of disease they cause
When genes encoding virulence factors are inactivated, virulence in the pathogen is diminished
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Toxins
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Endotoxin- the lipopolysaccharide (LPS) found on the outer membrane of Gram(-) bacteria; has a high LD50 (lethal dose)
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Neurotoxins- type of exotoxin; botulinum toxin & tetanus toxin; consists of light A subunit & heavy protein chain B subunit
Intracellular Targeting Toxins- cholera toxin, tetanus toxin, botilinum toxin, diptheria toxin
AB Toxins- Diptheria toxin mechanism inhibits protein synthesis by stopping protein elongation, killing the cell
Exoenzymes
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Pathogen-produced nucleases, such as DNAse produced by S. aureus, degrade extracellular DNA as a means of escape and spreading through tissue
Hyaluronidase degrades the adhesive polymer hyaluronan allowing passage between cells that shouldn't be there
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Microbes in Bloodstream
Edema- bacteria causes the release of pro-inflammatory molecules from immune cells, allowing fluid to escape bloodstream & enter into tissue
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