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Microbial Mechanisms of Pathogenicity
Chapter 15
Mechanisms of Pathogenicity
Pathogenicity: The ability to cause diseaseV irulence: The extent of pathogenicityPrimary pathogenOpportunistic pathogen
How Microbes Enter a HostPortals of Entry
Mucous membranesSkinParenteral routePrefer red portal of entry
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mucous membran is the most used portal of entry of microbes.
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sometimes micros can enter through intact skin ( not broken skin) through the opening of hair particles. opening of swet glandes
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is when the skin barrier if broken (also burned skin or contaminated skin)
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different micros prefer different ways of entry. some have one way others have multiple ways, but each one has a preferred portal of entry even tho they have multiple ways of entry. ( when they enter through the preferred portal of entry they have a higher chance of infection)
Numbers of Invading Microbes
ID50: Infectious dose for 50% of the test population
L D50: Lethal dose (of a toxin) for 50% of the test population
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ID 50 (infection dose, number of microbes that are required to make 50 out of 100 people ill)
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lethal dose ( not for the pathogen but for the toxin. amount of toxin to kill 50% of the test population.)
Coagulase: Coagulates fibr inogenK inases: Digest fibr in clotsHyaluronidase: Hydrolyzes hyaluronic acidCollagenase: Hydrolyzes collagenIgA proteases: Destroy IgA antibodies
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coaguates fibrinogen leads to formation of blood cloth. if bacteria are within the blood cloth they are invisible to defense mechanisms.
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kinases spread the microbes in ur body by desolving the blood cloth
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hyaluronic acid that closes the gaps between the cells. some microbes can digest the hydrolyzes and sperate the cells
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collagenase will damage collagen which allow the microbes to spread in ur body
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the reason Iga is the only antibody that is being destroyed because iga is everywhere in ur body.
Membrane Ruffling
Figure 15.2
Antigenic Variation
Alter surface proteins
Figure 22.16
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many bacteria and viruses have the ability to change their antigens
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by the time antibodies are ready for A pili the microbes have switched to type B pili so the antibodies are never effective. same is for the flu virus thats why we need vaccines every year
InvasinsSalmonella alters host actin to enter a host cell
Use actin to move from one cell to the next
Listeria
Penetration into the Host Cell Cytoskeleton
Figure 15.2
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sometimes bacteria can penetrate inside ur cells. trying to hide and also use the nutrients inside the cell.
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dont need to know
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these invasins will cause membrane ruffling ( the alteration of the membrane)
Figure 15.4
How Pathogens Damage Host Cells:Exotoxins and Endotoxins
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toxins are the by produces of microbial growth. they are not intentional for avoiding the immume system.
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lipid A serves as Endotoxin Gram negative. it can cause a person to into a shock.
Exotoxin
Source Mostly Gram +Relation to microbe By-products of growing cell
Chemistry ProteinFever? NoNeutralized by antitoxin? YesLD50 Small
Figure 15.4a
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small quantity
Source Gram
Relation to Microbe Outer membrane
Chemistry Lipid A
Fever? Yes
Neutralized by Antitoxin? No
LD50 Relatively large
Endotoxins
Figure 15.4b
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large amount of it
Superantigens
Cause an intense immune response due to release of cytokines from host cells
Symptoms: fever , nausea, vomiting, diar rhea, shock, and death