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MicrobiologyChapter 34


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What are pathogens, Opportunistic pathogens, etiologic agents.
Pathogens-the causative (etiologic) agent.
Opportunistic Pathogens-host pathogens may become pathogenic under certain circumstances(immune system compromised).
etiologic agent-causes the disease.
pathogenesis, virulence, infections, and intoxications?
Pathogenesis-The process of causing disease.
Virulence-the intensity of the disease caused.
Infections-When a parasite is growing in or on the host
Intoxications-Disease resulting from the entrance of a specific toxin into the body of a host. The toxin can produce the disease in the absence of the toxin-producing organsim (bad guy)
How do we measure the virulence of a pathogen?
Virulence measured by LD50 or ID50. (Inject 100 mice with 100units of organism and 50 will die)
What are the three determinats of virulence? What are virulence traits (determinants)?
Infectivity-the ability to establish an infection.
Invasiveness-the ability to spread within the body.
Pathogenic potential-the ability to cause damage.
How can a virulence trait affect and get into the host
Direct-cough, bumping uglies
Indirect-airborne, water, letters
How can a virulence trait affect and gain access to the host site?
Ectoparasites-remain on host surface
Endoparasites-invade/enter host tissues by passive (vectors like flea or trama like nail) or Active-Induced uptake(Salmonella type III secretion system) like needle sticks it in and pumps proteins into host tissue which allow host cells to take up the virulence.
Spread within the host-Spreading factors, Blood-lymphatic-nerve tracts-mucosal secretions, Tropisms are tissue specificities (receptors)
How can a virulence trait affect and colonize a host site?
Attach to the host and reproduce. Adhesins required for areas of flow-adapt to growth conditions.
Need to obtain nutrients-acquisition of Fe.
How can a virulence trait affect and defeat host defenses?
Evasion of complement, Resisting phagocytosis, Survivng phagocytosis, Antigenic variation, Phase variation aIgA proteases, Binding Ig by Fc.
How can a virulence trait affect and damage the host?
What are two ways other then a toxin that a microb may damage its host?
Host response-virulence gone, but your body still acting on it.
Growth within the cell-
How can a virulence trait affect and escape from the host?
Cough, Diarrhea
What role has horizontal gene transfer played in the development of pathogens?
Transfers from one organism to another adds to mutation and variations-antibiotic resistance.
What are pathogenicity islands?
clusters of virulence genes on chromosomes. They are acquired en bloc by horizontal transfer (flanked by IS elements, diff G+C ratio, Distinguish pathogenic strains)
How do bacteria regulate their virulence genes?
Virlence genes must be regulated-bacteria live in diff environs, need diff traits in diff stages of an infection
How do exotoxins differ from endotoxins?
Exotoxins-secreted proteins that cause damage to or dysfunction of the host. Often encoded on extrachromosomal elements.
Endotoxins-Lipid A of LPS.
Can you describe an example of an AB type toxin? What do each of its subunits do?
B-binds and promotes entry through cell or vacuolar membrane for A-active, enzymatic which modifies host structure.

Example: Diphteria toxin-AB cleaved and ADP-ribosylates all EF-2 which prevents cell from protein sythesis=cell death
What are two types of membrane-disrupting toxins?
Two types of membrane-disrupting toxins are pore-forming toxins and phospholipases.
What are superantigens?
Superantigens are bacterial proteins that stimulate the immune system much more extensively than do normal antigens.
What are four broad pathways by which endotoxins exert their effects?
Four broad pathways by which endotoxins exert their effects are by clotting (hemorrhage), fibrinolysis (break down of clots=more hemorrhage), complement activation (inflammation), and kininogen system (release vasoactive substances=shock).
Give examples of evasion of complement
Three examples of bacterial evasion of host complement are sialic acid capsules (stops ACP), Long LPS, and addition of host sugars to LPS.
Give examples of resisting phagocytosis
Bacteria resist phagocytosis by host cells by having capsules (prevent opsonization), producing C5a protease (prevents chemotaxis), and secreting leukocidins (kill phagocytes).
Give examples of surviving phagocytosis
Bacteria survive phagocytosis by escaping from the phagosome, inhibition of fusion with lysosome, and surviving the lysosome.
Give examples of antigenic variation
Antigenic variation is random changing of antigenic determinants to avoid the immune response. An example of this is Neisseria gonorrhoeae which changes its pilus antigens.
Give examples of sIgA protease
Two examples of sIgA protease are in N. gonorrhoeae adn Haemophilus influenzae.
Give examples of Binding Ig by Fc
An example of binding Ig by Fc is in Staph aureus protein A.
How does antigenic variation differ from phase variation?
Antigenic variation is the changing of antigenic determinants while Phase variation is teh turning on or off of an entire antigen.
Do they occur in response to a stimulus? Why?

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