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3 factors important for bacterial survival
- food
- accessibility (adherence/colonization)
- escape clearance (immune system)
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Normal Flora
- a type of bacterial growth
- usually found in GI tract, mouth, skin and upper respiratory tract
- aid in digestion of food, vitamin production & protection from pathogens
- can cause disease if invading a normally sterile area
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Opportunistic Pathogen
normally harmless, but can cause disease when immuno-defense is lowered
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Virulent bacteria
growth occurs at expense of host
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bind specific receptors or sugars on tissue surface (e.g cell surface, fimbriae)
Adhesins
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bacteria bound within sticky web of polysaccharide that binds cells to each other and to a surface
(exists wherever surfaces contact water)
Biofilms
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Bacterial effector proteins pass through needle into host cell
Type III Secretion
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Name some virulence factors
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Exotoxins
found in both GM + and Gm-
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Endotoxins
- Only ound in Gm- (in LPS)
- stimulates release of cytokines and prostoglandins
- can cause fever, shock or death
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Mechanisms of escaping host defense
- capsule
- intracellular growth
- antigentic variation
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Susceptibility & severity of disease from a viral infection depend on
- mechanisms of exposure/ site of infection
- hosts immune status, age and health
- viral dose
- genetics of virus and host
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Transport of a virus in the blood is called
viremia
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A viral infection can either result in one of 3 outcomes. They are:
- failed infection
- lytic infection (host cell death)
- persistent infection ( viral replication without cell death)
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Levels of Cell Supsceptibility (3)
- Nonpermissive cell- expresses antiviral mechanism
- Permissive cell- supports complete replicative cycle
- Semipermissive cell- may support some, but not all steps in replication
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Two types of viral infection
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Apoptosis
- "cell suicide"
- can facilitate viral release from cell, but limits viral production
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What is Syncytia formation
Fusion of neighboring cells into multi-nucleated giant cells triggered by surface glycoproteins
Allows spread of virus and escape from antibody detection
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