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13 Cards in this Set
- Front
- Back
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Shigella spp based serologically on what?
What antigen do they not have? Four spp and severity of infections |
serologically based on O antigen (LPS)
don't have H antigen (no flagella) S. dysenteriae- most severe infections S. flexneri- infections in developing countries S. boydii- not commonly isolated S. sonnei- most infections in developing countries |
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Shigella physiology and structure
gram? shape? oxygen use? fermentation? resistant to what in humans? oxidase rxn? outer membrane effect on org? similarity to e. coli |
gram neg bacilli
facultative anaerobe fermenter highly resistant to stomach acids oxidase neg outer membrane makes org susceptible to drying shigella spp are pathogenic clones of e. coli, and hard to distinguish from it |
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Shigella plasmid
fcn can transfer to what sp? what genes encoded? how are the genes regulted? |
plasmid encodes virulence
can be transferred to E. coli K12 (causes shigella phenotype) Has genes for adherence, invasion, replication, and cell-to-cell spread Regulated by chromosomal genes |
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Type III secretion genes on plasmid
function? |
Invasion plasmid antigens (IpaA,B,C,D)
these are secreted into macs and epithelial cells and induce membrane ruffling on the target cell, leading to engulfment of bacteria |
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Other genes encoded on plasmid
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Mxi- membrane expression of invasion plasmid genes
Ics- intracellular spread Spa- surface presentation of antigens Ipg- invasion plasmid gene |
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Other shigella virulence factors
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permeability barrier (outer membrane)
endotoxin Shiga toxin |
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Shiga toxin
produced by what spp? function? how does it work? decreases absorption of what? contribues to what symptom of shigella infection? |
produced by S. dysenteriae type 1
Cytotoxic exotoxin that kills epithelial and endothelial cells inhibits protein synthesis by cleaving 60S ribo subunit decreases sodium absorption= excess fluid in lumen conributes to bloody diarrhea by damaging mucosal endothelial cells |
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Shigella invasion
initially invade thru which cells? then enter what cells? once there, what cytokines do they induce? how? this generates an influx of what? what does this influx cause? this then allows shigella to invade what cells? then what do the bact do? what results from the infection? |
initially enter mucosa via M cells
then they can enter macrophages Type III secretion system secretes proteins (Ipas), causes mac apoptosis, inducing cytokines IL-1 and IL-8 This generates an influx of PMNs the PMNs cause separation of tight junctions between epithelial cells, allowing the orgs to penetrate and invade the basal surface of epithelial cells Internalized bact can escape from phagosomes and spread to neighboring cells using host actin to make COMET TAILS infection causes cell death, resulting in focal ulcers and exudation of inflammatory cells into lumen, along w/RBCs to produce dysentery stool |
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Shigellosis
infectious dose onset symptoms |
low infectious dose (100-200 orgs) means rapid spread possible
onset 16-72 hours after ingestion initial profuse, watery diarrhea is caused by enterotoxin cardinal features: lower abdom. cramps, tenesmus, abdundant blood, pus, and mucus in stools (stool volume usually small) |
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Shigellosis
site of infection invasion? |
ileum and large intestine
invasion present- microabsesses in wall lead to ulcers, bleeding, and formation of pseudomembrane on ulcer |
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Shigella
cases annually worldwide host transmission mostly in what age group? |
150 million cases annually worldwide
humans are primary host person-to-person transmission, fecally contaminated food/water, raw veggies, fruits, poor hygiene 70% of infections are in kids under 15 |
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At risk populations
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young kids in daycare/nursery and custodial institutions
siblings/parents of these kids male homosexuals travelers to underdeveloped countries |
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Shigella diagnosis
treatment |
stool specimen isolation
ID of serotype treatment- Abx shorten disease and bacterial shedding to limit transmission can initiate w/fluoroquinolones or trimeth/sulfa, but should do drug susceptibility testing avoid antidiarrheals!!! |
