Lecture%203

Lecture%203 - Background: Most common cause of bacterial...

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Background: Most common cause of bacterial dysentery worldwide Infectivity dose (ID) extremely low 10 cells of Shigella dysenteriae can cause clinical disease 100-200 cells are needed for Shigella sonnei or Shigella flexneri infection
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All Shigella are pathogenic Shigella dysenteriae : Cytotoxin production in the intestines and colon Incubation period: several days Illness duration: usually 2-7 days, longer in the more susceptible individuals
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Closest known relative to E. coli Shigella are strictly human parasites Only humans can carry Disease is always the result of poor sanitation especially “water” Transmission: Spread through fecal-oral transmission No natural food products harbor endogenous Shigella , a variety of foods
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Involves both chromosomal and plasmid coded genes Siderophores: control acquisition of iron from host cells from its protein-bound state Siderophores chelate iron from the intestinal fluids and then are taken up by bacteria to release iron inside the bacterium for its metabolic needs
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Shiga toxin: many pathogenic features are brought about by Stx1 and Stx2 These toxins are lethal for animal enterotoxic for ligated rabbit intestinal segments; and cytotoxic for vero, HeLa and some selected endothelial cells Diarrhea, dysentery and hemolytic-uremic syndrome
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Stx1 and Stx2 both are encoded by a bacteriophage inserted into the chromosome Shigella species are invasive, spread directly from cell to cell by actin-based motility Pathology: disruption of the mucosal and epithelial layers of the intestine, causes focal mucosal hemorrhage leads to blood in the stool
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Lecture%203 - Background: Most common cause of bacterial...

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