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59 Cards in this Set
- Front
- Back
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What is gastroenteritis?
What is its timeframe for onset? |
-An intestinal infection caused by proliferation of bacteria.
-12 hours to days after ingestion |
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What makes food poisoning different from gastroenteritis?
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The GI symptoms appear within a few hours of eating.
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What is Diarrhea?
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>300 g of stool daily with increased liquidity and frequency.
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What is Secretory diarrhea?
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Water and ion loss but no damage
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What is Malabsortive diarrhea?
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Diarrhea in which there is damage to mucosal cells that impairs water uptake
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What is Dysenterey?
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Multiple, bloody, mucoid stools
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What are 6 features of ALL enterobacteriaceae?
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1. Gram neg rods
2. Non spore forming 3. Facultatively anaerobic 4. Ferment glucose 5. Reduce nitrates 6. Oxidase neg |
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What is the motility of enterobacteriaceae?
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All are MOTILE except
-Shigella -K. pneumoniae -Yersinia -one salmonella |
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What is the flagella of Salmonella like?
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Peritrichous
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How is Salmonella differentiated on MAC?
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It is a lactose nonfermentor
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What Salmonella species are highly adapted to humans?
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-S. typhi
-S. paratyphi -S. sendai |
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What disease is caused by S. typhi?
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Typhoid fever
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How is typhoid fever different from typhus?
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It has enlarged Peyers patches and mesenteric lymph nodes.
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What causes typhus?
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Rickettsia rickettsii
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What are the 2 species of Salmonella classification?
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S. enterica
S. bongori |
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How many subspecies of S. enteritica are there? How are they differentiated?
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7 - ID'd by biochemical characteristics and serotyping
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What is Salmonella Typhi really?
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S. enterica, serotype group I
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What is the most frequent human isolate of Salmonella?
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S. typhimurium
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What are the 2 clinical syndromes that S. typhimurium causes?
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1. Gastroenteritis
2. Systemic infection |
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What is the mode of Salmonella transmission?
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Ingestion of contaminated food or water
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How are Salmonella bacteria able to colonize the gut?
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They survive the stomach's acidity
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What cells do Salmonella bacteria target to invade GALT/peyers patches?
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M cells
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What are the steps in Salmonella invasion of the gut?
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1. Salmonella ruffles Mcell membrane and gets taken up
2. Infected M cells die and leave a hole in the GI epithelium 3. bacteria move down into lymphocytes |
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What is the virulence factor that Salmonella bacteria use to get into cells?
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Type III secretion system
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What did the type III secretion system evolve from?
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Motility mechanisms
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How many type III secretion pathways does each salmonella bug use? What are they called?
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Two:
-SPI1 -SPI2 |
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What is SPI1 required for?
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-Salmonella entry into cells
-Translocation of effectors across the plasma membrane |
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What is the effect of the translocated effectors that are stimulated by SPI1?
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-Actin bundles and polymerizes to inhibit host phagocytosis pathways
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What does SPI2 do?
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Allows the bacterium to survive intracellularly by maintaining SVC integrity and preventing lysosomal fusion with it.
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So the two diseases caused by salmonella infections are:
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-Nontyphoidal gastroenteritis
-Typhoid fever |
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How does typhoid fever develop?
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By entry of bacteria into M cells and proliferation in lymphoid follicles.
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How can typhoid fever be prevented?
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By vaccinating
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What bacterium causes Dysentery?
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Shigella
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What is the special feature of Shigella?
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Nonmotile
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How is Shigella transmitted?
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Fecal to oral in contaminated food and water
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What are the four species of Shigella?
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S. dysenteriae
S. boydii S. flexneri S. sonnei |
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In what patients do 70% of all Shigellosis cases occur?
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Pediatrics
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What is the illness caused by Shigella indistinguishable from?
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Illness caused by invasive strains of E. coli
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Why do E. coli and Shigella cause the same illness?
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They have the same virulence plasmid
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What does the virulence plasmid of E.coli and Shigella encode?
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a Type III secretory system
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What are the 5 effectors associated with the virulence of Shigella?
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IpaA-B-C-D-IpgD
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What is IPA?
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Invasion protein antigens
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What do humans do in response to IPAs?
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Make antibodies to them
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What is the first step in Shigella invasion of an intestinal epithelial cell?
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IpaB-C complex binds an integrin on the epithelial cell, inducing a signalling cascade for ACTIN POLYMERIZATION (IpaA)
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What happens after initial binding of shigella to the cell?
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The membrane ruffles via actin polymerization, then it depolymerizes to form a vacuole containing Shigella.
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Does Shigella like being in a vacuole? Why?
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No - it has no SPY2 analog to maintain the vacuole and prevent lysosomal fusion.
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What happens to shigella once it is free within an enterocyte's cytoplasm?
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It forms its own motility mechanism by polymerizing ACTIN
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Why does Shigella form an actin Comet Tail?
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To propel itself into neighboring enterocytes
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So what direction do Salmonella bacteria invade the intestine?
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Vertically - down into lymphatic tissue
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What direction do Shigella bacteria invade the intestine?
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Laterally - into neighboring cells
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In addition to Invasiveness, how does shigella damage the host?
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Via Shiga toxin - Stx
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What type of toxin is the shiga toxin?
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An AB5 toxin
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What is the enzyme activity of the A subunit of shigatoxin?
What is the receptor for B? |
RNA N-glycosidase that cleaves Adnine from the 28s ribosome and inhibits host protein synthesis.
B targets Gb3 terminal galactose residues. |
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What is achieved by shigatoxin?
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It stops host protein synthesis
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What are the 3 names for shigatoxin?
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-Shigatoxin
-Verotoxin -Shigalike toxins |
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What is the range of pathology caused by the shigatoxins?
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-Mild and watery stools
to -Severe bloody diarrhea to HUS (e.coli o157H7) |
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Which strains of shigatoxin are most likely to cause HUS? Why?
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Stx2 in E. coli - because it is encoded on a phage
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How are Salmonella and Shigella similar?
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Both have Acid tolerance
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Which bacterium causes more host damage? Why?
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Shigella - because it results in mucosal abscesses.
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