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Flashcards in Invasive gram negative pathogens of GI tract Deck (26)
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what are the 3 mechanisms bacteria can use to cause infections

1 - invade the mucous membrane
2 - toxin producers
3 - hybrid of the two above


what are the 2 main gram (-) bacterial species that cause infections by invasion of the mucous membrane

salmonella and shigella


shigella species of gram negative pathogens has 4 subgroups distinguished by what antigen

O antigen (based on structure of LPS


what is RpoS ?

transcription factor that causes acid resistance in shigella allowing pathogen to pass through stomach


which gram negative bacteria has a small inoculum size ? large ?

shigella is small, salmonella is large


explain how shigella pathogens invade humans

1 - enter host M cells for transport to basal surface
2-released at lamina propria and ate by macrophages causing inflammatory response
3- pathogens not eaten ingested by epithelial cells and put in vesicle
4-shigella proteins lyse the vesicle
5- spread locally intracellulary via IcsA


which is resistant to pathogen infection in humans, the mucous surface or basal surface

basal surface


what do shigella pathogens produce to signal human M cells to pick them up for transport to basal surface

shigella pathogens have proteins called "invasion plasmid antigens"


what is IcsA

protein ATPase of shigella causing polymerization of actin which pushes shigella cells into adjacent epithelial cells w/o going into cytoplasm and getting destroyed by immune system


is shigella a localized infection or systemic ? why ?

localized because just stays in epithelial cells and away from blood stream


what develops when the invaded epithelial cells die off from shigella infection



what specific subgroup of shigella induces a watery diarhea stool

shigella sonnei (most common)


what specific type of shigella produces the Shiga toxin and is the most severe of shigella diseases

Shigella dysenteria type 1


what does the Shiga toxin in shigela dysenteria cause

-kills intestinal epithelial and endothelial cells=more diarhea
-dirsupts Na absortion


Salmonella pathogen can cause what 2 diseases

1- Gastroenteritis
2-Typhoid fever


how is salmonella transmitted to humans

fecal (human or animal) to mouth


Is salmonella acid resistant or not ?

Not as acid resistant as shigella


if salmonella pathogens survive through the low acidity of the stomach, the low pH will induce what ?

pathogenicity islands on large virulence proteins
aka - virulence proteins


how does salmonella pathogen invade the human

1-approach cell mucosal surface and increase Ca levels
2-induces surface "ruffles" and uptake of pathogens into vesicles
3-remain in vesicles for hours
4 - released into lamina propria and induces Na and Cl loss causing diarhrea
5 - Macrophages eat or if escape become transient


how is salmonella typhi, which causes typhoid fever, different from normal salmonella species

it is not killed by macrophages, these survive and grow/replicate inside macrophages then enter lymphatic system becoming system (much more severe)


T/F Salmonella typhi has an animal resovoir

F, it is strictly a human pathogen


Who is typhoid mary and explain her situation

she was a carrier of salmonella typhi w/o knowing


where in the body do salmonella typhi carriers have colonized pathogens

gall bladders


how do you diagnose what species of invasive pathogens are causing a disease

stool cultures


how do you treat enteric/GI diseases



which pathogen invades the mucous membrane by altering the hosts ion signalling pathways ?