Acute Gastroenteritis Flashcards by Sara Johnson

Common clinical feature of acute gastroenteritis?

acute infectious diarrhea w/ > 12h incubation

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Response of SI to infection?

secretory diarrhea

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Response of LI to infection?

dysentery - scant diarrhea, cramps, tenesmus (need to defecate without relief)

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What is necessary for inflammatory acute infectious diarrhea?

invasion or killing of intestinal cells
stool contains PMNs, blood due to damage
typically fever

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Vibrio cholerae morphology and unique cultural characteristic?

GN motile curved rod (marine)

- acid-sensitive = require selective medium pH 8.6

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Two serotypes of V. cholerae? Where are they found?

O1 (classic and El Tor) - El Tor is causing worldwide pandemic
O139 - more recent; Bangladesh and India; resembles O1 El Tor

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Reservoirs of V. cholerae?

coastal waters + fecal contamination
copepods (egg sacs) and shellfish (filter water and copepods)
asymptomatic human shedding

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What organism is associated with reduced gastric acidity and Type O blood risk factors?

V. cholerae

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What two phages are required for V. chol virulence?

Tcp pilus

- Ctx (AB enterotoxin) - requires Tcp

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How does cholera toxin work?

ADP ribosylates adenylate cyclase generates inc cAMP
activation of apical CFTR Cl- channel
results in hypersecretion of Cl-, K+, bicarb and water (hypokalemia, acidosis, hypoglycemia)

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Classic cholera stool description?

rice water

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Treatment for cholera?

restore fluid and electrolyte balance

- AB’s dec duration/volume of diarrhea

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Most commonly isolated vibrio from human disease in US?

Vibrio parahaemolyticus

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Disease observed with V. parahaemolyticus?

mild cholera
bug has many toxins (hemolysis, proteins)
low grade to mild fever
wound infections

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What is unique about the clinical presentation of cholera?

NO FEVER

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How is V. parahaemolyticus transmitted?

contaminated shellfish in the spring and summer

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Leading cause of Traveler’s Diarrhea in US? How?

ETEC - enterotoxigenic

- imported on produce

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Where and how does ETEC adhere?

covered in pili

- ileum

Two toxins associated with ETEC?

LT = heat-labile (similar to Ctx, inc cAMP)
ST = heat-stable (inc cGMP)
both cause Cl- mediated fluid loss

Which EC causes persistent watery diarrhea for ~ 2 weeks?

Enteroaggregative EC (EAEC)

How does EAEC adhere?

‘stacked brick’ (aggregative) pattern of adherence mediated by pili via formation of BIOFILM –> thick mucus layer (diagnostic)

Which EC is an important cause of infant diarrhea in developing countries and can adhere to plant matter?

EPEC - enteropathogenic

How infective is EPEC?

VERY - low infective dose

Pathogenesis of EPEC?

“attaching and effacing lesion”
attach w/ pili to form microcolonies (pedestal); intimately attach and secrete/inject toxins/proteins
destroy microvilli
injected proteins and deranged cell signaling cause diarrhea

What EC is a problem of developed countries? Reservoir?

- EHEC - enterohemorrhagic | - GIT of cattle

Phasic progression of EHEC?

watery diarrhea (ileum) - hemorrhagic colitis - HUS

Major EHEC serotype in US?

O157:H7 - low infective dose + acid resistant

When is EHEC shed?

warm months

What does EHEC infection look like in the beginning?

EPEC - A/E lesion via pili

What toxins has EHEC acquired?

STx1, STx2 or both (on phage)

Structure and receptor of Stx?

- AB enterotoxin | - Gb3 - glycolipid; distribution of receptor in tissue causes localization of effects

What does the Stx toxin do to protein synthesis?

- removes adenine from 28S rRNA of host ribosome - inhibits protein synthesis - Intermediate ER stress on endo cells in colon (receptor) produces hypercoaguable state

How does Stx cause hemorrhagic colitis?

- pro-coagulant state due to ER stress results in microvascular thrombosis - thrombosis lyses RBC's - frank bloody diarrhea BUT IT IS NOT INVASIVE! so little to no fever

What happens in HUS?

- Stx travels through blood to kidney where it binds glomerular endo cells (Gb3 receptor) - dec GF, ARF, hemolytic anemia, thrombocytopenia

What % of hemorrhagic colitis cases progress to HUS? Who doesn't get it?

- 5-10% - < 5 yo and elderly | - AA's do not get it

How is HUS treated?

aggressive - fluid and kidney dialysis (may be brain manifestation in elderly due to Gb3 on neurons = 50% mortality)

When are anti-motility drugs and antibiotics not given?

EHEC - want to get Stx out

Why are antibiotics not give in EHEC hemorrhagic colitis?

- AB's cause stress response in bacteria so bacteriophage enters lytic phase, leaves and produces a ton of Stx - can cause progression to HUS

What is the new EC pathotype that appeared in 2011?

Stx-EAEC - shiga producing enteroaggregative EC (EAEC acquired shiga toxin and drug resistance)

Who gets Stx-EAEC?

- 90% in young, mid-aged adults | - HUS mostly in women --> 22% of STEAEC cases

What two gram positive spore forming organisms are agents of food poisoning in the US?

Clostridium perfringens and Bacillus cereus

What is the major protozoan cause of persistent diarrhea?

Giardia lamblia - adheres in gut and causes persistent water diarrhea (Hiker's disease in contaminated water)

What zoonotic infection is a problem for IC patients and causes persistent diarrhea?

Cryptosporidium parvum