Gram Negative Bacteria of the GI tract

Question 1

1. Differntiate dysentery and non-dysenteric diarrhea.

Answer 1

diarrhea: frequent stools, often loose; often painless and without fever, with many causes; mechanisms result in increased secretion and/or decreased absorption in the small or large intestine
dysentery: damage to the host cells, cytoxins or deep invasion causing pus or blood in the stool, which is often painful due to resulting tissue distraction in large intestine

Question 2

2. Describe the pathogenic mechanisms by which bacteria cause enteric disease and their sequelae.

Answer 2

intoxication (pre-formed toxin)– severe N/V and or diarrhea (S. aureus, bacillus cereus)

secretory toxin: profuse watery diarrhea, painless or mild pain +/- fever (ETEC, Vibrio cholarae, rotavirus)

cytoxin: bloody diarrhea, painful cramps, fever (EHEC O157: H7 or Shigella)

mucosal colonization: diarrhea, fever, N/V (EPEC, Salmonella, Campylobacter, rotavirus)

deep invasion: purulent bloody dysentery, painful cramps, fever (EIEC, Shigella, Campylobacter, Entameoba histolytic)

systemic dissemination: systemic signs and symptoms (enteric fever)

Question 3

3. Describe the toxin-mediated enteric disease and invasive enteric disease and identify organisms responsible for each. Ie. Differentiate between gastroenteritis and enteric fever.

Answer 3

gastroenteritis is a catch all used to describe numerous syndromes with symptoms including some combination of NVD

enteric fever is bacteremia sepsis entering through the gut (a systemic infection starting in the GI tract

Question 4

4. Identify which bacteria cause this common syndrome: watery diarrhea.

Answer 4

ETEC, Vibrio cholera, rotavirus

Question 5

4. Identify which bacteria cause this common syndrome: dysentery.

Answer 5

EIEC, Shigella, Campylobacter (late) and Enteameoba

Question 6

4. Identify which bacteria cause this common syndrome: enteric fever.

Answer 6

S. typhi

Question 7

5. Distinguish enterotoxigenic E. coli (ETEC) associated disease and mechanism.

Answer 7

(enterotoxigenic) traveler’s diarrhea caused by secretory toxins (heat stable and labile)

Question 8

5. Distinguish enteropathogenic E coli (EPEC) associated disease and mechanism.

Answer 8

(enteropathogenic) infantile diarrhea caused by mucosal colonization and destruction

Question 9

5. Distinguish enterohemorrhagic E.coli (EHEC) associated disease and mechanism.

Answer 9

(enterohemorrhagic- O157: H7) hemorrhagic colitis, HUS; zoonosis from cow intestines or from infected humans and caused by cytotoxin (verotoxin, Shiga-like toxin)

Question 10

5. Distinguish enteroinvasive E. coli. (EIEC) associated disease and mechanism.

Answer 10

(enteroinvasive) bacilliary dysentery that is caused by to deep invasion of GI tissue

Question 11

6. Discuss common sources of enteric infection for E. coli and Salmonella and the syndromes they cause.

Answer 11

E coli transmission fecal/oral, from contaminated foods, variable incoculum required; causes ETEC, EPEC, EHEC, EIEC

Samonella: fecal/oral, contaminated food (eggs and poultry) animals (non-typhi); causes gastroenteritis with rotten egg stool, S. tymphi causes enteric fever

Question 12

6. Discuss the common sources of enteric infection for Shigella, Campylobacter, Vibrio and Yersinia and the syndromes they cause.

Answer 12

Shigella: obligate human pathogen, small incoulum required, transmission (fecal to oral) leads to bacillary dysentery and some strains make cytotoxin

Campyloacter (fecal/oral, contaminated food (milk, poultry) or animals causing early gastroenteritis from mucosal colonization and destruction, occasional late dysentery from deep invasion and rare enteric fever (***darting motility)

Yersinia: transmission fecal/oral and animals causing gastroenteritis, diarrhea, and occasional pseudoappendicitis (Y.pestis completely different, cause of plague)

Vibrio cholearae: large incoulum required, recall/oral tramission; secretary toxin causes voluminous watery diarrhea

Vibrio parahemolyticus: tramission via salt water, shellfish and sushi, gastroenteritis

Vibrio vulnificus: transmission via salt water and shellfish, abrasions esp in immunocomp. causing wound infection and septicemia (50% mortality)

Question 13

7. Explain the route of transmission, clinical syndromes and mechanisms of pathogenesis of Helicobacter pylori.

Answer 13

transmission fecal/oral

colonization of gastric mucosa may be asymptomatic or lead to acute or chronic gastritis; leading came of gastric and duodenal ulcers and contributes to development of gastric cancer

Question 14

What is hemolytic uremia syndrome?

Answer 14

caused by cytotoxin (verotoxin, Shiga toxin or Shiga-like toxin that is produced in intestinal lumen and enters blood circulation leading to systemic disease

associated with EHEC, some Shilgella strain etc.

other clinical features can include: thrombotic microangiopathy, hemolytic anemia, thrombocytopenia with renal lesions and renal failure

most common in children and the elderly

Question 15

Describe the characteristics of enteric fever infection.

Answer 15

organisms enter through Peyer’s patches and invade blood stream causing bacteremia, replicate in liver and return to gut in large numbers via common bile duct

blood culture positive before stool

Cause by S. typhi, S. paratyphoid, S. enteritidis, Yersinia enterocolitica, Campylobacter jejuni

Question 16

What cases are antibiotics reserved for regarding enteric infections?

Answer 16

at risk patients: infant, elderly, immunocomprimsed

fluroquinolones used, do not use antibiotics for EHEC (do not diminish symptoms, worse outcomes)

Helicobacter pylori- 2 or more antibiotics- amoxicillin and clarithromycin, with antibacterial activity and PPI