Enteric Pathogens I

Question 1

enteric pathogens

Answer 1

*ubiquitous organisms that are part of the normal intestinal flora
*infections enter the body through mouth and intestinal tract
*cause a variety of human diseases

Question 2

MacConkey agar

Answer 2

*selective and differential media
**INHIBITS gram POS bacteria (only gram - can grow)
*differentiates lactose fermenters (PINK) vs. non-lactose fermenters (colorless)
*neither salmonella or shigella ferment lactose

Question 3

epidemic watery diarrhea - common cause

Answer 3

vibrio cholerae

Question 4

epidemic dysentery - common cause

Answer 4

shigella dysenteriae

Question 5

vibrio species - summary

Answer 5

*curved, gram negative rods
*fermentative, facultative anaerobic, require salt for growth
*LPS with lipid A (endotoxin) and O polysaccharide side chain

Question 6

vibrio species - most important virulence factor

Answer 6

**toxin co-regulated pilus (occurs in epidemic strains of V. cholera)

Question 7

unique characteristics of V. vulnificus and non-O1 V. cholera

Answer 7

*acidic polysaccharide capsule (to avoid opsonization and phagocytosis)
*important for disseminated infections

Question 8

cholera (disease overview)

Answer 8

*endemic in many countries, and we see many epidemics and outbreaks
*significant killer

Question 9

Vibrio cholerae

Answer 9

*O1 and O139 produce cholera toxin
*requires a LARGE DOSE (HIGH ID50) to get infected

Question 10

vibrio cholerae virulence

Answer 10

*disease mediated by:
1. cholera toxin (complex A-B toxin)
AND
2. toxin co-regulated pilus

Question 11

cholera toxin (complex A-B toxin) subunits

Answer 11

ctxA and ctxB
*5 B subunits that mediate binding to receptors on intestinal epithelial cells
*1 A subunit: controls adenylate cyclase, triggering conversion of ATP to cAMP, resulting in hypersecretion of water and electrolytes

Question 12

cholera symptoms

Answer 12

*rice-water appearance of stool (flecked with mucus)
*diarrhea presents very suddenly (stool output outrageously high)
*vomiting and abdominal cramping
*fever NOT common
*dehydration
*“washer woman” fingers

Question 13

treatment for cholera

Answer 13

*fluid and electrolyte replacement (oral rehydration salts)
*antibiotic therapy can reduce toxin production and clinical symptoms

Question 14

prevention of cholera

Answer 14

clean water and food
sanitation

Question 15

vibrio parahemolyticus

Answer 15

*associated with shellfish
Kanagawa phenomenon:
-beta hemolysis on Wagatsuma agar
-blue-green colonies on TCBS agar
*causes a gastroenteritis

Question 16

vibrio vulnificus

Answer 16

*presents as a wound infection or primary sepsis
*exposure through wound or ingestion
*leading cause of SHELLFISH-ASSOCIATED DEATHS in the US (esp. oysters)
*more prevalent in people with liver disease or hemachromatosis
*gulf of mexico and chesapeake bay

Question 17

vibrio vulnificus - virulence factors

Answer 17

1. polysaccharide capsule
2. RtxA toxin
3. iron acquisition systems

Question 18

campylobacter overview

Answer 18

*gram negative, helical morphology
*“gull-winged” on gram stain
*polar flagella
*microaerophilic

Question 19

campylobacter jejuni- overview and associated syndrome

Answer 19

*most common bacteria cause of diarrhea in developed countries
*zoonotic infection (birds, poultry, pigs, etc)
*peak incidence in < 1 yo and 15-24 yo
*more common in asia
*associated with Guillan-Barre syndrome

Question 20

Guillan-Barre syndrome & campylobacter

Answer 20

*leading cause of paralysis worldwide
*immune response to specific O-antigens cross-reacts with components of peripheral nerves
*acute inflammatory demyelinating neuropathy
*classic question: ASCENDING PARALYSIS
*most frequent antecedent pathogen = campylobacter jejuni

Question 21

H. pylori

Answer 21

*curved, gram-negative rods
*produces urease
*fecal-oral spread
*blocks acid production (with bacterial acid-inhibitory protein)
*neutralization of gastric acids with the ammonia produced by bacterial urease activity

Question 22

clinical implications of H. pylori

Answer 22

*acute and chronic gastritis
*peptic ulcers
*can lead to cancers long-term

Question 23

diagnosis of H. pylori

Answer 23

*stool antigen test
*carbon urea breath test

Question 24

treatment of H. pylori

Answer 24

“triple therapy” consisting of proton pump inhibitors and the antibiotics clarithromycin and amoxicillin