Enteric Pathogens I Flashcards
enteric pathogens
*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
MacConkey agar
*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
epidemic watery diarrhea - common cause
vibrio cholerae
epidemic dysentery - common cause
shigella dysenteriae
vibrio species - summary
*curved, gram negative rods
*fermentative, facultative anaerobic, require salt for growth
*LPS with lipid A (endotoxin) and O polysaccharide side chain
vibrio species - most important virulence factor
*toxin co-regulated pilus (occurs in epidemic strains of V. cholera)
unique characteristics of V. vulnificus and non-O1 V. cholera
*acidic polysaccharide capsule (to avoid opsonization and phagocytosis)
*important for disseminated infections
cholera (disease overview)
*endemic in many countries, and we see many epidemics and outbreaks
*significant killer
Vibrio cholerae
*O1 and O139 produce cholera toxin
*requires a LARGE DOSE (HIGH ID50) to get infected
vibrio cholerae virulence
*disease mediated by:
1. cholera toxin (complex A-B toxin)
AND
2. toxin co-regulated pilus
cholera toxin (complex A-B toxin) subunits
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
cholera symptoms
*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
treatment for cholera
*fluid and electrolyte replacement (oral rehydration salts - work bc glucose allows cotransport of sodium)
*antibiotic therapy can reduce toxin production and clinical symptoms
prevention of cholera
clean water and food
sanitation
vibrio parahemolyticus
*associated with shellfish
Kanagawa phenomenon:
-beta hemolysis on Wagatsuma agar
-blue-green colonies on TCBS agar
*causes a gastroenteritis
vibrio vulnificus
*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
vibrio vulnificus - virulence factors
- polysaccharide capsule
- RtxA toxin
- iron acquisition systems
campylobacter overview
*gram negative, helical morphology
*“gull-winged” on gram stain
*polar flagella
*microaerophilic
campylobacter jejuni- overview and associated syndrome
*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
Guillan-Barre syndrome & campylobacter
*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
H. pylori
*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
clinical implications of H. pylori
*acute and chronic gastritis
*peptic ulcers
*can lead to cancers long-term
diagnosis of H. pylori
*stool antigen test
*carbon urea breath test
treatment of H. pylori
“triple therapy” consisting of proton pump inhibitors and the antibiotics clarithromycin and amoxicillin
