Gram Negative Enteric Rods

Gram Negative Enteric Rods

1. E. Coli

   • Enterotoxigenic (ETEC)
     • Travelers Diarrhea
     • Enterotoxins
       • Labile: resembles cholera toxin, activates adenylate cyclase, increases cAMP levels, increases secretion of ions & water, inhibits reabsorption of sodium
       • Stable: stimulates guanyl cyclase coupled receptor, increases cGMP, and increases efflux of ions and water
     • Pills facilitates binding to intestinal mucosa
   • Enteroaggregative (EAEC)
     • Causes travelers diarrhea, persistent diarrhea in young children
     • Adhere to mammalian cells and each other with fimbriae; shortens microvili—> affects absorption
     • Produce heat stable toxin that is plasmid encoded
   • Enteropathogenic (EPEC)
     • Diarrhea in infants (poor sanitation)
     • Bundle forming pili adhere to surface of enterocytes
     • Type III secretion system injects proteins into host cell—> destroys brush border form characteristic A/E lesions
   • Enterinvasive (EIEC)
     • Dysentery-like syndrome; fever; bloody stools
     • Plasmid encoded virulence factors -invasion plasmid antigens—>allows invasion by actin based motility
     • Produces a hemolysis alpha (Hal)
   • Enterohemorrhagic (EHEC)
     • Bloody diarrhea
       • Damages vascular endothelium
     • Binds to large intestine by bundle forming pili and produces A/E lesions
     • Exotoxin
       • Shiga like toxins; cleave post-ribosomal RNA inhibition of protein synthesis —> apoptosis
     • Hemolytic uremic syndrome

2. Campylobacter

   • Leading cause of food borne illness in US
   • Polar Flagellum, daring motility, and microaerophilic
   • Virulence Factors
     • Cytotoxic- inflammatory colitis
     • Enterotoxin- increased adenylyl cyclase activity—> electrolyte fluid imbalance
   • Needs selective Campy-BAP media for microaerophilic
   • Acute enteritis, ulcers, bacteremia, travelers diarrhea, pseudoappendicitis

3. Salmonella

   • Most are Lac-, ferments glucose; produces acid & gas, produce H2S from sulfur containing a.a.
   • Facultative intracellular parasites; survive inside phagocytic cells (macrophages)
   • Typhoidal
     • Causes Typhoid Fever and Paratyphoid Fever
   • Non-Typhoidal
     • Causes gastroenteritis and food poisoning

4. Shigella

   • Baciliary dysentery
   • Non-motile, unencapsulated, Lac -, do not produce gas in a mixed acid
   • Most commonly among young children
   • Type 3 secretion system, polymerize actin

5. Vibrio

   • Short, curved, rapidly motile, single polar flagellum
   • O and H Ags are present
   • Facultative anaerobes
   • NaCl stimulates growth
   • Cholera toxin (loss of fluids & blocks uptake of Na and Cl), hypokalemia, cardiac arrhythmia, renal failure,
   • El Tor strain- produces hemolysis, higher carriage rates, survives in water longer