USMLE

Vibrio spp.

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Bacteria - Gram Negative
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Vibrio spp.

  • Includes Vibrio cholerae, Vibrio parahemolyticus, Vibrio vulnificus
  • Characteristics
    • Gram negative comma-shaped rod
      • First test in algorithm, narrows scope of bacteria
    • Oxidase +
      • All gram negative curved rods are oxidase positive 
    • Grows in alkaline media
      • Specific to Vibrio cholerae
    • Motile (has flagella)
    • Can grow in highly alkaline environments
      • TCBS (thiosulfate-citrate-bile salt) agar is selective for Vibrio
  • Virulence factors
    • Cholera toxin (choleragen)
      • exotoxin permanently activates Gs
      • increased cAMP levels promotes fluid secretion (e.g. causing diarrhea)
  • Transmission
    • Endemic to developing countries
    • In US, caused by ingestion of contaminated water or shellfish (e.g. oysters)
    • Infectious dose (ID50) is high
      • Acid-labile (inactivated by gastric acid) → Requires a large inoculum (dose)
      • Note: taking PPIs or other acid-lowering medications will increase risk
  • Presentation: Cholera
    • Produces profuse rice-water diarrhea via Cholera enterotoxin
      • Exotoxin increased ion secretion, resulting in secretory diarrhea and water efflux 
      • Does not invade GI mucosa (usually does not cause bloody diarrhea) -- watery diarrhea is purely toxin-mediated
  • Diagnosis
    • Stool culture in alkaline media
      • No WBCs or RBCs seen in stool (no invasion of GI mucosa occurs)
  • Treatment
    • Aggressive rehydration
      • IV fluids
      • Oral rehydration solution
    • Antibiotics only used in severe cases as adjunct treatment
      • macrolides, fluoroquinolones, and tetracyclines may be used (UTD)