MICROBIOLOGY

• Aerobic, Gram-negative, comma-shaped rod (1-3 x 0.5-0.8µm, Fig).
• Grows best in warm, low-salinity marine water. Coastal waters/estuaries are ideal. As marine environments warm, these organisms have spread to new areas (e.g., northern coastal states) and are increasingly important causes of human infections.
• Rates of infections in the U.S. have tripled over the past two decades. Estimated to cause approximately 80,000 cases and 100 deaths each year (most are not laboratory-confirmed).
• The most important non-cholera species are V. parahaemolyticus (most cases), V. alginolyticus (second most cases), and V. vulnificus (most dangerous with ~20% or higher mortality).
  
  • Vibrio parahaemolyticus:
    • The most common non-cholera vibrio to cause infections.
    • Typical presentations:
      • GI disease: diarrhea associated with consumption of contaminated fish/seafood.
      • It can also cause skin infections from exposure to open wounds to seawater.
    • Most environmental strains are non-pathogenic.
    • Pathogenic strains carry a hemolysin toxin: thermostable direct hemolysin (TDH) and/or TDH-related hemolysin (TRH).
      • Strains with TDH cause hemolysis on special blood agar plates (Kanagawa reaction).
  • Vibrio vulnificus is less common but more lethal. This organism is related to 95% of seafood-associated mortality.
    • It is part of the normal microbial ecology of estuarine water and mollusks (e.g., in the Chesapeake Bay and areas of the coast off the Gulf of Mexico).
    • Infection can be acquired via direct inoculation into skin/soft tissues or ingesting raw or undercooked seafood (~10% of cases).
    • There are three recognized biotypes, of which biotype 1 is the most important cause of human infection.
    • Important toxins are collagenases, metalloproteinases, and lipases/phospholipases, which lead to tissue destruction, and endotoxin, which leads to hypotension and organ failure.
  • Vibrio alginolyticus:
    • An emerging pathogen typically impacts people in coastal communities.
      • Causes about 20% of vibriosis.
    • Non-foodborne infections predominate (~86%) and typically affect lower extremity skin or external ears after swimming in warm coastal waters.
  • Other occasional Vibrio species causing human infection: V. fluvialis, V. fumissii, V. hollisae, V. damsela, V. cincinnatiensis.
  • V. cholerae causes cholera (see that module for details)
• Diagnosis:
  • Culture:
    • Obtain from suspected source, e.g., blood (sepsis), wound (wound infection), stool (gastroenteritis).
    • Organisms grow well on routine media and in blood cultures.
    • Notify the micro lab if it is suspected to cause gastroenteritis and use special selective media for stool specimens such as thiosulfate citrate bile salt sucrose (TCBS).
      • Some labs in endemic areas routinely use this media as part of stool culture protocol during summertime/warmer weather.
  • Molecular:
    • The diagnosis of GI illness due to V. parahaemolyticus is increasingly made via non-culture-based (e.g., molecular) assays as part of a multiplex panel.