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 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 death each year (most are not laboratory confirmed).
• Most important non-cholera species are V. parahaemolyticus (62% of cases), V. alginolyticus (13%) and V. vulnificus (10% of cases and ~50% mortality).
  
  • Vibrio parahaemolyticus:
    • Most common non-cholera vibrio to cause infections.
    • Typical presentations:
      • GI disease: diarrhea, associated with consumption of contaminated fish/seafood.
      • Can also cause skin infections from direct exposure of open wounds to sea water.
    • 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 hhemolysis on special blood agar plates (kanagawa reaction).
  • Vibrio vulnificus: Less common but more lethal. ~95% of seafood associated mortality is related to this organism.
    • Part of the normal microbial ecology of estuarine water and mollusks (e.g. in Chesapeake Bay, areas of coast off of Gulf of Mexico).
    • Infection can be acquired via ingestion of contaminated seafood or direct inoculation of water onto skin.
    • There are 3 recognized biotypes, of which biotype 1 is most important cause of human infection.
    • Important toxins are collagenases, metalloproteinases and lipases/phospholipases that lead to tissue destruction, and endotoxin which leads to hypotension and organ failure
  • Vibrio alginolyticus:
    • Emerging pathogen typically impacting people in coastal communities
    • 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.
  • Cholera is caused by V. cholerae (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 micro lab if suspected as cause of gastroenteritis to use special selective media for stool specimen 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:
    • Diagnosis of GI illness due to V. parahaemolyticus is increasingly made via non-culture based (e.g. molecular) assays as part of multiplex panel.