MICROBIOLOGY

• Facultatively anaerobic, oxidase-positive, curved/comma-shaped Gram-negative bacillus.
  • Cary-Blair transport medium is recommended for stool specimens.
  • Selective thiosulfate–citrate–bile salts-sucrose agar (TCBS, Fig. 1) for culture facilitates organism isolation.
• Human infection follows ingestion of fecally contaminated water or food; raw or undercooked seafood may also transmit infection.
  • V. cholerae persists naturally in freshwater, brackish, estuarine, and coastal aquatic environments.
  • Toxigenic strains cause epidemics and are reported as cholera.
    • Cholera toxin activates adenylate cyclase in small-intestinal enterocytes, increasing intracellular cAMP and CFTR-mediated chloride secretion while inhibiting sodium absorption, resulting in massive electrolyte and water loss without mucosal invasion or significant inflammation.
    • Toxigenic V. cholerae O1 and O139 strains can cause cholera.
      • O1 El Tor lineage organisms account for the ongoing seventh pandemic and all recent outbreaks.
      • Classical O1 strains have largely disappeared from circulation.
      • O139 emerged in India and Bangladesh in 1992 and caused outbreaks in Asia, but is now detected only sporadically.
    • Reagents for serotyping isolates are available through state health departments in the U.S.
      • Send all isolates to the CDC via state health department labs for subtyping and cholera toxin testing.
    • Aquatic environments are an important natural reservoir.
      • V. cholerae can persist in association with plankton, copepods, shellfish, and chitinous surfaces.
    • Antimicrobial susceptibility varies substantially by geography and outbreak and may also evolve over time.
      • Treatment should be informed by contemporary local susceptibility data whenever available.
  • Non-O1/non-O139 V. cholerae (NOVC)
    • NOVC strains are usually nontoxigenic and cause vibriosis rather than epidemic cholera.
    • They can cause gastroenteritis and, less commonly, invasive infections such as wound infection and bacteremia, particularly in patients with cirrhosis or other immunocompromising conditions.