MICROBIOLOGY

• Aerobic, Gram-negative, comma-shaped bacillus.
  • Cary Blair media suggested transport.
  • Selective thiosulfate–citrate–bile salts agar (TCBS, Fig 1) is best used for culture.
• Humans usually acquire infection through ingesting contaminated waters (brackish or marine) or food as a water-borne pathogen. Countries may have endemic infections (ongoing continuously, often with spikes during the rainy season) or epidemics.
  
  • Only toxigenic strains cause epidemics and are reported as cholera.
    • V. cholerae serogroup O1 has two biotypes, and each has distinct serotypes, although the clinical infection is not distinguishable:
      • Classical is now rarely seen except in regions of Bangladesh and India.
      • El Tor originated in Asia but has caused infection (seventh cholera pandemic) throughout Africa and South America for >47 yrs.
    • A newer serogroup, O139, described in SE Asia in 1992 now endemic.
    • Reagents for serotyping isolates are available through state health departments in the U.S.
      • Send all isolates to CDC via state health department labs for subtyping and cholera-toxin testing.
  • V. cholera doesn’t have a known animal reservoir; however, bacteria do attach to the chitin in shells of crustaceans and shellfish, which then can be a source of infection.
• Isolates are described with resistance to ampicillin, tetracycline, ampicillin, aminoglycosides, sulfonamides, fluoroquinolones and trimethoprim.
• Non-01 V. cholerae strains (also water-borne, may be non-toxigenic) can rarely cause non-diarrheal illnesses such as bacteremia and wound infections, especially in cirrhotics.
  • Infections may be from fresh or brackish waters.