Corynebacterium diphtheriae (Diphtheria)

Paul Auwaerter, M.D.

MICROBIOLOGY

  • Pleomorphic Gram-positive bacillus that is club-shaped appears like Chinese characters on Gram stain [Fig1].
    • Facultative anaerobe.
    • Humans are only known hosts.
  • Diphtheria is caused only by exotoxin-producing strains of C. diphtheriae.
  • Three Corynebacterium strains may produce diphtheria toxin:
    • C. diphtheriae (epidemic diphtheria w/ person-person spread)
    • C. ulcerans
    • C. pseudotuberculosis
    • C. ulcerans and C. pseudotuberculosis are less common and associated with farm/dairy contacts.
  • Virulent C. diphtheria strains carry a bacteriophage with the diphtheria toxin gene. Without this bacteriophage, the microbe is unable to cause serious disease.
  • Culture is best performed on tellurite-selective media, e.g., Tinsdale agar.
  • The demonstration of an immunoprecipitation band confirms toxin production.
    • CDC provides laboratory support for state/local health departments.
      • Elek immunodiffusion assay for C. diphtheriae and C. ulcerans isolates

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