Francisella tularensis

Valeria Fabre Fabre, M.D.


  • Small, pleomorphic, intracellular and extracellular fastidious aerobic Gram-negative coccobacillus [Fig 1].
  • Culture: poor or no growth on standard media.
    • Media most often employed: Thayer-Martin, BCYE or chocolate agar with the addition of cysteine and/or cysteine (thioglycolate).
      • MacConkey and other conventional media will not yield growth.
    • A slow grower may require CO2 supplementation.
  • Considered an important laboratory hazard to laboratory personnel requiring specialized safety procedures. Notify the lab if considering diagnosis when submitting specimens; higher level labs may be required.
  • Recognized subspecies that vary in location and virulence:
    • F. tularensis: distinguished by PCR and the only relatively common human pathogen.
      • F. tularensis subsp. tularensis often are worse than those caused by F. tularensis subsp. holarctica
    • F. novidicida and F. philomiragia
      • A rare disease in humans, mostly immunocompromised.
    • F. hispaniensis
    • F. opportunistica
    • F. salimarina
    • Notes:
      • Biovar tularensis (Type A), typically associated with lagomorphs (hares, rabbits, pikas)
        • Biovar holarctica (B), frequently associated with rodents and aquatic environments
        • Biovar mediasiatica and subspecies novicida
      • Multiple other Francisella species have been isolated from animal and environmental samples.

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Last updated: March 18, 2023