Francisella tularensis

F. tularensis is highly infectious. Once this organism is suspected on the basis of clinical and/or laboratory information, additional testing MUST be performed within a certified biosafety cabinet.

Safety:

  • Biosafety Level 2 for processing clinical specimens.
  • Biosafety Level 3 practices for all culture manipulations that might produce aerosols.

Key Characteristics

  • Gram-negative, very tiny coccobacillus
  • Does not grow on MacConkey or EMB agar
  • Grows slowly at 35-37C, on sheep blood, chocolate or Thayer-Martin agar, does not require CO2.
  • Catalase negative, or weakly positive
  • Non-motile
  • Oxidase negative
  • Urease negative
  • X and V factors are not required.

Colony Characteristics:

  • Grows poorly on sheep blood agar: 1-2 mm, gray-white, non-hemolytic at 48-72 hrs.
  • On chocolate or Thayer-Martin agar: 1-3 mm, gray-white to bluish-gray with entire border and smooth flat surface at 48-72 hrs. Growth in thioglycollate broth is slow, with denser band near top, diffusing with age.
  • Ability to grow on sheep blood agar usually lost on subculture.

Microscopic Characteristics:

Faintly staining, very tiny Gram-negative coccobacillus (0.2-0.7 x 0.7-1.0 µm), seen mostly as single cells. Bipolar staining is not a distinctive feature. Cells are smaller than those of Brucella spp.

Resource

 

F. tularensis Sentinel Laboratory Flowchart

 

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