Brucella species

Brucella species are 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.


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

Key Characteristics

  • Gram-negative, coccobacillus
  • Grows slowly at 35-37C. CO2 enhances growth of some biovars of B. abortus.
  • Catalase positive
  • Non-motile
  • Oxidase positive (B. canis is variable)
  • Urease positive; strong, typically <2h, some within 5 minutes.
  • X and V factors are not required.

Colony Characteristics:

  • Usually not visible or pinpoint at 24 hrs.
  • Grows slowly on most standard laboratory media (ie. sheep blood, chocolate and tryptic soy agars). Pinpoint, smooth, with an entire border, translucent, non-hemolytic at 48 hrs.
  • Some strains grow on MacConkey agar.
  • Grows on Martin-Lewis and Thayer-Martin agars.

Microscopic Characteristics:

Faintly-staining, small Gram-negative coccobacillus (0.5-0.7 x 0.6-1.5 µm), seen mostly as single cells and appearing like “fine sand”. Bipolar staining is not a distinctive feature. Although a small Gram-negative coccobacillus, cells are typically larger than those of F. tularensis.


Brucella species flowchart

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