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Doneen Hollingsworth, Secretary of Health

Brucella species — Key Characteristics

Brucella is the most commonly reported agent of laboratory-associated infection. It is a virulent, highly infectious organism. Once this organism is suspected on the basis of clinical and/or laboratory information, do not perform additional testing. Send the isolate to the South Dakota State Laboratory for identification.

  • Slow growing organisms.
  • Faintly staining gram-negative coccobacillus.
  • Punctate (minute spots) colonies on sheep blood agar.
  • Nonhemolytic.
  • Catalase positive.
  • Oxidase positive.
  • Urease positive. (May be positive within 1 hour. If not, read at 24 and 48 hours.)

Identification Pitfalls to Avoid

  • May be confused with Haemophilus - does not require X/Vfactors.
  • Consider the possibility that an organism with characteristics similar to Brucella which is oxidase and urease negative may be Francisella tularensis.
  • Brucella isolates may be misidentified by commercially available identification systems, often as Psychrobacter phenylpyruvicus (formerly Moraxella phenylpyruvica).

Look-a-likes (Other OX=/Ur+/GN/Oxidisers)

  • Achromobacter
  • Acidovorax
  • Agrobacterium
  • EO-2/EO-3
  • Flavobacterium
  • Methylobacterium
  • Psychrobacter
  • Ochrobactrum
  • Pseudomonas
  • Riemerella
  • Roseomonas
  • O-2
  • II-I
  • Oligella

positive urease test
The pink tube on the left is a positive urease test.

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