BRUCELLA

SPECIES

Brucella abortus
Brucella canis
Brucella melitensis
Brucella neotomae
Brucella ovis
Brucella suis

MICROSCOPIC APPEARANCE

Gram Stain: Negative. They do not usually show true bipolar staining.
Morphology: Rods, coccobacilli and coccoid.
Size: 0.5-0.7 micrometers by 0.6-1.5 micrometers.
Motility: True capsules are not produced and all species are non-motile.
Capsules: No.
Spores: No.
Other: Arranged singly and less frequently in pairs, short chains or small groups.

MACROSCOPIC APPEARANCE

Colonies appear transparent, raised, convex with an entire edge and a smooth, shiny surface on transparent media after 4-5 days of incubation. Non-smooth variants of the smooth species occur, but there are also stable non-smooth species with a distinctive host range.

METABOLIC PROPERTIES

Aerobic. Chemoorganoheterotrophic, having a respiratory type metabolism. Complex, enriched media are needed for culture.

KEY BIOCHEMICAL REACTIONS

HABITAT

Intracellular parasites, transmissible to a wide range of animal species, including man. Although easily cultivated in vitro , under natural conditions Brucella spp. behave as obligate parasites and do not pursue an existence independent of their natural host. Their distribution is worldwide.

PATHOGENICITY

Potentially all Brucella spp. are pathogenic. The more pathogenic strains usually produce local abscesses at the site of inoculation followed by bacteremia of varying duration. The severity of the infection varies considerably with the virulence of the infecting strain. Disease caused by Brucella spp. is referred to as "Brucellosis".

Routes of infection are genital, nasopharyngeal, gastrointestinal, conjunctival, respiratory and through abraded skin. Infection in pregnant animals often results in placental and fetal infection and this frequently causes abortion. The organisms may localize in mammary tissue and can be excreted in the milk. Transmission by milk, milk products, meat, and direct contact with infected animals has been documented. Symptoms at onset of infection include fever, arthralgia, malaise, weight loss, anorexia, arthritis, splenomegaly, hepatomegaly, chills and sweating.

RECOMMENDED MEDIA

For culture: Brucella Agar with H & K, TSA with 5% Bovine Serum
For selective isolation: BCYE, Thayer Martin
For maintenance: Brucella Agar with H & K

INCUBATION

Temperature: 35 degrees C. in 10% CO 2 .
Time: Up to 10 days.
Atmosphere: Aerobic.
Optimum pH: 6.6-7.4.

REFERENCES

1. Holt, J.G., et al. 1994. Bergey's Manual of Determinative Bacteriology , 9th ed. Williams & Wilkins, Baltimore, MD.

2. Holt, J.G., et al. 1986. Bergey's Manual of Systemic Bacteriology, Volumes I & II. Williams & Wilkins, Baltimore, MD.

3. The Oxoid Vade-Mecum of Microbiology . 1993. Unipath Ltd., Basingstoke, UK.

4. Internet: www.hardlink.com /Bacterial Database Search, February, 1998.

5. Murray, P.R., et al. 1995. Manual of Clinical Microbiology , 6th ed. American Society for Microbiology, Washington, D.C.


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