Brucella

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Brucella
By
Dr. Emad AbdElhameed Morad
Lecturer of Medical Microbiology and Immunology
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Species

• Members of this genus are pathogenic to animals
  from which they are transmitted to man causing
  brucellosis (Malta or undulant fever).
• Species are
• Brucella abortus causing abortion in the cattle.
• Brucella melitensis causing infection in goats
  and sheep.
• Brucella susis causing infection in the pigs.
• Brucella canis causing infection in dogs.

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Morphology

• Gram negative short cocco-bacilli, non motile,
  non spore forming and non capsulated.

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Cultural characters

• Aerobe.
• Require enriched media for growth such as
  brucella agar, trypticase soy agar, chocolate
  agar, brain heart infusion agar, serum dextrose
  agar.
• Colonies are small, convex and translucent.
• 10 CO2 is required for isolation of Brucella
  abortus.

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Biochemical reactions

• All are oxidase positive.
• All are catalase positive.
• All are urease positive.

H2S production CO2 required for growth Inhibition of growth by thionine 1/30000 Inhibition of growth by basic fuchsin 1/25000 Organism
No No No No Brucella melitensis
Yes Yes Yes No Brucella abortus
Yes No No Yes Brucella suis
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Virulence factors

• Lipopolysaccharide (LPS) is the major virulence
  factor because it has endotoxic activity.
• It can survive intracellular, so immunity is
  mainly cell mediated immunity.

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Brucellosis Undulant fever

• Brucellosis is a zoonotic disease.
• Man is infected by consumption of infected cow
  or goat milk or milk products.
• Farmers and butchers are infected by contact
  with diseased animals.
• Incubation period1-6 weeks.

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• The disease is characterized by acute bacteremic
  phase followed by a chronic stage during which
  the bacteria localize in reticuloendothelial
  tissues (LNs, liver, spleen, bone marrow).
• Manifestations of the disease include
• Fever for 3-4 weeks followed by afebrile period
  of similar duration, so it is called undulant
  fever.
• Weakness, bone pain, profuse sweating enlarged
  LNs, liver and spleen.
• Brucella melitensis is the most severe form.

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Laboratory diagnosis

• Specimen blood, bone marrow, lymph node biopsy.
• Blood culture
• Isolation requires repeated blood cultures.
• Blood culture is considered negative after 4
  weeks incubation.
• Subculture is done on enriched media.
• Small convex translucent colonies are identified
  by biochemical reactions, serologically or PCR.

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• Serological diagnosis
• We use a wide range of dilutions of the
  patients serum (1/20 to 1/5120) to avoid prozone
  phenomenon.
• A titer of 1/160 or more is diagnostic.
• However, interpretation of the titer is done in
  light of endemicity of the disease and occupation
  of the patient.
• Used to detect non agglutinating IgA antibodies
  which interfere with agglutination by IgG or IgM
  in STAT.

Standard tube agglutination test (STAT)
Coombs antiglobulin test
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Prozone phenomenon
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Rapid slide agglutination test

• Direct detection of brucella in the specimen by
  PCR.
• Brucellin skin test.

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ELISA
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Treatment

• Due to chronicity and intracellular survival of
  the bacteria, combined prolonged antibiotic
  therapy with tetracycline and either
  streptomycin, rifampicin or gentamycin is
  recommended.

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Prophylaxis

• Live attenuated vaccine is used for the cattle.
• No vaccine is available for humans.
• The disease could be prevented by pasteurization
  of milk which kill the bacteria.

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GOOD LUCK