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Brucella is a genus of gram negative, small, non-encapsulated coccobacilli which are strict aerobes.

Route of entry

  • Ingestion of contaminated milk products
  • Through the skin by direct contact
  • Inhaled in aerosols


  • Majority are killed by macrophages, rest survive in macrophages
  • Invade the body through mucous of upper intestinal and respiratory tracts or skin lesions.
  • Enter sub serosa and are transported by macrophages to lymph nodes of liver, spleen and bone marrow
  • Enter bloodstream
  • Host response is granulomatous, which progresses to focal abscesses
  • Produce endotoxin but no exotoxin

Virulence factors
•    Endotoxin

Predisposing factors
•    Inflected animals
•    Unpasteurized milk

Clinical symptoms
•    Incubation period is 01-03 weeks
•    Fever is seen in minority of cases and it is undulating fever
•    Chills
•    Fatigue
•    Malaise
•    Anorexia
•    Weight loss
•    Enlarged spleen, liver, lymph nodes
•    Pancytopenia
•    Osteomyelitis –a complication

Lab Diagnosis

•    Blood
•    Bone marrow

•    Gram negative
•    Small, coccobacilli
•    Non-encapsulated
•    Strict aerobes

Brucella melitensis
Brucella melitensis

Strict aerobes, requiring 5-10% CO2

Tryptone soya diphase medium
Produce variety of colonies, e.g smooth, mucoid, colourless or grey, white colonies

TSI agar      
No H2S is produced

Biochemical Tests
•    Catalase         +ve
•    Oxidase          +ve
•    Indole              -ve
•    Hydrolyze       urea

Serological tests
•    Slide agglutination test with Brucella antiserum.
•    Rapid IgM/IgG immunochromatographic assay
•    PCR



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