Brucella melitensis

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Brucella melitensis / (Redirected from Brucellosis)


  • Causes brucellosis, also called Malta fever


  • Facultative intracellular, Gram-negative coccobacillus
  • Catalase positive, oxidase positive, nitrate positive, and urease positive
  • Non-motile
  • Risk group 3 organism
  • When suspected, plates should be sealed and it should not be set up for mass spectrometry


  • Zoonotic transmission transmitted by ingesting contaminated food (such as unpasteurized milk products), direct contact with an infected animal, or inhalation of aerosols

Clinical Manifestations


  • Exposure to unpasteurized milk products or animals
  • A common cause of fever without a focus in endemic countries
  • Incubation period is usually 2-4 weeks (range 5 days to 6 months)
  • Undulating fever
  • Headache, arthralgia, night sweats, fatigue, anorexia
  • Arthritis, spondylitis (especially sacroiliac and other large lower-extremity joints), osteomyelitis
  • Hepatomegaly, splenomegaly, and lymphadenopathy
  • Orchitis and epididymitis, prostatitis, and tubo-ovarian abscess
  • Foul-smelling sweat
  • Can have mild pancytopenia

Relapsed Brucellosis

  • Occurs within six months of completing treatment in about 10% of patients


  • Culture
    • May be isolated from blood culture, but only intermittent and is a fastidious organism
      • Sensitivity is 50-70%
      • Cultures should be held for 10 days
    • Grows slowly on blood and chocolate agar; better on Brucella agar
    • On gram stain, the small coccobacilli look like fine grains of sand
  • Serology
    • Acute and convalescent serology showing a fourfold rise in titres
    • Serum agglutination test titres of 1:160 or greater in the right clinical context


  • Uncomplicated infection
  • Neurobrucellosis:
    • First-line: ceftriaxone 2 g IV q12h for 1+ month, plus doxycycline 100 gm PO bid and rifampin 600 to 900 mg (15 mg/kg) PO daily for 4-5 months
    • Alternative: TMP-SMX 160/800 mg PO bid, plus doxycycline 100 mg PO bid, plus rifampin 600 to 900 mg (15 mg/kg) PO daily for 5 to 6 months
  • Pregnancy
    • Rifampin 900 mg PO daily for 6+ weeks, ± TMP-SMX between the 13th and 36th weeks of gestational


Lab Safety

  • Assess risk and provide prophylaxis and monitoring per CDC guidelines
  • Assess risk
    • Minimal risk
      • Manipulating routine specimen or enriched material in BSL2 with PPE
      • Being present while someone manipulates a routine specimen in BSL2, or on an open bench without aerosol-generating procedures
      • Manipulating or being present while someone manipulates enriched material in BSL2
    • Low risk
      • Being present more than 5 feet from someone manipulating enriched material on an open bench, without aerosol-generating procedures
    • High risk
      • Manipulating a routine specimen resulting in contact with broken skin or mucous membranes
      • Being present less than 5 feet from someone manipulating enriched material outside of a BSL2
      • Manipulating enriched material within a BSL2 without PPE
      • Being present in the lab during an aerosol-generating procedure
  • Aerosol-generating procedures include centrifuging without sealed carriers, vortexing, sonicating, spillage/splashes
  • Enriched material includes positive blood cultures, and reproductive clinical specimens (amniotic fluid, placental products) should be treated similarly
  • People with high-risk exposures should have post-exposure prophylaxis and follow-up
    • PEP with doxycycline 100 mg PO bid plus rifampin 600 mg PO daily for 21 days
      • Either can be replaced by TMP-SMX if contraindications exist, but should ensure two effect antibiotics are used
    • Follow-up
      • Daily fever checks and weekly symptom watch for 24 weeks after last known exposure
      • Serial serology at 0, 6, 12, 18, and 24 weeks after last known exposure