Brucella melitensis

Background

• Causes brucellosis, also called Malta fever

Microbiology

• 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

Epidemiology

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

Clinical Manifestations

Brucellosis

• Exposure to unpasteurized milk products or animals
• A common cause of fever without a focus in endemic countries
• 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

Diagnosis

• 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
    • Cross-reacts with Francisella tularensis and Vibrio cholerae

Management

• Gentamicin, streptomycin, doxycycline, TMP-SMX