Microbiology · MU Plovdiv

33. Brucella. Species. Morphology, biology, biochemical production and pathogenic factors. Pathogenesis and immunity Microbiological diagnosis. Specific prophylaxis. Francisella tularensis. General characteristics. Legionella pneumophila. General characteristics.

Inside: 3 sections · 8 labelled pictures · 3 tables · 16 flashcards · 3 min

Topic 33 of 50 in the MU Plovdiv syllabus for Microbiology (Medicine, Years 2 and 3). The free AceMed note covers it in 3 sections, about 378 words (3 min of reading), with 16 flashcards.

In this note

  1. Genus Brucella. Genus Francisella
  2. Brucella spp.
  3. Francisella tularensis

Brucella spp.

General Characteristics

  • Gram-negative small coccobacilli, non-motile
  • Non-encapsulated
  • Strict aerobes, oxidase (+), catalase (+)
  • Facultative intracellular bacteria — live in macrophages
  • Grow slowly on enriched media (3 days to 3 weeks)
  • No exotoxins, only endotoxins

Epidemiology & Transmission

  • Zoonosis: transmitted from animals to humans
  • Reservoirs:
  • B. melitensis – goats/sheep (most pathogenic)
  • B. abortus – cattle
  • B. suis – pigs
  • B. canis – dogs
  • Infection via:
  • Unpasteurised dairy
  • Occupational contact (e.g. veterinarians, slaughterhouse workers)
  • Direct contact with animal secretions
  • No human-to-human transmission

Pathogenesis

  • Enters via mucous membranes, skin, or ingestion → local replication
  • Phagocytosed by macrophages but survive intracellullarly
  • Spread via lymphatics to reticuloendothelial organs: liver, spleen, BM
  • Causes granulomatous inflammation, focal abscesses, and chronic infection

Virulence Factors

Diagnosis

  • Specimens: blood, bone marrow, tissue biopsy
  • Culture: enriched media + 10% CO₂, slow growth
  • Serology:
  • Slide agglutination test with Brucella antiserum
  • ELISA or standard agglutination test (SAT)
  • PCR available in reference labs

Clinical Manifestations – Brucellosis

  • Incubation: 1–3 weeks
  • Nonspecific flu-like symptoms:
  • Undulant fever (intermittent), chills, fatigue
  • Muscle aches, night sweats, weight loss
  • Hepatosplenomegaly, lymphadenopathy
  • Chronic form: depression, arthritis, endocarditis, orchitis

Treatment

  • DOC: Doxycycline + Rifampin (min. 6 weeks)
  • Alternative (children, pregnancy): TMP-SMX
  • Avoid monotherapy to prevent relapse

Prevention

  • Avoid raw milk/cheese
  • Control infection in livestock
  • Protective clothing for high-risk workers
  • No human vaccine available

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