Bacillus anthracis

• Aetiology

  (1)Morphology and staining

  • spores are located in the centre of the non-motile bacilli

  (2) Culture

  • cut-glass appearance in transmitted light.
  • haemolysis is uncommon
  • gelatin stabs resembles a inverted fir tree

  (3) Growth characteristics

  • spores are resistant to dry heat and certain chemical disinfectants
  • sterilized by autoclaving
• Pathogenesis

  (3) Virulence factors

  • poly-d-glutamic acid is antiphagocytic
  • capsule gene is present on a plasmid
  • anthrax toxin is made up of three portions: protective antigen(PA), edema factor(EF) and lethal factor(LF).
• Laboratory diagnosis

  (1) Specimens

  (2) Microscopic examination of smear

  (3) Culture

  (4) Definitive identification

  (5) Serology