Bacillus anthracis

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  • Biosafety Level 2 for processing clinical specimens.
  • Biosafety Level 3 practices for all culture manipulations that might produce aerosols.

Key Characteristics

  • Gram-positive rods
  • Non-hemolytic
  • Non-motile
  • Catalase positive
  • Spores present when cultured aerobically without CO2

Colony Characteristics:

  • Rapidly-growing colonies 2-5 mm overnight at 35C.
  • Non-pigmented, dry “ground glass” surface, flat or slightly convex, irregular edges with comma projections (Medusa head).
  • Sticky (tenacious) consistency. When teased with loop, will stand up like beaten egg white.
  • Colonies are not hemolytic on sheep blood agar.

Microscopic Characteristics:

  • Large Gram-positive bacillus, singly and in chains. May become Gram-variable after 72 hours. May be encapsulated in clinical material and blood cultures.
  • Terminal/subterminal spores do not swell vegetative cells. Spores may be seen on Gram stain, malachite green stain or by phase contrast microscopy.
  • Spores are not present in clinical material unless exposed to low CO2 levels, such as those found in the atmosphere. Higher levels will inhibit sporulation.


Bacillus anthracis Sentinel Laboratory Flowchart

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