Public Health & Environmental Laboratories | Bacillus anthracis

Bacillus anthracis

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Safety:

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.

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