Anthrax bacillus

The anthrax bacillus (Bacillus anthracis) is the infectious agent responsible foranthrax.

Features of the anthrax bacillus

The anthrax bacillus is a bacterium belonging to the Bacillusgenus, which are spore-forming Gram positive bacteria. They are rod shaped, approximately a micrometre in width, and three to five micrometres long. Their genome is composed of one chromosome with 5.2 million base pairs. Plasmids pXO1 and pXO2 have also been found.

They are facultative anaerobic bacteria. The spores that they form can resist extreme conditions (UV irradiation, dryness, high temperatures, etc.).

Anthrax bacillus and anthrax

The anthrax bacilli have two virulence factors, coded for by genes located on the plasmids:

• they form a protective capsule which surrounds the bacterium and enables it to avoid phagocytosis, one of the mechanisms used by the immune system.
• They also produce two toxins (a lethal toxin and an oedema-producing toxin).