Bacillus anthracis is a Gram-positive, facultatively anaerobic, rod-shaped bacterium of the genus Bacillus. A spore-forming bacterium, B. anthracis is a natural soil-dwelling organism, as well as the causative agent of anthrax.

Each cell is about 1 by 6 μms in size.

Historical background

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B. anthracis was the first bacterium conclusively demonstrated to cause disease, by Robert Koch in 1877. The species name anthracis is from the Greek anthrakis (ἄνθραξ), meaning coal and referring to the most common form of the disease, cutaneous anthrax, in which large black skin lesions are formed.

Pathogenicity

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Under conditions of environmental stress, B. anthracis bacteria naturally produce endospores which rest in the soil and can survive for decades in this state. When ingested by a cattle, sheep, or other herbivores, the bacteria begin to reproduce inside the animal and eventually kill it, then continue to reproduce in its carcass. Once the nutrients are exhausted, new endospores are produced and the cycle repeats.

B. anthracis has as least 89 known strains, ranging from highly virulent strains with biological warfare and bioterrorism applications (Ames and Vollum) to benign strains used for inoculations (Sterne). The strains differ in presence and activity of various genes, determining their virulence and production of antigens and toxins.

Treatment

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Infections with B. anthracis can be treated with β-lactam antibiotics such as penicillin, and others which are active against Gram-positive bacteria.

References

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Bacillaceae

Bacillus anthracis | Bacillus anthracis | Charbon (bacille) | Bacillus anthracis | בצילוס אנתרציס | 炭疽菌 | Bacillus anthracis | 炭疽桿菌