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Bacillus anthracis

Morphology

Bacillus anthracis is a rod-shaped Gram-positive bacterium of size about 1 by 6 micrometres, and is the cause of the disease known as anthrax.

B. anthracis was the first bacterium ever to be shown to cause disease, by Robert Koch in 1877. The specific name anthracis originates from the Greek word meaning coal, referring to the black skin lesions on the victims. The bacteria normally rest in spore form in the soil, and can survive for decades in this state. Once taken in by a herbivore, the bacteria start multiplying inside the animal and eventually kill it, then continue to reproduce in the carcass. Once they run out of nutrients there, they revert back to the dormant spore state.

Cultural characteristics

They are aerobes, and can be grown on nutrient agar at 37 degrees.

Pathogenesis

There is one antigenic type that possesses 3 major antigens:

  • Cell wall polysaccharide
  • Capsular polypeptide
  • Complex of protein toxins

The toxin is composed of 3 components: protective antigen (PA), lethal factor (LF), edema factor (EF). Together they are cytolytic for macrophages and increase vascular permeability causing edema and shock.

Diseases caused by Bacillus anthracis


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