Bacillus Anthracis

The bacteria Bacillus anthracis, the etiologic agent of Anthrax, is a large, gram positive, sporulating rod.Approximately 2-6 µm in length, this bacterium can be cultivated in ordinary nutrient medium under aerobic or anaerobic conditions.More commonly recognized by the name Anthrax, this bacterial pathogen is primarily a disease of domesticated and wild animals, particularly herbivorous animals, such as cattle, sheep, horses, mules, and goats.Humans become infected incidentally when brought into contact with diseased animals, which includes their flesh, bones, hides, hair and excrement.Recent bio-terrorism events in history dictate the necessity for a complete understanding of Anthrax and its infectious abilities.Unfortunately, the road to such discovery is long and arduous.
The virulence of Anthrax depends on two factors:the bacterial capsule and the toxin complex.All virulent strains of B. anthracis form a single antigenic type of capsule consisting of a poly-D-glutamate polypeptide.The unusual poly-D-glutamyl acid capsule is itself nontoxic, but functions to protect the organism against the bactericidal components of serum and phagocytes and against phagocytic engulfment.Capsule production depends on a 60-megadalton plasmid, pX02; its transfer to nonencapsulated B. anthracis via transduction produces the encapsulated phenotype.The capsule plays its most important role during the establishment of the infection and a less significant role in the terminal phases of the disease, which are mediated by the Anthrax toxin.
The Anthrax toxins are composed of three proteins:the protective antigen, the lethal factor and the edema factor.The protective antigen is an 83-kd protein that binds to the target cell receptors.Once bound, a 20-kd fragment is proteolysed, thus exposing an additional binding site.This binding site can combine with either edema factor (89-kd protein) to form edema toxin, or lethal factor…

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