anthrax toxin

The toxin follows an AB model with one shared B component. Protective antigen binds host cell receptors and forms a pore through which the two enzymatic A subunits enter; it is so named because antibody against it is protective and it is the immunogen in the anthrax vaccine. Edema factor is a calmodulin-dependent adenylate cyclase that raises intracellular cAMP, causing the characteristic massive non-pitting gelatinous oedema, and it also impairs neutrophil function. Lethal factor is a zinc metalloprotease that cleaves MAP kinase kinases, disabling signalling and killing macrophages with release of inflammatory mediators and shock. B. anthracis is a gram-positive spore-forming rod, unique in having a protein capsule of poly-D-glutamate rather than polysaccharide, which is antiphagocytic and poorly immunogenic. Cutaneous anthrax, the commonest form, produces a painless black eschar with surrounding oedema; inhalational anthrax produces haemorrhagic mediastinitis with a widened mediastinum; gastrointestinal anthrax follows ingestion of contaminated meat. Treatment is ciprofloxacin or doxycycline, with antitoxin for systemic disease.