Does anyone know?

Gangrene is caused by a bacteria Clostridium perfringens.It is a Gram positive Bacillus (rod) anaerobic bacteria Under a microscope, they have blunt ends and look like boxcars. Clostridia actually are found in small amounts in the normal flora of the human intestinal tract. However they are kept in check by the other inhabitants of normal intestinal flora. However, if something upsets the balance of normal flora, Clostridium can gain a toe hold and take over.

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Gangrene is just the decay of dead tissue. The causes of dead tissue are primarilly, infection or ischemic (where there isn’t enough oxygen being supplied – because of narrowed or blocked blood vessels).