Anthrax oedema factor. Molecular model of oedema factor (EF) from the anthrax bacterium Bacillus anthracis complexed with a calmodulin protein molecule. EF is one of three protein components that form the anthrax toxin. It is an enzyme that interferes with water homeostasis, leading to the accumulation of fluid in the tissues. Anthrax most commonly affects cattle, sheep and goats, but can also infect humans.