What is the Sterne strain (34F2) of Bacillus anthracis?
Bacillus anthracis is a spore-forming bacterium that causes anthrax in humans and animals. B. anthracis has 3 main virulence factors coded on 2 plasmids, pXO1 and pXO2. If one of these two plasmids is missing, the organism cannot produce all of its virulence factors. The resulting organism is attenuated, meaning its virulence and the ability to cause illness in people or animals have been reduced. The pXO1 plasmid controls the production of the anthrax edema and lethal toxins, which are made of three proteins, the edema factor, the protective antigen, and the lethal factor. The pXO2 plasmid codes for the capsule, a layer of polysaccharides outside of the cell wall that protects the bacteria against phagocytosis, or consumption by defensive cells from the immune system. Without its capsule, the bacteria can be phagocytised and destroyed. The Sterne strain, discovered in the 1930s, has naturally lost its pXO2 plasmid, and consequently its ability to produce a capsule. Compared with norma