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Bacillus anthracisRANK: SpeciesTAXONOMY: Firmicutes -> Bacilli -> Bacillales -> Bacillaceae -> Bacillus -> Bacillus cereus group -> Bacillus anthracis OVERVIEW: Under starvation conditions this group of bacteria initiate a pathway that leads to endospore formation, a process that is thoroughly studied and is a model system for prokaryotic development and differentiation. Spores are highly resistant to heat, cold, dessication, radiation, and disinfectants, and enable the organism to persist in otherwise inhospitable environments. Under more inviting conditions the spores germinate to produce vegetative cells. Bacillus anthracis. This organism was the first to be shown to cause disease by Dr. Robert Koch, leading to the formulation of Koch's postulates, which were verified by Dr. Louis Pasteur (the organism, isolated from sick animals, was grown in the laboratory and then used to infect healthy animals and make them sick). This organism was also the first for which an attenuated strain was developed as a vaccine. Herbivorous animals become infected with the organism when they ingest spores from the soil whereas humans become infected when they come into contact with a contaminated animal. Anthrax is not transmitted due to person-to-person contact. The three forms of the disease reflect the sites of infection which include cutaneous (skin), pulmonary (lung), and intestinal. Pulmonary and intestinal infections are often fatal if left untreated. Spores are taken up by macrophages and become internalized into phagolysozomes (membranous compartment) whereupon germination initiates. Bacteria are released into the bloodstream once the infected macrophage lyses whereupon they rapidly multiply, spreading throughout the circulatory and lymphatic systems, a process that results in septic shock, respiratory distress and organ failure. The spores of this pathogen have been used as a terror weapon. Virulence factors that distinguish Bacillus anthracis from Bacillus cereus are encoded on two plasmids, pXO1 (anthrax toxin) and pXO2 (capsule genes). The capsule protects against phagocytosis once the vegetative bacterium enters the bloodstream. The anthrax toxin consists of 3 components, a protective antigen (PA), lethal factor (LF), and edema factor (EF). PA/LF and PA/EF complexes are internalized by host cells where the LF (metalloprotease) and EF (calmodulin-dependent adenylate cyclase) components act. At high levels LF induces cell death and release of the bacterium while EF increases host susceptibility to infection and promotes fluid accumulation in the cells. |