Bacillus anthracis is an aerobic, spore-forming bacterium that causes disease in humans and animals. It is an enscapulated gram-positive, non-motile, aerobic, spore forming rod with a spore size of approximately 1um X 2um. Its spores are resistant to adverse environmental conditions and remain viable for years in soil, and dried or processed hides. When conditions for growth are good, with plentiful nutrients and water available, they are rod-shaped organisms that grow and divide. When conditions are unfavorable, each forms a very resistant dormant spore that is able to survive extreme environmental conditions. Spores are highly resistant to drying, heat, and sunlight; adequate sterilization requires direct exposure to about 121°C for at least 30 minutes. Spores remain viable in soil, skins and hides of infected animals and contaminated air and wool for decades.
Bacillus anthracis forms a single antigenic type of capsule that consists of a poly-D-glutamate polypeptide. Virulent strains of Bacillus anthracis form this capsule. The capsule itself is nontoxic, but functions to protect the organism against bactericidal components of serum and phagocytes. The capsules major role is in the terminal phases of the disease, which are mediated by the anthrax toxin.
Production of the anthrax toxin is mediated by a temperature sensitive plasmid called pX01. The toxin consists of 3 antigenic components. Each of these components is a thermolabile protein. The first one is called the edema factor, (EF), and is necessary for the edema producing activity of the toxin. Once inside the cell, it causes fluid to accumulate at the site of the infection. It can contribute to a fatal buildup of fluid in the cavity surrounding the lungs and can also inhibit some of the body’s immune functions. The second protein is called the protective antigen, (PA), which binds to select cells of an infected person or animal and forms a channel that allows the edema factor and lethal factor to enter those cells. It induces protective antitoxic antibodies. The third protein is the lethal factor, (LF), because it is essential for the lethal effects of the anthrax toxin. Once inside the cell, it disrupts a molecular switch that regulates the cell’s functions. Lethal factor can kill infected cells or prevent them from working properly. Each separate factor has no significant activity in an animal. However, when two of the three are combined, or all three combine, the toxin components produce the following results in animals:
PA + LF produces lethal activity
EF + PA produces edema
EF + LF inactive
PA + LF + EF produces edema and necrosis and is lethal
Virulence of Bacillus anthracis is attributable to three components. These are capsular material, edema factor, and lethal factor. Virulent anthrax bacilli multiply at the site of the lesion. Phagocytes will move to this area but the Bacillus anthracis organism can resist Phagocytic engulfment. If it is by chance engulfed it can resist killing and digestion. It can have a lethal effect on the leukocytes and phagocytes at the site.
Bacillus anthracis causes the serious disease Anthrax. Bacillus anthracis can infect hosts such as; cattle, sheep, goats, horses, pigs and even humans. Infection can occur in three forms: Cutaneous (skin), inhalation, and gastrointestinal. Meningitis can sometimes be due to Bacillus anthracis but is very rare and may result from a primary infection elsewhere. Humans can become infected with the Bacillus anthracis bacterium by handling animal products from infected animals or by inhaling anthrax spores from contaminated animal products. It can also be spread by eating undercooked meat from infected animals. Direct person-to-person spread of anthrax is unlikely. Infection is also possible by biting flies feeding on such animals.
Most anthrax infections occur when the bacteria enters a cut or abrasion on the skin. Skin infection begins as a raised itchy bump that looks like an insect bite but within 1-2 days develops into a vesicle and then a painless ulcer, with a black necrotic (dying) area in the center. Lymph glands in the adjacent area may swell. About 20% of untreated cases of cutaneous anthrax will result in death, although deaths are rare with appropriate antimicrobial therapy.
For inhalation anthrax, the initial symptoms may resemble a cold or sore throat. The spores travel from the lungs to immune cells, (macrophages), in the nearby lymph nodes. There they begin to reproduce and secrete their toxins, causing severe breathing problems and shock.
The intestinal disease form of anthrax may follow the consumption of contaminated meat and is characterized by an inflammation of the intestinal tract. Initial signs of nausea, loss of appetite, vomiting, and/or fever are followed by abdominal pain, vomiting of blood, and severe diarrhea. Intestinal anthrax results in death in 25% to 60% of cases.
Antibiotics should be given to unvaccinated individuals exposed to inhalation anthrax. Penicillin, tetracyclines and fluoroquinolones are effective. Antibiotic treatment is also known to lessen the severity of disease in individuals who acquire anthrax through the skin. Inhalation anthrax was formerly thought to be nearly 100% fatal despite antibiotic treatment, particularly if treatment is started after symptoms appear. A recent Army study resulted in successful treatment of monkeys with antibiotic therapy after being exposed to anthrax spores. The antibiotic therapy was begun one day after exposure.
The anthrax vaccine for humans is a cell-free filtrate vaccine, which means it uses dead bacteria as opposed to live bacteria. Anthrax vaccine is indicated for individuals who come in contact in the workplace with imported animal hides, furs, bone meal, wool, animal hair (especially goat hair), and bristles; and for individuals engaged in diagnostic or investigational activities which may bring them into contact with anthrax spores. The vaccine is reported to be 93% effective in protecting against cutaneous anthrax.
Work Cited
1. http://www.tarakharper.com/b_anthrx.htm
2. http://www.channing.harvard.edu/20.htm
3. http://www.ourfood.com/Anthrax.html
4. http://www.intelihealth.com/anthrax.htm
5. http://www.eye-on-israel.org/anthrax/anthrax.html
6. http://www.the-scientist.com/yr2002/feb/research1_020218.html
7. http://www.biology.lsa.umich.edu/courses/bio118/anthrax.htm
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