Bacillus anthracis
Joshua Erickson

Bacillus anthracis (from the Greek anthrakis meaning charcoal, referring to the black skin lesions which develop from cutaneous exposure1) is a gram-positive endospore forming bacteria which arranges itself into a streptobacillus formation.2 The microbe is found throughout the world and can survive with or without atmospheric oxygen. The toxin that is produced by B. anthracis is composed of three parts: the lethal factor, the edema factor, and the protective antigen.  The protective antigen allows the lethal factor and the edema factor entry into the target cell by binding to a surface cell receptor. The protective antigen then undergoes heptamerization and binds the two factors which are then endocytosed into the target cell.  Once inside the cell, the lethal factor first begins to disrupt the immune response by cleaving parts of proteins which would normally be used to send signals that would recruit other immune cells to assist in fighting off the infection. The edema factor increases cyclic AMP levels in the cell which impairs the energy and water balance, resulting in swelling. The disruption of the signaling pathway lyses the cell which releases messenger molecules and results in toxic shock.

The infection caused by B. anthracis is known as anthrax. It can occur in three different forms: from cutaneous exposure, respiratory exposure and gastrointestinal exposure. Cutaneous exposure results in a small papular lesion that turns into a vesicular ulcer and then develops into a black eschar within seven to ten days of the lesion’s appearance. If untreated, the mortality rate is about twenty percent. The most dangerous type of exposure is respiratory; if contracted in this manner, the endospores can lay dormant for a period of two months or more, during which time the alveolar macrophages transport the spores to the mediastinal lymph nodes where they germinate. The initial symptoms are similar to the flu (such as fever, vomiting, chest and abdominal pain); then the symptoms progress rapidly to maladies such as a massively enlarged mediastinum3 and edema. If untreated, nearly all cases proceed to shock and eventually death within three days of initial symptoms.

Also commonly fatal is the gastrointestinal version of anthrax which can present in two different ways. If the bacteria invade the small intestine, the patient will show ulceration of the mouth and esophagus followed by localized lymphadenopathy edema and sepsis. If the bacteria were to invade the large intestine, the patient would present with nausea and vomiting which would rapidly progress to sepsis. Fortunately, B. anthracis is vulnerable to a wide variety of antibiotics currently available such as ciproflaxin, doxycline, penicillin and erythromycin. However, B. anthracis can also be genetically modified to be resistant to these antibiotics. There is a vaccine to guard against anthrax for people who work in areas with high risk of anthrax infection such as people who work with imported animal hides, military personnel, and individuals who work with B. anthracis in a laboratory setting.

Recent research with B. anthracis has discovered that the bacteria competes with L-arginine for a position in nitric oxide synthase, which is interesting because the molecule produced from the coupling of L-arginine and the nitric oxide synthase (NO-) is an important step in the microbe killing pathway. There has also been research done into the exact ramifications of the lethal and edema factors on the body. The study showed that while the edema factor causes an increase in heart rate, the lethal toxin results in a reduction of systolic function in the left ventricle.  Other research being done is focused on the capsule of the bacteria which normally prevents phagocytosis.  It was discovered that the capsule could be degraded using a polyglutamic acid polymerase known as CapD. Once the capsule of the bacteria has been degraded by CapD, neutraphils can phagocytize the bacteria.

Sources

http://iai.asm.org/cgi/content/full/74/4/2268

http://webs.wichita.edu/mschneegurt/biol103/lecture20/anthrax_hand.jpg

http://student.ccbcmd.edu/courses/bio141/lecguide/unit2/bacpath/diseases/banthracis/banthracis.html

http://student.ccbcmd.edu/courses/bio141/lecguide/unit2/bacpath/diseases/banthracis/banthracis.html

http://pathmicro.med.sc.edu/ghaffar/inhal-anthrax.jpg

http://jcb.rupress.org/cgi/content/full/166/5/645

http://ssrl.slac.stanford.edu/research/highlights_archive/anthrax.html

http://www.bt.cdc.gov/agent/anthrax/anthrax-hcp-factsheet.asp

http://www.cdc.gov/nczved/dfbmd/disease_listing/anthrax_gi.html

http://en.wikipedia.org/wiki/Bacillus_anthracis

http://microbewiki.kenyon.edu/index.php/Bacillus_anthracis

*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.

 

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