Difference between revisions of "The pathogenesis of Bacillus anthracis"

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==Overview==
 
==Overview==
[[Image:Bacillus2.jpg|thumb|250px|right|<b>Figure1. Vegetative form of Bacillus Anthracis with stain</b>. http://www.sciencedirect.com/science/article/pii/S0378113509003769].]]
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<b>By [Tony Amolo]</b>
<br><b>By [Tony Amolo]</b>
 
  
 
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[[Image:Bacillus2.jpg|300px|thumb|left|<b>Figure1. Vegetative form of <i>Bacillus Anthracis</i> with stain</b>. http://www.sciencedirect.com/science/article/pii/S0378113509003769].]]<br>Anthrax is an infectious disease caused by the bacteria <i>Bacillus anthracis</i>. <i>Bacillus anthracis</i> is a microorganism from the family <i>Bacillaceae</i>. Figure 1 shows its vegetative form. Unlike other bacillus microorganisms which are harmless saprophytes, <i>Bacillus anthracis</i> is an obligate bacillus pathogen that infects many vertebrates. Based on its physical characteristics, <i>Bacillus anthracis</i> can be categorized with other microorganisms such as <i>Bacillus cereus</i>, <i>Bacillus thuringiensis</i> and <i>Bacillus mycoides</i>. This categorization exists because it is difficult to characterize these organisms based on their 16s rRNA sequences [[#References|[10]]]. Organisms from the bacillus genus are mostly extremophiles. They have the ability to grow in severe conditions which other microorganisms cannot withstand [[#References|[4]]].  
 
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Anthrax is as old as man, it was given its name by a Greek physician named Hippocrates because of the black sore it causes on the skin of human and animals(1). It generally affects warm blooded animals including humans. Aloys Pollender, a German physician who was acknowledged for identifying the disease described <i>Bacillus anthracis</i> as “chyllus corpuscles” after analyzing the abdomen of infected cows that had died of anthrax [[#References|[2]]]. Anthrax was broadly studied in the 1870s by Robert Koch and Louis Pasteur. Koch applied the suspended drop culture method to understand the life cycle of the bacteria and found that the spores formed could survive for long period in harsh environment [[#References|[3]]].Koch’s studies on <i>Bacillus anthracis</i> helped him come up with the germ theory of disease.<br>
<br>Anthrax is an infectious disease caused by the bacteria Bacillus anthracis. Bacillus anthracis is a microorganism from the family Bacillaceae. Unlike other bacillus microorganisms which are harmless saprophytes, bacillus anthracis is an obligate bacillus pathogen in mostly vertebrates. Based on its physical characteristics, bacillus anthracis can be categorized with other microorganisms such as Bacillus cereus, Bacillus thuringiensis and Bacillus mycoides. This classification holds because it is difficult to characterize these organisms based on their 16s rRNA sequences (10). Organisms from the bacillus genus are thermophilic, psychrophilic, acidophilic, alkaliphilic, halotolerant, and halophilic. They have the ability to grow in severe conditions which other microorganisms cannot withstand (4).  
 
Anthrax is as old as man, it was given its name by a Greek physician named Hippocrates because of the black sore it causes on the skin of human and animals(1). It generally affects warm blooded animals including humans. Aloys Pollender, a German physician who was acknowledged for identifying the disease described bacillus anthracis as “chyllus corpuscles” after analyzing the abdomen of infected cows that had died of anthrax (2). Anthrax was broadly studied in the 1870s by Robert Koch and Louis Pasteur. Koch used suspended drop culture methods to trace the complete life cycle of the bacteria and found that the spores formed could remain viable for long period of adverse environments (3).Koch’s studies on Bacillus Anthracis helped him come up with the germ theory of disease.
 
 
 
.<br>
 
  
 
==Cell Structure and Metabolism==
 
==Cell Structure and Metabolism==
[[Image:Fulton2.jpg|thumb|280px|Right|<b> Figure 2. The spore form of Bacillus Anthracis with Shoeffer Fulton Stain </b>. http://www.sciencedirect.com/science/article/pii/S0378113509003769.]]
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[[Image:Fulton2.jpg|thumb|200px|Right|<b> Figure 2. The spore form of <i>Bacillus Anthracis</i> with Shoeffer Fulton Stain </b>. http://www.sciencedirect.com/science/article/pii/S0378113509003769.]]
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<br> <i>Bacillus anthracis</i> is a gram positive, endospore forming bacteria. Figure 2 shows <i>Bacillus anthracis</i> in its spore form. It is capsulated, immobile and rod shaped. <i>Bacillus anthracis</i> has the ability to make ATP in the presence or absence of oxygen and cannot be seen unless with a microscope. It is  5-6 micrometer long, 1-1.5micrometer wide and  looks like bamboo canes in tissue [[#References|[13]]]. Despite its small size, the diverse abilities of many species of its genus allows them to survive in different environments [[#References|[4]]]. They have the ability to form chains, colonies and biofilms.<br>
  
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==Habitat and Ecology==
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<br><i>Bacillus anthracis</i> is a soil borne bacteria. It lives best in black steppe soils with lots of  calcium and at pH levels between (7-9). Endemic anthrax areas have been associated with warmer temperatures, higher soil moisture content and topography [[#References|[15]]].<br>
  
<br> Bacillus anthracis is a gram positive, endospore forming bacteria. It is capsulated, immobile and rod shaped. Bacillus anthracis has the ability to make ATP in the presence or absence of oxygen. Bacillus anthracis cannot be seen unless with a microscope. It is 5-6 micrometer in length by 1-1.5micrometer wide and looks like bamboo canes in tissue (13). Despite its small size, the diverse abilities of many species of its genus allows them to survive in different environments (4). They have the ability to form chains, colonies and biofilms.<br>
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==Spore Formation, Anatomy and Germination==
 
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[[Image:neww2.jpg|280px|thumb|left|<b> Figure 3. Transmission Electron Micrograph of <i>Bacillus Anthracis</i> endospore </b>. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC303457/.]]
==Habitat and Ecology==
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<i>Bacillus anthracis</i> forms one endospore per cell. Its spores form when its non reproductive cells are deficient of certain nutrients . The spores are oval in shape and sporulation occurs within 48 hours.
<br>Bacillus anthracis is a soil borne bacteria. It lives best in black steppe soils with lots of  calcium and at pH levels between (7-9). Endemic anthrax areas have been associated with warmer temperatures, higher soil moisture content and topography (15).<br>
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<i>Bacillus anthracis</i> requires oxygen to sporulate. Spores can tolerate heat, cold, dehydration, radiation and even antibacterials [[#References|[8]]]. The formation of spore commences when cells septate asymmetrically to create a forespore and a mother cell. After septation, the mother cell swallows the forespore and covers it with different layers. The spore is made up of several layers. These layers are the coat, the exosporium and the cortex. Figure 3 reveals these layers through a transmission electron micrograph. The innermost layer is the core. It contains proteins which holds the chromosome. Half of the spore is composed of the spore coat. The flexibility of the spore coat enables the spore to hold the core especially during germination. It protects the spore from harmful chemicals and aids germination. The cortex containing peptidoglycan protects the spore from radiation, heat and makes the core dry. The exosporium is the outermost layer of the spore. It is a protein rich, balloon-like, loose fitting structure covering a spore [[#References|[8]]]. The exosporium has been studied to understand the use of anthrax as a weapon because of its quality and unique structure.  
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The disintegration of the mother cell to produce the spore indicates the completion of spore formation.
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The mature spores have a structured arrangement that enables them withstand and endure physical damage and severe environmental conditions. Outside a host, the mature spores of <i>Bacillus anthracis</i> are inactive. Upon entry into a host, they have the ability to germinate and become non reproductive cells that can easily replicate all around the host's internal organs and cause damage.The availability of host’s environment with sufficient nutrients causes germination to occur[[#References|[17]]]. Non reproductive cells transform back to spores whenever the host dies. Germination and growth of spores in the host cells are essential for the release of its virulence factors.
  
 
==Pathogenesis and Virulence factors==
 
==Pathogenesis and Virulence factors==
[[Image:path2.gif|thumb|500px|Right|<b> Figure 3. Mechanism of action of the Anthrax Toxin.</b> http://www.biocarta.com/pathfiles/h_anthraxPathway.asp]]
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[[Image:antt2.jpeg|thumb|445px|Right|<b> Figure 4. Mechanism of action of the Anthrax Toxin.</b> http://jama.jamanetwork.com/article.aspx?articleid=194886]]
<br>Bacillus anthracis depends on two toxic factors from two plasmids:<br>
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<br><i>Bacillus anthracis</i> contains two toxic plasmids: the pX01, which produces the edema factor, the protective antigen and the lethal factor, and the pX02, which encodes the production of the capsule. <i>Bacillus anthracis</i> carries out its pathogenic process by using its capsule and producing toxics consisting of three proteins(EF, LF and PA)[[#References|[13]]]. The combination of lethal toxin, which constitutes the protective antigen and the lethal factor and edema toxin which constitutes the protective antigen and the edema factor can induce severe cases of the disease [[#References|[7]]]. Out the three factors, the protective antigen plays a crucial  role in the toxic action of <i>Bacillus anthracis</i>. Figure 4 shows the three different ways humans and animals can be exposed to anthrax. It reveals how the toxins of <i>Bacillus anthracis</i> enters the cell. It also indicates other pathogenic mechanisms of the bacteria. Protective antigen is important in anthrax poisoning because it allows the connection and entry of the lethal factor and Edema factor into the cytosol. It also helps bind the cell receptor, the lethal factor and the edema factor to the host cell. Protective antigen is a primary antigen that exists in anthrax vaccines [[#References|[11]]]. The edema factor is a cyclase that causes an imbalance of water homeostasis. The edema toxin may increase host susceptibility to infection by disrupting the cytokine response of monocytes and by suppressing neutrophil functions [[#References|[11]]]. The lethal factor is a metalloprotease that cleaves major pathways to surface receptors for the transcription of certain genes within the nucleus [[#References|[12]]] while the capsule enhances the virulence by inhibiting the phagocytosis of <i>Bacillus anthracis</i>. <br>
the <b>pX01</b>, 182kb,this plasmid encodes the genes for the lethal factor (LF), the edema factor (EF) and the protective antigen (PA), <br>
 
<b>pX02</b>, 96kb, this plasmid encodes the genes for the biosynthesis of the capsule. The pathogenic effect of bacillus anthracis is through its capsule and through the production of toxin(EF, LF and PA)(13)(Figure 3).The lethal toxin(LT, the combination of PA and LF) and edema toxin (ET, the combination of PA and EF) are enough to produce and cause the anthrax infection.(7) Of the three factors, the PA plays an important role in the toxic action of Bacillus anthracis. Protective antigen (735 amino acids) plays an important role in anthrax intoxication by allowing the attachment and entry of the lethal factor and Edema factor into the cytosol. It contains regions involved in binding to the cell receptor, binding LF and EF, membrane insertion, and translocation of the anthrax toxin. Protective antigen is a major immunogen present in anthrax vaccines(11). The edema factor(89kDa) is a calcium and calmodulin-dependent adenylate cyclase that causes an increase in cytoplasmic cAMP. This leads to an imbalance of water homeostasis in the cell. The edema toxin disrupts the cytokine response of monocytes which may increase the chance of the host being infected by the disease(11). The lethal factor is a Zn2+ dependent metalloprotease that attaches major pathways to surface receptors for the transcription of certain genes within the nucleus(12) while the capsule inhibits the phagocytosis of bacillus anthracis.
 
They study of Anthrax toxins has provided a mechanism of trans-membrane translocation of proteins and the discovery of plasmids pXO1 and pXO2 which allowed the study of toxic factors at a genetic level(5). <br>
 
 
 
==Transmission and Pathology==
 
  
 
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==Transmission and Prevention==
<br>Bacillus anthracis is not an invasive organism. The ways of transmission of the anthrax disease are through wounds, mucous membranes of the mouth, pharynx, gastrointestinal tract, the digestive tract after ingestion of spore contaminated food or water, skin abrasions, sore, lesions caused by biting flies and the inhalation of dust containing spores. After transmission through one of these route, the spores of Bacillus anthracis are carried from the site of entry to the draining lymph nodes where they begin to multiply rapidly and the produce spores which germinate to produce the toxic factors (13). The pathogenicity of Bacillus anthracis depends on the sensitivity of the host, the infectious dose(amount of toxin produced), the quality of the capsular coat and the route of penetration (13).<br>
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[[Image:catt2.jpg|300px|thumb|left|<b> Figure 5. A goat infected by anthrax disease being disposed by burning in Indonesia.</b> http://go.galegroup.com/ps/i.do?id=GALE%7CCX3045200023&v=2.1&u=kenyon&it=r&p=GVRL&sw=w&asid=8b34ef35c63fa98997477f3845a915f4]]
 
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The common ways of transmission of the anthrax disease are through wounds, the pharynx, gastrointestinal tract, the digestive system after ingesting spore contaminated food or water, skin lesions or abrasions caused by biting flies and the breathing in of air containing anthrax spores. After transmission through one of these route, the spores travel to the lymph nodes where they begin to multiply rapidly and the produce spores which germinate to produce the virulence factors [[#References|[13]]]. The disease can infect humans in 3 different ways namely the cutaneous anthrax, the pulmonary or inhalation anthrax and the gastrointestinal anthrax. Each type of anthrax disease is unique in its method of infection and symptoms. The lethal dose of inhalation anthrax in humans is approximately 8,000 to 10,000 spores, however, scientists have revealed that little dosage inhaled did not cause or show symptoms of the disease [[#References|[23]]]. Transmission of anthrax between animals occurs when infected animals are placed in the same environment as healthy animals. Proper prevention measures in mostly agricultural settings include proper disposal of infected animals, polluted equipment and vaccination. Figure 5 shows how the animal husbandry department of Indonesia tries to prevent the escalation of the disease by burning an infected goat in a pit in October 2004 [[#References|[23]]].<br>
==Symptoms==
 
[[Image:zigg2.jpg|thumb|250px|Right|<b>Figure 4. Cutaneous Anthrax at 10 days</b>. http://www.sciencedirect.com/science/article/pii/S0738081X0200250X]]
 
[[Image:juju2.jpg|thumb|240px|Right|<b>Figure 5. Chest x-ray showing early pulmonary edema marked by widening of the thoracic cavity</b>. http://www.sciencedirect.com/science/article/pii/S0738081X0200250X]]
 
<br><b>Anthrax in Humans</b>
 
<br><b>Cutaneous anthrax</b>
 
Cutaneous anthrax is also called malignant pustule. It is usually localized around the face, arms, hands, and neck. It occurs when a contaminated cut creates a path of entrance for the organism. A primary lesion is formed with a few days and a ring of vesicles develops around the central papule. This dries up to form a black lesion (Figure 4). The lesion develops for 12-14 days leaving a shallow ulcer that heals in 2-3 weeks. Patients show symptoms of headaches, fever of up to 102 degree Fahrenheit, discomfort and even death.
 
<br><b>Pulmonary(inhalation) anthrax</b>
 
Also known as woolsorter’s disease, pulmonary anthrax is caused by inhaling the anthrax spores. Spores are phagocytosed by alveolar macrophages and carried to the lymph nodes where they germinate and multiply (Figure 5). Fatal bacteraemia and toxaemia then occurs. (10) During the initial stage, the patient experiences mild fever, malaise, fatigue and cough. The second stage include symptoms like acute dyspnea, cyanosis and profuse perspiration.
 
<br><b>Gastrointestinal anthrax</b>
 
Also known as splenic fever, gastrointestinal anthrax is extremely rare and occurs mainly in Africa, the Middle East and central and Southern Asia. It is caused by eating an insufficiently cooked meat contaminated with spores. Symptoms include diarrhea, ulcer, liver disease and fever. Another rare form of anthrax in man is anthrax meningitis. (6)<br>
 
  
 
==Vaccines and Treatment==
 
==Vaccines and Treatment==
<br> The first bacterial disease that a preventive treatment (prophylaxis) was developed for was the Anthrax disease(11). Prophylaxis helped in controlling anthrax in animals and preventing the spread of the infection.
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<br>Anthrax was the first bacterial disease for which effective preventive treatment (prophylaxis) was developed [[#References|[11]]]. Prophylaxis played a major role in controlling anthrax in animals and protection to individuals from infection.
Several vaccines have been produced for the anthrax disease since Louis Pasteur first produced the attenuated anthrax vaccine in 1881 (2). The vaccines used to fight anthrax are composed of spores from weakened strains of Bacillus anthracis. They are classified into two categories namely;<br>
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Several vaccines has been produced for the anthrax disease. Louis Pasteur is known as the first microbiologist to produce the first anthrax vaccine in 1881 [[#References|[2]]]. The vaccines were made of spores from weakened genetic variant of <i>Bacillus anthracis</i>. Vaccines produced to combat the disease include non-living vaccines, In vitro protective antigen, Boor and Tresselt vaccine, production in non-proteinaceous media, UK vaccine, American vaccines(Aerobic antigen and Anaerobic antigen) and Russian antigen [[#References|[6]]]. Special therapy can also be  provided to treat anthrax if it is applied immediately to the infected animal or human. Aside from vaccines, antitoxin and antibiotics have been used to treat the disease. Penicillin, ciprofloxacin and doxycycline have been used to treat the susceptible genetic variants of anthrax [[#References|[14]]]. Different methods have been adopted to create an enhanced vaccine for humans. The objective is to develop a vaccine that is non reactogenic and involves little administration to perform efficiently [[#References|[11]]]. However, the difficult aspect of checking the potency of anthrax vaccine is making an assessment in humans. Tests using this pathogenic bacteria is not safe for humans and animals and requires special precautions.<br>
Live attenuated vaccines, capsulated and atoxigenic cap<br>
 
Live attenuated spore vaccines, not capsulated and toxigenic cap. For example, Sterne and sexually transmitted infection (STI) vaccines. (13)<br>
 
Other vaccines include non-living vaccines, In vitro protective antigen, Boor and Tresselt vaccine, production in non-proteinaceous media, UK vaccine, American vaccines(Aerobic antigen and Anaerobic antigen) and Russian antigen (6). Special therapy can also be  provided to treat anthrax if it is applied immediately to the infected animal or human. Aside from vaccines, antitoxin and antibiotics have been used to treat the disease. Penicillin, doxycycline and ciprofloxacin have been used for treatment of susceptible strains of anthrax (14). Several methods have been adopted to create an improved human vaccine. Recombinant DNA methodology is being used to create live vaccine strains of Bacillus anthracis. The goal is to create a new vaccine that is safe, non reactogenic, efficacious against all disease and requires a little number of inoculations to achieve maximum lasting immunity (11). The challenging and difficult aspect of evaluating the efficacy of anthrax vaccine is making an assessment in humans because it is not safe to be tested on humans. Animals can be used as a model but the process can be dangerous.<br>
 
  
 
==Application to Bioterrorism==
 
==Application to Bioterrorism==
<br>Out of many pathogenic bacteria, Bacillus anthracis is one that can be used for bioterrorism. It makes a good model weapon for bioterrorism because it spores can be produced in the lab,last for a long time in the environment and can be found easily in nature. Also because of its small size, it can be placed in food and letters like in 2001 when powdered anthrax was mailed to the U.S postal office. Twenty-two cases of anthrax infections were confirmed. Half of these cases involved cutaneous anthrax and no death resulted. The remaining eleven were identified as inhalational anthrax and produced five deaths. A global awareness should be created to reject the development of such weapons and provide means of developing a vaccine for this deadly disease. <br>
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<br>Out of many pathogenic bacteria, <i>Bacillus anthracis</i> is one that can be used for bioterrorism. Of its three types (cutaneous, inhalation and gastrointestinal), inhalation anthrax has been related to bioterrorism because of its mode of transmission. <i>Bacillus anthracis</i> makes a good model weapon for bioterrorism because its spores can be produced in the laboratory,it survives longer in the environment and can be found easily. Also, because of its small size, it can be placed in food and letters like in 2001 when powdered anthrax spores were mailed to the U.S postal office. Twenty-two cases of anthrax infections were confirmed. Half of these cases involved cutaneous anthrax and no death resulted. The remaining eleven were identified as inhalational anthrax and produced five deaths. Several countries like the past Soviet Union and Iraq have been known to produce <i>Bacillus anthracis</i> as a bioweapon [[#References|[22]]]. Aside from inflicting this pathogenic bacteria through letters, aerosol delivery can also be implemented. It entails aiding the bacteria to travel a longer distance while keeping it odorless and unseen before release by the use of technology [[#References|[22]]]. A global awareness should be created to reject the development of anthrax as weapons and provide a better means to fight this deadly disease. Health Agencies and organizations should emulate the work of agencies such as the Centers for Disease Control and Prevention (CDC), the Federal Bereau of Investigation (FBI) and the World Health Organization (WHO) to find a better understanding of this deadly disease and ensure the safety of human and animal lives, and property. <br>
  
 
==References==
 
==References==
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17] [http://www.sciencedirect.com/science/article/pii/S0098299709000557 Adam Driks. "The Bacillus anthracis spore."2009.]<br><br>
 
17] [http://www.sciencedirect.com/science/article/pii/S0098299709000557 Adam Driks. "The Bacillus anthracis spore."2009.]<br><br>
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18] [http://www.fbi.gov/about-us/history/famous-cases/anthrax-amerithrax]<br><br>
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19] [http://www.sciencedirect.com/science/article/pii/S0098299709000521 Theresa M. Koehler. "Bacillus anthracis physiology and genetics."2009.]<br><br>
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20] [http://www.ncbi.nlm.nih.gov/pubmed/11964119 Nicholson WL. "Roles of Bacillus endospores in the environment."2002.]<br><br>
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21] [20] [http://www.ncbi.nlm.nih.gov/pubmed/11964119 Hongbin Liu1, Nicholas H. Bergman, Brendan Thomason, Shamira Shallom, Alyson Hazen, Joseph Crossno, David A. Rasko, Jacques Ravel, Timothy D. Read, Scott N. Peterson, John Yates, and Philip C. Hanna. "Formation and Composition of the Bacillus anthracis Endospore."2003.]<br><br>
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22] [http://jama.jamanetwork.com/article.aspx?articleid=194886 Thomas V. Inglesby, Tara O'Toole, Donald A. Henderson, John G. Bartlett, Michael S. Ascher,Edward Eitzen,MPH; Arthur M. Friedlander, Julie Gerberding, Jerome Hauer,James Hughes, Joseph McDade, Michael T. Osterholm, Gerald Parker,Trish M. Perl, Philip K. Russell,Kevin Tonat, DrPH. "Anthrax as a Biological Weapon, 2002 Updated Recommendations for Management"2002.]<br><br>
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23] [http://go.galegroup.com/ps/i.do?id=GALE%7CCX3045200023&v=2.1&u=kenyon&it=r&p=GVRL&sw=w&asid=8b34ef35c63fa98997477f3845a915f4 Ed. Brenda Wilmoth Lerner and K. Lee Lerner. "Anthrax."2008.]<br><br>
  
 
Edited by student of [mailto:slonczewski@kenyon.edu Joan Slonczewski] for [http://biology.kenyon.edu/courses/biol238/biol238syl09.html BIOL 238 Microbiology], 2009, [http://www.kenyon.edu/index.xml Kenyon College].
 
Edited by student of [mailto:slonczewski@kenyon.edu Joan Slonczewski] for [http://biology.kenyon.edu/courses/biol238/biol238syl09.html BIOL 238 Microbiology], 2009, [http://www.kenyon.edu/index.xml Kenyon College].
  
 
<!--Do not edit or remove this line-->[[Category:Pages edited by students of Joan Slonczewski at Kenyon College]]
 
<!--Do not edit or remove this line-->[[Category:Pages edited by students of Joan Slonczewski at Kenyon College]]

Latest revision as of 19:02, 8 May 2015

Overview

By [Tony Amolo]

Figure1. Vegetative form of Bacillus Anthracis with stain. http://www.sciencedirect.com/science/article/pii/S0378113509003769].


Anthrax is an infectious disease caused by the bacteria Bacillus anthracis. Bacillus anthracis is a microorganism from the family Bacillaceae. Figure 1 shows its vegetative form. Unlike other bacillus microorganisms which are harmless saprophytes, Bacillus anthracis is an obligate bacillus pathogen that infects many vertebrates. Based on its physical characteristics, Bacillus anthracis can be categorized with other microorganisms such as Bacillus cereus, Bacillus thuringiensis and Bacillus mycoides. This categorization exists because it is difficult to characterize these organisms based on their 16s rRNA sequences [10]. Organisms from the bacillus genus are mostly extremophiles. They have the ability to grow in severe conditions which other microorganisms cannot withstand [4].

Anthrax is as old as man, it was given its name by a Greek physician named Hippocrates because of the black sore it causes on the skin of human and animals(1). It generally affects warm blooded animals including humans. Aloys Pollender, a German physician who was acknowledged for identifying the disease described Bacillus anthracis as “chyllus corpuscles” after analyzing the abdomen of infected cows that had died of anthrax [2]. Anthrax was broadly studied in the 1870s by Robert Koch and Louis Pasteur. Koch applied the suspended drop culture method to understand the life cycle of the bacteria and found that the spores formed could survive for long period in harsh environment [3].Koch’s studies on Bacillus anthracis helped him come up with the germ theory of disease.

Cell Structure and Metabolism

Figure 2. The spore form of Bacillus Anthracis with Shoeffer Fulton Stain . http://www.sciencedirect.com/science/article/pii/S0378113509003769.


Bacillus anthracis is a gram positive, endospore forming bacteria. Figure 2 shows Bacillus anthracis in its spore form. It is capsulated, immobile and rod shaped. Bacillus anthracis has the ability to make ATP in the presence or absence of oxygen and cannot be seen unless with a microscope. It is 5-6 micrometer long, 1-1.5micrometer wide and looks like bamboo canes in tissue [13]. Despite its small size, the diverse abilities of many species of its genus allows them to survive in different environments [4]. They have the ability to form chains, colonies and biofilms.

Habitat and Ecology


Bacillus anthracis is a soil borne bacteria. It lives best in black steppe soils with lots of calcium and at pH levels between (7-9). Endemic anthrax areas have been associated with warmer temperatures, higher soil moisture content and topography [15].

Spore Formation, Anatomy and Germination

Figure 3. Transmission Electron Micrograph of Bacillus Anthracis endospore . http://www.ncbi.nlm.nih.gov/pmc/articles/PMC303457/.

Bacillus anthracis forms one endospore per cell. Its spores form when its non reproductive cells are deficient of certain nutrients . The spores are oval in shape and sporulation occurs within 48 hours. Bacillus anthracis requires oxygen to sporulate. Spores can tolerate heat, cold, dehydration, radiation and even antibacterials [8]. The formation of spore commences when cells septate asymmetrically to create a forespore and a mother cell. After septation, the mother cell swallows the forespore and covers it with different layers. The spore is made up of several layers. These layers are the coat, the exosporium and the cortex. Figure 3 reveals these layers through a transmission electron micrograph. The innermost layer is the core. It contains proteins which holds the chromosome. Half of the spore is composed of the spore coat. The flexibility of the spore coat enables the spore to hold the core especially during germination. It protects the spore from harmful chemicals and aids germination. The cortex containing peptidoglycan protects the spore from radiation, heat and makes the core dry. The exosporium is the outermost layer of the spore. It is a protein rich, balloon-like, loose fitting structure covering a spore [8]. The exosporium has been studied to understand the use of anthrax as a weapon because of its quality and unique structure. The disintegration of the mother cell to produce the spore indicates the completion of spore formation. The mature spores have a structured arrangement that enables them withstand and endure physical damage and severe environmental conditions. Outside a host, the mature spores of Bacillus anthracis are inactive. Upon entry into a host, they have the ability to germinate and become non reproductive cells that can easily replicate all around the host's internal organs and cause damage.The availability of host’s environment with sufficient nutrients causes germination to occur[17]. Non reproductive cells transform back to spores whenever the host dies. Germination and growth of spores in the host cells are essential for the release of its virulence factors.

Pathogenesis and Virulence factors

Figure 4. Mechanism of action of the Anthrax Toxin. http://jama.jamanetwork.com/article.aspx?articleid=194886


Bacillus anthracis contains two toxic plasmids: the pX01, which produces the edema factor, the protective antigen and the lethal factor, and the pX02, which encodes the production of the capsule. Bacillus anthracis carries out its pathogenic process by using its capsule and producing toxics consisting of three proteins(EF, LF and PA)[13]. The combination of lethal toxin, which constitutes the protective antigen and the lethal factor and edema toxin which constitutes the protective antigen and the edema factor can induce severe cases of the disease [7]. Out the three factors, the protective antigen plays a crucial role in the toxic action of Bacillus anthracis. Figure 4 shows the three different ways humans and animals can be exposed to anthrax. It reveals how the toxins of Bacillus anthracis enters the cell. It also indicates other pathogenic mechanisms of the bacteria. Protective antigen is important in anthrax poisoning because it allows the connection and entry of the lethal factor and Edema factor into the cytosol. It also helps bind the cell receptor, the lethal factor and the edema factor to the host cell. Protective antigen is a primary antigen that exists in anthrax vaccines [11]. The edema factor is a cyclase that causes an imbalance of water homeostasis. The edema toxin may increase host susceptibility to infection by disrupting the cytokine response of monocytes and by suppressing neutrophil functions [11]. The lethal factor is a metalloprotease that cleaves major pathways to surface receptors for the transcription of certain genes within the nucleus [12] while the capsule enhances the virulence by inhibiting the phagocytosis of Bacillus anthracis.

Transmission and Prevention

Figure 5. A goat infected by anthrax disease being disposed by burning in Indonesia. http://go.galegroup.com/ps/i.do?id=GALE%7CCX3045200023&v=2.1&u=kenyon&it=r&p=GVRL&sw=w&asid=8b34ef35c63fa98997477f3845a915f4

The common ways of transmission of the anthrax disease are through wounds, the pharynx, gastrointestinal tract, the digestive system after ingesting spore contaminated food or water, skin lesions or abrasions caused by biting flies and the breathing in of air containing anthrax spores. After transmission through one of these route, the spores travel to the lymph nodes where they begin to multiply rapidly and the produce spores which germinate to produce the virulence factors [13]. The disease can infect humans in 3 different ways namely the cutaneous anthrax, the pulmonary or inhalation anthrax and the gastrointestinal anthrax. Each type of anthrax disease is unique in its method of infection and symptoms. The lethal dose of inhalation anthrax in humans is approximately 8,000 to 10,000 spores, however, scientists have revealed that little dosage inhaled did not cause or show symptoms of the disease [23]. Transmission of anthrax between animals occurs when infected animals are placed in the same environment as healthy animals. Proper prevention measures in mostly agricultural settings include proper disposal of infected animals, polluted equipment and vaccination. Figure 5 shows how the animal husbandry department of Indonesia tries to prevent the escalation of the disease by burning an infected goat in a pit in October 2004 [23].

Vaccines and Treatment


Anthrax was the first bacterial disease for which effective preventive treatment (prophylaxis) was developed [11]. Prophylaxis played a major role in controlling anthrax in animals and protection to individuals from infection. Several vaccines has been produced for the anthrax disease. Louis Pasteur is known as the first microbiologist to produce the first anthrax vaccine in 1881 [2]. The vaccines were made of spores from weakened genetic variant of Bacillus anthracis. Vaccines produced to combat the disease include non-living vaccines, In vitro protective antigen, Boor and Tresselt vaccine, production in non-proteinaceous media, UK vaccine, American vaccines(Aerobic antigen and Anaerobic antigen) and Russian antigen [6]. Special therapy can also be provided to treat anthrax if it is applied immediately to the infected animal or human. Aside from vaccines, antitoxin and antibiotics have been used to treat the disease. Penicillin, ciprofloxacin and doxycycline have been used to treat the susceptible genetic variants of anthrax [14]. Different methods have been adopted to create an enhanced vaccine for humans. The objective is to develop a vaccine that is non reactogenic and involves little administration to perform efficiently [11]. However, the difficult aspect of checking the potency of anthrax vaccine is making an assessment in humans. Tests using this pathogenic bacteria is not safe for humans and animals and requires special precautions.

Application to Bioterrorism


Out of many pathogenic bacteria, Bacillus anthracis is one that can be used for bioterrorism. Of its three types (cutaneous, inhalation and gastrointestinal), inhalation anthrax has been related to bioterrorism because of its mode of transmission. Bacillus anthracis makes a good model weapon for bioterrorism because its spores can be produced in the laboratory,it survives longer in the environment and can be found easily. Also, because of its small size, it can be placed in food and letters like in 2001 when powdered anthrax spores were mailed to the U.S postal office. Twenty-two cases of anthrax infections were confirmed. Half of these cases involved cutaneous anthrax and no death resulted. The remaining eleven were identified as inhalational anthrax and produced five deaths. Several countries like the past Soviet Union and Iraq have been known to produce Bacillus anthracis as a bioweapon [22]. Aside from inflicting this pathogenic bacteria through letters, aerosol delivery can also be implemented. It entails aiding the bacteria to travel a longer distance while keeping it odorless and unseen before release by the use of technology [22]. A global awareness should be created to reject the development of anthrax as weapons and provide a better means to fight this deadly disease. Health Agencies and organizations should emulate the work of agencies such as the Centers for Disease Control and Prevention (CDC), the Federal Bereau of Investigation (FBI) and the World Health Organization (WHO) to find a better understanding of this deadly disease and ensure the safety of human and animal lives, and property.

References

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3] George Sternbach "The history of anthrax."2003.

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5] Maxime Schwartz "Dr. Jekyll and Mr. Hyde: A short history of anthrax."2009.

6] Peter Hambleton, J.Anthony Carman, Jack Melling "Anthrax: the disease in relation to vaccines."1984.

7] Mahtab Moayeri, Stephen H Leppla "The roles of anthrax toxin in pathogenesis."2004.

8] Jeremy A. Boydston, Ling Yue, John F. Kearney, and Charles L. Turnbough, Jr. "The ExsY Protein Is Required for Complete Formation of the Exosporium of Bacillus anthracis."2006.

9] W. Beyer, P.C.B. Turnbull. "Anthrax in animals."2009.

10] Les Bailliea, , Timothy D Read. "Bacillus anthracis, a bug with attitude!."2001.

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12] Laurence Abrami, Nuria Reig, F. Gisou van der Goot. "Anthrax toxin: the long and winding road that leads to the kill."2005.

13] Antonio Fasanellaa, Domenico Galantea, Giuliano Garofoloa, Martin Hugh Jones. "Anthrax undervalued zoonosis."2010.

14] Martin Hugh-Jonesa, Jason Blackburn. "The ecology of Bacillus anthracis."2009.

15] Jocelyn C. Mullins, Giuliano Garofolo, Matthew Van Ert, Antonio Fasanella, Larisa Lukhnova, Martin E. Hugh-Jones, Jason K. Blackburn. "Ecological Niche Modeling of Bacillus anthracis on Three Continents: Evidence for Genetic-Ecological Divergence?."2013.

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17] Adam Driks. "The Bacillus anthracis spore."2009.

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19] Theresa M. Koehler. "Bacillus anthracis physiology and genetics."2009.

20] Nicholson WL. "Roles of Bacillus endospores in the environment."2002.

21] [20] Hongbin Liu1, Nicholas H. Bergman, Brendan Thomason, Shamira Shallom, Alyson Hazen, Joseph Crossno, David A. Rasko, Jacques Ravel, Timothy D. Read, Scott N. Peterson, John Yates, and Philip C. Hanna. "Formation and Composition of the Bacillus anthracis Endospore."2003.

22] Thomas V. Inglesby, Tara O'Toole, Donald A. Henderson, John G. Bartlett, Michael S. Ascher,Edward Eitzen,MPH; Arthur M. Friedlander, Julie Gerberding, Jerome Hauer,James Hughes, Joseph McDade, Michael T. Osterholm, Gerald Parker,Trish M. Perl, Philip K. Russell,Kevin Tonat, DrPH. "Anthrax as a Biological Weapon, 2002 Updated Recommendations for Management"2002.

23] Ed. Brenda Wilmoth Lerner and K. Lee Lerner. "Anthrax."2008.

Edited by student of Joan Slonczewski for BIOL 238 Microbiology, 2009, Kenyon College.