Introduction
Anthrax is an infectious disease that is primarily caused by the bacterium Bacillus anthracis (spore-forming bacterium). The spores of B. antracis is often associated with gastrointestinal anthrax and inhalation cutaneous. The spores are highly ineffective in most environmental conditions. Inhalation anthrax is considered as a great threat since it is caused by inhalation of anthrax spores and is associated with high fatality rate. However, the rate of person-to-person rate is rarely observed. (Sternbach G. 2003)
In the wild, anthrax is commonly observed (naturally found). The disease is also observed unvaccinated domestic animals. The disease is common among U.S workers who are exposed to infected animals. Infection can spread if workers are exposed to products or meat of infected animals. In many cases B. anthracis is used as a biological weapon. In such cases, many people are at risk of developing anthrax infection. Some of the people who are at high-risk of acquiring anthrax infection during an outbreak or biological warfare are healthcare workers, emergency response, public health and law enforcement workers.
Anthrax is also known as the disease of the livestock. However, many humans have been infected with anthrax over the past 50 years. Bacillus anthracis belongs to the genus Bacillus and is the only unique pathogen under the genus. It is the only etiological agent of anthrax. B. anthracis is a rod-shaped, endospore forming, gram-positive bacterium. It has a length of 3–5 µm and a width of 1.0 µm. The bacterial strain can be grown under both, anaerobic and aerobic conditions and in any nutritional medium. It is one of the most infectious bacterial strains and is known to spread from infected animals to humans at a rapid rate. As mentioned earlier, it is a common biological weapon that had been extensively used in the past. Lastly, B. anthracis belongs to the strain B. cereus. This paper would highlight the morphology, classification, and the environment niche of Anthrax. (Sternbach G. 2003)
There are very few bacterial strains that can synthesize a protein capsule. The protein capsule consists of poly-D-gamma-glutamic acid. However, B. anthracis is one of the few bacterial strains to synthesize the protein. Along with a lethal factor, the bacteria forms edema factor which is also known as a adenylate cyclase exotoxin which is dependent on calmodulin. This is found in the bacterial stain, Bordetella pertussis. B. anthracis is similar to Bacillus cereus in terms of genotype and phenotype. It also resembles Bacillus thuringiensis. In respect to cellular morphology and dimensions, all three bacterial strains or species have some or the other resemblance. A common aspect of all three strains is that they all form oval spores that are round and contained in an un-swollen sporangium. Some of the common features of B. anthracis have ability to survive in low-nutrient conditions and extreme temperatures. The strain is also capable to withstand harsh chemical treatment and can survive in any environment for over 10 years or even more. (R C Spencer. 2003)
The spore consists of a dry cell wall (dehydrated) that is often thick. The wall consists of many layers of cell that eventually form the cell membrane. The spores can thrive in any environment and can remain dormant (inactive) for years together. However, the spores can grow again if a suitable environment is developed. During its initial developmental stage (often within the rod-shape form), it is referred to as an endospore. Some of the key characteristics of the Bacillus species are the size and shape of the endospore, the location within the rod. And the association of the bulging of the wall of the rod during development. Endospores are often oval or round in shape but a few of them appear to be cylindrical. Most of the species contain dipicolinic acid. Many electron micrograph studies revealed that this species consists of a thin outer film, thick cortex (spore), and spore membrane (inner). The inner membrane in turn surrounds the contents of the spores.
Most of the spores have the ability to resist drying, heat, and most disinfectants including alcohol (95%). B, anthracis spores are common biological weapons because of its extraordinary characteristics. Moreover, B. anthracis can be transformed to aerosol or powdered form which makes it easier for it to be used as a biological weapon. Many countries have witnessed the use of anthrax as a biological weapon. Some of them include United Kingdom, Russia, United States, and Iraq. (Hicks CW, et al. 2012)
Classification of B. anthracis
Domain: Bacteria
Kingdom: Bacteria
Phylum: Firmicutes
Order: Bacillales
Family: Bacillaceae
Genus: Bacillus
Species: anthracis (Mock M, et al. 2001)
Environmental Niche of Bacillus anthracis
Infectious cells (bacteria) are ingested by grazing herbivores. These cells then grow within the host (animal) to germinate and produce the disease (anthrax). This phase is highlighted as solid arrows in figure 1 below. The process of scavenger action or terminal hemorrhage is observed after the host death. This process is associated with the release of 100 to 109 milliliter of blood in the environment. Sporulation or starvation are the only two options for the vegetative cells although their fate in the soil still remains unknown.
In the same figure, the alternatives to starvation or sporulation through which these cells form a biofilm are highlighted using dashed arrows. Most of the cells persist in the environment for a long time and are often found in rhizospehe system (model). (Mullins, CJ, et al. 2013)
Certain soil conditions would prefer the growth of these vegetative cells and often lead to an outbreak. Most biologists refer this as an ‘incubator area’ according to Van Ness. It is still unclear if B. anthracis (vegetative) is involved in DNA transfer or exchange within the soil. However, for B. cereus and B. thuringiensis, horizontal gene transfer can be considered as a major factor in environmental niche expansion.
Figure 1. The B. anthracis lifecycle.
The persistence and occurrence of anthrax reservoirs in any environment in terms of genetic and ecological factors is still vague. Many biologists suggest that in order to survive, most of the vegetative forms of Bacillus anthracis need to sporulate or need to thrive within the host.
Many biologists have also provided evidence of unique lifecycle of Bacillus anthracis. Most of these cycles are dependent different bacteriophages, bacterial viruses, and other alterations (phenotype) in Bacillus anthracis. Lysogens or infected derivatives have also played an important role in the life cycle of Bacillus anthracis that is often associated with superior survival abilities. Biologists have also proven that Bacillus anthracis stains are completely dependent on the lysogeny in terms of sporulation (both environmental and laboratory). There are many phases of Bacillus anthracis in the environment. One such example of Bacillus anthracis would include a pseudolysogenic-like state, wherein most of the cells are present in both worm gut and soil. These cells are often associated with shedding phages that correspond to non-lysogenic B. anthracis strains. (L Doganay & P D Welsby. 2006)
Thus, it can be concluded that anthrax is a severe acute disease found in herbivores animals and humans. The morphology, classification, and environmental niche of B. anthracis was briefly described using relevant scholarly sources.
References
- R C Spencer. J Clin Pathol. Mar 2003; 56(3): 182–187.
- Mock M, Fouet A. Anthrax. Annu Rev Microbiol. 2001;55:647-71.
- Sternbach G. The history of anthrax. J Emerg Med. 2003 May;24(4):463-7.
- Hicks CW, Sweeney DA, Cui X, Li Y, Eichacker PQ. An overview of anthrax infection including the recently identified form of disease in injection drug users. Intensive Care Med. 2012 Jul;38(7):1092-104.
- L Doganay and P D Welsby Anthrax: a disease in waiting? Postgrad Med J. Nov 2006; 82(973): 754–756.
- Mullins, CJ, et al. Ecological Niche Modeling of Bacillus anthracis on Three Continents: Evidence for Genetic-Ecological Divergence? PLoS One. 2013; 8(8): e72451.
