Bacillus anthracis taxonomy, characteristics, diseases

Anthony Golden
Bacillus anthracis taxonomy, characteristics, diseases

Bacillus anthracis it is a pathogenic bacterium with the ability to produce spores that can enter the body of some living beings. This bacterium has a place of honor in the world of microbiology, since it holds several recognitions: First bacterium seen under the microscope by Aloys Pollender in 1849, and First bacterium recognized as a pathogen, thanks to Robert Koch in 1877.

It is one of the bacteria that has been most studied, since due to its morphological and physiological characteristics, in addition to its virulence, it has even been used as a biological weapon.

Source: By Photo Credit: Content Providers (s): CDC [Public domain], via Wikimedia Commons

Article index

  • 1 Taxonomy
  • 2 Morphology
  • 3 General characteristics
    • 3.1 It is gram positive
    • 3.2 It is catalase positive
    • 3.3 It is thermophilic
    • 3.4 It is gamma hemolytic
    • 3.5 Produces spores
    • 3.6 It is facultative anaerobic
    • 3.7 Metabolism
  • 4 Pathologies
    • 4.1 Mechanism of infection
    • 4.2 Types of infection
  • 5 Symptoms
    • 5.1 Cutaneous anthrax
    • 5.2 Lung anthrax
    • 5.3 Gastrointestinal anthrax
  • 6 Treatment
  • 7 References


The taxonomic classification of Bacillus anthracis is the next:

Domain: Bacterium.

Edge: Firmicutes.

Class: Bacilli.

Order: Bacillales

Family: Bacillaceae.

Gender: Bacillus.

Species: Bacillus anthracis.


Because they belong to the genus bacillus, bacterial cells are rod-shaped, with straight ends. In addition, within the standard parameters regarding the size of the bacteria, they are considered large. They measure approximately 1 x 3-8 microns.

On the other hand, they do not present any type of extensions or flagella.

By studying infected tissue under the electron microscope, individual cells have been observed, as well as a few forming short chains of 3 to 4 cells. However, in crops in vitro the formation of long chains is observed.

In the central part of each bacterial cell it is possible to notice a round structure, the sporangium, which is where the spores develop.

In the observed cultures, the formation of colonies measuring between 2 and 5 mm, white in color, with an appearance similar to that of ground glass is evidenced..

Similarly, the bacteria is protected by a very resistant capsule. This capsule is peptide, made up of a homopolymer known as poly-g-D-glutamate. This compound has an important role in the survival of the bacteria to the defense mechanisms of the host. This is due to its low immunogenicity..

General characteristics

It is gram positive

This means that it has a thick cell wall made up of peptidoglycan, which makes it adopt a purple-violet color when subjected to Gram staining..

It is catalase positive

They contain the enzyme catalase through which they have the ability to break down the hydrogen peroxide compound into oxygen and water. This is a characteristic that contributes to the correct identification of the bacteria in the laboratory..

Is thermophilic

The ideal temperature for its growth is at 37 ° C. Above 43 ° C growth is totally inhibited.

It is gamma hemolytic

The Bacillus anthracis it does not have the ability to cause the destruction of erythrocytes present in the blood. This has been fully demonstrated in blood agar cultures..

Produces spores

Spores are cells that are in a dormant state. In the case of Bacillus anthracis, They are endospores and their function is to guarantee the survival of the bacteria when the environmental characteristics are unfavorable..

Endospores are produced when bacteria are in contact with oxygen. They are highly resistant to hostile environmental conditions such as high temperatures (over 100 ° C) and lack of nutrients..

Likewise, they can remain dormant for many years in different places. For example, in water they can be kept for 2 years and in silk threads a period of 70 years.

It is facultative anaerobic

The bacteria can survive both in environments with oxygen, and in the absence of it. However, to develop spores it must be in a habitat where oxygen is available..


When found in EYA agar (Egg Yolk Agar, "Egg Yolk Agar"), it has been shown to be able to hydrolyze casein, starch and gelatin..

In the same way, it has been proven that it can metabolize some carbohydrates such as trehalose and glycogen, to produce acid.


The spores of the Bacillus anthracis They are highly pathogenic, so when they enter the body of human beings, as well as other animals, they generate health problems that in a large percentage of cases lead to death.

Likewise, those who are most at risk are people who have jobs related to agriculture, forestry, contact activities with animals or their products, laboratories, among others..

Mechanism of infection

The spores enter the body and are immediately recognized by cells of the immune system known as macrophages, which engulf them.

Once inside these cells, the spores germinate and the bacterial cells begin to reproduce with their respective capsule and the consequent toxins that are going to generate the damage in the various tissues..


Types of infection

Now, the word "Anthrax" refers to the infection by this bacterium, also specifying the area of ​​the body affected.

In such a way that several pathologies can be studied:

Cutaneous anthrax

It constitutes 95% of the cases. It occurs when the spores of the bacteria enter the body through a wound or injury to the skin. Has an incubation period of 1 to 12 days.

Generally the injury evolves favorably, after which only the scar remains. If it is not treated promptly, it can have a mortality rate of 20%.

Pulmonary anthrax

It corresponds to 55% of the cases. It occurs when spores are inhaled and enter the body through the respiratory tract, to the lungs. The incubation period is approximately 1-7 days.

Has a mortality rate close to 100%.

Gastrointestinal anthrax

It represents a tiny percentage of the reported cases. It is very unusual. It originates when there is the ingestion of raw meat contaminated with spores. Symptoms appear after 1 to 7 days.


The clinical picture that manifests in a Bacillus anthracis infection depends on the route of entry into the body and the affected tissues.

Cutaneous anthrax

  • Bulging lesion, similar to a mosquito bite, that later evolves into a painless, festering ulcer, eventually becoming a necrotic eschar.
  • Fever (37 ° C - 38 ° C)
  • Increase in nearby lymph nodes.
  • General discomfort.

Pulmonary anthrax

  • Fever (38 ° C)
  • Non-productive cough
  • General discomfort
  • Chills and tiredness

Later these symptoms evolve until the critical phase of the infection, in which the following symptoms appear:

  • High fever (39 ° C - 40 ° C)
  • Tachycardia
  • Difficulty breathing
  • Cyanosis

Eventually shock and septicemia occur, which in most cases lead to the death of the patient.

Gastrointestinal anthrax

It presents quite nonspecific symptoms:

  • Abdominal pain
  • Fever
  • Sickness
  • Bloody diarrhea

These symptoms progress to severe bacteremia and, if not treated in time, can cause death..


The main element to consider when treating a bacterial infection is the antibiotic. There are a wide variety of antibiotics today, which have proven their effectiveness as bactericidal agents..

In the case of Bacillus anthracis, has been shown to be susceptible to penicillin, tetracycline, gentamicin, chloramphenicol, and erythromycin.

Of course, the most indicated is the doctor to determine the treatment guidelines to follow, taking into account the specific characteristics of each clinical case..


  1. Anthrax. Retrieved from:
  2. Bacillus anthracis. Retrieved from:
  3. Bacillus anthracis. Retrieved from:
  4. Carrada, T. (2001, December). Anthrax: diagnosis, pathogenesis, prevention and treatments. Recent advances and perspectives. Journal of the National Institute of Respiratory Diseases. 14 (4). 233-248
  5. Center for Disease Control and Prevention. (2014, October). Anthrax Overview: A Basic Guide to Understanding Anthrax. Retrieved from:
  6. Duery, O., (2014). Bacillus anthracis. Chilean Journal of Infectology. 31 (4). 457-458.
  7. National Institute of Safety and Hygiene at Work. (2013, August). Bacillus anthracis. Obtained from:
  8. Koehler, T. (2009, August). Bacillus anthracis Physiologic and Genetics. Molecular Aspects of Medicine Journ 30 (6). 386-396
  9. Pavan, M., Pettinari, M., Cairo, F., Pavan, E. and Cataldi, A. (2011, December). Bacillus anthracis: a molecular look at a famous pathogen. Argentine Journal of Microbiology. 43 (4) .294-310.
  10. Perret, C., Maggi, L., Pavletic, C., Vergara, R., Abarca, K., Debanch, J., González, C., Olivares, R. and Rodríguez, J. (2001). Anthrax (Anthrax). Chilean Journal of Infectology. 18 (4). 291-299
  11. Sánchez, N. and Rodríguez, R. (2001, October). Anthrax: characteristics, current epidemiological situation and recent scientific research. Surveillance Technical Report. 6 (4).
  12. Todar, K., Bacillus anthracis and Anthrax. Retrieved from
  13. Valdespino, J. and García, M. (2001). The ABC on anthrax for health personnel. Public Health of Mexico. 43. 604-613.

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