MYCOBACTERIUM BOVIS: CHARACTERISTICS, MORPHOLOGY AND PATHOGENESIS - BIOLOGY - 2025

The Mycobacterium bovis is one of the bacteria belonging to the complex of bacteria that can cause tuberculosis. It is a known pathogen of mammals such as cattle, although it has been isolated from others such as buffalo, elk and deer, among others.

It owes its name to the researchers Karlson and Lessel, who instituted it in 1970. This bacterium is responsible for generating tuberculosis in animals, the first case being described in 1909. Likewise, through various studies it has been established that it is also responsible for a small percentage of tuberculosis cases in humans.

Mycobacterium bovis. Source: By Y tambe (Y tambe's file), via Wikimedia Commons

Because it has many similarities with Mycobacterium tuberculosis, when a case is suspected, it is necessary to apply certain tests in order to reliably determine the causative agent.

In this case, the basic difference is determined by applying the niacin production and nitrate reduction tests. In Mycobacterium bovis these tests are negative.

On very rare occasions, Mycobacterium bovis affects humans, especially due to sanitary regulations regarding food handling, as well as the extension of pasteurization as a mechanism to eliminate microorganisms from milk and its derivatives.

Taxonomy

The taxonomic classification of the bacterium Mycobacterium bovis is:

Domain: Bacteria

Phylum: Actinobacteria

Order: Actinomycetales

Suborder: Corynebacterineae

Family: Mycobacteriaceae

Genus: Mycobacterium

Species: Mycobacterium bovis.

Morphology

Mycobacterium bovis shares many of its morphological characteristics with other members of the same genus.

Its cells are shaped like an elongated rod, which can be straight or slightly curved. Similarly, when viewed under the microscope, individual cells or small groups can be seen.

They have an average size of 0.2-0.7 microns wide by 1-10 microns long. Also, their cells do not have a protective capsule nor do they produce spores.

Its cell wall, as in other bacteria of the genus Mycobacterium, is quite thick. It is made up of a peptidoglycan known as lipoarabinomannan. Similarly, more than 60% of the membrane is composed of lipids.

The cell wall has a broad, middle layer that is made up of a polysaccharide called arabinogalactan.

In addition to these compounds, there is an abundance of others in the cell wall such as mycolic acids, which in the case of mycobacteria, is a molecule that has more than 90 carbon atoms. Likewise, glycolipids can also be seen in the structure of the cell wall.

In the cultures, colonies with a rough waxy appearance can be seen, which can later become thick and wrinkled. It extends over the entire surface of the crop.

The genetic material of the bacterium is found on a single circular chromosome that contains approximately 3,952 genes that encode the expression of certain proteins. Its genome is very similar to that of the bacterium Mycobacterium tuberculosis.

General characteristics

It is mesophilic

For its proper growth and development, Mycobacterium bovis requires a temperature range of between 32 ° C and 38 ° C, with its optimum temperature being 37 ° C.

It is an acid bacteria - alcohol resistant

In standard staining procedures, one of the steps is discoloration, either by acid or alcohol. In the case of Mycobacterium bovis, thanks to the structure of its cell wall it is resistant to this procedure. Therefore, it cannot be discolored through these traditional methods.

Is a parasite

The Mycobacterium bovis, in order to replicate, develop and grow, it must be inside a host. In this case, it parasitizes macrophages, blood cells largely responsible for dealing with bacterial infections.

It is microaerophilic

The bacterium Mycobacterium bovis is strict aerobic. Within the group of aerobic bacteria, there is the subgroup of microaerophiles.

These are those that must be developed in an environment with oxygen availability. However, it requires very low levels than those normally found in the atmosphere.

Susceptible to certain conditions, but highly resistant to others

This bacterium is very sensitive to sunlight, ultraviolet light, and heat, as high temperatures tend to cause denaturation of its constituent proteins.

Also, Mycobacterium bovis is very resistant to low temperatures, including freezing. They also effectively resist desiccation.

It is catalase positive

Mycobacterium bovis produces a variety of catalase enzyme that is heat-sensitive, that is, its effectiveness is conditioned by the temperature of the environment in which the microorganism is found.

This means that at room temperature it is positive, but at high temperatures (about 68 ° C) it is inactive.

It is slow growing

This bacterium has a slow growth pattern. It may take 16-20 hours as the build time.

The culture medium is the one used for all mycobacteria, the Löwenstein-Jensen. When glycerol is present, the growth of Mycobacterium bovis is poor, while with pyruvate it is more effective.

It is pathogenic

Mycobacterium bovis is a known pathogen in various mammals such as cattle. Likewise, it can be an occasional pathogen in humans, when they eat meat contaminated with the bacteria or milk that has not been subjected to the pasteurization process.

Pathogeny

The most common route of transmission of this bacterium is through the air. The healthy individual (animal or human) acquires the bacteria through inhaled particles.

Once inside the body, the bacterium is attacked by macrophages, which engulf it. Within macrophages, through a series of mechanisms, the bacterium is able to prevent the lytic action of lysosomes, which is why they begin to replicate both inside and outside the cells.

Later they can spread through the lymphatic ducts and affect various organs and tissues.

If contagion occurs by ingestion of contaminated milk, the pathogenic process begins in the digestive tract, showing lesions in the intestinal mucosa, involvement of mesenteric lymph nodes, liver, lungs, spleen and other organs.

Virulence factors

Virulence factors are each and every one of the mechanisms and means that a pathogen uses to infect a host. In the case of Mycobacterium bovis, its virulence factors are mainly oriented towards two purposes:

• Facilitate the entry of bacteria into their target cells (macrophages).
• Prevent the proper functioning of the defense mechanisms of macrophages.

Among the most representative virulence factors are:

Cord factor

It is a glycolipid. Its function is to stimulate the growth of cord-shaped bacteria (hence its name). In addition to this, it has been determined to be toxic to leukocytes.

Sulfolipids

They are extremely important, as they interfere with the binding of phagosomes to lysosomes. In this way, the enzymes contained in the latter are prevented from coming into contact with the bacterial cells and causing their destruction.

Mycobacterium bovis

Mycobacterium bovis infection in humans is very rare. It can occur from the consumption of dairy products that have not undergone an adequate pasteurization process.

Those most at risk of infection are those in occupations in which they are in constant contact with animals, such as working in a slaughterhouse, being a butcher, or working in dairy production sites.

The symptoms that occur are similar to those of tuberculosis caused by Mycobacterium tuberculosis. These include:

• Fever
• Weightloss
• Night sweats
• Cough with bloody expectoration.

In the case of a location other than the lung, for example gastrointestinal, symptoms can range from abdominal pain to severe diarrhea.

The treatment to be applied is with antibiotics. However, it is the doctor who decides the antibiotic to be prescribed, taking into account the susceptibility and resistance studies performed on the diagnostic culture.

References

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