Mycobacterium leprae characteristics, morphology, culture

Abraham McLaughlin

Mycobacterium leprae is an acid-resistant bacteria that is well known to be a known human pathogen. It is the causal agent of leprosy, a pathology that is widely spread throughout the world and causes skin and nerve lesions..

It was discovered in 1874 by the Norwegian doctor Armauer Hansen. She is often referred to as Hansen's Bacillus. This bacterium has special characteristics that have not allowed it to grow adequately in artificial culture media, so its study has been based on inoculation in animals such as mice or its natural presence in the armadillo (reservoir)..

Mycobacterium leprae. Source: By Libell hanna [GFDL (, CC-BY-SA-3.0 ( or CC BY 2.5 (], from Wikimedia Commons

Leprosy is a disease that has existed forever, because in the records of history there are registered cases, whose symptoms and description of lesions suggest that it is this. For many years, being diagnosed with leprosy was a sentence of social exclusion and death..

It was in the 1980s when the Venezuelan doctor Jacinto Convit developed an effective vaccine against leprosy. With the implementation of this, the cases of the pathology have been decreasing in frequency. However, in developing countries this is still a serious disease..

Article index

  • 1 Morphology
  • 2 Features
  • 3 Taxonomy
  • 4 Habitat
  • 5 Cultivation
  • 6 Diseases
  • 7 Pathogenesis
  • 8 Signs and symptoms
  • 9 Diagnosis
  • 10 Treatment
  • 11 References


The Mycobacterium leprae It is a bacterium that is shaped like a thin rod, with a small curvature at one end. Each bacterial cell is approximately 1-8 microns long by 0.2-0.5 microns in diameter..

The cell is surrounded by a capsule that protects it from the action of lysosomes and certain metabolites. It is made up of two types of lipids: phthiocerol dimicocerosate and phenolic glycolipid.

When viewed under the microscope, individual cells are seen close together, parallel to each other, similar to the way cigarettes are distributed in a pack.

The cell wall that surrounds the bacterial cell is made up of peptidoglycan, as well as arabinogalactan. Both are linked through phosphodiester type bonds. The cell wall is approximately 20 nanometers thick.

Its genetic material is made up of a single circular chromosome, in which a total of 3,268,203 nucleotides are contained, which together constitute 2,770 genes. These encode the synthesis and expression of 1605 proteins.


It is a parasite

The Mycobacterium leprae it is an obligate intracellular parasite. This means that it requires lodging inside the host's cells in order to survive..

It reproduces by binary fission

Binary fission is a process by which the bacterial cell divides into two cells exactly the same as the cell that gave rise to them..

This process involves a duplication of the bacterium's chromosome and the subsequent division of the cytoplasm to give rise to the two resulting cells..

It's acidic - alcohol resistant

During the staining process, bacterial cells from Mycobacterium leprae are highly resistant to fading, which is one of the basic steps of the procedure.

Because of this, Mycobacterium leprae It cannot be stained through the Gram stain, but it is necessary to go to another type of staining.

Is thermophilic

Although it has not been possible to establish an effective culture of Mycobacterium leprae, it has been determined that its optimum growth temperature is below 37ºC.

This has been concluded taking into account the data collected on the type of animal that infects (preference for armadillos whose body temperature is 35-37ºC), as well as the location of the lesions (on low-temperature body surfaces).

It's Ziehl - Nielsen positive

The staining method used to observe bacterial cells from Mycobacterium leprae is that of Ziehl Nielsen. In this procedure, the sample is stained with a reddish dye that stains the cells. Later, another pigment such as methylene blue is added to generate a contrast.

It's aerobic

The Mycobacterium leprae it requires to develop in an environment with ample oxygen availability. This is because it needs this chemical element to carry out its various metabolic processes..


This is a slow growing bacteria. Although it has never been possible to cultivate in an artificial medium, it has been determined that it has a generation time of approximately 12.5 days.

Your survival rate depends on the environment

The Mycobacterium leprae it can remain intact in a humid environment for a period of approximately 9 to 16 days. If it is in moist soil, it can lie dormant for an average of 46 days.

Moreover, it is highly sensitive to light. When exposed to sunlight, it only lives for about 2 hours and resists UV light for just 30 minutes..


This bacterium belongs to the broad group of mycobacteria. Its taxonomic classification is as follows:

  • Domain: Bacterium
  • Edge: Actinobacteria
  • Order: Actinomycetales
  • Family: Mycobacteriaceae
  • Gender: Mycobacterium
  • Species: Mycobacterium leprae.


This bacterium is mainly found in tropical countries with a warm climate. It also lives in many places. Can be found in water, soil, and air.

It is known that in the organisms that host it, it prefers places with low temperatures. For example, it is found in the hands, feet, and nose, as well as human peripheral nerves..


Despite advances in the field of microbiology, it has never been possible to cultivate the Mycobacterium leprae in artificial media. It just doesn't unfold.

Among the many reasons that have been raised for this, one of the ones that seems more accurate is that since the bacterium is an obligate cellular parasite, it does not have the necessary genes to reproduce freely..

Due to the impossibility of achieving a culture, the studies focused on observing the infection in the pad of mice, as well as in armadillos (leprosy is endemic in them).

Thanks to the fact that these studies have been carried out, there have been advances in the knowledge of leprosy as a pathology. One of those most significant advances was the development of a vaccine against this disease.


The Mycobacterium leprae is a pathogenic bacterium that causes a disease known as leprosy in humans.

Leprosy, also known as "Hansen's disease", is a chronic infectious disease that mainly affects the skin, the mucosa of the upper respiratory tract, the eyes, as well as the peripheral nerves..


The cells that are the main bank of Mycobacterium are Shwann cells and macrophages.

Shwann cells are located on the surface of the axons of neurons and their function is to produce myelin. This is a kind of layer that covers the axon and that works as an electrical insulator. Its main function is to accelerate the transmission of the nerve impulse along the axon.

The Mycobacterium leprae invades these cells and interferes with the production of myelin, thus causing demyelination of the nerve fiber and the consequent loss of nerve impulse conduction.

Signs and symptoms

This bacteria is slow growing, so symptoms can take a long time to manifest. There are people who manifest symptoms a year, but the average time to manifest is about five years.

Among the most representative symptoms are:

  • Skin lesions that are lighter than the surrounding skin. These can be totally flat and numb.
  • Bumps, growths, or nodules on the skin.
  • Painless ulcerative lesions on the soles of the feet
  • Thick, dry, or stiff skin
  • Loss of sensation or numbness of the affected areas
  • Vision problems Especially when the facial nerves are affected.
  • Enlarged nerves that are felt under the skin
  • Muscular weakness

Once these symptoms have appeared, it is important to go to the doctor so that he can take the respective measures to diagnose and apply treatment. Otherwise, the disease can progress and become more severe..

If the disease is not treated in time, the symptoms advance, presenting:

  • Paralysis of upper and lower limbs.
  • Long-standing ulcerative lesions that do not heal
  • Disfigurement of the nose
  • Total loss of vision
  • Shortening of fingers and toes
  • Constant intense burning sensation on the skin


The signs and symptoms of leprosy can easily be confused with other pathologies. Hence, it is vitally important to go to the specialist, in this case, the dermatologist to apply the required diagnostic tests..

The diagnosis of the disease is clinical. The doctor relies on the presence of typical lesions and their biopsy.

For the biopsy, a small sample is taken and sent to the pathological anatomy specialist. He subjects it to the required staining process and observes it under a microscope to determine if there is presence of Mycobacterium leprae (Hansen bacilli).


Because leprosy is a disease caused by bacteria, the first-line treatment is antibiotics. Among the most used are: rifampin, clofazamine, minocycline, fluoroquinolones, macrolides and dapsone.

Treatment for this disease lasts between six months and two years.


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