What Is Mycobacterium Intracellulare?

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  • Written By: Jillian O Keeffe
  • Edited By: PJP Schroeder
  • Last Modified Date: 11 October 2019
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The bacterial species Mycobacterium intracellulare can cause lung disease in humans as well as lymphadenitis and more serious diseases. It is a common species and is found in soil, water, and in house dust. M. intracellulare is related to the bacterium that causes tuberculosis and shares some of the same features.

Each of the individual M. intracellulare bacteria are shaped like a rod when viewed under a microscope. They are Gram-positive, which means they look blue instead of pink when stained with a Gram stain. Human body temperature, which is 98.6 degrees Fahrenheit (37 degrees Celsius), is the optimum growth temperature for the species.

Hot water systems in the home or in hospitals can harbor the species, especially when the water is present in an aerosol, such as from a showerhead. House dust and farm animals are other sources. The bacteria can even be found in soil, saltwater, and freshwater, so they are very common in the environment.

Mycobacterium intracellulare is very similar to a close relative known as Mycobacterium avium. Initial tests may not be able to differentiate between the two, and for this reason, the presence of one or the other of the bacteria is known as Mycobacterium avium-intracellulare. Both species are related to Mycobacterium tuberculosis.


All of these bacterial species infect the lungs, although Mycobacterium intracellulare does not cause tubercles in the lungs, which is typical of tuberculosis. Sometimes it may be present in an infected patient along with M. avium or M. tuberculosis. M. intracellulare causes a disease of the lungs that can show symptoms similar to tuberculosis, but it can also colonize the lungs without causing any obvious symptoms.

People whose immune systems are weak are more vulnerable to M. intracellulare infection than those who have healthy immune systems. Patients with Acquired Immunodeficiency Syndrome (AIDS) are one such group. Those people who do not suffer from AIDS but who already have lung infections are also more susceptible to this disease.

The route by which Mycobacterium intracellulare infects people is through inhalation or through ingestion. When someone inhales the bacterium, it can then cross the protective outer layer of the lungs. In the gastrointestinal system, it can also cross the skin barrier. Then, it infects macrophage cells, and they carry it to the lymph glands.

Children with swollen lymph glands, a condition also known as lymphadenitis, may have a M. intracellulare infection. In immuno-compromised people, the lymph glands may be the starting points for the bacteria to spread further and affect the liver, bone marrow, or other organs. That can cause the dangerous condition called bacteremia.


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