Nontuberculous Mycobacteria



Last Review Date: June 7, 2017


What are nontuberculous mycobacteria?

Mycobacteria are a diverse group of rod-shaped bacteria that include more than 150 different species. Most mycobacteria live in the soil and water in both rural and urban settings throughout the world. Mycobacteria except for Mycobacterium tuberculosis complex (which cause the disease tuberculosis (TB)) and the causative agents of leprosy (Mycobacterium leprae and Mycobacterium lepromatosis) are referred to in the literature variously as nontuberculous mycobacteria (NTM), mycobacteria other than tuberculosis (MOTT), atypical mycobacteria, and/or environmental mycobacteria. The terms are used interchangeably, depending on author preference when writing journal articles. For the purpose of this article, this group will be referred to as NTM.

NTM are found widely in the environment. They can be found in aerosols, rivers and swamps, in treated city water, public swimming pools, hot spas, humidifiers, aquariums, garden soils, food, and many other places. Because they are protected by their waxy lipid-rich cell wall, mycobacteria are resistant to disinfectants and water treatment measures.

Almost half of the NTM species identified are associated with opportunistic infections in animals and humans, and several have caused sporadic outbreaks. NTM are acquired through environmental exposure to water, aerosols, soil, and dust – through inhalation, ingestion, and through breaks in the skin due to injuries, tattoos, surgical procedures, IV catheters and the like. Unlike M. tuberculosis, they are generally not passed from person-to-person. NTM can cause infections of almost any organ, but most commonly the lungs, lymph nodes, bones and skin and soft tissues. In heavily immunocompromised persons NTM infections may be spread widely through the body infecting many sites.

Under the right circumstances anyone may develop an infection with a NTM, but people with suppressed immune systems (such as those with HIV/AIDS and transplant recipients), people with pre-existing lung damage (for example from smoking or previous tuberculosis) and those with chronic lung diseases (such as emphysema or cystic fibrosis) are most likely to be affected. NTM infections can be challenging and time-consuming to treat since the organisms are often resistant to commonly prescribed antibiotics.


Common Species

The table below identifies several different NTM species and provides a brief description of each.

MYCOBACTERIA

EXAMPLES – MANY OVERLAP

M.avium-intracellulare  complex (MAC)

MAC has become one of the most common infections in patients with AIDS; often in the lungs and disseminated throughout the body; found widely around the world

M. kansasii

Most frequently causes lung infections; tap water is the likely reservoir

M. abscessus complex

May cause skin, pulmonary, soft tissue or bony disease

M. chelonae

Most commonly causes skin, bone or soft tissue infections.

M. fortuitum

Most commonly causes skin, bone or soft tissue infections, and rarely causes lung disease

M. haemophilum

Skin lesions, cervical adenitis and joint infections. Occasionally causes disseminated infection in immunosuppressed patients.

M. scrofulaceum

May cause cervical adenitis, especially in children. Also skin infections, pulmonary infections and disseminated infections.  This organism is not commonly isolated.

M. marinum

Found in fresh and salt water, aquariums and swimming pools; infects through breaks in the skin and may cause persistent sores. Causes “swimming pool granuloma” or “fish tank granuloma”.

M. ulcerans

Endemic in the tropics; skin infection can result in a large lesion called a Buruli ulcer or Daintree ulcer or Bairnsdale ulcer; worldwide, the 3rd most common mycobacterial infection in healthy people

M. leprae and M. lapromatosis

As the causative agent of leprosy, it infects mucous membranes and cool areas such as skin; causes nerve damage and numbness and skin nodules; can lead to skin damage and infection


Signs and Symptoms

The symptoms associated with nontuberculous mycobacteria (NTM) infections depend on which part(s) of the body are involved. Pulmonary infections may cause TB-like symptoms, including:

  • Chronic cough, sometimes with bloody sputum
  • Fever
  • Chills
  • Weight loss
  • Weakness

Skin-related NTM infections may cause persistent sores, boils, ulcers, and granulomas that do not respond to routine antibiotics. Those affecting lymph nodes may cause inflammation in the node.

All of these symptoms may also be seen in a variety of other conditions. The diagnosis of most NTM infections depends on the positive identification of mycobacteria in body fluids or tissues.


Tests

The goals of testing are to detect nontuberculous mycobacteria (NTM) infections and to distinguish between mycobacteria species. It is not possible to distinguish between TB and NTM infections without testing. Mycobacterial species sometimes colonise the lungs of patients with significant pre-existing lung damage without causing substantial disease. At present there is no laboratory test that can distinguish between colonisation and infection with an NTM.

Laboratory Tests

  • AFB smears and cultures. These are the primary methods used to detect mycobacterial infections. The sample(s) collected for analysis depend on the part(s) of the body that the doctor suspects are infected. For pulmonary infections, 3 to 5 sputum specimens are collected first thing in the morning on different days as this is when sputum is likely to contain the most mycobacteria. For other parts of the body, washings/aspirates, swabs of the infected area, fluids and/or tissue samples (biopsy) may be collected.

Because of their unique cell wall, acid will not remove a stain called carbol fuchsin from mycobacteria. Bacteria with this unique staining property are referred to as "acid fast" (AFB) and can be detected when the stained slide is viewed under the microscope.

AFB cultures are performed on samples that have been treated to liquefy mucus and reduce contaminating bacteria. This process also concentrates any AFB in the sample to enhance recovery of organisms in culture. Nutrients and incubation at appropriate temperature provide a supportive environment for the slow-growing mycobacteria. The results of positive cultures tell the doctor what organisms are present and may provide some guidance on appropriate drugs to treat an infection. However, as mycobacteria are slowly growing compared to other bacteria (5-20 hours for each bacteria to divide, compared to 20 minutes for Escherichia coli), results from mycobacterial culture take time — usually several weeks for final results. Cultures are held for six to eight weeks before being reported as negative. 

M. leprae and M. lepromatosis are infrequently detected by culture as these species will not grow on culture media. They are diagnosed primarily through clinical signs and AFB stain of split skin smears. In specialised circumstances PCR tests may be performed to identify these bacteria from samples submitted for testing, or the organism may be cultured in tissues of the nine-banded armadillo, or in the footpads of particular strains of immunocompromised mice.

Once the mycobacteria species has been identified and treatment has begun, AFB smears and cultures are used to monitor the effectiveness of treatment.

  • Susceptibility testing. This may be performed. The treatment of NTM infections is difficult and for many infections susceptibility testing can only act as a guide to therapy.
  • Molecular tests. Other more rapid methods, such as the molecular detection of the organism's genetic material (DNA/RNA), may be performed on the primary specimen and also used as a means to identify the species of mycobacteria once the bacteria are grown in culture.

Non-Laboratory Tests
X-rays or CTs may be ordered to look for changes caused by a mycobacterial infection. NTM infections (and TB infections) can cause a number of characteristic findings on x-rays, including cavities (holes) and calcification in organs such as the lungs and kidneys.


Treatment

The goals with treatment are to resolve the nontuberculous mycobacteria (NTM) infection in the affected person and prevent further damage to tissues and organs. If there is evidence of widespread infection due to a common exposure, the medical community investigates the outbreak to find and eliminate the source of the infection(s). With leprosy, treatment is also necessary to prevent the spread of the infection.

The treatment of NTM infections is difficult and usually involves multiple antibiotics for prolonged periods of time. The length of treatment depends on the results of the AFB smears and cultures used to monitor the effectiveness of treatment. Where possible, NTM infections are best treated through surgical debridement (removal of damaged infected skin). In certain cases, such as an infected lymph node where the infection is localised, the surgical removal of the infected tissue may be curative.

Although symptoms often resolve after several weeks, it is crucial that those affected continue to take their drugs for the time period recommended by their doctor. There are often a large number of mycobacteria to kill and it may take several months or longer to make sure that all of them have been eradicated. Many treatments for mycobacterial infections have a wide range of undesirable side effects which must be carefully monitored. People with NTM infections should be in close contact with their doctor, report any new sumptoms and follow their doctor's recommendations closely for the best management of their specific condition.


Related Pages

On This Site
Tests: AFB Smear and CultureSusceptibility Testing
Conditions: HIV/AIDSTuberculosisLung Diseases

Elsewhere On The Web
Lung Foundation Australia: NonTuberculous Mycobacteria (NTM) 
MedlinePlus: Mycobacterial Infections 
American Lung Association: Learn about Nontuberculous Mycobacteria (NTM)
NTM Info and Research, Inc 
Centers for Disease Control and Prevention: Mycobacterium abscessus in Healthcare Settings