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Microbiology · Mycobacteria

Mycobacterium avium complex and other non-tuberculous mycobacteria !

  • Bacterium
  • Acid-fast
  • Exam priority: medium

Mycobacteria from water and soil that do not spread between people; they sicken those with damaged lungs or very weak immunity.

Updated 2026-11-01

Also called: MAC, atypical mycobacteria, NTM

At a glance

Gram
Acid-fast
Shape
Rods
Oxygen
Aerobes
Family
Mycobacteriaceae
Stain
Ziehl-Neelsen: acid-fast, indistinguishable from M. tuberculosis under the microscope

Morphology

  • Acid-fast like M. tuberculosis
  • Slow growers (MAC, M. kansasii) or rapid growers (M. abscessus, M. fortuitum, M. chelonae)
  • Form biofilms in pipes and showerheads

Transmission

  • Inhalation of aerosols from contaminated water (showers, hot tubs) or dust
  • Inoculation into wounds, surgery, injections or cosmetic procedures
  • Generally not person-to-person

Reservoir: Natural and tap water, soil, dust

Isolation precautions

What the care team adds to standard precautions.

  • Standard

Virulence factors

  • Survive inside macrophages like M. tuberculosis
  • Biofilms and disinfectant resistance drive healthcare-associated outbreaks
  • In AIDS with very low CD4 counts, MAC spreads through the bloodstream

Diseases it causes

  • Non-tuberculous mycobacterial lung disease (bronchiectasis, COPD, cystic fibrosis)
  • Disseminated MAC in advanced HIV infection HIV infection and AIDS →
  • Cervical lymphadenitis in children; skin and soft-tissue infections (M. marinum, M. abscessus)

Clinical picture

  • Chronic cough and nodules with bronchiectasis, often in thin older women
  • Disseminated MAC: fever, sweats, diarrhoea, weight loss, anaemia and hepatosplenomegaly
  • M. marinum: hand nodules after contact with fish tanks

Diagnosis

  • Culture with species identification (several positive sputa needed to call lung disease)
  • Mycobacterial blood culture in disseminated MAC
  • Molecular tests for M. tuberculosis are negative, which helps tell them apart

Treatment

MAC: a macrolide (clarithromycin or azithromycin) combined with ethambutol and a rifamycin, for months; the macrolide is the key drug and resistance to it worsens the outlook. M. abscessus is highly resistant and usually needs amikacin and other drugs guided by susceptibility testing.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

Prevention

  • Timely antiretroviral therapy to keep CD4 counts up
  • Proper sterilisation of instruments and water used in procedures
  • No airborne isolation is required

Test yourself

Think of the answer, then tap the question to see it.

What is the usual source of non-tuberculous mycobacterial infection?

The environment: water (showers, pipes, hot tubs), soil and dust; not another person.

In which HIV patients does disseminated MAC appear?

In advanced AIDS with a very low CD4 count.

Which antibiotic class is the backbone of MAC treatment?

Macrolides (clarithromycin or azithromycin), combined with ethambutol and a rifamycin.

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← Back to the group: Mycobacteria

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: About Nontuberculous Mycobacteria (NTM) Infections (Centers for Disease Control and Prevention (CDC), 2024); Disseminated tuberculosis: MedlinePlus Medical Encyclopedia (MedlinePlus (U.S. National Library of Medicine), 2024).

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Representative model, for educational purposes only.