[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Mycobacteria](https://durgical.com/en/microbiology/groups/mycobacteria/) › Mycobacterium avium complex and other non-tuberculous mycobacteria

[Microbiology](https://durgical.com/en/microbiology/) · [Mycobacteria](https://durgical.com/en/microbiology/groups/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

## Key points

- No person-to-person spread: standard precautions
- Disseminated MAC = AIDS with very low CD4 counts
- A macrolide is the backbone of MAC treatment
- M. marinum: fish-tank granuloma; M. abscessus: infections after cosmetic surgery

## 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 →](https://durgical.com/en/conditions/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:

- [Clarithromycin](https://durgical.com/en/pharmacology/clarithromycin/)
- [Azithromycin](https://durgical.com/en/pharmacology/azithromycin/)
- [Ethambutol](https://durgical.com/en/pharmacology/ethambutol/)
- [Rifampicin](https://durgical.com/en/pharmacology/rifampicin/)
- [Amikacin](https://durgical.com/en/pharmacology/amikacin/)

## Prevention

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

## Memory aid

They are «water cousins»: they live in the shower and the fish tank, do not travel person to person and only enter houses with the door open (damaged lungs or advanced HIV).

## 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.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/microbiology/mycobacterium-avium-complex-and-other-non-tuberculous-mycobacteria/)

## Related

- [Mycobacterium tuberculosis](https://durgical.com/en/microbiology/mycobacterium-tuberculosis/)
- [Mycobacterium leprae](https://durgical.com/en/microbiology/mycobacterium-leprae/)

## Related conditions

- [HIV infection and AIDS](https://durgical.com/en/conditions/hiv-infection-and-aids/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

[← Back to the group: Mycobacteria](https://durgical.com/en/microbiology/groups/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](https://www.cdc.gov/nontuberculous-mycobacteria/about/index.html) (Centers for Disease Control and Prevention (CDC), 2024); [Disseminated tuberculosis: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000624.htm) (MedlinePlus (U.S. National Library of Medicine), 2024).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/mycobacterium-avium-complex-and-other-non-tuberculous-mycobacteria/