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[Microbiology](https://durgical.com/en/microbiology/) · [Bacteria](https://durgical.com/en/microbiology/#d-bacteria)

# Mycobacteria

- Bacteria

Rods with a lipid-rich wall that resists acid-alcohol: they cause tuberculosis, leprosy and environmental infections.

Updated 2026-11-01

## What they are

Mycobacteria are slow-growing aerobic rods whose wall contains mycolic acids. That is why they barely take the Gram stain and are recognised with the Ziehl-Neelsen stain as acid-fast bacilli (AFB). The group includes M. tuberculosis, M. leprae and the environmental non-tuberculous mycobacteria.

## What they share

- Mycolic-acid wall: acid-fast (Ziehl-Neelsen, auramine)
- Slow growth: culture takes weeks
- They survive inside macrophages and form granulomas
- Treated with drug combinations for months to prevent resistance

## Key points

- Ziehl-Neelsen: red acid-fast bacilli on a blue background
- M. tuberculosis needs airborne precautions with an N95 respirator; M. leprae and NTM need only standard precautions
- M. leprae does not grow on laboratory media
- Disseminated M. avium complex appears in advanced AIDS

## Microorganisms in this group

- [**Mycobacterium tuberculosis** The tuberculosis bacterium: it travels in the air when people cough, mainly infects the lungs and is cured with several antibiotics over months. Exam priority: high](https://durgical.com/en/microbiology/mycobacterium-tuberculosis/)
- [**Mycobacterium leprae** The leprosy bacterium: it damages skin and peripheral nerves, spreads poorly and is cured with several free antibiotics. Exam priority: medium](https://durgical.com/en/microbiology/mycobacterium-leprae/)
- [**Mycobacterium avium complex and other non-tuberculous mycobacteria** Mycobacteria from water and soil that do not spread between people; they sicken those with damaged lungs or very weak immunity. Exam priority: medium](https://durgical.com/en/microbiology/mycobacterium-avium-complex-and-other-non-tuberculous-mycobacteria/)

## Test yourself

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

## Which wall component makes mycobacteria acid-fast?

Mycolic acids, long-chain lipids that hold the carbol fuchsin after the acid-alcohol wash.

## Which mycobacterium requires airborne isolation?

M. tuberculosis in active pulmonary or laryngeal disease: a negative-pressure room and an N95 respirator.

## Why can M. leprae not be cultured in the clinical lab?

It does not grow on artificial media; it has been kept in mouse footpads and armadillos.

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

Sources: [Tuberculosis](https://www.who.int/news-room/fact-sheets/detail/tuberculosis) (World Health Organization (WHO), 2025); [Leprosy](https://www.who.int/news-room/fact-sheets/detail/leprosy) (World Health Organization (WHO), 2025); [About Nontuberculous Mycobacteria (NTM) Infections](https://www.cdc.gov/nontuberculous-mycobacteria/about/index.html) (Centers for Disease Control and Prevention (CDC), 2024).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/microbiology/groups/mycobacteria/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/groups/mycobacteria/