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
Microorganisms in this group
- Mycobacterium tuberculosisThe 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
- Mycobacterium lepraeThe leprosy bacterium: it damages skin and peripheral nerves, spreads poorly and is cured with several free antibiotics.Exam priority: medium
- Mycobacterium avium complex and other non-tuberculous mycobacteriaMycobacteria from water and soil that do not spread between people; they sicken those with damaged lungs or very weak immunity.Exam priority: medium
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.
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Tuberculosis (World Health Organization (WHO), 2025); Leprosy (World Health Organization (WHO), 2025); About Nontuberculous Mycobacteria (NTM) Infections (Centers for Disease Control and Prevention (CDC), 2024).
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Representative model, for educational purposes only.