Mycobacterium: A large family of bacteria that have unusually waxy cell walls that are resistant to digestion.

The mycobacteria includes:

• Mycobacterium avium -- which causes tuberculosis in birds and immunodeficient people;
• Mycobacterium leprae -- which causes leprosy;
• Mycobacterium marinum -- which causes swimming pool granuloma;
• Mycobacterium tuberculosis -- which causes most cases of tuberculosis; and
• Mycobacterium ulcerans -- which causes Buruli ulcer.

The mycobacteria are acid-fast rod-shaped bacteria. They are usually slow-growing. Many are intracellular parasites.