Mycobacteria are a type of germ. There are many different kinds. The most common one causes tuberculosis. Another one causes leprosy. Still others cause infections that are called atypical mycobacterial infections. They aren't "typical" because they don't cause tuberculosis. But they can still harm people, especially people with other problems that affect their immunity, such as AIDS.

Sometimes you can have these infections with no symptoms at all. At other times, they can cause lung symptoms similar to tuberculosis:

  • Cough
  • Weight loss
  • Coughing up blood or mucus
  • Weakness or fatigue
  • Fever and chills
  • Night sweats
  • Lack of appetite and weight loss

Medicines can treat these infections, but often more than one is needed to cure the infection.


    Nontuberculous Mycobacterium Infections (NTM) Symptoms, Causes, and Risk Factors (American Lung Association)

Diagnosis and Tests

 Acid-Fast Bacillus (AFB) Tests


Mycobacteria are Gram-positive, catalase positive, non-motile, non-spore forming rod-shaped bacteria (0.2–0.6 μm wide and 1.0–10 μm long). The colony morphology of mycobacteria varies with some species growing as rough or smooth colonies. Colony colour ranges from white to orange or pink (Iivanainen, 1999). Most mycobacteria are aerobic organisms, although some species are microaerophilc.

he cell walls of mycobacteria are very thick and consist of four layers. The innermost layer is composed of peptidoglycan and the others of lipids. The presence of lipid provides the bacteria with resistance to acid and alkaline environments and renders the cells relatively impermeable to various basic dyes, which need to be combined with phenol to allow penetration of the cell wall. The cell wall composition renders mycobacteria hydrophobic, and as a result these bacteria tend to grow in aggregates that ‘float’ on the surface of liquid media. Detergents, such as Tween® 80 can be added to culture media to disperse the organisms. Certain mycobacteria, including Mycobacterium paratuberculosis (MAP), can shed their cell walls, forming spheroplasts which are not detected using the acid-fast stain test (Hines and Styer, 2003).

Clinically, the most important species is Mycobacterium tuberculosis, which causes tuberculosis in humans. Tuberculosis in cattle and humans is also caused by Mycobacterium bovis, whilst Mycobacterium africanum is a rare cause of human tuberculosis in central Africa. Whilst these pathogenic species exhibit some phenotypic differences, they are genetically very similar and are therefore often classed as the ‘Mycobacterium tuberculosis complex’. Other pathogenic mycobacteria include the Mycobacterium avium complex (MAC) and the non-tuberculous mycobacteria (NTM, atypical mycobacteria, or environmental mycobacteria). Both these groups are frequent opportunistic pathogens, particularly in immunosuppressed individuals.

Media Contact: 

Liza Parker
Journal Manager 
Microbiology: Current Research