Mycobacterium is a genus of Actinobacteria, given its own family, the Mycobacteriaceae. The genus includes pathogens known to cause serious diseases in mammals, including tuberculosis (Mycobacterium tuberculosis) and leprosy (Mycobacterium leprae). The Greek prefix myco- means “fungus,” alluding to the way mycobacteria have been observed to grow in a mold-like fashion on the surface of cultures.
Mycobacterium avium-intracellulare infection (MAI) is an atypical mycobacterial infection, i.e. one with nontuberculous mycobacteria or NTM, caused by Mycobacterium avium complex. This infection causes respiratory illness in birds, pigs, and humans, especially in immunocompromised people. It usually first presents as a persistent cough. It is typically treated with a series of three antibiotics for a period of at least six months.
Mycobacterium avium and M. intracellulare (the M. a. complex, or MAC) are saprotrophic organisms present in soil and water; entry into hosts is usually via the gastrointestinal tract, but also can be via the lungs.
MAC can cause fevers, diarrhea, malabsorption, as well as loss of appetite and weight loss, and can disseminate to the bone marrow. Therapy for MAI is typically resistant to standard mycobacterial therapies.