text: Mycobacterium avium complex is a group of mycobacteria comprising Mycobacterium intracellulare and Mycobacterium avium that are commonly grouped because they infect humans together; this group, in turn, is part of the group of nontuberculous mycobacteria.  These bacteria cause Mycobacterium avium-intracellulare infections or Mycobacterium avium complex infections in humans. These bacteria are common and are found in fresh and salt water, in household dust and in soil. MAC bacteria usually cause infection in those who are immunocompromised or those with severe lung disease.
  Description
  In the Runyon classification, both bacteria are nonchromogens.  They can be differentiated from M. tuberculosis and each other by commercially available DNA probes.
  They are characterized as Gram-positive, nonmotile, acid-fast, short to long rods.
  Colony characteristics
  Usually, colonies are smooth, rarely rough, and not pigmented colonies. Older colonies may become yellow.
  Physiology
  Growth on Löwenstein-Jensen medium and Middlebrook 7H10 agar occurs at 37°C after seven or more days.
  The complex can be (but is not often) resistant to isoniazid, ethambutol, rifampin, and streptomycin.
  Differential characteristics
  M. intracellulare and M. avium form the M. avium complex (MAC).
  Remarkable ITS heterogeneity is seen within different M. intracellulare isolates.
  Species
  Mycobacterium avium
  Mycobacterium avium subsp. paratuberculosis