Mycobacterium avium complex

noun

Mycobacterium avi·​um complex -ˈā-vē-əm-, -ˈä- 

: two bacteria of the genus Mycobacterium (M. avium and M. intracellulare) that account for most mycobacterial infections in humans other than tuberculosis, that usually affect the lungs but may involve the lymph nodes, bones, joints, and skin, and that may cause disseminated disease in immunosuppressed conditions (as AIDS)

—abbreviation MAC