General Information: It was derived from an AIDS patient and has been characterized for virulence in the murine model of low-dose aerosol infection in that it could colonize the lung, proliferate within the tissue and disseminate to other organs. Environmental organism which causes infections in birds and humans. This genus comprises a number of Gram-positive, acid-fast, rod-shaped aerobic bacteria and is the only member of the family Mycobacteriaceae within the order Actinomycetales. Like other closely related Actinomycetales, such as Nocardia and Corynebacterium, Mycobacteria have unusually high genomic DNA GC content and are capable of producing mycolic acids as major components of their cell wall. Mycobacterium avium is ubiquitous in the environment, and can be found in stagnant waters and soils. This organism causes tuberculosis in birds and disseminated infections in immunocompromized humans (the elderly, children, and especially patients with AIDS). Infection results in a characteristic pulmonary disease which requires expensive drug therapy for successful treatment. Most prevalent colony morphotypes are smooth opaque, smooth transparent and rough, with the last two being the faster growers in vivo.