Diseases caused by mycobacteria, a diffuse group of acid-fast, rod-shaped bacteria in the genus Mycobacterium. Some mycobacteria are saprophytes, while others can cause disease in humans. The two most important species are M. tuberculosis (the cause of tuberculosis) and M. leprae (the cause of leprosy); other species have been called by several names, particularly the atypical mycobacteria or the nontuberculous mycobacteria. Tuberculosis These bacteria are classified according to their pigment formation, rate of growth, and colony morphology. The most commonly involved disease site is the lungs. Nontuberculous mycobacteria are transmitted from natural sources in the environment, rather than from person to person, and thus are not a public health hazard. Nontuberculous mycobacteria have been cultured from various environmental sources. The diagnosis of disease caused by nontuberculous mycobacteria can be difficult, since colonization or contamination of specimens may be present rather than true infection. Pulmonary disease resembling tuberculosis is a most important manifestation of disease caused by nontuberculous mycobacteria. The symptoms and chest x-ray findings are similar to those seen in tuberculosis. Mycobacterium kansasii and M. avium intracellulare are the most common pathogens. The disease usually occurs in middle-aged men and women with some type of chronic coexisting lung disease. The pathogenic mechanisms are obscure. Pulmonary infections due to M. kansasii can be treated successfully with chemotherapy. The treatment of pulmonary infections due to M. avium intracellulare complex is difficult. Chronic infection involving joints and bones, bursae, synovia, and tendon sheaths can be caused by various species. Localized abscesses due to M. fortuitum or M. chelonei can occur after trauma, after surgical incision, or at injection sites. The usual treatment is surgical incision. The most common soft tissue infection is caused by M. marinum, which may be introduced, following an abrasion or trauma, from handling fish or fish tanks, or around a swimming pool. Treatment is surgical. Mycobacterium ulcerans causes a destructive skin infection in tropical areas of the world. It is treated by wide excision and skin grafting. Disseminated M. avium intracellulare is one of the opportunistic infections seen in the acquired immune deficiency syndrome (AIDS). In individuals with AIDS, the organism has been cultured from lung, brain, cerebrospinal fluid, liver, spleen, intestinal mucosa, and bone marrow. No treatment has yet been effective in this setting. Acquired immune deficiency syndrome (AIDS) | 
