Mycobacterium

Mycobacterium is the only genus in the family Mycobacteriaceae and includes more than 180 species. Based on the epidemiology and disease presentation, isolates of human relevance are divided into four major groups: Mycobacterium tuberculosis complex (MTBC), Mycobacterium leprae, Mycobacterium ulcerans, and the nontuberculous mycobacteria. In addition to MTBC, other slow-growing mycobacteria of human significance include the nontuberculous Mycobacterium avium complex (MAC), Mycobacterium kansasii, Mycobacterium haemophilum, and Mycobacterium marinum. MAC infections are common in middle-aged male smokers and postmenopausal females with bronchiectasis. The noncultivable nontuberculous mycobacteria include Mycobacterium leprae, which causes leprosy (Hansen's disease), a chronic granulomatous disease that usually manifests with anesthetic skin lesions and peripheral neuropathy. Mycobacterium leprae cannot be cultured in vitro, and thus, the diagnosis is primarily based on the clinical presentation and skin biopsy. The most frequently utilized immunodiagnostic test for the diagnosis of tuberculosis is the tuberculin skin test.