Deoxyribonucleic Acid Relatedness Among Selected Strains of Mycobacterium tuberculosis, Mycobacterium bovis, Mycobacterium bovis BCG, Mycobacterium microti, and Mycobacterium africanum

Deoxyribonucleic acids (DNAs) of selected strains of the Mycobacterium tuberculosis complex, including strains of M. tuberculosis, Mycobacterium bovis, M. bovis BCG, Mycobacterium microti, and Mycobacterium africanum, were isolated and analyzed spectrophotometrically. The genome molecular weight and the guanine-plus-cytosine content of the DNA samples were approximately 1.9 × 109and 62.9 mol%, respectively. DNA relatedness among the strains was studied by both spectrophometric DNA hybridization and restriction endonuclease cleavage methods. All strains of the four species showed more than 90% DNA relatedness, except for slightly lower levels (85 to 89%) of relatedness between M. microti and some strains of M. bovis, M. bovis BCG, or M. africanum. The distribution patterns of the DNA fragments produced with restriction enzymes, such as EcoRI, EcoRV, BglII, BclI, and KpnI, were indistinguishable upon agarose gel electrophoresis. In contrast, the levels of DNA relatedness between M. tuberculosis and other slowly growing mycobacteria, including Mycobacterium nonchromogenicum, Mycobacterium intracellulare, Mycobacterium kansasii, Mycobacterium avium, Mycobacterium scrofulaceum, Mycobacterium haemophilum, Mycobacterium marinum, and Mycobacterium asiaticum, were significantly heterogeneous, ranging from 9 to 53%. My data indicate the extremely close evolutionary relationship among four species of the M. tuberculosis complex.