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The mycobacteria are rod-shaped, aerobic bacteria that do not form spores. Although they do not stain readily, after being stained, they resist decolorization by acid or alcohol and are therefore called “acid-fast” bacilli. Mycobacterium tuberculosis causes tuberculosis and is a very important pathogen of humans. Mycobacterium leprae causes leprosy. Mycobacterium avium-intracellulare (M avium complex, or MAC) and other nontuberculous mycobacteria (NTM) frequently infect patients with AIDS, are opportunistic pathogens in other immunocompromised persons, and occasionally cause disease in patients with normal immune systems. There are more than 200 Mycobacterium species, including many that are saprophytes. The mycobacteria that infect humans are listed in Table 23-1.

TABLE 23-1Mycobacteria That Infect Humans

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