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A genus of gram-positive, aerobic bacteria. Most species are free-living in soil and water, but the major habitat for some is the diseased tissue of warm-blooded hosts.

A genus of Mycobacteriaceae, which includes many organisms usually denominated Bacillus, such as those of tuberculosis, leprosy, diphtheria, influenza, glanders, etc.

A genus of the bacteria, consisting of short rods, often bent, swollen and clavate, which at times show Y-shaped or true branching forms. According to the authorities on determinative bacteriology, this genus includes the organism of tuberculosis, of leprosy, and of diphtheria, as well as other bacteria.