Noun | 1. | mycobacterium - rod-shaped bacteria some saprophytic or causing diseases eubacteria, eubacterium, true bacteria - a large group of bacteria having rigid cell walls; motile types have flagella genus Mycobacterium - nonmotile Gram-positive aerobic bacteria Mycobacterium tuberculosis, tubercle bacillus - cause of tuberculosis leprosy bacillus, Mycobacterium leprae - cause of leprosy |