n 1  cap  :  a genus of nonmotile acid-fast aerobic bacteria of the family Mycobacteriaceae that are usu. slender and difficult to stain and that include the causative agents of tuberculosis (M. tuberculosis) and leprosy (M. leprae) as well as numerous purely saprophytic forms  2  pl  -ria  :  any bacterium of the genus Mycobacterium or a closely related genus my*co*bac*te*ri*al adj 
 
 
 
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