Ultrastructure of Mycobacterium leprae and other acid-fast bacteria as influenced by fixation conditions.

A procedure using aldehydes, OsO4, Ca++ and uranyl acetate was selected for study of the fixation of Mycobacterium leprae in skin biopsies of leprosy patients. The ultrastructural pattern of recognized normal M. leprae cells fixed by the above procedure was characterized, and was found to be similar to that of other acid-fast bacteria fixed by the same procedure, except for the geometry of the membrane profile. Under such fixation conditions, this profile is always asymmetric in in vitro-cultured normal Nocardia asteroides, M. aurum and M. tuberculosis, whereas in skin biopsies no M. leprae cells with asymmetric membranes have been found so far. The implications of this observation for the interpretation of the ultrastructure of damaged M. leprae cells found in skin biopsies are discussed.