Comparative Studies of the Cell Structures of Mycobacterium leprae and M. tuberculosis Using the Electron Microscopy Freeze-Substitution Technique

The cell envelope and cytoplasmic architecture of the Mycobacterium leprae Thai‐53 strain were examined using the freeze‐substitution technique of electron microscopy and compared with those of the M. tuberculosis H37Rv strain. Both strains had similarly multilayered envelope architectures composed of an electron‐translucent layer, a peptidoglycan layer and the plasma membrane, from outside to inside. A comparison of the structures of these two mycobacteria revealed that the M. leprae cell was smaller in size and had a thinner peptidoglycan layer than the M. tuberculosis cell. The cell widths measured on electron micrographs were 0.44 μm for M. tuberculosis and 0.38 μm for M. leprae. The peptidoglycan layer of M. leprae was 4–5 nm, while the corresponding layer of M. tuberculosis was 10–15 nm.