According to Todar, M. tuberculosis is a fairly large nonmotile rod-shaped bacterium distantly related to the Actinomycetes. The rods are 2-4 micrometers in length and 0.2-0.5 um in width. Many non-pathogenic mycobacteria are components of the normal flora of humans, found most often in dry and oily locations. M. tuberculosis is an obligate aerobe. For this reason, in the classic case of tuberculosis, MTB complexes are always found in the well-aerated upper lobes of the lungs. The bacterium is a facultative intracellular parasite, usually of macrophages, and has a slow generation time, 15-20 hours, and a physiological characteristic that may contribute to its virulence. Todar also states that the cell wall structure of M. tuberculosis deserves special
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