Shape variation in Mycobacterium tuberculosis

Over several decades, morphological variation of Mycobacterium tuberculosis (M. tuberculosis) has engaged the attention of numerous investigators. The single point on which all investigators have agreed is that tubercle bacillus does not always manifest itself in the classical rod shape. While most commonly the organism appears as a granular rod, the other forms i.e., coccid, filament and club shapes are also present. Aside from the more purely academic aspect of the subject, the possible significance of variant forms in the etiology, prognosis, and control of tuberculosis infection were objects of heated controversies, even before 1900. These differences have never been resolved, and have been ignored by most recent workers. The main questions were centered on the following points: (1) Dose the tubercle bacillus produce endospore? (2) Does it normally undergo a complicated life cycle? (3) What is the importance of the non-acid-fast forms? (4) And what happens to the bacteria during latent infection? Today, based on various in-vitro and in-vivo models, the researchers agreed to consider M. tuberculosis as a two-phase microorganism which can appear either in its metabolically active acid-fast or in its inactive forms. It is the purpose of this chapter to review and discuss morphological variation and its challenges in M. tuberculosis. Furthermore, the cell shape and cell division were illustrated using atomic force microscopy. The present information will discuss the adaptation mechanism in M. tuberculosis and may help scientists to identify targets for novel therapies