Life Cycle of Mycobacterium Tuberculosis

In this week’s post, we’ll be discovering how M. tuberculosis bacteria grow and thrive in our bodies and ultimately cause infection. 

Highly pathogenic species such as M. tuberculosis are slow growing mycobacteria. Specifically, the generation time for M. tuberculosis is between 15 to 20 hours or 900 to 1200 min (Ozimek, 2003). Because M. tuberculosis has an extremely slow growth rate and has the tendency to clump together in liquid growth media, it is much more difficult to study its bacterial growth by traditional methods used for other bacteria (Groll et al., 2010).  

M. tuberculosis generation time

Additionally, M. tuberculosis bacteria are heterotrophs and strict aerobes. These bacteria are metabolically adaptable organisms, as they can grow on a variety of components such as carbohydrates, alcohols, organic acids, and much more (Mycobacterium). Uniquely, once M. tuberculosis infects macrophages in culture or in animal models, the bacteria reorients its metabolism in response to the brand new environments it comes across (Abramovitch et al., 2010).

Via Meme Generator

Metabolic pathways of M. tuberculosis 

For pathogenic bacteria like M. tuberculosis to thrive and cause disease in us, the bacteria must compete for its supply of iron within our bodies. M. tuberculosis depends on iron for normal growth but is limited to the metal due to its low solubility at biological pH and because we don’t like to share it with bacteria! Iron is an incredibly essential nutrient for a plethora of aerobic bacteria like M. tuberculosis because it plays a critical role in electron transport, specifically in oxidation and reduction reactions (Sritharan, 2016).    

Transport of Iron in M. tuberculosis 

Binary Fission of M. Tuberculosis 

Via gyfcat

Furthermore, binary fission is the process in which bacteria divide and form two new identical daughter cells. The diagram below depicts all the steps in detail of binary fission. 

Bacterial Binary Fission 

M. tuberculosis bacteria divide through binary fission but the process is a little bit more unique. The bacteria produces cells with a new pole closer to the invagination and an old pole further away from the invagination. Primarily, all cell divisions in rod-shaped bacteria are unsymmetrical, meaning that one daughter cell inherits the new pole from a preceding division and the other daughter cell inherits the old pole. In M. tuberculosis, bacterial cells more favorably grow at the old pole. The daughter cells that inherit the old pole are deemed accelerators and those inheriting the new pole are called alternators. Interestingly, alternators have to form a new growth pole to proceed  with elongation (Aakre & Laub, 2012).

      Binary Fission in M. Tuberculosis 

M. tuberculosis growth in Lab

M. tuberculosis is non-motile, non-spore forming, and a strict aerobic pathogenic bacteria. It grows inside the phagocytic vacuoles of macrophages, where it experiences a moderately acidic and nutrient-restricted environment (Buchmeier et al., 2000). As for laboratory conditions, the most advantageous growth temperature for M. tuberculosis is between 33 to 32°C. The typical temperature for isolation of M. tuberculosis is between 36 to 37°C (Martin, 2019). In addition, the bacteria grows more favorably in liquid mediums as opposed to solid egg-based or solid agar-based growth mediums (11). High levels of magnesium ion are integrated within growth media to ensure that M. tuberculosis has a mildly acidic environment ( pH between 6-6.5) to thrive in (Buchmeier et al., 2000). To emphasize, using culture to test for Tuberculosis can take weeks because of the slow growth of M. tuberculosis.  

Colonies of M. tuberculosis growth on a culture plate 

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