The Cell Structure of Mycobacterium tuberculosis

Welcome back! 

As you already know Mycobacterium tuberculosis is the causative agent of tuberculosis. But did you ever researched this bacterium and get to know what its what it looks like and its properties? 

Mycobacterium tuberculosis, the causative agent of tuberculosis, is characterized by a rod-shaped bacterium, ranging in 2-4 micrometers in length by 0.2-0.5 micrometers in width. The bacterium has neither cilia, pili, or flagella and hence non- motile. 

Pictured above is Mycobacterium tuberculosis. The shape of this bacteria is rod-shaped or bacillus.

http://blogs.nature.com/freeassociation/2017/04/mutation-rates-of-mycobacterium-tuberculosis-from-the-archives-2013.html

Mycobacterium tuberculosis is a unicellular bacteria meaning that its cell structure is much simpler than those of multicellular bacteria. For example, unicellular bacteria do not have a nucleus or membrane-bound organelles. 

The H37Rv strain best characterizes the genome of Mycobacterium tuberculosis. It is sized at over 4 million base pairs with approximately 4,000 genes. There are plasmids present in M. tuberculosis which are small circular pieces of DNA. The genes in the plasmids can be given to the bacteria providing it with some genetic advantages. In the case of M. tuberculosis, plasmids are essential in transferring virulence because the genes on the plasmids are easier to transferred than those on the chromosomes. Furthermore, an 18 kb plasmid in M. tuberculosis H37Rv strain was confirmed to conduct gene transfer.  

The cell structure of M. tuberculosis is the most distinguishable structure among other prokaryotes. The cell wall complex consists of peptidoglycan, and 60% of the cell wall is lipids. The lipid portion of the cell wall has three major components: mycolic acids, cord factor, and wax-D. Mycolic acids are strong hydrophobic molecules that can arrange a lipid shell and affect permeability properties at the cell surface. The cord factor is a glycolipid which causes the cells to grow in serpentine cords and the wax- D is believed to be the part of M. tuberculosis that activates the immune system. The high concentration of lipids in the cell wall of Mycobacterium tuberculosis plays a part in the resistance to many antibiotics. 

Pictured above is the cell structure of Mycobacterium tuberculosis. 

https://www.researchgate.net/figure/The-structure-of-the-Mycobacterium-tuberculosis-cell-wall-This-figure-shows-a-schematic_fig1_51156793 

M. tuberculosis is not considered Gram- positive or Gram- negative because it does not have the chemical characteristics to be considered either one. If a Gram- stain is performed, it will stains very weakly Gram-positive or not at all. The lipid layer is impermeable to stains and dyes. Instead, M. tuberculosis is classified as acid-fast bacteria.  The Ziehl- Neelsen stain, an acid-fast staining method, can be used on  M. tuberculosis. When performing this method, the smear is fixed, stained with carbol- fuchsin (a pink dye), and decolorized with acid- alcohol. The smear is counterstained with methylene- blue and resulting in a pink bacterium. 

 

Pictured above is the Ziehl- Neelsen stain. As you can see the bacterium are stained pink. 

https://en.wikipedia.org/wiki/Ziehl%E2%80%93Neelsen_stain

Here is a quick animated video about Mycobacterium tuberculosis and TB. 

 

That’s it for the cell structure of Mycobacteria tuberculosis. Next time, we will discuss the life cycle of Mycobacteria tuberculosis.

 

Citations: 

http://textbookofbacteriology.net/tuberculosis.html

http://shodhganga.inflibnet.ac.in/bitstream/10603/24556/7/07_chapter%202.pdf

https://microbewiki.kenyon.edu/index.php/Mycobacterium_tuberculosis

https://www.nature.com/articles/31159

http://www.austincc.edu/microbio/2704w/mt1.htm