What is the function of fimbriae and pili?

There are many organisms that exist on earth. Some are seen by the naked eyed, some may need tools such as a microscope to be seen. In the vast ecology and environment, all living organisms have a relationship with another organism. This creates an ideal environment for organisms to thrive and strive. Disruption in the balance of the ecosystem may lead to many problems related to medicine. In this article, we will know more about bacteria and the function of fimbriae and pili that bacteria have.

Bacteria is a small single-cell organism. This translates to bacteria as microbes with simpler structure compared to many other organisms. It exists in millions inside of an environment and is vital to the planet’s ecosystem. The only way to see bacteria is by using a microscope. While we may have heard bacteria are bad and harmful, some actually are beneficial for humans and play a role in human health. For example, probiotics such as Lactobacillus and Bifidobacterium aid in digestion and provide immunity. Bacteria that cause diseases in humans are usually bacteria that produce toxins, chemicals that induce cell damage, alter the body’s immune response and eventually lead to sickness. Some bacteria cause this reaction by directly invading and damaging the tissues.

Fimbriae and pili are appendages on the cell wall of bacteria. Cell wall is a coating that provides shape and viability of the bacteria. Both are thin protein tubes that originate from the cytoplasmic membrane (a barrier regulating solutes between cell and outer environment) of the bacteria and protrude from the surface of the bacteria. Fimbriae and pili have similar functions when exposed to the human body.

Fimbriae are tiny brush-like fibres from the surface of bacterial cells. It is shorter than pili and thin. It exists in both gram-positive and gram-negative bacteria. Around 200-400 fimbriae occur per bacteria cell. Fimbriae are less rigid. It does not have the ability for active motility. Fimbriae plays a role in formation of bacterial clusters. Function of fimbriae is as an attachment for the bacteria to attach on cells. Fimbriae allows bacteria to colonise cells or surfaces and resist flushing or cleaning mechanisms by the host.  For example, Shigella dysenteriae is an example of bacteria that form fimbriae. Fimbriae in this case help to attach the bacteria onto the surface of the small intestine.

Pili are fine hair-like fibres with thick structure made up of pilin. It is longer and thicker than fimbriae. It only exists in gram-negative bacteria. Pili is more rigid. Only 1-10 pili occur per bacterial cell. It aids in bacterial conjugation which is a way bacteria reproduce sexually by attachment of bacteria and transferring genes between bacteria. Some pili have receptors for certain viruses. Pili has the ability for active motility due to the presence of type IV pili producing twitching motility. Pili helps to attach the cells to the surface of the bacteria. For example, Neisseria gonorrhoeae use pili to attach itself to the urogenital and cervical epithelium.

Proteins associated with bacterial fimbriae and pili act as antigen. Antigen triggers the body’s immunity to react as antigen is a foreign substance. This will lead to the body producing antibodies to help remove or neutralise the microorganism and its toxin.

It can be concluded that fimbriae and pili have different structures but perform almost similar functions, which attach to tissue. Both have the ability to trigger the body’s immune system and cause reaction, which is known as inflammation signs and sickness. Knowing the differences and similarities of these structures helps healthcare providers and scientists to understand how disease can spread and affect humans. It also helps to understand more on treatment options.

Also read – Dengue prevention.

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