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What is Fimbriae?

Most bacterial organisms have certain external appendages, especially the ones that have a cell wall structure that is gram-negative. These appendages are the delicate protein strands that extend beyond the cell wall surface. There are different forms of these external structures and these include the flagella, the fimbriae, and the sex pili.

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The fimbriae are defined as the shorter versions of these extensions that enable the bacterial cells to adhere to different surfaces of the host and hence cause an infection in the areas. While the flagella are used for movement purposes and the sex pili help in the process of reproduction of bacterial cells, the fimbriae are responsible for providing the means of attaching the bacterial cells to the host cells.

What is Fimbriae?

The fimbriae are also known as short attachment pili. This name is used due to the function of the fimbriae that is to attach the bacterial cells to different host surfaces. The actions of the fimbriae actually help the bacteria in sticking to things and hence causing infections. These fimbriae are mostly present all over the surface and are more concentrated towards the poles of the cell. Most of the species of aerobic bacteria tend to use the fimbriae in order to attach themselves to different surfaces. This structure allows the bacteria to properly colonize near the air and the cells can also achieve some nutrients from the air. Most of the bacterial cells that are gram-negative might have these projections. However, in the case of gram-positive bacteria, there are no fimbriae present.

Some Physical Characteristics of Fimbriae

  • The fimbriae resemble the structure of hair and are filamentous appendages that exist on the cells of bacteria.

  • There are more than 1000 fimbriae that are present on the bacterial cell surface. It is possible to see these fimbriae by using the electron microscope.

  • The fimbriae are comparatively shorter than both the sex pili and the flagella. The fimbriae are about 0.5 𝝁m in length and about 10 nm in thickness.

  • The origin of the fimbriae is from the cytoplasmic membrane. Hence, the fimbriae are present in both the non-motile as well as motile cells.

  • The composition of fimbriae in bacteria is from a protein that is helically arranged and is known as pilin. The aggregation of pilin results in the creation of the slender tubes of both the fimbriae and the sex pili.

  • Fimbriae tend to be antigenic in nature and hence bacteria belonging to different genera can be included in this group.

What is Fimbriae Function?

The bacteria that contain fimbriae are known as fimbriae bacteria. These projections have certain adhesive properties that tend to help the bacteria when they need to attach themselves to any organism. The fimbriae also have an important role to play in the agglutination of certain blood cells such as leukocytes, erythrocytes as well as epithelial cells.

A primary fimbriae function is associated with the antigenic properties that they have. These properties allow the fimbriae to act as certain thermolabile nonspecific agglutinogens. The fimbriae also have a very pivotal role in metabolic activity. The cells that contain the fimbriae tend to have a higher rate of metabolism than the ones that don’t have the fimbriae. Also, fimbriae in bacteria can act as aggregation organelles.

​How Fimbriae Help Bacteria Cause Disease

The fimbriae are considered as the primal factor for the ability that bacterial cells have to cause certain diseases. The fimbriae structure enables the bacteria to colonize certain epithelial cells in the organisms. There are special proteins provided in the ends of the fimbriae that are known as adhesins. These adhesins tend to allow the fimbriae bacteria to properly attach themselves to the cells of the host through a process known as docking. The procedure is mostly similar to a lock and key. The receptor proteins present in the fimbriae will be attached to the surface of the epithelial cells.

This can cause various diseases via the mucous membrane in the organisms. Some of the common examples of diseases caused due to fimbriae are bacterial meningitis, gonorrhea, and certain other infections.

According to the anatomy of fimbriae, these are the constituents of the bacterial cells and they help in the colonizing of these cells which can lead to different diseases in human beings as well as other organisms. One of the main properties present in the fimbriae of bacteria is the ability to adhere to the host cells. This is one of the main reasons why the fimbriae bacteria are more capable of spreading the diseases than the bacteria that don’t contain the fimbriae. Some of the common examples of bacteria that contain fimbriae are E. coli and staphylococcus bacteria.

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FAQs on Fimbriae

1. What is the difference between pili and fimbriae? 

Both the fimbriae and the pili are important protein-filled filaments that originate from the membrane of the bacterial cell and are extended in an outward direction. However, there are differences in the functions and the size of the filaments. For example, when compared to the flagella of the bacterial cells, both of them are shorter. However, the pili tend to have a longer size than the fimbriae. Apart from that, the appearance of the fimbriae is mostly bristle-like while the pili have a hair-like appearance. The pili act as the agents for DNA transfer and fimbriae help in the adhesion of the bacterial cells to the host cells.

2. What role do fimbriae play in the causing of diseases?

The diseases that are caused by the fimbriae bacteria are some of the most common examples in the clinical field. One major function of the fimbriae is to suppress the immune booster present in the body of the host by adhering the bacterial cells to the mucous membrane that is found in the organisms. There are certain receptor proteins present in the fimbriae that also tend to affect the other blood cells of the organisms. So, the fimbriae can be considered a very important component of the bacterial cells. With the use of fimbriae, the bacterial cells will not be able to adhere to the surface of the host cells and hence will not be able to cause any infectious diseases in the organisms.

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