Bacteria are single-celled organisms that can be found almost everywhere on Earth.
As they are so small and abundant, they are constantly exposed to threats from their environment, including attacks from predators like phagocytes.
However, bacteria have developed various structures and mechanisms to protect themselves from being phagocytized.
We will explore one such structure that bacteria use to evade the immune system and survive in their natural habitats.
Specifically, we will discuss how capsule formation helps protect bacteria from being phagocytized.
Which structure protects bacteria from being phagocytized by white blood cells?
One of the ways that the human body defends itself against bacterial infections is through the process of phagocytosis.
Phagocytosis involves the engulfment and destruction of bacteria by specialized immune cells called phagocytes.
But some bacteria have developed structures that allow them to evade phagocytosis and persist in the human body.
One such structure is the capsule, a protective layer that surrounds the bacterial cell.
Understanding the mechanisms by which bacteria can evade phagocytosis is an important area of research because it can lead to the development of new treatments for bacterial infections.
Researchers, for example, may be able to create drugs that disrupt the capsule and make bacteria more vulnerable to phagocytosis.
What is a bacterial capsule?
Bacterial capsules are a common feature of many bacterial species and they are composed of a variety of different molecules, including polysaccharides, proteins, and lipids.
The exact composition of the capsule can vary between bacterial species and the capsule itself can also vary in thickness and density.
Regardless of its composition or thickness, the capsule plays a critical role in protecting bacteria from phagocytosis.
The capsule is an important structure that allows bacteria to avoid detection by the human immune system and survive in the body.
What are encapsulated bacteria?
The capsule is encapsulated bacteria and acts as a physical barrier between the bacterial cell and the immune system.
When a bacterium is engulfed by a phagocyte, the phagocyte attempts to destroy the bacterium by engulfing it and subjecting it to a range of toxic substances.
However, if the bacterium has a capsule, the capsule can prevent the phagocyte from being able to effectively engulf the bacterium.
This is because the capsule makes the bacterial cell more slippery and difficult for the phagocyte to grab onto.
In addition, the capsule can also block the phagocyte’s receptors which are the molecules that allow the phagocyte to recognize and engulf the bacterium.
What is the function of the bacterial capsule?
In addition to acting as a physical barrier, the capsule can also interfere with the immune system in other ways.
For example, some capsules contain molecules that are similar to molecules found in the human body.
This can cause the immune system to mistakenly recognize the bacterium as a self-molecule and ignore it.
Even some capsules can interfere with the signaling pathways that are activated during phagocytosis.
This can prevent the phagocyte from being able to effectively communicate with other immune cells and mount a coordinated response against the bacterium.
Difference between capsule and slime layer of bacteria
The capsule and slime layer are two types of extracellular polymeric substances (EPS) that surround bacterial cells. While they share some similarities, there are also some key differences between these two structures.
The capsule is a well-defined and tightly packed layer that surrounds the bacterial cell. This layer is made up of either polysaccharides or proteins and is firmly affixed to the cell wall.
It is normally more rigid and thicker than the slime layer and can be visualized under a microscope.
The capsule performs various crucial roles, such as shielding the bacterial cell from phagocytosis by the host’s immune system, affixing it to surfaces, and hindering desiccation.
In contrast to the capsule, the slime layer that encompasses the bacterial cell is more loosely arranged and consists of a blend of polysaccharides, proteins, and various other organic and inorganic molecules.
The slime layer is not as clearly defined as the capsule and is more susceptible to disruption by physical or chemical methods.
Under a microscope, the slime layer is frequently less noticeable than the capsule.
Nonetheless, the slime layer has significant roles to play, such as allowing the bacteria to move over surfaces, attaching to surfaces, and shielding the bacterial cell from desiccation.
To differentiate between the capsule and slime layer, it’s worth noting that the capsule is manufactured by numerous pathogenic bacteria, while the slime layer is more frequently produced by non-pathogenic bacteria.
The rationale behind this is that the capsule plays an essential part in defending bacteria from the host immune system, which is especially crucial for pathogenic bacteria that require extended persistence within a host to elicit a disease response.
Capsule bacteria example
- Streptococcus pneumoniae: commonly causes pneumonia, meningitis, and other infections in humans.
- Klebsiella pneumoniae: commonly found in the human gut. K. pneumoniae can cause a range of infections, including pneumonia, urinary tract infections, and sepsis.
- Bacillus anthracis: causes anthrax, a serious infectious disease that can affect humans and animals. The capsule of B. anthracis is composed of a protein called poly-D-glutamic acid
- Neisseria meningitides: cause meningitis and sepsis in humans.
- Haemophilus influenza: can cause a range of infections, including pneumonia, meningitis, and sepsis.
By understanding how bacteria are able to evade the immune system, we can develop new ways to combat bacterial infections and improve human health.
Last Updated on May 24, 2023 by Our Editorial Team