We how bacteria and viruses are able to

We will discuss what virulence means and get a working definition of virulence factors. We are going to explore different virulence factors that are used and how they affect our bodies.

What are Virulence Factors?

Have you ever wondered how bacteria and viruses are able to just make their way into our bodies and wreak havoc? We obviously didn’t invite them in, and wouldn’t allow them in if we had a choice. So, how do these pathogens get in and set up shop in our bodies? The answer to that question is virulence factors.

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Let’s break this term down. Virulence refers to the ability of a pathogen to cause a disease process to occur in our bodies. Virulence factors are the different agents used by the pathogen to sneak the disease into our system. They give them access into our bodies and allow them to establish a place to reside.

Examples of Virulence Factors

Let’s look at some of the factors used to start and maintain the disease process. The first thing the pathogen has to do is get into the tissues of the body and/or bloodstream. Invasion enzymes are the virulence factors that allow this to happen.

Hyaluronidase is an enzyme that dissolves hyaluronic acid, which is the substance that glues the cells together that make up the tissues of your body. This makes the tissues separate and allows the pathogen a way to penetrate into the different tissue layers. This virulence factor is utilized by Streptococcus pyogenes.

Fibrinolytic enzyme is another invasion enzyme. The immune system forms clots to trap pathogens and repair tissues when pathogens are trying to penetrate them. Fibrinolytic enzyme breaks apart the fibrin, preventing the clots from staying together.

This allows the pathogen to escape and gain further access to the tissues. Streptokinase is a fibrinolytic enzyme that is used by some species of strep bacteria.Other virulence factors allow the pathogen to stick to the tissues or membranes of the body once they have invaded and are in the desired location. Adhesins are proteins that are able to attach to the receptors on the surface of the tissues and membranes in the body. These are used by most pathogens, especially bacteria. One example of a bacteria that uses adhesins is Neisseria gonorrhoeae.

Glycocalyx is a capsule that will surround bacteria to help them avoid the immune system and to adhere to the body’s membranes. The capsule is made up of polysaccharide, which is a substance that we normally have in our bodies. Since they are surrounded by something that is not seen as foreign, it makes them invisible to the immune system. Polysaccharide is also able to stick to the membranes. Glycocalyx are used by many species of bacteria. It has been well established that it is used by Streptococcus pneumoniae.

There are toxins that also help to make bacteria more virulent. Some toxins are released outside of the cell, and these are known as exotoxins. Other toxins are only released when the bacterial cell splits apart, and these are known as endotoxins. One exotoxin is necrotoxin. This is used by certain species of strep bacteria. Necrotoxin is able to cause tissue death and results in the ‘flesh-eating disease.

Lipopolysaccharide or LPS is an endotoxin that is a part of the cell wall of gram-negative bacteria. It is able to cause fever and inflammation to occur in our body’s tissues.

Lesson Summary

In this lesson, we learned that virulence factors are what pathogens use to cause a disease to develop in your body.

They allow the pathogens a way to get into the tissues and/or bloodstream, attach themselves to the membranes in the body, and escape the immune system of our bodies. They also cause fever and tissue damage in the body. Some examples of virulence factors include: hyaluronidase, streptokinase, LPS, necrotoxin, adhesins and glycocalyx.


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