Virulence Factors or Factors Responsible for Pathogenicity of a Pathogens

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What is virulence factors?

Virulence factors define the intensity of a pathogen to cause disease. The Virulence factors varies among different microbial species. Virulence enables the microorganism to carry a specific character which can damage the tissue of the host cell. Virulence helps the microorganism to better survive its residency in the host.

Before we know about the virulence factors first of all we need to know how a pathogen infects a host or how pathogenicity of a pathogen works. During infection, a pathogen follows these following steps;

1 Adherence and Colonization

In this step, pathogen gets attached to the host cell surface.

2. Invasion

Enter into the host cell cytoplasm and started to multiply.

3 Toxin Synthesis

Synthesis of different types of Toxins that alter the function of the host.

For More detail study about the Mechanism of Infection Follow My Previous Article, “What is Infection?“, here i have already discussed this points in detail.

virulence factor of pathogen

There are present different factors which determine the virulence or pathogenicity of a pathogen, such as;

1. Capsule

Capsule play an vital role in the pathogenicity of a pathogen. Capsules surround many bacterial cells that protect the bacteria from the immune and phagocytic response.

Capsule inhibits phagocytosis by preventing interaction between antibody and C3 bond to the outer membrane of the bacterial capsule also help in the attachment of the host cell.

2. Adherence and Colonization

The first and most important step of an infectious disease process is the entrance and attachment of a pathogen to a host body. Its one of the most important virulence factors.

Some of the pathogens are entering the host body through the skin, respiratory system, gastrointestinal system, conjunctiva of the eye. There are other pathogens which can enter the host body by sexual contact, needle sticks, blood transfusion, and organ transplant.

The pathogenicity of many microorganisms depends on the ability to addhere with the mucosal cell as a first step. With the help of the adhesion factor, many bacteria adhere to the epithelial cell line of the blunder intestine and blood vessel.

There are present several factors that help in the adhesion of a pathogen to the host surface these factors are known as adhesion factors, such as the surface like structure a pill, lipopolysaccharide side Chain, and M protein of Streptococcus progenies.

3. Invasion

The pathogenicity depends on the infectivity and invasiveness of a pathogen. Infectivity refers to the ability of pathogens to establish a discrete focal point of infection. The invasiveness refers to the ability of the pathogen to spread to adjacent or other tissues.

Invasiveness is a multifactorial and complex process. Invasive bacteria either destroy the cell wall or penetrate the cells of the barrier. A pathogen can penetrate the host mucosa membrane by two methods, such as;

  1. Actively penetrate
  2. Passively penetrate

A. Actively penetrate

A pathogen accomplished her active penetration through the production of a lytic substance that alters the host tissue. This produced substance can alter the tissue function by this following process

  • By attacking the extracellular matrix and basement membranes of integuments and intestinal linings.
  • degrading carbohydrate-protein complexes between cells or on the cell surface (the glycocalyx).
  • disrupting the host cell surface.

B. Passively penetrate

Passive mechanisms of penetration are not related to the pathogen itself. Examples include

  • wounds, abrasions, or burns on the skin’s surface;
  • arthropod vectors that create small wounds while feeding; and
  • tissue damage caused by other organisms (e.g., a dog bite).

Once the pathogen can penetrate to the mucosa membrane, it penetrates to the deeper tissue and continuities disseminating throughout the body of the host.

4. Co-enzyme

Many bacteria release enzyme that can damage hostess in a variety of machines such as;

  1. The pathogen will release some enzyme which will help to break down the collagen and fibrin, which help in the beta penetration of microorganisms in the tissue.
  2. They will release a few enzymes (Proteases, etc) that will help in the background of cellular material.
  3. Pathogens will release enzymes which will modify and inactivate the antibiotics. For example, beta-lactamase hydrolyze the beta lectum ring in the beta-lactam cross of antibiotic and inactive at the antibiotic.

5. Toxins

The virulence factors of a pathogen also depends on the toxin production by the pathogen. After entering the host cell, the microorganism started to synthesize different types of toxins which will alter the normal functions of the host body cell. Bacterial toxins directly harm tissues or Trigger destructive biological activities. There are present different types of toxins such as Exotoxin and Endotoxin.

All these virulence factors are responsible for the pathogenicity of a pathogen. The pathogenicity varies in different species of pathogens.


  • Prescott’s Microbiology by Joanne Willey (Author), Linda Sherwood (Author), Christopher J. Woolverton (Author)
  • Microbiology Principles and Explorations by Jacquelyn and Laura Black
  • wikipedia,”Virulence factors

Writer and Founder of I am from India and my main purpose is to provide you a strong understanding of Microbiology. shares notes related to different branches of microbiology.

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