The key difference between colonization and infection is that colonization is the process of establishment of the microbe in the body tissues while infection is the process of invading body tissues by the microbe to cause the symptoms of the disease.
The pathogenicity of microbes is a complete biochemical and structural process which is defined by the complete mechanism in which the microorganism causes the disease. For example, the pathogenicity of bacteria may be associated with different components of the bacterial cell such as capsule, fimbriae, lipopolysaccharides (LPS) and other cell wall components. We can also associate it with the active secretion of substances that damage the host tissues or protect the bacteria from host defenses. Colonization and infection are two terms in microbial pathogenicity. The first stage of the microbial pathogenicity is colonization. It is known as the correct establishment of the pathogen in the host tissues. On the contrary, infection is the invasion of body tissues by the pathogen to cause the disease.
CONTENTS
1. Overview and Key Difference
2. What is Colonization
3. What is Infection
4. Similarities Between Colonization and Infection
5. Side by Side Comparison – Colonization vs Infection in Tabular Form
6. Summary
What is Colonization?
This is the first step of the microbial and pathogen colonization. It is the correct establishment of the pathogen at the right portal of entry of the host. The pathogen is normally colonized with the host tissues that are in contact with the external environment. The portal of entries in humans are urogenital tract, digestive tract, respiratory tract, skin, and conjunctiva. The usual organisms that colonize these regions have tissue adherence mechanisms. These adherence mechanisms have the ability to overcome and withstand the constant pressure that is expressed by the host defenses. It can be simply explained by the adherence mechanism that is shown by the bacteria when attaching to the mucosal surfaces in humans.
Figure 01: Colonization of a Pathogen
The bacterial attachment to the eukaryotic surfaces needs two factors, namely receptor and a ligand. The receptors are usually carbohydrates or peptides residues that reside on the eukaryotic cell surface. Bacterial ligands are called as adhesions. It is typically a macromolecular component of the bacterial cell surface. The adhesions are interacting with the host cell receptors. The adhesions and the host cell receptors normally interact in a specific complementary fashion. This specificity is comparable to the type of relationship between enzyme and substrate or antibody and antigen. Moreover, some ligands in bacteria are described as, Type 1 fimbriae, Type 4 pili, S-layer, Glycocalyx, capsule, lipopolysaccharide (LPS), teichoic acid and lipoteichoic acid (LTA).
What is Infection?
Infection is the invasion of body tissues by infectious agents such as bacteria, viruses, their multiplication and the collective responses by the hosts to particular infectious factors or toxins. Communicable diseases and transmissible diseases are alternative names for infectious diseases. Hosts like humans can overcome infections by using their innate and adaptive immune systems. The innate immune system consists of cells like dendritic cells, neutrophils, mast cells and macrophages that can fight infections. Moreover, receptors like TLR’S (Toll-like receptors) in the innate immune system easily recognize the infectious agents. Bactericides like lysosomes enzymes are highly important in the innate immune system.
In the case of the adaptive immune system, the antigen presenting cells (APS), B cells and T lymphocytes are collectively inducing antigen-antibody reactions to eliminate the infectious agents from the human body completely. However, the pathogen has varied mechanisms in order to overcome the innate and adaptive immune system of a human. In addition, pathogens have evading mechanisms like preventing from attaching to human macrophages and lysosomes. Also, pathogens produce toxins like endotoxins, enterotoxins, Shiga toxins, cytotoxins, heat-stable toxins, and heat-labile toxins. Some of the well-known bacteria like Salmonella, E-coli produce toxins in the successful infection process. Furthermore, a successful infection can only be raised by overcoming the complete molecular immune mechanisms of the hosts.
What are the Similarities Between Colonization and Infection?
- Colonization and infection are the main steps of the microbial pathogenicity.
- They work together to cause the disease.
- Moreover, both these steps are extremely important for the occurrence of the disease or symptoms.
- Both of them are equally important for pathogen multiplication.
What is the Difference Between Colonization and Infection?
Colonization is the process of establishment of the microbe in the body tissues. In contrast, infection is the invasion of body tissues by a pathogen, their multiplication and, the collective responses by the hosts to particular infectious factors or toxins of the pathogen. Adhesins like pili, fimbriae, and LPS are extremely important for colonization while infection does not need adhesions. Moreover, The cell receptors are important in attaching to the pathogen for a successful colonization process; however, the cell receptors are not important for infection.
Another difference between colonization and infection is their toxin production. Colonization does not produce toxins whereas infection does. Furthermore, the former does not cause a disease or symptoms whereas the latter does. Another difference between colonization and infection is acute inflammation. Colonization does not cause acute inflammations or harming the host whereas infections cause acute inflammations and harm the host tissues.
Summary – Colonization vs Infection
The pathogenicity in cases of bacteria is associated with different components of the bacterial cell such as capsule, fimbriae, lipopolysaccharides (LPS), pili and other cell wall components like teichoic acid, glycocalyx, etc. It can also be due to the active secretion of substances that damage the host tissues or protect the bacteria from host defenses. Colonization and infection are two main steps in microbial pathogenicity. The first stage of microbial pathogenicity is colonization. It is the correct establishment of the pathogen in the host tissues or right portal of entry of the host. On the contrary, infection is the invasion of body tissues by the pathogen to cause the disease. This is the difference between colonization and infection.
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Reference:
1. WI, Kenneth Todar Madison. Colonization and Invasion by Bacterial Pathogens, Available here.
2. “Infection.” Wikipedia, Wikimedia Foundation, 18 Nov. 2017, Available here.
Image Courtesy:
1.’Pathogenic Infection’By Uhelskie – Own work, (CC BY-SA 4.0) via Commons Wikimedia
2.’Chain of Infection’ By Julesmcn – By Genieieiop – Own work (CC BY-SA 4.0) via Commons Wikimedia
