Difference Between Endotoxins and Exotoxins

The major difference between endotoxin and exotoxin lies in how bacteria produce these toxins. Endotoxins are produced by Gram-negative bacteria and exotoxins are produced by bacteria that release toxins into the surroundings. The toxins are toxic substances, including proteins, small molecules, and peptides, which cause disease upon contact with or absorption from body tissues.

The difference between endotoxin and exotoxin lies in their origins and how they affect the body. In this article, we will cover the difference between endotoxin and exotoxin in tabular form.

Endotoxins

Endotoxins are found in the outer membrane of bacteria. It is recommended as a cell-associated substance responsible for the structure of bacteria. Endotoxins are also known as lipopolysaccharides or LPS. LPS is found on the outer surface of Gram-negative bacteria. LPS is released when bacterial cells die.

Lipopolysaccharide causes multiple inflammations and activates complement via alternative pathways. When Gram-negative bacteria grow, small amounts of endotoxin are produced.

Endotoxin Function

The endotoxins have following functions:

• Gram-negative bacteria have lipopolysaccharides called endotoxins in their cell walls.
• They trigger the host immune response, leading to inflammation and potentially more severe immune reactions.
• Endotoxins can induce fever, hypotension (low blood pressure), and in severe cases, septic shock.
• They are potent activators of the innate immune system, particularly through the Toll-like receptor 4 (TLR4) pathway.
• Stimulate the release of pro-inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1), contributing to the overall inflammatory response.

Why Endotoxins are Harmful?

• Septic shock is an endotoxin-related illness. 
• This condition is distinguished by low blood pressure and restricted blood flow to vital organs such as the kidneys. 
• Endotoxins can also result in bleeding, shock, sepsis, bloody diarrhea, and fever. 

Endotoxin Examples

Some examples of bacteria releasing endotoxins and disease caused are:

• Salmonella typhi (causes typhoid fever)
• Vibrio cholerae (causes cholera)
• Escherichia coli (certain strains can cause severe food poisoning)
• Neisseria meningitidis (causes meningococcal meningitis)

Exotoxins

Exotoxin are protein or polypeptide. It acts on tissues away from the starting point of bacterial growth. Exotoxins are usually produced by bacteria or cellular action. It is released into the environment by bacteria.

Exotoxins are normally formed during bacterial cell growth. The production of toxins is characteristic of certain strains of disease-causing bacteria. For example, Corynebacterium diphtheria is responsible for producing diphtheria toxin and Clostridium tetani are responsible for producing tetanus toxin. These are virulent bacterial strains responsible for toxin production, whereas non-toxic strains are not responsible for such products at all. Exotoxins are considered the most dangerous and toxic substances.

Exotoxin Function

The exotoxins have following functions:

• Exotoxins target specific cells or tissues in the host organism.
• They can interfere with essential cellular processes, such as protein synthesis or cell signaling.
• Exotoxins may disrupt the host’s immune system, allowing the bacteria to evade detection and clearance.
• Some exotoxins can cause tissue damage or organ dysfunction, leading to symptoms of infection.
• Certain exotoxins have enzymatic activity, which can further contribute to their harmful effects on the host.

Types of Exotoxins

Exotoxins come in three primary categories:

• Superantigens (Type I toxins)
• Exotoxins (Type II toxins) that harm host cell membranes
• A-B toxins, and other toxins that impair host cell function (Type III toxins)

Why Exotoxins are Harmful?

• A toxin produced by bacteria is known as an exotoxin.
• An exotoxin can harm the host by killing cells or preventing normal cellular metabolism. 
• They are extremely powerful and capable of causing the host considerable harm. 
• Like endotoxins, exotoxins can release themselves or leak during cell lysis.

Exotoxin Example

Some examples exotoxins:

• Tetanospasmin (produced by Clostridium tetani, causing tetanus)
• Botulinum toxin (produced by Clostridium botulinum, causing botulism)
• Diphtheria toxin (produced by Corynebacterium diphtheriae, causing diphtheria)
• Cholera toxin (produced by Vibrio cholerae, causing cholera)

Differences Between Endotoxins and Exotoxins

The endotoxin vs exotoxin is given below:

Feature	Endotoxins	Exotoxins
Definition	It is a bacterial toxin and a lipopolysaccharide.	It is a soluble protein that is secreted to the outside of the bacterial cell.
Type of Molecule	Lipopolysaccharide	Protein
Produced By	Gram-negative bacteria	Both Gram-negative and positive bacteria.
Enzymatic activity	Does not act as enzymes.	Act as enzymes.
Toxicity	Less Toxic	Highly Toxic.
Mode of conversion	Cannot be converted to toxoid.	Can be converted to toxoid.
Fatal	It doesn’t prove to be fatal.	It is often fatal in larger quantities.
Diseases caused	Urinary Tract Infection Ischemic Heart Disease Meningococcal Meningitis	Scarlet fever Botulism Scalded skin syndrome
Location	Within the outer membrane of the bacterium.	In the extracellular fluid.
Antigenicity	Less antigenic	Highly antigenic
Example of toxin producing bacteria	Salmonella typhi (Typhoid), Vibrio cholerae (Cholera).	Clostridium tetani (Tetanus), Clostridium botulinum (Botox),

Conclusion – Difference Between Endotoxins And Exotoxins

In summary, the difference between endotoxin and exotoxin lies in the way they are produced by bacteria. Endotoxins, derived from the outer membrane of gram-negative bacteria, are generally less toxic and less antigenic compared to exotoxins. They cannot be converted into toxoids. On the other hand, exotoxins are secreted by both gram-negative and gram-positive bacteria. These proteins possess enzymatic activity, rendering them highly toxic and often fatal in larger quantities. Exotoxins are highly antigenic and can be converted into toxoids for vaccination purposes. Understanding these distinctions is crucial for accurate diagnosis and effective treatment of bacterial infections.

FAQs on Difference Between Endotoxins And Exotoxins

What Bacteria Produce Endotoxins?

Endotoxin is produced by Shigella, Escherichia coli, Salmonella, Pseudomonas, etc.

What Bacteria Produce Exotoxins?

Exotoxins are produced by Clostridium botulinum, Clostridium tetani, Corynebacterium diphtheriae, etc.

How do Exotoxins and Endotoxins Cause Infection?

Endotoxins release toxins only when bacteria are killed, while exotoxins immediately release toxins into the environment.

List some Exotoxins.

Saxitoxin, Tetrodotoxin, Eledoisin, and Conotoxin.

What are 2 Differences Between Endotoxin and Exotoxin?

Endotoxins originate from the outer membrane of gram-negative bacteria, while exotoxins are soluble proteins secreted by both gram-negative and gram-positive bacteria. Additionally, endotoxins cannot be converted into toxoids, whereas exotoxins can be converted into toxoids for vaccination.