What Is The Differences between Exotoxins and Endotoxins?

So, what is the main difference between exotoxins and endotoxins? The former is secreted as part of metabolisms while the latter is part of the cell wall and got released on the death of bacteria.

Microbiology is the study of microscopic organisms. These microorganisms are pathogenic since they produce toxins that cause infection.  These microbes are found everywhere whether inside and outside other living things. These toxins caused by these microorganisms are classified into endotoxin and exotoxin.  

This article provides a detailed insight into the differences between exotoxins and endotoxins. The similarities also provide information on the relationship between exotoxins and endotoxins. 

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Differences between Exotoxins and Endotoxins(With Table)

Basic Terms




It is a protein produced inside a pathogen as part of growth and metabolism.

It is a lipopolysaccharide that is part of the outer membrane of bacteria.

Produced by

Both Gram-Positive and Negative bacteria.

Only Gram-Negative bacteria.

Chemical Nature

Protein (polypeptide) complexes

Lipopolysaccharide-protein complexes

Molecular weight




A subunit for catalytic activity.

B subunit for binding with appropriate receptor cells.


Core oligosaccharide

Lipid A

Enzyme’s present

Hyaluronidase, Collagenase, certain protease, Nuclease, Neuraminidase, Certain protease, Phospholipase A

Catalase, Fibrolysin, IgA / IgG proteases

Chromosomal Location

Extrachromosomal genes

Chromosomal genes

Secreted by

Living cell

Lysed cell


Outside the cell

Within the cell

Cell Lysis

Not necessary

Quite necessary

Stability to heat

Heat labile (60-80°C)

Heat stable (250°C)



Not Filterable



Not denatured

Enzyme Activity


Limited or absent


Highly specific since they are enzymes.

Not very specific in nature.

Specific receptors

Bind to specific receptors


Specificity to a bacterial strain




Highly immunogenic.

Weakly immunogenic.

Fever Induction


Induced by interleukin 1 (IL-1) production.


Highly toxic

Moderate toxic

Mode of action

Various modes

Includes TNF and Interlukin-1





Either cytotoxin, enterotoxin, or neurotoxin with defined action on cells

Fever, diarrhea, vomiting

Neutralization by Antibodies

Can be neutralized

Cannot be neutralized


Through tests such as neutralization and precipitation.

Limulus lysate assay.

Conversion to Toxoids

Treatment by formalin

Not possible.

Availability of vaccines


Not available


Tetanus, diphtheria, botulism, etc.

Meningococcemia, sepsis by gram-negative rods, etc.


Staphylococcus aureus, Bacillus cereus, Streptococcus pyogenes, Bacillus anthracis

E.coli, Salmonella Typhi, Shigella, Vibrio cholera

What Is Exotoxins?

Exotoxins are potent proteins produced and actively secreted by live bacterial cells into their surrounding environment. These toxins play a significant role in the pathogenicity of certain bacteria, causing damage to host cells and contributing to the symptoms associated with bacterial infections. Exotoxins exhibit a diverse range of functions, affecting various cellular processes and often leading to specific clinical manifestations.

These toxins are typically produced by both Gram-positive and Gram-negative bacteria and can be associated with various diseases. Examples of diseases caused by exotoxins include diphtheria, tetanus, botulism, and certain types of food poisoning. The effects of exotoxins can be localized or systemic, depending on the specific toxin and the bacteria producing it.

One characteristic of exotoxins is their sensitivity to heat, which means they can be neutralized or destroyed by heat. This property has practical implications in the development of vaccines, as heat-inactivated toxins are sometimes used to stimulate the immune system and induce protective immunity.

Exotoxins act through various mechanisms, such as interfering with cellular metabolism, disrupting cell membranes, or modifying host cell signaling pathways. The specificity of these toxins for certain cell types contributes to the unique symptoms observed in different bacterial infections.

Understanding the nature of exotoxins is crucial for developing targeted therapies and vaccines to combat bacterial infections. By elucidating the mechanisms of action of these toxins, researchers and healthcare professionals can devise strategies to neutralize their effects and mitigate the impact of bacterial diseases on the human body.

What Is Endotoxins?

Endotoxins are complex molecules that constitute an integral part of the outer membrane of Gram-negative bacteria. Unlike exotoxins, which are actively secreted by live bacterial cells, endotoxins are released when these bacterial cells undergo lysis or destruction. This distinguishes them as a byproduct of bacterial death rather than a secreted, actively harmful substance.

The primary component of endotoxins is lipopolysaccharide (LPS), a complex molecule consisting of lipid and sugar portions. LPS is a major structural component of the outer membrane of Gram-negative bacteria, including well-known pathogens such as Escherichia coli and Salmonella.

Endotoxins are notable for their ability to induce a potent immune response in the host organism. When released into the bloodstream during bacterial infection or sepsis, endotoxins can trigger the activation of immune cells and the release of inflammatory mediators. This immune response can lead to symptoms such as fever, shock, and inflammation.

Unlike exotoxins, endotoxins are relatively heat-stable, and traditional sterilization methods may not completely eliminate their activity. This characteristic has implications for the prevention and treatment of infections caused by Gram-negative bacteria.

The recognition of endotoxins as a major contributor to the symptoms associated with Gram-negative bacterial infections has led to ongoing research efforts to develop therapies targeting these molecules. Understanding the role of endotoxins in the pathogenesis of infections is essential for devising strategies to modulate the immune response and improve outcomes for individuals affected by Gram-negative bacterial diseases.

Differences Between Exotoxins and Endotoxins

  1. Exotoxins are secreted by the living cell while endotoxins are an integral part of the cell wall.
  2. Exotoxins are found in both gram-positive bacteria and gram-negative bacteria whereas endotoxins are found only in gram-negative bacteria
  3. Exotoxins are a simple polypeptide while endotoxins is a complex lipopolysaccharide
  4. Exotoxins are relative heat liable at 60 degrees hence quite unstable while endotoxins are heat tolerant even at 100 degrees
  5. Endotoxins are weak immunogenic while exotoxins are highly antigenic
  6. Exotoxins releases toxoid used in treating with formalin while endotoxin cannot make toxoid.
  7. Exotoxins are highly toxic and fatal while endotoxins are moderately toxic and fatal
  8. Exotoxins are normally bound to specific receptors while endotoxins are not bound to specific receptors.
  9. Endotoxins are located on chromosomal genes while exotoxins are located on extrachromosomal genes.
  10. Exotoxins get denatured when exposed to high boiling points while endotoxins do not get denatured even after exposure to high boiling points.
  11. Examples of diseases caused by exotoxins are Tetanus, diphtheria, and botulism while those caused by endotoxins are Meningococcemia and sepsis by gram-negative rods.
  12. Endotoxin produce fever in the host whereas exotoxin does not 
  13. There are effective vaccines for exotoxins whereas there are no effective vaccines for endotoxins
  14. Exotoxins are very lethal even in minute quantities whereas endotoxins are very lethal in large quantities
  15. Exotoxins use specific receptors to enter the host cells while endotoxins have no specific receptors 
  16. Exotoxin show affinity towards specific tissues while endotoxin does not show affinity towards specific tissues
  17. The molecular weight of exotoxin is 10KDa whereas the molecular weight of endotoxin is about 50-1000KDa
  18. Exotoxins are filterable whereas endotoxins are not
  19. Exotoxin has the ability to trigger immune responses whereas endotoxin cannot trigger an immune response
  20. Exotoxin tends to stay active beyond 60 degrees whereas endotoxin tends to stay active beyond 100 degrees Celcius. 

Similarities between Exotoxins and Endotoxins

  1. Both are brought about by bacteria
  2. Both cause diseases to the host 
  3. Both are located on chromosomes
  4. Both are toxic 
  5. Both can be affected by heat 

Frequently Asked Question

  • Is Tetanus an Endotoxin or Exotoxin?

Exotoxin. They are mainly bound to the bacterial body that develops their pathogenic effects only after bacterial cell decay.

  • Are Endotoxins More Potent than Exotoxins?

Endotoxins are less potent and less specific. They are normally released and not secreted. They tend to disrupt the normal functioning of the cell. 

  • Why are Endotoxins Dangerous?

Dangerous endotoxins are released by gram-negative bacteria. Once they are released into the body, they weaken the immune system by attacking antibodies. 

  • Is Endotoxin Gram-Positive or Negative?

Gram-negative bacteria. 

  • Are Exotoxins Gram-Positive or Negative?

Both gram-positive and gram-negative. They are secreted by both gram-positive and gram-negative bacteria. 

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Exotoxins and endotoxins are two distinct types of toxins produced by bacteria, each with unique characteristics and mechanisms of action.

Exotoxins are proteins secreted by live bacterial cells into the surrounding environment. These potent toxins can cause harm to host cells at a distance from the bacterial site of infection. Exotoxins are often heat-sensitive and can be neutralized by antibodies. They are typically produced by Gram-positive and Gram-negative bacteria and can be associated with specific diseases or symptoms.

On the other hand, endotoxins are lipopolysaccharides (LPS) that form an integral part of the outer membrane of Gram-negative bacteria. Unlike exotoxins, endotoxins are released only when the bacterial cells are lysed or destroyed. They can trigger a strong immune response and are heat-stable. Endotoxins are commonly associated with symptoms such as fever, shock, and inflammation.

In summary, the key differences between exotoxins and endotoxins lie in their composition, release mechanisms, heat sensitivity, and association with bacterial cell structure. Exotoxins are secreted proteins with specific effects on host cells, produced by both Gram-positive and Gram-negative bacteria, while endotoxins are part of the outer membrane of Gram-negative bacteria and are released upon bacterial cell death, triggering a generalized immune response. Understanding these distinctions is crucial in the context of bacterial infections and the development of therapeutic interventions.

More Sources and References

  1. Exotoxin.Wikipedia

  2. Exotoxins and Endotoxins. NCBI

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