29 Differences between Exotoxins and Endotoxins(With Table)

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. 

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. 

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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Comparison Table (Exotoxins vs Endotoxins)

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 types of toxic substances that are released extracellularly. Exotoxins have the ability to spread to other parts from a focus infection causing a lot of damage.

Research shows that it is the most lethal toxic condition as compared to endotoxins. It normally occurs in three forms as Neurotoxin, Enterotoxin, and Cytotoxin.

Exotoxins only cause diseases that are specifically caused by that contamination. Some of the common health disorders caused by exotoxins are Cholera, tetanus, and Diphtheria.

What Is Endotoxins?

Endotoxins are a type of toxic substance that spread into the surrounding medium and causing a lot of damage to the host by disrupting the normal function of the cell.

Also, they are heat stable liable proteins that form the structural component of the cell wall of the gram-negative bacteria. They are only liberated on cell lysis or the death of bacteria.

Endotoxins are quite common in Vibrio cholera, Neisseria, E Coli, Pseudomonas, Salmonella, Haemophilus influenza, and Shigella.

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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Toxic substances are chemical components produced by the bacteria to cause damages to the host and also diseases. They occur in the form of exotoxins and endotoxins.

Exotoxins are fatal in small quantities while endotoxins are relatively less fatal. The differences between exotoxins and endotoxins listed above are suitable for you.

More Sources and References

  1. Exotoxin.Wikipedia

  2. Exotoxins and Endotoxins. NCBI

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