Differences Between Exotoxins and Endotoxins

Many bacteria produce toxins, enzymes and pigments. Toxins and enzymes play important role in pathogenecity. Toxins are of two types:

Exotoxins are usually heat labile proteins secreted by certain species of bacteria which diffuse into the surrounding medium.

Endotoxins are heat stable lipopolysaccharide-protein complexes which form structural components of cell wall of Gram Negative Bacteria and liberated only on cell lysis or death of bacteria.

Differences Between Exotoxins and Endotoxins

Some of the differences between Exotoxins and Endotoxins are as follows:



Excreted by organisms, living cellIntegral part of cell wall


Found in both Gram positive and Gram Negative bacteriaFound mostly in Gram Negative Bacteria


It is polypeptideIt is lipopolysaccharide complex.


Relatively unstable, heat labile (60°C)Relatively stable, heat tolerant


Highly antigenicWeakly immunogenic


Toxoids can be madeby treating with formalinToxoids cannot be made


Highly toxic, fatal in µg quantitiesModerately toxic


Usually binds to specific receptorsSpecific receptors not found


Not pyrogenic usually, Toxin SpecificFever by induction of interleukin 1 (IL-1) production, Shock


Located on extrachromosomal genes (e.g. plasmids)Located on chromosomal genes


FilterableNot so


It has mostly enzymatic activityIt has no enzymatic activity


Its molecular weight is 10KDaIts molecular weight is 50-1000KDa


On boiling it get denatured.On boiling it cannot be denatured.


Detected by many tests (neutralization, precipitation, etc)Detected by Limulus lysate assay


Examples: Toxins produced by Staphylococcus aureus, Bacillus cereus, Streptococcus pyogenes, Bacillus anthrcis(Alpha-toxin, also known as alpha-hemolysin (Hla))Examples: Toxins produced by E.coli, Salmonella Typhi, Shigella, Vibrio cholera(Cholera toxin- also known as choleragen)


Diseases: Tetanus, diphtheria, botulismDiseases: Meningococcemia, sepsis by gram negative rods

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40 thoughts on “Differences Between Exotoxins and Endotoxins”

  1. Antigens are allmost proteins and exotoxins are proteins thus it is more antigenic and endotoxins are lipobolysacchrides which are less immunogenic

  2. Requested to know the moleculecular weight of exo and endotoxins, where other sources shows endotoxins (10kDa) and exotoxins (50-1000kDa), the exact oppposite to this version, hope i will get exact answer

  3. I am confused little bit, why and how after mostly gram negative bacteria after die or cell lysis produce endotoxin?
    It means that in gram negative treatment, clinicallu treatment is based on endotoxin or bacteria itself.
    Eg. You are given medicine to treat endotoxin or bacteria itself.
    If you treat bacteria itself, how can bacteria causes diseases if it still live in host organisms??

    • Remember that this endotoxin are being produced by the bacteria cell as a way of damaging host cell / host defense ….once the bacterial cell kills some host cell then endotoxin are produced drugs are offered to counter attack of more cells which might lead to production of more endotoxin

  4. In book Lange Microbiology Review 14th edition Page 39 it is written E.coli, V.cholerae, Bordetella pertussis produces Exotoxin but they are Gram negative bacteria. Can they produces both Exotoxin and Endotoxin ?

    • It is written that exotoxin cab be produced in both gram positive and negative, but only endotoxin are special products by gram negative.
      But endotoxin is only produced in negative bacteria.

    • Exotoxins are mainly proteins, hence get denatured due to increase in temperature, but endotoxins are poly saccharides that do not denature by increase in temperature hence heat stable.

    • bacteria produces exotoxins which are protein in nature hence heat labile while bacteria producing endotoxins have cell wall which is structurally lipopolysaccharide protein complex hence tolerate high temperatures.

  5. Thank you for your post! It really helps me easily understand more about endotoxins and exotoxins.

    However, I wonder that choleragen is a heat-labile protein in V. cholerae which is a gram-negative bacteria, and which feature we order it as an endotoxin?

    Thank you!

    • Outer membrane of all gram negative bacteria (endotoxin) is Lipopolysaccharides and V.cholera is Gram negative so we order it as an endotoxin.

    • Too many endotoxins in the bloodstream disrupt the functioning of the immune system. This is the trigger and the source of virtually every chronic and neurological disease. When they overwhelm the immune system with too many endotoxins in the bloodstream it is more of an instant kill rather than death by a thousand cuts. Exotoxins are not as subtle. You know when they have infected you and if you don’t do something about it, you die.

  6. endotoxin release when bacteria is lysed or dead. after lysis of bacteria the cell wall of gram negative (lps) bacteria work as a endotoxin. endotoxin increase the temperature of human body so it is fever producing toxin. so endotoxin testing is necessary in all IM & IV fluid.

  7. I am a student of microbiology…nice write up but my question goes this way…
    Why is exotoxin highly antigenic and endotoxins weakly immunogenic since the molecular weight of endotoxins(50-1000kDa) is greater than that of exotoxins(10kDa)?

      • its not true,exotoxin are in gram positive but at the same time can be found in gram negative,endotoxin are found only in gram negative, gram negative bacteria whin they get susceptable host they cause infection when they get lysed or die hence producing alot of heat which result to fever.

  8. I am a master student of microbiology. I wonder if anyone could help me find the answers of the two questions below:
    1-Are there any bacterial toxins that are not secreted out and are kept within the cell?
    2-Are there any lipid toxins?

    • 1st :endotoxins are not secreted out of the cell , they only act when lysis of bacteria occurs.
      2nd : endo toxins are lipid toxins , they are structural component of bacterial cell wall , in form of lipopolysachride

      • Endotoxins are part of the outer membrane of the cell wall of Gram negative bacteria. Gram positive bacteria do not have an outer membrane as part of their cell wall.

  9. there is a small mistake regarding the enzymatic activity of toxins. the exotoxins have enzymatic activity which can e denatured on heating while endotoxins being LPS has no enzymatic activity and has no effect of heating because of lipid nature.

    • Your comment is correct. The lipopolysaccharide component of Gram negative bacterial cell wall has no enzymatic activity, and is chemically not related to the protein enzyme composition.

      Bacterial pyrogens are not affected by most sterilization processes, such as steam, ethylene gas, and gamma or electron beam irradiation.

  10. I need you to help me find more information on why E.coli is sensitive to brilliant green. Thanks

  11. That cool, am a graduate of Microbiology, this question was part of the question asked from me during my seminar presentation. Was working on global health issue of Aflatoxin in food and agriculture. Its nice keep it up. Microbiology is all encompassing


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