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:

S.N. Exotoxins Endotoxins


Excreted by organisms, living cell Integral part of cell wall


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


It is polypeptide It is lipopolysaccharide complex.


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


Highly antigenic Weakly immunogenic


Toxoids can be madeby treating with formalin Toxoids cannot be made


Highly toxic, fatal in µg quantities Moderately toxic


Usually binds to specific receptors Specific receptors not found


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


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


Filterable Not so


It has no enzymatic activity It has mostly enzymatic activity


Its molecular weight is 10KDa Its 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, botulism Diseases: Meningococcemia, sepsis by gram negative rods

19 thoughts on “Differences Between Exotoxins and Endotoxins”

  1. 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!

    • No, because Staphylococcus aureus is Gram positive. Endotoxins are part of the structure of Gram negative cell walls

  2. 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.

  3. 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)?

  4. 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.

  5. 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.

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

  7. 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

Leave a Comment