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

1

Excreted by organisms, living cellIntegral part of cell wall

2

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

3

It is polypeptideIt is lipopolysaccharide complex.

4

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

5

Highly antigenicWeakly immunogenic

6

Toxoids can be madeby treating with formalinToxoids cannot be made

7

Highly toxic, fatal in µg quantitiesModerately toxic

8

Usually binds to specific receptorsSpecific receptors not found

9

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

10

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

11

FilterableNot so

12

It has no enzymatic activityIt has mostly enzymatic activity

13

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

14

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

15

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

16

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)

17

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

20 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!

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

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

      Reply
  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.

    Reply
  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)?

    Reply
  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?

    Reply
    • 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

      Reply
      • 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.

        Reply
  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.

    Reply
    • 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.

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

    Reply
  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

    Reply

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