29 Difference between exotoxins and endotoxins

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Last Updated on July 8, 2020 by Sagar Aryal

Differences between Exotoxins and Endotoxins

Toxins are small molecules, peptides, or proteins produced by living cells that are capable of causing diseases or structural damage when they come in contact or are absorbed by tissues. Toxins and enzymes play an important role in the pathogenicity of pathogenic bacteria. Toxins may aid in invasiveness, damage cells, inhibit cellular processes, or trigger immune response and damage.

Differences between Exotoxins and Endotoxins

Toxins are of two types: Exotoxins and Endotoxins.




1.      DefinitionProteins produced inside pathogenic bacteria as a part of their growth and metabolism.Lipid portions of lipopolysaccharides (LPSs) that are the part of outer membrane of bacteria.
2.      Produced byMostly Gram positive bacteria and also Gram negative bacteria.Gram negative bacteria.
3.      Chemical NatureProtein (polypeptide) complexesLipopolysaccharide-protein complexes 
4.      Molecular weight 10KDa. 50-1000KDa.
5.      ComponentsUsually composed of two subunits A and B.
The A subunit is seen to have catalytic activity, whereas the B subunit is required for binding with an appropriate cell receptor. 
Composed of three basic components:

1.  O-antigen

2.  Core oligosaccharide

3.  Lipid A

6.      Enzymes presentHyaluronidase, Collagenase, certain protease, Nuclease, Neuraminidase, Certain protease, Phospholipase ACatalase, Fibrolysin, IgA / IgG proteases
7.      Chromosomal LocationLocated on extrachromosomal genes (e.g. plasmids).Located on chromosomal genes.
8.      Secreted bySecreted by organisms ; living cellIntegral part of cell wall ; lysed cell
9.      SecretionSecreted out of the cell.Generally not released outside the cell until death of cell.
10.   Cell LysisNot requiredRequired
11.   Stability to heatHeat labile (60-80°C)Heat stable (250°C)
12.   FiltrationFilterableNot Filterable
13.   BoilingDenatured on boilingNot denatured on boiling.
14.   Enzyme ActivityMostly has enzymatic activity.Enzymatic activity absent or limited.
15.   SpecificityExotoxins are enzymes; this makes them highly specific in their mechanism and for their host cells.Endotoxins are comparatively not very specific in nature.
16.   Specific receptorsUsually binds to specific receptors.Specific receptors not found.
17.   Specificity to bacterial strainSpecific to certain bacterial strain.Not specific to any bacterial strain.
18.   ImmunogenicityHighly immunogenic.Weakly immunogenic.
19.   Fever InductionNoFever by induction of interleukin 1 (IL-1) production.
20.   ToxicityHighly toxic, fatal in µg quantities.Moderately toxic, fatal in mg quantities.
21.   Mode of action


Various modes (Mostly by enzyme-like mechanisms).Includes TNF and Interlukin-1
22.   PotencyHigh: A single toxin molecule can act on a large number of host cells.Low: A large amount of toxin is needed to cause a disease.
23.   EffectsEither cytotoxin, enterotoxin or neurotoxin with defined action on cells or tissues.General symptoms such as fever, diarrhea, vomiting etc.
24.   Neutralization by AntibodiesCan be neutralized.Cannot be neutralized.
25.   DetectionDetected by many tests (neutralization, precipitation, etc)Detected by Limulus lysate assay.
26.   Conversion to Toxoids


Possible (On treatment with formalin). eg. For the prevention of diphtheria, botulism, and tetanus.Not possible
27.   Availability of vaccinesEffective vaccines available.No effective vaccines available.
28.   Diseases causedTetanus, diphtheria, botulism etc.Meningococcemia, sepsis by gram negative rods etc.
29.   ExamplesToxins produced by Staphylococcus aureus, Bacillus cereus, Streptococcus pyogenes, Bacillus anthracisToxins produced by E.coli, Salmonella Typhi, Shigella, Vibrio cholera


  1. Murray, Patrick R. (2016). Medical Microbiology.Eighth edition. India: Elsevier Inc.
  2. https://microbiologyinfo.com/differences-between-exotoxins-and-endotoxins/
  3. http://medimoon.com/2013/04/difference-between-endotoxin-and-exotoxin/
  4. https://biologywise.com/endotoxins-vs-exotoxins
  5. http://www.differencebetween.net/science/difference-between-endotoxins-and-exotoxins/
  6. http://www.easybiologyclass.com/difference-between-bacterial-endotoxin-and-exotoxin-comparison-table/
  7. Microbiology and Immunology. Kaplan Medical.

Differences between Exotoxins and Endotoxins

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