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Differences between Exotoxins and Endotoxins

Exotoxins are usually heat labile proteins secreted by certain species of bacteria that diffuse into the surrounding environment.
Endotoxins are heat-stable lipopolysaccharide-protein complexes that form structural components of the cell wall of gram-negative bacteria and are released only by cell lysis or death of bacteria.

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Exotoxins:

Toxins that are released extracellularly as the body grows are called exotoxins. Exotoxins can travel from a source of infection to a distant part of the body and cause damage. E.g. Neurotoxin (botulinum toxin, tetanus toxin), enterotoxin (cholera toxin), cytotoxin

Endotoxins:

Endotoxins are lipopolysaccharide toxins produced by Gram negative bacteria. The name endotoxin is derived from the fact that these toxins generally bind to cells and are released only when the cell is lysed.

Basic properties and differences between Exotoxins and Endotoxins

Sr #ExotoxinsEndotoxins
1Excreted by organisms, living cellIntegral part of cell wall
2Found in both Gram positive and Gram Negative bacteriaFound mostly in Gram Negative Bacteria
3It is polypeptideIt is lipopolysaccharide complex.
4Relatively unstable, heat labile (60°C)Relatively stable, heat tolerant
5Highly antigenicWeakly immunogenic
6Toxoids can be madeby treating with formalinToxoids cannot be made
7Highly toxic, fatal in µg quantitiesModerately toxic
8Usually binds to specific receptorsSpecific receptors not found
9Not pyrogenic usually, Toxin SpecificFever by induction of interleukin 1 (IL-1) production, Shock
10Located on extrachromosomal genes (e.g. plasmids)Located on chromosomal genes
11FilterableNot so
12It has mostly enzymatic activityIt has no enzymatic activity
13Its molecular weight is 10KDaIts molecular weight is 50-1000KDa
14On boiling it get denatured.On boiling it cannot be denatured.
15Detected by many tests (neutralization, precipitation, etc)Detected by Limulus lysate assay
16Examples: 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)
17Diseases: Tetanus, diphtheria, botulismDiseases: Meningococcemia, sepsis by gram negative rods

29 Difference between exotoxins and endotoxins

S.N.CharacterExotoxinsEndotoxins
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-antigen2.  Core oligosaccharide3.  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 aureusBacillus cereusStreptococcus pyogenesBacillus anthracisToxins produced by E.coliSalmonella Typhi, ShigellaVibrio cho

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References

  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.

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Differences between Exotoxins and Endotoxins



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