Differences between Exotoxins and Endotoxins

February 1, 2021 | by fttower.com

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.

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 #	Exotoxins	Endotoxins
1	Excreted by organisms, living cell	Integral part of cell wall
2	Found in both Gram positive and Gram Negative bacteria	Found mostly in Gram Negative Bacteria
3	It is polypeptide	It is lipopolysaccharide complex.
4	Relatively unstable, heat labile (60°C)	Relatively stable, heat tolerant
5	Highly antigenic	Weakly immunogenic
6	Toxoids can be madeby treating with formalin	Toxoids cannot be made
7	Highly toxic, fatal in µg quantities	Moderately toxic
8	Usually binds to specific receptors	Specific receptors not found
9	Not pyrogenic usually, Toxin Specific	Fever by induction of interleukin 1 (IL-1) production, Shock
10	Located on extrachromosomal genes (e.g. plasmids)	Located on chromosomal genes
11	Filterable	Not so
12	It has mostly enzymatic activity	It has no enzymatic activity
13	Its molecular weight is 10KDa	Its 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, botulism	Diseases: Meningococcemia, sepsis by gram negative rods

29 Difference between exotoxins and endotoxins

S.N.	Character	Exotoxins	Endotoxins
1.	Definition	Proteins 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 by	Mostly Gram positive bacteria and also Gram negative bacteria.	Gram negative bacteria.
3.	Chemical Nature	Protein (polypeptide) complexes	Lipopolysaccharide-protein complexes
4.	Molecular weight	10KDa.	50-1000KDa.
5.	Components	Usually 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 present	Hyaluronidase, Collagenase, certain protease, Nuclease, Neuraminidase, Certain protease, Phospholipase A	Catalase, Fibrolysin, IgA / IgG proteases
7.	Chromosomal Location	Located on extrachromosomal genes (e.g. plasmids).	Located on chromosomal genes.
8.	Secreted by	Secreted by organisms ; living cell	Integral part of cell wall ; lysed cell
9.	Secretion	Secreted out of the cell.	Generally not released outside the cell until death of cell.
10.	Cell Lysis	Not required	Required
11.	Stability to heat	Heat labile (60-80°C)	Heat stable (250°C)
12.	Filtration	Filterable	Not Filterable
13.	Boiling	Denatured on boiling	Not denatured on boiling.
14.	Enzyme Activity	Mostly has enzymatic activity.	Enzymatic activity absent or limited.
15.	Specificity	Exotoxins 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 receptors	Usually binds to specific receptors.	Specific receptors not found.
17.	Specificity to bacterial strain	Specific to certain bacterial strain.	Not specific to any bacterial strain.
18.	Immunogenicity	Highly immunogenic.	Weakly immunogenic.
19.	Fever Induction	No	Fever by induction of interleukin 1 (IL-1) production.
20.	Toxicity	Highly 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.	Potency	High: 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.	Effects	Either cytotoxin, enterotoxin or neurotoxin with defined action on cells or tissues.	General symptoms such as fever, diarrhea, vomiting etc.
24.	Neutralization by Antibodies	Can be neutralized.	Cannot be neutralized.
25.	Detection	Detected 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 vaccines	Effective vaccines available.	No effective vaccines available.
28.	Diseases caused	Tetanus, diphtheria, botulism etc.	Meningococcemia, sepsis by gram negative rods etc.
29.	Examples	Toxins produced by Staphylococcus aureus, Bacillus cereus, Streptococcus pyogenes, Bacillus anthracis	Toxins produced by E.coli, Salmonella Typhi, Shigella, Vibrio cho

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References

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

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