Exotoxins vs. Endotoxins: 29 Major Differences

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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.


Character Exotoxins


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-antigen

2.  Core oligosaccharide

3.  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 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

About Author

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Sagar Aryal

Sagar Aryal is a microbiologist and a scientific blogger. He is doing his Ph.D. at the Central Department of Microbiology, Tribhuvan University, Kathmandu, Nepal. He was awarded the DAAD Research Grant to conduct part of his Ph.D. research work for two years (2019-2021) at Helmholtz-Institute for Pharmaceutical Research Saarland (HIPS), Saarbrucken, Germany. Sagar is interested in research on actinobacteria, myxobacteria, and natural products. He is the Research Head of the Department of Natural Products, Kathmandu Research Institute for Biological Sciences (KRIBS), Lalitpur, Nepal. Sagar has more than ten years of experience in blogging, content writing, and SEO. Sagar was awarded the SfAM Communications Award 2015: Professional Communicator Category from the Society for Applied Microbiology (Now: Applied Microbiology International), Cambridge, United Kingdom (UK). Sagar is also the ASM Young Ambassador to Nepal for the American Society for Microbiology since 2023 onwards.

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