Differences 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. |
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 |
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