Toxins and differences between endotoxins and exotoxins

May 28, 2018 Sushil Humagain Bacteriology, Differences between, Microbiology 0

source: https://nomoremoldblog.wordpress.com/2015/11/18/endotoxin-part-1/
  • The chemical substances produced by microorganisms in order to harm the host and cause diseases in them are called toxins.
  • The ability of a microorganism to produce a toxin that contributes in the development of a disease is called toxigenicity.
  • Toxins produced by microorganisms (bacteria) are generally classified into two groups; endotoxins and
  • The primary differences between them are as follows:
S.N. Exotoxins Endotoxins
1. They are released by living bacterial cell and in high concentration in the liquid medium. They are the integral part of the cell wall of gram-negative bacteria and are released on bacterial death and in part during growth (or may not need to be released to have biologic activity).
2. They are produced by both gram-positive and gram-negative bacteria. They are found only in gram-negative bacteria.
3. They are polypeptides of molecular weight of 10,000-900,000. They are lipopolysaccharide complexes and the Lipid A portion probably is responsible for toxicity.
4. They are relatively unstable. They are relatively stable.
5. Their toxicity is often destroyed rapidly by heating at temperatures above 600C. They can withstand heating at temperatures above 600C for hours without loss of toxicity.
6. They are highly antigenic. They are weakly immunogenic.
7. They stimulate the formation of high-titer anti-toxin which neutralizes the toxin. Antibodies are anti-toxic and protective but the relationship between antibody titers and protection from disease is less clear than with exotoxins.
8. They can be converted to antigenic, non-toxic toxoids by formalin, acid, heat etc. Toxoids are used in immunization (e.g. tetanus toxoid). They cannot be converted to toxoids.
9. They are highly toxic and are fatal to animals in microgram quantities or less. They are moderately toxic and fatal for animals in tens to hundreds of micrograms.
10. They usually bind to specific receptors on cells. Their specific receptors are not found in the cells.
11. They usually don’t produce fever in the host. They usually produce fever in the host by the release of interleukin-1 and other mediators.
12. They are frequently controlled by extra-chromosomal genes (e.g. plasmids). Their synthesis is directed by chromosomal genes.
13. They are generally proteins. They are lipopolysaccharides.

Source: Jawetz, Melnick and Adelberg’s Medical Microbiology, 24th edition.

Toxins and differences between endotoxins and exotoxins