
Introduction of Exotoxins and Endotoxins
Table of Contents
Numerous bacteria produce toxins, enzymes, and pigments. Toxins and enzymes play significant roles in pathogenicity. Toxins are of two types-
- Exotoxins: They are usually heat-labile proteins secreted by certain species of bacteria which diffuse into the surrounding medium. Mainly Gram-positive bacteria and also some Gram-negative bacteria produce e.xotoxins
- Endotoxins: They are heat-stable lipopolysaccharide-protein complexes that form structural components of the cell wall of Gram-negative bacteria. They are the liberation of only one cell lysis (death) of bacteria and Gram-negative bacteria produce them.
Differences Between Exotoxins and Endotoxins
The differences between exotoxins and endotoxins are as follows-
S. No | Exotoxins | Endotoxins |
1. | Exotoxins are proteins (polypeptides) of molecular weight 10KDa-900KDa. | Endotoxins are lipopolysaccharide of molecular weight 50KDa-1000KDa. |
2. | They are found in both Gram-positive and Gram-negative bacteria. | They are found mostly in Gram-negative bacteria. |
3. | They are actively secreted by living cells into a medium. | They form an integral part of the cell wall; released only on disruption of the bacterial cell. |
4. | Heat labile at >60° C | Heat stable |
5. | They are highly antigenic and stimulate the formation of antitoxin which neutralizes the toxin. | They are comparatively weakly antigenic. Anatoxins are not formed but antibodies against polysaccharides are raised. |
6. | Toxoids can be made by treating with formaldehyde. | Toxoids can not be made. |
7. | They are enzymic in action. | No enzymic action |
8. | They express very high potency. | They express low potency. |
9. | They are non-pyrogenic and thus don’t produce fever in the host. | They are usually pyrogenic and feverish by induction of interleukin 1 (IL-1) production. |
10. | Usually binds to specific receptors e.g. tetanus toxin in neurons | Lacking specific receptor |
11. | They are filterable. | Not filterable |
12. | On boiling, they get denatured. | Do not occur so. |
13. | They are present on extrachromosomal genes (e.g. plasmids). | They are located on chromosomal genes. |
14. | They are detected by tests like neutralization, precipitation, etc. | They are detected by Limulus lysate assay. |
15. | Some exotoxins-producing bacteria are Staphylococcus aureus, Bacillus cereus, Streptococcus pyogenes, and Bacillus anthrcis. | Some endotoxins-produced bacteria are Escherichia coli, Salmonella enterica serotype Typhi, Shigella, and Vibrio cholerae. |
16. | Diseases caused by exotoxins-producing bacteria are tetanus, diphtheria, and botulism. | Diseases caused by endotoxins-producing bacteria are meningococcemia, and sepsis by Gram-negative rods (GNRs). |
Keynotes
- Tetanus toxin binds to ganglioside-containing receptors at the nerve termini.
- Alpha-toxin of Bacillus anthrcis is also known as alpha-hemolysin (Hla).
- The cholera toxin of Vibrio cholerae is also known as choleragen.
Some Footages of Gram-Positive and Negative Bacteria
Gram-positive cocci of Staphylococcus aureus

Gram-negative diplococci of Neisseria gonorrhoeae in Urethral Discharge Gram Staining

Gram-positive bacilli or rods of Bacillus species

Gram-Negative Rod or Bacilli of E. coli
