Exotoxins:
Definition: Toxins that are released extracellularly as the organism grows are called exotoxins. Exotoxins may travel from a focus of infection to distant part of the body and cause damage. E.g. Neurotoxin (botulinum toxin, tetanus toxin), Enterotoxin (cholera toxin), Cytotoxin
Endotoxins:
Definition: Endotoxins are lipopolysaccharides toxin produced by Gram negative bacteria. The name endotoxin is derived from the fact that these toxins are generally cell bound and released only when the cell lyses.
Basic properties and differences between Exotoxins and Endotoxins
| Property | Exotoxins | Endotoxins |
| Biomolecule/Chemistry | Proteins | Lipopolysaccharide-Lipoprotein complex |
| Location of genes | Plasmid or bacteriophage | Bacterial chromosome |
| Source | Excreted by certain gram positive or gram negative bacteria | Cell wall of Gram Negative bacteria, released only after lysis of cells |
| Heat Stability | Destroyed rapidly at 60oC (except staphylococcal enterotoxin) | Stable at 100oC for one hour |
| Mode of Action (Symptoms) | Specific. Either cytotoxin, enterotoxin or neurotoxin with defined action on cells or tissues | General. fever, diarrhea, vomiting |
| Toxicity | Highly toxic, often fatal (fatal dose on the order of 1 µg) | Weakly toxic, rarely fatal (fatal dose on the order of hundreds of micrograms) |
| Immunogenicity | Highly immunogenic, stimulate the production of neutralizing antibody (antitoxins) | Relatively poor immunogenicity |
| Toxoid potential/Vaccines | Treatment of toxin with formaldehyde will destroy toxicity, but treated toxins remain immunogenic. Toxids used as vaccines |
No toxoid formed and no vaccine available |
| Typical disease | Tetanus, diphtheria, botulism | Meningococcemia, sepsis by gram negative rods |
