Exotoxins and Endotoxins and Difference between Exotoxins and Endotoxins


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


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



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