Differences between Exotoxins and Endotoxins

Last updated on June 26th, 2021

Bacterial toxins are broadly divided into two general categories: exotoxins and endotoxins.

Exotoxins

They are polypeptide released extracellularly as the organism grows. Exotoxins may travel from a focus of infection to a distant part of the body and cause damage.  E.g. neurotoxin (botulinum toxin, tetanus toxin), enterotoxin (cholera toxin), cytotoxin.

Exotoxins are produced by several Gram-positive and Gram-negative bacteria and are among the most toxic substances known. Many exotoxins have an A-B subunit structure; the A (or active) subunit possesses the toxic activity, and the B (or binding) subunit is responsible for binding the exotoxin to specific receptors on the membrane of the human cell.

Exotoxins vs. Endotoxins (created with BioRender.com)

Endotoxins:

Endotoxins are lipopolysaccharide, which is an integral part of the cell wall of 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.

Differences between Exotoxins and Endotoxins

PropertyExotoxinsEndotoxins
Biomolecule/ChemistryProteinsLipopolysaccharide-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 60°C (except staphylococcal enterotoxin) Stable at 100°C 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 are used as vaccines. No toxoid formed and no vaccine available
Typical diseaseTetanus, diphtheria, botulismMeningococcemia, sepsis by gram negative rods
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Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. I am working as an Asst. Professor and Microbiologist at Department of Microbiology and Immunology, Patan Academy of Health Sciences, Nepal. If you want me to write about any posts that you found confusing/difficult, please mention in the comments below.