Differences between Exotoxins and Endotoxins

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.

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.

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 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 disease	Tetanus, diphtheria, botulism	Meningococcemia, sepsis by gram negative rods

Acharya Tankeshwar

Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. As an asst. professor, I am teaching microbiology and immunology to medical and nursing students at PAHS, Nepal. I have been working as a microbiologist at Patan hospital for more than 10 years.