Difference Between Exotoxins vs. Endotoxins

Main Difference

Exotoxins are toxic substances secreted by bacteria and released outside the cell. Whereas Endotoxins are bacterial toxins consisting of lipids that are located within a cell.

What is Exotoxins?

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. An exotoxin is a toxin secreted by bacteria. An exotoxin can cause damage to the host by destroying cells or disrupting normal cellular metabolism. They are highly potent and can cause major damage to the host. Exotoxins may be secreted, or, similar to endotoxins, may be released during lysis of the cell

What is Endotoxins?

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. a heat-stable toxin associated with the outer membranes of certain gram-negative bacteria, including Brucella, Neisseria, and Vibrio species. Endotoxins are not secreted but are released only when the cells are disrupted; they are less potent and less specific than the exotoxins; and they do not form toxoids. In large quantities they produce hemorrhagic shock and severe diarrhea; smaller amounts cause fever, altered resistance to bacterial infection, leukopenia followed by leukocytosis, and numerous other biologic effects.

Key Differences

  1. Exotoxins are usually heat labile proteins secreted by certain species of bacteria which diffuse into the surrounding medium.Endotoxins are heat stable lipopolysaccharide-protein complexes which form structural components of cell wall of Gram Negative Bacteria and liberated only on cell lysis or death of bacteria.
  2. Exotoxins are Excreted by organisms, living cell, Endotoxins are the integral part of cell wall.
  3. Exotoxins are Found in both Gram positive and Gram Negative bacteria. Endotoxins are Found mostly in Gram Negative Bacteria.
  4. Exotoxins are Detected by many tests (neutralization, precipitation, etc. Endotoxins are Detected by Limulus lysate assay.
  5. Exotoxins have no enzyme activity as compared to endotoxins.
  6. Exotoxins are filterable as compared to endotoxins.
  7. Exotoxins are Highly antigenic. Endotoxins are Weakly immunogenic.
  8. Chemical composition exotoxins : protein, Chemical composition endotoxins.