What is the Difference Between Endotoxin and Exotoxin?

The main difference between endotoxins and exotoxins lies in their origin, composition, and toxicity. Here is a comparison between the two:

• Origin: Endotoxins are lipopolysaccharide-protein complexes (LPS) that are part of the cell wall of Gram-negative bacteria and are released upon the death of the bacteria. Exotoxins, on the other hand, are proteins secreted by certain species of bacteria, both Gram-positive and Gram-negative, during their metabolism.
• Composition: Endotoxins are composed of a Lipoglycan complex, while exotoxins are mostly polypeptides.
• Toxicity: Exotoxins are generally more potent and often fatal compared to endotoxins. Examples of exotoxins include tetanus, diphtheria, and botulinum toxin. Endotoxins, such as Cholera toxin, are relatively less toxic.
• Heat Stability: Endotoxins are heat-stable and do not denature at high temperatures, while exotoxins are heat-labile and get denatured at high temperatures.
• Antigenicity: Exotoxins are highly antigenic proteins and can elicit potent antibody responses, which underpins vaccine development. Endotoxins do not elicit durable antibody responses and are not readily denatured by heat.
• Detection: Exotoxins can be detected by various tests like neutralization, precipitation, etc., while endotoxins are detected by the Limulus lysate assay.

Comparative Table: Endotoxin vs Exotoxin

Here is a table summarizing the differences between endotoxins and exotoxins:

Endotoxins are heat-stable complexes of lipopolysaccharide-protein, whereas exotoxins are heat-labile proteins secreted by certain species of bacteria. Endotoxins are released upon bacterial death or lysis and are part of the bacterial cell wall, while exotoxins are secreted by living cells and are not released until bacteria are killed. Exotoxins are generally more toxic and antigenic than endotoxins.