Endotoxins: Definition & Examples

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  • 0:05 Endotoxins
  • 0:40 Where Endotoxins Come From
  • 2:13 Immune Response to Endotoxins
  • 3:25 Diseases Caused by Endotoxins
  • 4:31 Lesson Summary
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Lesson Transcript
Instructor: Catherine Paul

Catherine has taught high school science and has a master's degree in biology.

Let's investigate the potentially deadly endotoxins. Endotoxins are a substance unique to gram-negative bacteria. Uncover how our immune system copes with endotoxins and their associated health effects in this lesson.


Suppose you were feeling ill from a bacterial infection. Chances are the doctor would prescribe an antibiotic and in a few days, you would be feeling better. But there are two main categories of bacteria: gram-positive bacteria and gram-negative bacteria. Unfortunately, gram-negative bacteria are harder to kill with antibiotics. To make matters worse, when gram-negative bacteria are destroyed, say by antibiotics or by our immune system, they release toxins into our body called endotoxins. Endotoxins can make us very sick, and in some cases, even cause death.

Where Endotoxins Come From

Both gram-negative and gram-positive bacteria have a plasma membrane and a peptidoglycan layer in their cell wall. The peptidoglycan layer is made of a sugar and peptide chain that adds structural strength to the cell wall. However, gram-negative bacteria have characteristics that separate them from gram-positive bacteria. The peptidoglycan layer of gram-negative bacteria is much thinner than that of gram-positive bacteria but they have an outer membrane covering it.

This outer membrane contains a fatty sugar layer called lipopolysaccharide (LPS). The term lipopolysaccharide can be broken into two words: lipo (fat) and polysaccharide (sugar). Within the lipid portion of this LPS layer is lipid A, which is a dangerous endotoxin. Antibiotics have a difficult time penetrating this outer membrane, rendering them more resistant.

Gram-negative bacteria release dangerous endotoxins primarily when they are killed. This can occur when the immune system or antibiotics attack the bacteria and break down their cell walls. When the cell walls are broken, fragments of the outer membrane are released into the body, including the endotoxins. 'Endo' means internal or within, and, in this case, refers to the endotoxin's existence within the outer cell membrane.

This is in contrast to exotoxins, which are toxins that are secreted or released from the cell. The prefix 'exo', means external, implying that the toxin is excreted to the outside of the cell. Exotoxins have the ability to be secreted from gram-positive or gram-negative bacteria at any point or they can be released when a cell dies.

Immune Response to Endotoxins

Picture your immune system playing a game of tennis and the opponent is gram-negative bacteria. The play is for the winning point and your immune system lines up to return its opponent's volley. After a perfect swing, hitting the sweet-spot on the racket, the immune system ends up putting too much force into the hit. The ball flies out of bounds, losing its chance to win the game point. This tennis play is very similar to the way the immune system responds to endotoxins. It's not that the immune system is not capable of handling endotoxins that can make us so ill but rather it's that the immune system's response is often too strong for our body to manage.

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