Exotoxins vs. Endotoxin Review: Videos & Practice Problems

Exotoxins, produced by both gram-positive and gram-negative bacteria, are protein-based toxins found in the cytoplasm, while endotoxins, specifically lipopolysaccharides (LPS), are associated with the outer membrane of gram-negative bacteria. Exotoxins can form toxoids and are heat-sensitive, causing high toxicity even in small doses. In contrast, endotoxins are heat-resistant and can lead to septic shock if they enter the bloodstream, exhibiting low toxicity otherwise. Understanding these differences is crucial for developing effective vaccines and treatments against bacterial infections.

Exotoxins vs. Endotoxin Review

In this video, we're going to highlight some of the main differences between exotoxins and endotoxins by completing the interactive blinks in this table that you see down below. And notice that this table has exotoxins in the middle column, then it has endotoxin in the far right column, and then, of course, in the far left, we have the property that we're going to be covering. And so in terms of the bacterial source, recall that exotoxins can be produced by either gram-positive or gram-negative bacteria. And so both gram-positive and gram-negative can be a source of exotoxins. Whereas recall that endotoxin specifically is associated with gram-negative only. And so in terms of the location in or on the bacterium where the exotoxin or endotoxin can be found, recall that the exotoxins are proteins, and so they are going to be found within the cytoplasm of the cell on the inside of the cell. And these exotoxin proteins may or may not be secreted into their environments. And so, if they are secreted into their environments, then, of course, it would be those exotoxins that would be able to cause toxic effects. However, if they're not secreted into the environment, if they're not actively secreted, they could still be released into the environment if the cell is lysed or ruptured, then the components of the cytoplasm may be released, and it could cause the toxic effect that way. Now recall that endotoxin, on the other hand, is a component of the outer membrane. Recall that the endotoxin is going to be the lipopolysaccharide or LPS found in the outer membrane of gram-negative bacteria. And so that's what we're showing you right here. This is the endotoxin. And so this leads us to the chemical nature of these substances. Exotoxins recall are going to be made of proteins. So they are going to be protein-based and that means that they're made of amino acids, chains of amino acids. Whereas, the endotoxin, on the other hand, specifically refers to the lipopolysaccharide molecule or LPS. And again, that is a component of the outer membrane of gram-negative bacteria. Now recall that it's specifically the lipid A component of the endotoxin, which is going to be this portion down below right here, that is going to be the toxic portion of the lipopolysaccharide. And of course, Lipopolysaccharides, they're going to have this lipid A region and then they'll have the Polysaccharide region, at the top here, the carbohydrate region. Now in terms of their ability to form a toxoid or the ability to form a toxoid for the exotoxins and the endotoxins. Recall that a toxoid is really just a vaccine against a toxin. For most exotoxins, toxoids are able to be generated. So the answer is yes. The ability to form toxoids, in most cases normally is going to be available for exotoxins. However, for endotoxin, that is not going to be the case. There is not the ability to create a toxoid for endotoxin, as of now. Now, in terms of the heat stability, it turns out that exotoxins, because they are made of proteins, they are going to be sensitive to heat. And so they can easily be inactivated by heat under most circumstances. And so things like autoclaving and exposing substances to high temperatures and high pressures, usually the exotoxins will be inactivated. However, the endotoxin, on the other hand, tends to be heat resistant. And so that means that other methods of handling the endotoxin are going to need to be implemented to inactivate them and to make them not a concern. But heat alone and autoclaving alone, in many cases, is not enough to inactivate the endotoxin. Now in terms of the effect on the human body, exotoxins can have a wide variety of different effects. Effects. They can affect cell functions, cause cell lysis. They can affect specific tissues such as the nerves or any part of the nervous system. They can infect the gastrointestinal tract. And so they can have several different effects on the human body depending on the type of exotoxin. Now endotoxin, on the other hand, can lead to septic shock if it's able to enter into the bloodstream. And so it could lead to things such as fever, weakness, body aches, and, again, septic shock. And septic shock could potentially lead to death. And again, this is specifically if the endotoxin gets into the bloodstream. But if we look at the toxicity or the ability to cause disease, what you'll notice is that for exotoxins, the toxicity is generally high. And so, the presence of exotoxins will generally lead to disease. However, notice that for endotoxin, the toxicity is generally low unless the endotoxin gets into the bloodstream. And then if the endotoxin gets into the bloodstream, then again it could lead to septic shock and it can be very toxic. But otherwise, if the endotoxin remains loca

Endotoxins are _________ and need to be in _________ concentrations to cause disease in a host.

• A. Extremely toxic; small.
• B. Extremely toxic; large.
• C. Slightly toxic; small.
• D. Slightly toxic; large.

Answer: (D)

Which of the following is not a major difference between endotoxins and exotoxins?

• A. Exotoxins are more toxic than endotoxins.
• B. Endotoxins are made by viruses while exotoxins are made by bacteria.
• C. Exotoxins are made of proteins while endotoxins are made of lipopolysaccharides.
• D. A small concentration of exotoxins can be lethal while a large concentration of endotoxins is lethal.

Answer: (B)

The diphtheria toxin is secreted by Corynebacterium diphtheriae bacteria. This toxin has two components, one that binds the host cell and one that causes disease. Which of the following about the diphtheria toxin is false?

• A. An endotoxin.
• B. An exotoxin.
• C. An A-B toxin.
• D. A protein toxin.
• E. Highly toxic.
• F. Lethal in small doses.

Answer: (A)

Here’s what students ask on this topic:

What are the main differences between exotoxins and endotoxins?

Exotoxins are protein-based toxins produced by both gram-positive and gram-negative bacteria, found in the cytoplasm, and can be secreted into the environment. They are heat-sensitive and can form toxoids, which are used in vaccines. Exotoxins exhibit high toxicity even in small doses and can affect various body systems. In contrast, endotoxins are lipopolysaccharides (LPS) associated with the outer membrane of gram-negative bacteria. They are heat-resistant and cannot form toxoids. Endotoxins have low toxicity unless they enter the bloodstream, where they can cause septic shock, fever, and other severe symptoms.

How do exotoxins and endotoxins affect the human body differently?

Exotoxins can have a wide range of effects on the human body, including disrupting cell functions, causing cell lysis, and targeting specific tissues such as the nervous system or gastrointestinal tract. They are highly toxic even in small doses. Endotoxins, on the other hand, primarily cause symptoms like fever, weakness, and body aches. If endotoxins enter the bloodstream, they can lead to septic shock, which is potentially fatal. However, endotoxins generally exhibit low toxicity unless they spread through the bloodstream.

Why are exotoxins heat-sensitive while endotoxins are heat-resistant?

Exotoxins are heat-sensitive because they are made of proteins, which can denature and lose their functional structure when exposed to high temperatures. This makes them susceptible to inactivation by heat treatments such as autoclaving. In contrast, endotoxins are heat-resistant because they are composed of lipopolysaccharides (LPS), which are more stable and less likely to be denatured by heat. This stability requires alternative methods for inactivation beyond just heat exposure.

Can toxoids be formed from both exotoxins and endotoxins?

Toxoids can be formed from exotoxins but not from endotoxins. Exotoxins, being protein-based, can be inactivated to form toxoids, which are used in vaccines to elicit an immune response without causing disease. This process is not possible with endotoxins, as they are lipopolysaccharides and do not have the same properties that allow for the formation of toxoids. Therefore, vaccines against endotoxins are not currently available.

What is the role of lipopolysaccharides (LPS) in endotoxins?

Lipopolysaccharides (LPS) are the main component of endotoxins and are found in the outer membrane of gram-negative bacteria. The LPS molecule consists of a lipid A region, which is the toxic component, and a polysaccharide region. When gram-negative bacteria die and their cell walls break down, LPS is released, potentially entering the bloodstream and causing severe immune responses such as septic shock, fever, and inflammation. The lipid A component is particularly responsible for the toxic effects associated with endotoxins.