On this occasion we discuss the difference between Endotoxin and Exotoxin. Endotoxins are Lipopolysaccharide-protein complexes (LPS) which are responsible for making an integral part of the cell wall of Gram-Negative Bacteria and are released upon cell death or bacterial lysis. Exotoxins are proteins that are secreted by some species of bacteria and spread to the nearby or surrounding medium. Endotoxins are heat stable, weakly immunogenic, whereas exotoxins are heat labile, highly antigenic.
Endotoxins are produced by Gram-negative bacteria, whereas exotoxins are generally produced by Gram-positive or partially by Gram-negative bacteria. The underlying mechanism through which many pathogenic bacteria produce disease or the ability to produce toxins is known as Toxigenesis.
If we discuss at the chemical level, there are two types of bacterial toxins. The first is related to the cell wall of Gram-negative bacteria known as lipopolysaccharide, while the other is a protein, which acts on tissue sites after releasing from the bacterial cell. Thus, endotoxin is a cell-associated toxin, whereas exotoxin is an extracellular diffuse toxin.
Bacterial toxins are proteins capable of accomplishing a variety of tasks. They function as individual molecular devices, targeting specific cells of an organism and destroying them in several ways. The venom can trigger the host in various ways, for example by activating an immune response (S, aureus superantigen), inhibiting protein synthesis (diphtheria toxin), activating secondary messenger pathways (cholera toxin) by damaging cell membranes (E. metalloprotease activity (tetanus toxin).
Toxins can function in many forms, among which Lipopolysaccharide (LPS) is considered the most potent endotoxin. In this content, we will discuss the important points of difference between endotoxin and exotoxin of the two poisons with a brief description.
Definition of Endotoxin
Endotoxins are located in the cells of the cells or the outer membrane of bacteria, these are referred to as cell-associated substances which are responsible for the structural components of bacteria. Endotoxins are also referred to as Lipopolysaccharides or LPS. LPS is present on the outer surface of Gram-negative bacteria and under certain conditions becomes toxic to the adhering host.
In bacteriology, the term ‘Lipopolysaccharides’ is reserved for the complexity associated with the outer surface of Gram-negative pathogens such as Escherichia coli, Pseudomonas, Shigella, Haemophilus influenza, Vibrio cholerae, and Bordetella pertussis. LPS is secreted upon bacterial cell lysis or cell death. In this case, the toxicity is related to the lipid component (Lipid A), whereas the immunogenicity is to the polysaccharide component.
In animals, LPS evokes multiple inflammatory responses and activates complement by alternative pathways. Gram-negative bacteria release small amounts of endotoxin as they grow, which plays an important role in enhancing natural immunity.
Definition of Exotoxin
Exotoxins are generally secreted by bacteria and act enzymatically or by direct action of host cells. It is released by the bacteria into the surroundings. Exotoxins are proteins or polypeptides, and most of them act at tissue sites far from the starting point of bacterial growth or invasion.
Normally, exotoxins are secreted at the exponential phase of the bacterial cell. Production of toxins specific to certain bacterial species known to produce disease such as Clostridium tetani which is known to produce tetanus toxin; Cornybacterium diphtheria is known to produce diphtheria toxin.
These are virulent strains of bacteria that produce toxins, whereas nonvirulent strains do not. Exotoxins are considered to be the most toxic and lethal substances and they are toxic even in concentrations of nanograms per kilogram.
Key Difference Between Endotoxin and Exotoxin
The points below show some of the main differences between endotoxin and exotoxin:
- Endotoxin is a protein-lipopolysaccharide (LPS) complex that is responsible for making an integral part of the cell wall of Gram-Negative Bacteria. Exotoxins are proteins secreted by several species of bacteria. In fact, endotoxins are considered more toxic than exotoxins.
- Endotoxins are part of the cell because they are associated with the outer membrane of Gram-negative bacteria and are released upon cell lysis, whereas exotoxins are secreted inside the cell and are active in Gram-positive and Gram-negative bacteria. Exotoxins are released from cells.
- The molecular weight of the endotoxin may be between 50-1000KDa and is associated with the Lipopolysaccharide complex, on the other hand, the exotoxin has a molecular weight of 10KDa and is associated with the protein complex.
- Endotoxins are stable at 250 °C and do not undergo denaturation, whereas exotoxins are 60-80 °C and are denatured on boiling.
- The immune reaction becomes weak when endotoxin triggers cells and has high enzymatic activity but poor antigenicity, whereas during exotoxin reaction the immune reaction is strong, although there is no enzymatic activity and high antigenicity.
- Sepsis, meningococcemia are diseases caused by endotoxins, while Diptheria, botulism, tetanus are caused by exotoxins.
- Examples of bacteria that trigger LPS or endotoxins are Salmonella typhi, E.coli, Vibrio cholera, Shigella, while Bacillus cereus, Bacillus anthracis, Staphylococcus aureus, Streptococcus pyrogens are examples for triggering exotoxins.
Conclusion: Bacterial toxins are the most potent and effective human toxins and are highly active at high dilutions. In this article, we have learned about endotoxins and exotoxins and how they differ and affect animals and their immune systems by their chemical properties.
