Difference between endotoxin and exotoxin

Main difference

The main difference between endotoxin and exotoxin is that endotoxin are lipopolysaccharide protein complexes that are the structural component of the bacterial cell wall, while exotoxin is the protein secreted by specific bacteria …

Endotoxin vs. exotoxin

Endotoxins are lipopolysaccharides that are an integral part of the cell membrane of gram-negative bacteria and are found in toxins under some conditions. Exotoxins are protein substances or thermolabile toxoids that are released mostly by gram-positive bacteria, but sometimes also by gram-negative bacteria in their environment. Endotoxins are the associated cellular toxins, while exotoxins are the extracellular diffusible toxins. The molecular weight of endotoxins ranges from 50 to 1000 kDa and is associated with the lipopolysaccharide complex, while the molecular weight of exotoxin is approximately ten kDa and is associated with the protein complex. Endotoxins show heat stability at approximately 250 ° C and does not denature on heating,

Comparative chart

Endotoxin Exotoxin
Endotoxin is the lipid portion of lipopolysaccharides that is part of the outer membrane of the cell wall of gram-negative bacteria. Exotoxin is the protein produced within the pathogenic bacteria most commonly gram-positive bacteria, as a result of growth and metabolism.
Lipopolysaccharide from gram-negative bacteria Proteins secreted by bacteria
Located within the cell wall of the bacteria and released by lysis. Both types of bacteria (gram positive and negative) secrete toxins outside of cells
Action mode
The mechanism of action is TNF and interleukin-1. A different method of actions
Thermal stability
Heat stable Thermolabile
Screening tests
Limulus lysate assay test ELISA method, Precipitation, Neutralization,
Weak immunogenicity Immunogenic in nature
No vaccines available Vaccines are available
Typhoid fever, coronary artery disease, meningococcal meningitis, neonatal necrotizing enterocolitis, ulcerative colitis, Crohn’s disease, hemorrhagic shock, cystic fibrosis, sepsis, meningococcemia, urinary tract infection Scarlet fever, diphtheria, gas gangrene, botulism, scalded skin syndrome, antibiotic-associated diarrhea, tetanus
Causes fever
Yes Do not
Enzymatic activity
No enzymatic activity Most of the activities are enzymatic
Cannot be denatured Can be denatured
Poor Tall
Nonspecific Specific for a particular strain of bacteria
Moderately toxic Highly toxic
Gentle filtration Good filtration
Molecular weight
50 to 1000 KDa 10 kDa
E-Coli, Shigella, Salmonella typhi S. Aureus, Vibrio Cholera, Bacillus cereus, B Anthrcis, Streptococcus Pyrogenes
What is endotoxin?

Endotoxins are present in the cell envelope or outer membrane of bacteria, which is why they are called cell-associated components that are responsible for the structural elements of bacteria. Endotoxins are also known as lipopolysaccharides (LPS). These are found on the outer surface of gram-negative bacteria and, under certain conditions, become toxic to the host to which they are attached. In bacteriology, the term lipopolysaccharides is reserved with the outer surface of gram-negative pathogens such as E-Coli, Pseudomonas, Shigella, H Influenza, Vibrio Cholera, and Bordetella Pertussis. These endotoxin LPS are released from bacteria upon cell lysis or death. In lipopolysaccharides, toxicity is associated with lipid content, while immunogenicity is associated with polysaccharide content. In animals, endotoxins evoke various inflammatory responses and activate complement through the alternative pathway. Growing bacteria produce a small amount of endotoxin that plays an important role in their growth.

What is exotoxin?

Exotoxins are usually secreted by bacteria and act enzymatically or with direct action on the host cell. These are secreted by bacteria to the surrounding area. These are proteins or polypeptides and, for the most part, act at the site of the tissue that is far from the original site of bacterial growth or invasion. Normally, exotoxins are secreted in the exponential phase of bacterial cell growth. The production of toxins is particular to certain species of bacteria that are known to cause disease such as, for example, Clostridium tetani, which are named to provide tetanus toxoid, whereas Cornybacterium diphtheria is known to secrete diphtheria toxin. These types are the virulent strains of the bacteria that secrete toxins, while the non-virulent strains do not.

Exotoxins can trigger the host in multiple ways, inhibiting protein synthesis (diphtheria toxin), activating immune responses (S. aureus), activating secondary messenger pathways (cholera toxin), through the action of metalloprotease activity (tetanus toxin). and even damaging the membrane cells (hemolysis of E. coli).

Key differences
  1. Endotoxin is an integral part of the bacterial cell wall, while exotoxin is secreted by the bacteria.
  2. Endotoxin is present only in gram-negative type bacteria, while exotoxin is present in both gram-positive and gram-negative type bacteria.
  3. Endotoxin is the lipopolysaccharide complex while exotoxin is the polypeptide.
  4. Endotoxin is heat stable while exotoxin is heat labile (60 ° C)
  5. Endotoxin is weakly immunogenic while exotoxin is highly antigenic.
  6. Endotoxin has no specific receptors, while exotoxin has specific receptors to bind to.

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