Difference Between Endotoxins and
Exotoxins in Microbiology
Toxins are harmful chemical substances that are produced by living cells or organisms.
Toxins are tiny molecules, peptides, or proteins that can cause disease when they come into
contact with or are absorbed by human tissues and interact with biological macromolecules
such as enzymes or cellular receptors. Toxins were the first bacterial virulence agents
discovered, and they also provided the first link between bacteria and cell biology.
Bacterial Toxigenesis
The ability to produce toxins is an underlying mechanism by which many bacterial infections
cause disease. Lipopolysaccharides, which are associated with Gram-negative bacteria's cell
wall, and proteins, which are released from bacterial cells and may act at tissue sites away
from the area of bacterial growth. Endotoxins are toxins that are associated with bacterial
cells, while exotoxins are toxins that are diffusible outside of cells.
Endotoxins are structural components of bacteria that are linked to cells. The majority of
endotoxins are present in the cell envelope. The lipopolysaccharide (LPS) or
lipooligosaccharide (LOS) found in Gram-negative bacteria's outer membrane is referred to
as endotoxin. Although soluble endotoxins are not structural components of cells, they can
be released by growing bacteria or cells that have been lysed as a result of successful host
defense mechanisms or antibiotic activity. Endotoxins are toxins that are produced in the
presence or in the presence of bacteria.
Exotoxins are heat labile proteins released by specific bacteria species and permeate into the
surrounding medium.
Differences between Endo and Exotoxins
S.N.
Character
1.
Definition
2.
3.
4.
Exotoxins
Exotoxins are Proteins mostly produced by gram
positive bacteria. Exotoxins are produced inside a
bacteria as a part of their growth and metabolism.
Bacteria
Mostly Gram positive bacteria and can also be
produced by certain Gram negative bacteria.
Chemical Nature of Protein complexes in nature
the toxin
Molecular weight
High
Endotoxins
Lipid parts of lipopolysaccharides (LPSs) produced by
bacteria are the part of outer membrane of bacteria.
Produced by Gram negative bacteria.
They are Lipopolysaccharide-protein complexes in nature
50-1000KDa.
5.
Components
6.
Enzymes present
7.
Chromosomal
Location
Secreted by
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
It's usually made up of two subunits, A and B.
The A subunit appears to have catalytic activity,
whereas the B subunit is necessary for cell receptor
interaction.
It's usually made up of two subunits, A and B.
The A subunit appears to have catalytic activity,
whereas the B subunit is necessary for cell receptor
interaction.
Hyaluronidase, Collagenase, certain protease, Nuclease,
Neuraminidase, Certain protease, Phospholipase A
Located on extrachromosomal genes for example;
plasmid
Secreted by living cell organisms when the bacteria is
actively dividing
Secreted out of the bacterial cell.
Composed of three basic components:
1. O-antigen
2. Core oligosaccharide
3. Lipid A
Catalase, Fibrolysin, IgA / IgG proteases
Present in chromosomal genes or DNA.
Integral part of cell wall ; produced only when the cell is
lysed
Secretion
Generally not released outside the cell. Only when the
bacterial cell is lysed.
Cell Lysis
Not required
Required
Stability to heat
Heat labile about 60-80°C
Heat stable 240°C
Filtration
Filterable
Not Filterable
Boiling
Denatured on boiling
Not denatured on boiling.
Enzyme Activity
Mostly has enzymatic activity.
Enzymatic activity limited.
Specificity
Exotoxins are enzymes, which means they have a very Endotoxins, on the other hand, are not extremely specific in
particular mechanism and target cells.
nature.
Specific receptors
Mostly binds to specific receptors.
Specific receptors not found.
Specificity
to Specific to certain bacterial strain.
Not specific to any bacterial strain.
bacterial strain
Immunogenicity
Highly immunogenic.
Weakly immunogenic.
Fever Induction
No
Induction of interleukin 1 (IL-1) production causes fever.
Toxicity
Highly toxic, deadly or harmful in µg quantities.
Moderately toxic, fatal in mg quantities.
Mode of action
Various modes (Mostly by enzyme-like mechanisms).
Includes TNF and Interlukin-1
Potency
High: A single toxin molecule can act on a large Low: A large amount of toxin is needed to cause a disease.
number of host cells.
Effects
Either cytotoxin, enterotoxin or neurotoxin with General symptoms such as fever, diarrhea, vomiting etc.
defined action on cells or tissues.
Neutralization by Can be neutralized.
Cannot be neutralized.
Antibodies
Detection
Detected by many tests (neutralization, precipitation, Detected by Limulus lysate assay.
etc)
Conversion
to Possible (On treatment with formalin). eg. For the Not possible
Toxoids
prevention of diphtheria, botulism, and tetanus.
Availability
of Effective vaccines available.
No effective vaccines available.
vaccines
Diseases caused
Tetanus, diphtheria, botulism
Meningococcemia.
Examples
of Toxins produced by Staphylococcus aureus, Bacillus Toxins
produced
by
pathogenic
strains
bacteria
cereus, Streptococcus pyogenes, Bacillus anthracis
of E.coli, Salmonella Typhi, Shigella, Vibrio choler
CONCLUSION
Bacterial toxin is one of the most severe and active human toxins. We now understand the
distinctions and effects of endotoxins and exotoxins on animals and their immunity according
to their chemical makeup.