Differences between Exotoxins and Endotoxins

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S.N.

Character

Exotoxins

Endotoxins

1.      

Definition

Proteins produced inside pathogenic bacteria as a part of their growth and metabolism.

Lipid portions of lipopolysaccharides (LPSs) that are the part of outer membrane of bacteria.

2.      

Produced by

Mostly Gram positive bacteria and also Gram negative bacteria.

Gram negative bacteria.

3.      

Chemical Nature

Protein (polypeptide) complexes

Lipopolysaccharide-protein complexes 

4.      

Molecular weight

 10KDa.

 50-1000KDa.

5.      

Components

Usually composed of two subunits A and B.
The A subunit is seen to have catalytic activity, whereas the B subunit is required for binding with an appropriate cell receptor. 

Composed of three basic components:

1.  O-antigen

2.  Core oligosaccharide

3.  Lipid A

6.      

Enzymes present

Hyaluronidase, Collagenase, certain protease, Nuclease, Neuraminidase, Certain protease, Phospholipase A

Catalase, Fibrolysin, IgA / IgG proteases

7.      

Chromosomal Location

Located on extrachromosomal genes (e.g. plasmids).

Located on chromosomal genes.

8.      

Secreted by

Secreted by organisms ; living cell

Integral part of cell wall ; lysed cell

9.      

Secretion

Secreted out of the cell.

Generally not released outside the cell until death of cell.

10.   

Cell Lysis

Not required

Required

11.   

Stability to heat

Heat labile (60-80°C)

Heat stable (250°C)

12.   

Filtration

Filterable

Not Filterable

13.   

Boiling

Denatured on boiling

Not denatured on boiling.

14.   

Enzyme Activity

Mostly has enzymatic activity.

Enzymatic activity absent or limited.

15.   

Specificity

Exotoxins are enzymes; this makes them highly specific in their mechanism and for their host cells.

Endotoxins are comparatively not very specific in nature.

16.   

Specific receptors

Usually binds to specific receptors.

Specific receptors not found.

17.   

Specificity to bacterial strain

Specific to certain bacterial strain.

Not specific to any bacterial strain.

18.   

Immunogenicity

Highly immunogenic.

Weakly immunogenic.

19.   

Fever Induction

No

Fever by induction of interleukin 1 (IL-1) production.

20.   

Toxicity

Highly toxic, fatal in µg quantities.

Moderately toxic, fatal in mg quantities.

21.   

Mode of action

 

Various modes (Mostly by enzyme-like mechanisms).

Includes TNF and Interlukin-1

22.   

Potency

High: A single toxin molecule can act on a large number of host cells.

Low: A large amount of toxin is needed to cause a disease.

23.   

Effects

Either cytotoxin, enterotoxin or neurotoxin with defined action on cells or tissues.

General symptoms such as fever, diarrhea, vomiting etc.

24.   

Neutralization by Antibodies

Can be neutralized.

Cannot be neutralized.

25.   

Detection

Detected by many tests (neutralization, precipitation, etc)

Detected by Limulus lysate assay.

26.   

Conversion to Toxoids

 

Possible (On treatment with formalin). eg. For the prevention of diphtheria, botulism, and tetanus.

Not possible

27.   

Availability of vaccines

Effective vaccines available.

No effective vaccines available.

28.   

Diseases caused

Tetanus, diphtheria, botulism etc.

Meningococcemia, sepsis by gram negative rods etc.

29.   

Examples

Toxins produced by Staphylococcus aureus, Bacillus cereus, Streptococcus pyogenes, Bacillus anthracis

Toxins produced by E.coli, Salmonella Typhi, Shigella, Vibrio cholera