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Differences Between Exotoxins and Endotoxins

 Many bacteria produce toxins, enzymes and pigments. Toxins and enzymes play important role in pathogenecity. Toxins are of two types:

Exotoxins are usually heat labile proteins secreted by certain species of bacteria which diffuse into the surrounding medium.
Endotoxins are heat stable lipopolysaccharide-protein complexes which form structural components of cell wall of Gram Negative Bacteria and liberated only on cell lysis or death of bacteria.





Some of the differences between Exotoxins and Endotoxins are as follows:


S.N.
Exotoxins
Endotoxins
1
Excreted by organisms, living cell
Integral part of cell wall
2
Found in both Gram positive and Gram Negative bacteria
Found mostly in Gram Negative Bacteria
3
It is polypeptide
It is lipopolysaccharide complex.
4
Relatively unstable, heat labile (60°C)
Relatively stable, heat tolerant
5
Highly antigenic
Weakly immunogenic
6
Toxoids can be madeby treating with formalin
Toxoids cannot be made
7
Highly toxic, fatal in µg quantities
Moderately toxic
8
Usually binds to specific receptors
Specific receptors not found
9
Not pyrogenic usually, Toxin Specific
Fever by induction of interleukin 1 (IL-1) production, Shock
10
Located on extrachromosomal genes (e.g. plasmids)
Located on chromosomal genes
11
Filterable
Not so
12
It has no enzymatic activity
It has mostly enzymatic activity
13
Its molecular weight is 10KDa
Its molecular weight is 50-1000KDa
14
On boiling it get denatured.
On boiling it cannot be denatured.
15
Detected by many tests (neutralization, precipitation, etc)
Detected by Limulus lysate assay
16
Examples: Toxins produced byStaphylococcus aureus, Bacillus cereus, Streptococcus pyogenes, Bacillus anthrcis(Alpha-toxin, also known as alpha-hemolysin (Hla))
Examples: Toxins produced by E.coli, Salmonella Typhi, Shigella, Vibrio cholera(Cholera toxin- also known as choleragen)
17
Diseases: Tetanus, diphtheria, botulism
Diseases: Meningococcemia, sepsis by gram negative rods







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