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:
|Excreted by organisms, living cell
|Integral part of cell wall
|Found in both Gram positive and Gram Negative bacteria
|Found mostly in Gram Negative Bacteria
|It is polypeptide
|It is lipopolysaccharide complex.
|Relatively unstable, heat labile (60°C)
|Relatively stable, heat tolerant
|Toxoids can be madeby treating with formalin
|Toxoids cannot be made
|Highly toxic, fatal in µg quantities
|Usually binds to specific receptors
|Specific receptors not found
|Not pyrogenic usually, Toxin Specific
|Fever by induction of interleukin 1 (IL-1) production, Shock
|Located on extrachromosomal genes (e.g. plasmids)
|Located on chromosomal genes
|It has mostly enzymatic activity
|It has no enzymatic activity
|Its molecular weight is 10KDa
|Its molecular weight is 50-1000KDa
|On boiling it get denatured.
|On boiling it cannot be denatured.
|Detected by many tests (neutralization, precipitation, etc)
|Detected by Limulus lysate assay
|Examples: Toxins produced by Staphylococcus 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)
|Diseases: Tetanus, diphtheria, botulism
|Diseases: Meningococcemia, sepsis by gram negative rods