Toxin:
Toxins are poisons, protein or conjugated protein produced by some higher plants, certain animals and pathogenic bacteria that is highly toxic to other living organisms.
Toxoid:
Toxoids are derivatives of bacterial exotoxins produced by chemically altering the natural toxin, or by engineering bacteria to produce harmless variants of the toxin.
Difference between exotoxin and endotoxin are given below:
| Exotoxin | Endotoxin |
| 1.Excreted by living cells. | 1.Integral part of the cell wall of Gram-negative bacteria.Released on bacterial death and in part during growth.Release is not required for biologic activity. |
| 2.Produced by both Gram-positive and Gram-negative bacteria. | 2.Produced only by Gram-negative bacteria. |
| 3.Highly antigenic | 3.Weakly antigenic |
| 4.Polypeptide in nature | 4.Lipopoly saccharide in nature. |
| 5.Toxoid can be produced | 5.Toxoid is not produced. |
| 6.Heat labile | 6.Heat stable |
| 7.Usually do not produced fever in the host | 7.Usually produced fever in the host by release of interleukin-1,and other mediators. |
| 8.Usually controlled by extra-chromosomal genes e.g-plasmid ,phage gene. | 8.Synthesis directed by chromosomal genes. |