Compare and contrast endotoxins and exotoxins.

Both endotoxins and exotoxins are produced by Gram-negative bacteria. Exotoxins are also produced by Gram-positive bacteria. Endotoxins and exotoxins differ in their mechanism of release and composition: exotoxins are proteins or peptides that are secreted, leaving the cell intact, whereas endotoxins are lipids released only when the cell dies because they are a part of the outer membrane. The toxicity of exotoxins is higher than that of endotoxins, but both can be fatal. Both are heat stable, but endotoxins can survive an hour of autoclaving at 121°C, whereas exotoxins are not stable above 60°C. Exotoxins produce a strong immune response, and therefore toxoid immunization is possible. Endotoxins produce fever, but only a weak immune response, so toxoid immunization is not an option.