Endotoxins are lipopolysaccharides (LPS): molecules made of a lipid part joined to a chain of carbohydrate. They are built into the outer membrane of the cell wall of Gram-negative bacteria, such as Salmonella and E. coli. The toxic part is the lipid, called lipid A.Because endotoxins are part of the cell structure, they are not secreted. They are released mainly when bacteria die and break open, for example when they are attacked by the immune system or by some antibiotics. Small amounts are also shed from the surface of growing cells.Endotoxins act on the host's immune system rather than on one type of cell. They trigger macrophages and other cells to release chemical signals (cytokines), causing:
• fever;
• inflammation, which in the gut can cause diarrhoea and vomiting;
• in large amounts in the blood, widespread dilation of blood vessels, a fall in blood pressure and possibly septic shock.Key properties of endotoxins:
• they are relatively heat-stable, so cooking may not destroy endotoxins already present in food;
• they are less potent than most exotoxins, so a larger amount is needed to cause harm;
• they cannot easily be made into toxoids (inactivated toxins used as vaccines).Because killing large numbers of Gram-negative bacteria quickly can release a burst of endotoxin, symptoms can briefly get worse when treatment begins.
• fever;
• inflammation, which in the gut can cause diarrhoea and vomiting;
• in large amounts in the blood, widespread dilation of blood vessels, a fall in blood pressure and possibly septic shock.Key properties of endotoxins:
• they are relatively heat-stable, so cooking may not destroy endotoxins already present in food;
• they are less potent than most exotoxins, so a larger amount is needed to cause harm;
• they cannot easily be made into toxoids (inactivated toxins used as vaccines).Because killing large numbers of Gram-negative bacteria quickly can release a burst of endotoxin, symptoms can briefly get worse when treatment begins.