What is an Endotoxin? Is it in my water?
Q&A with Dr. Andreas Capewell
March 14, 2022
What is an endotoxin and where does it come from?
It is released by Gram-negative bacteria. Bacteria can be divided into two groups, based on their reaction to a staining test devised by a Danish doctor, Hans Christian Gram. This staining technique differentiates bacteria because of their different outer layers, and those giving a negative reaction are termed Gram-negative. The outer layer of these Gram-negative bacteria is made up of endotoxin and protein. Gram-positive bacteria do not produce endotoxin.
The endotoxin is shed by the bacterial cell during normal cell growth and division and large amounts of it are liberated when the cell dies and bursts (undergoes lysis). This lysis can be rapidly induced by exposing the bacteria to some types of antibiotic1, physical or thermal stress.
Endotoxin is a large chemical structure consisting of fat (lipid A) and carbohydrate (polysaccharide), hence its other name lipopolysaccharide or LPS. The lipid A component carries a negative charge. Endotoxin is shed by the cell in large particles which have a high density of negative charges on their surface.
How does endotoxin get into the body?
One way is from the large number of Gram-negative bacteria in the gut2. In some cases, the lining of the gut breaks down or becomes leaky and these bacteria and/or their endotoxin can then pass into the bloodstream. This bacterial translocation is believed to be one of the causes of septic shock in critically ill patients. This route could be called endogenous endotoxin.
Another is from an infection, such as an abscess or a wound infection, or bacterial infection of a catheter.
The third way is from an external source, such as contaminated equipment or fluids. This could be called exogenous endotoxin. There have been many reports of Gram-negative bacterial contamination of intravenous infusion fluids leading to septicaemia3-13. Fluids and equipment used in IV therapy14, cardiopulmonary bypass15-17 and dialysis18-22 have all been found in the past to be the cause of endotoxic shock. Water can be harmful when it is used for flushing of critical parts of the patient body, e.g. lung23, wounds or mucous membranes.
What happens if endotoxin gets into the body?
Endotoxin are a type of pyrogen, which means that they can cause fever when they come into contact with mucous membranes and enter the blood in humans. They also activate a number of signaling pathways of immunocompetent cells that can lead to either inflammation or programmed cell death (apoptosis) of these cells. They are biologically effective even in the lowest concentrations.
How is endotoxin measured?
Currently, the most sensitive method for measuring endotoxin comes from a chemical isolated from horseshoe crabs. This is called the limulus amebocyte lysate test, or LAL test. This is a common way to test for endotoxin in water.
The monocyte activation test (MAT) is an in vitro test based on the human fever reaction with human blood cells (monocytes). The MAT not only records endotoxic pyrogens, but also non-endotoxin pyrogens (not possible in the LAL) and is just as easy to carry out as the LAL test.
How does endotoxin get into the water?
Domestic water installations are regularly contaminated with Gram-negative bacteria. The drinking water can therefore contain high concentrations of endotoxin (up to 4 ng/l24). It is important to also consider that the use of extremely high temperatures, such as for sterilization, can aid in the creation of large quantities of endotoxin.
Where do you need to monitor and control endotoxin in the water?
It is extremely important to monitor and control for endotoxin in water that is to be used for dialysis or in the reprocessing of equipment that can be used for surgeries, invasive procedures, and other use in the body.
Many countries have regulations, guidelines, and standards in place to set a limit for endotoxin found in the water for specific procedures and equipment.
How do you control endotoxin in the water?
In addition to monitoring endotoxin levels, certain types of filters can help reduce endotoxin in the water. In general, these filters remove endotoxin by either using filtration media with a positive charge or by using media with a very small pore size.
It may also be important to consider the necessity of heat-generating processes when endotoxin is of concern. If high temperatures can be reduced it will likely simplify monitoring and controlling for endotoxin.
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