endotoxin


Also found in: Dictionary, Thesaurus, Medical, Wikipedia.
Related to endotoxin: endotoxin shock

Endotoxin

A biologically active substance produced by bacteria and consisting of lipopolysaccharide, a complex macromolecule containing a polysaccharide covalently linked to a unique lipid structure, termed lipid A. All gram-negative bacteria synthesize lipopolysaccharide, which is a major constituent of their outer cell membrane. One major function of lipopolysaccharide is to serve as a selectively permeable barrier for organic molecules in the external environment. Different types of gram-negative bacteria synthesize lipopolysaccharide with very different polysaccharide structures. The biological activity of endotoxic lipopolysaccharide resides almost entirely in the lipid A component. See Cell membranes, Lipid, Polysaccharide

When lipopolysaccharides are released from the outer membrane of the microorganism, significant host responses are initiated in humans and other mammals. It is generally accepted that lipopolysaccharides are among the most potent microbial products, known for their ability to induce pathophysiological changes, in particular fever and changes in circulating white blood cells. In humans as little as 4 nanograms of purified lipopolysaccharide per kilogram of body weight is sufficient to produce a rise in temperature of about 3.6°F (2°C) in several hours. This profound ability of the host to recognize endotoxin is thought to serve as an early warning system to signal the presence of gram-negative bacteria.

Unlike most microbial protein toxins (which have been termed bacterial exotoxins), endotoxin is unique in that its recognized mode of action does not result from direct damage to host cells and tissues. Rather, endotoxin stimulates cells of the immune system, particularly macrophages, and of the vascular system, primarily endothelial cells, to become activated and to synthesize and secrete a variety of effector molecules that cause an inflammatory response at the site of bacterial invasion. These mediator molecules promote the host response which results in elimination of the invading microbe. Thus, under these circumstances lipopolysaccharide is not a toxin at all, but serves an important function by helping to mobilize the host immune system to fight infection. See Cytokine, Immunology

Even though endotoxin stimulation of host cells is important to host defense against infection, overstimulation due to excess production of endotoxin can lead to serious consequences. Endotoxin-induced multiple-organ failure continues to be a major health problem, particularly in intensive care; it has been estimated that as many as 50,000 deaths annually occur in the United States as the result of endotoxin-induced shock.

Immunization of humans with endotoxin vaccines to protect against endotoxin shock has not been considered practical. Efforts to provide immunologic protection against endotoxin-related diseases have focused upon development of antibodies that recognize the conserved lipid A structure of endotoxin as a means of passive protection against the lethal effects of this microbial product. See Bacteria, Medical bacteriology, Vaccination

endotoxin

[‚en·dō′täk·sən]
(microbiology)
A biologically active substance produced by gram-negative bacteria and consisting of lipopolysaccharide, a complex macromolecule containing a polysaccharide covalently linked to a unique lipid structure, termed lipid A.
References in periodicals archive ?
Benefits of Quantitative Methods for Endotoxin Detection
The company said the EndoPur Endotoxin 10" Filter is designed to provide hemodialysis quality water to dialysis machines.
Changes in pulmonary function due to endotoxin exposure showed decreased force vital capacity, flow rate and peak expiratory flow parameters significantly different (pless than 0.
Net fluxes of endotoxin across portal-and mesenteric-drained viscera were calculated from the following equations:
All patients subjected to BC tests for the analysis of the endotoxin or PCT levels during ICU stay were enrolled in this study.
Since endotoxin remains toxic after most sterilization methods, a lot release test is typically performed to make sure the device meets endotoxin limits as established by regulatory standards.
in the presence of chelating agents) and surfactants are present to form mixed micelles, the endotoxin units become masked from detection by the LAL test.
The major source of endotoxin in dairy cows is the gastrointestinal tract, which contains a high amount of gram negative bacteria, especially when diets include high amounts of NSC, resulting in a potential source of LPS when entering to the organism through the gastrointestinal tract 38.
The research objectives were: (1) to determine endotoxin concentrations present in [PM.
As with the daily endotoxin concentrations, bacterial concentrations near the barn increased significantly at night, but concentrations farther downwind did not.
The ultrapure water produced by Sartorius' arium pro VF system exhibits an endotoxin content that is far below the prescribed limits, and can be used for applications in the categories mentioned earlier.