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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


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 ?
ACC is an industry innovator and has been a leading global supplier of endotoxin and glucan detection products and services for 40 years.
The UV irradiation was found to effectively inactivate endotoxins (Anderson et al.
Unlike airborne microbes like bacteria and fungi, endotoxins are highly resistant to solar radiation and temperature.
Harte said that her research suggests this inflammatory insult could arise, in part, from a compromised gut mucosa that allows bacterial endotoxins to enter the circulation and initiate a systemic in-flammatory response.
The highest endotoxin levels were measured in small children and those whose heart defects resulted in compromised blood supply to the gut.
Cumulative exposure to endotoxins that was estimated at each survey was divided into two time windows: past endotoxin exposure, from date of hire up to the start of each survey interval, and recent endotoxin exposure within each current interval (Figure 1).
For endotoxins, Mycofix[R] was found to promote the adsorption of endotoxins but, most importantly, to positively counter the overall inflammatory effects of these substances.
Buffer was allowed to incubate in the tube for 24 h before endotoxin analysis using the Kinetic-QCL kit (Lonza).
Researcher Melisa Celaya, of the Arizona Respiratory Centre in Tucson, said homes with higher levels of endotoxin were over 30 years old, with "carpeting, a musty smell and interior water leaks".
Endotoxins, which are present in the cell walls of Gram-negative bacteria, pose a potential health hazard and must also be removed from process water, especially in high purity applications.
Endotoxin is a structural component found in the outer cell wall of Gram-negative bacteria.
In normal, low concentrations endotoxins are not dangerous and may even play a role in protecting people against allergies.