endotoxin

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.

endotoxin

[en´do-tok″sin] a heat-stable toxin associated with the outer membranes of certain gram-negative bacteria, including Brucella, Neisseria, and Vibrio species. Endotoxins are not secreted but are released only when the cells are disrupted; they are less potent and less specific than the exotoxins; and they do not form toxoids. In large quantities they produce hemorrhagic shock and severe diarrhea; smaller amounts cause fever, altered resistance to bacterial infection, leukopenia followed by leukocytosis, and numerous other biologic effects.

Results of endotoxin release. From Copstead, 1995.

en·do·tox·in

(en-dō-tok'sin), 1. A bacterial toxin not freely liberated into the surrounding medium, in contrast to exotoxin. 2. The complex phospholipid-polysaccharide macromolecules that form an integral part of the outer membrane of a variety of relatively avirulent as well as virulent strains of gram-negative bacteria. The toxins are relatively heat stable, are less potent than most exotoxins, are less specific, and do not form toxoids; on injection, they may cause a state of shock and, in smaller doses, fever and leukopenia followed by leukocytosis; they have the capacity of eliciting the Shwartzman and the Sanarelli-Shwartzman phenomena. Synonym(s): intracellular toxin

endotoxin

(ĕn′dō-tŏk′sən)n. A toxin produced by certain bacteria and released upon destruction of the bacterial cell.

en′do·tox′ic adj.

endotoxin

Bacterial endotoxin, lipid A Microbiology A heat-stable lipopolysaccharide on the outer coat of gram-negative bacteria–eg, those causing cholera, meningitis, pneumonia, plague, whooping cough, et al Clinical Leukopenia, thrombocytopenia, fever, chills, hemorrhagic shock, dec resistance to infection

en·do·tox·in

(en'dō-tok'sin) 1. A bacterial toxin not freely liberated into the surrounding medium, in contrast to exotoxin. 2. The complex phospholipid-polysaccharide macromolecules that form an integral part of the cell wall of strains of gram-negative bacteria. The toxins may cause a state of shock accompanied by severe diarrhea, and, in smaller doses, fever and leukopenia followed by leukocytosis.
Synonym(s): intracellular toxin.

endotoxin

A poisonous lipopolysaccharide formed in the cell wall of a GRAM-NEGATIVE bacterium by means of which the organism causes its damage to the host. Compare exotoxin.

endotoxin

a poison that is produced by and remains inside a living CELL. It is only released upon disintegration of the organism. An example is the delta-endotoxin produced by the BACTERIUM Bacillus thuringiensis, and active against certain insect larvae. GENES for such toxins have been introduced into plants by GENETIC ENGINEERING with a view to conferring insect resistance upon them.

en·do·tox·in

(en'dō-tok'sin) 1. A bacterial toxin not freely liberated into the surrounding medium. 2. The complex phospholipid-polysaccharide macromolecules that form an integral part of the cell wall of strains of gram-negative bacteria; may cause shock, severe diarrhea, and fever.
Synonym(s): intracellular toxin.

endotoxin

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Antonyms for endotoxin

noun a toxin that is confined inside the microorganisms and is released only when the microorganisms are broken down or die

Related Words

Antonyms