endotoxin

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 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. SYN: intracellular toxin.

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en·do·tox·in .en-dō-'täk-sən n a toxin of internal origin specif a poisonous substance present in bacteria (as the causative agent of typhoid fever) but separable from the cell body only on its disintegration compare EXOTOXIN

en·do·tox·ic -sik adj

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n.

a poison generally harmful to all body tissues, contained within certain Gram-negative bacteria and released only when the bacterial cell is broken down or dies and disintegrates. Compare exotoxin.

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en·do·tox·in (enґdo-tok″sin) [endo- + toxin] a heat-stable toxin associated with the outer membranes of certain gram-negative bacteria, including the brucellae, the enterobacteria, neisseriae, and vibrios. 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. They are composed of complex lipopolysaccharide molecules, of which the polysaccharide unit (somatic O antigen) is responsible for antigenicity, occurring in hundreds of variations, and the phospholipid moiety (lipid A) is the source of toxicity. When injected in large quantities the endotoxins produce hemorrhagic shock and severe diarrhea; smaller amounts cause fever, altered resistance to bacterial infection, leukopenia followed by leukocytosis, and numerous other biologic effects. Called also bacterial pyrogen. See also toxin.