- A specific, soluble, antigenic, usually heat labile, injurious substance elaborated by certain Gram-positive or Gram-negative bacteria; it is formed within the cell, but is released into the environment where it is rapidly active in extremely small amounts; most exotoxins are protein in nature (MW 70,000–900,000) and can have the toxic portion of the molecule destroyed by heat, prolonged storage, or chemicals; the nontoxic but antigenic form is a toxoid. SYN: ectotoxin, extracellular toxin.
* * *exo·tox·in .ek-sō-'täk-sən n a soluble poisonous substance produced during growth of a microorganism and released into the surrounding medium <tetanus \exotoxin> compare ENDOTOXINexo·tox·ic -'täk-sik adj
* * *n.a highly potent poison, often harmful to only a limited range of tissues, that is produced by a bacterial cell and secreted into its surrounding medium. It is generally unstable, being rendered inactive by heat, light, and chemicals. Exotoxins are produced by such bacteria as those causing botulism, diphtheria, and tetanus. Compare endotoxin.
* * *exo·tox·in (ekґso-tok″sin) [exo- + toxin] a toxic substance that is formed by species of certain bacteria, such as Bacillus, Bordetella, Clostridium, Corynebacterium, Escherichia, Pseudomonas, Salmonella, Shigella, Staphylococcus, Streptococcus, Vibrio, and Yersinia, and is found either on the outside of the bacterial cell or free in the culture medium. Exotoxins are protein in nature and heat-labile; they are detoxified with retention of antigenicity by treatment with formaldehyde (formol toxoid), and are the most poisonous substances known to humans. The LD50 of crystalline botulinum type A toxin for the mouse is 4.5 Ð§ 10−9 mg.
Medical dictionary. 2011.