Pronunciation key

( ek′sō-toksin )



Biochem. Exotoxin is defined as one from among a group of toxic substances excreted by certain disease-producing microorganisms: also called true toxin. Toxin is secreted during the life of the organism, either in the body tissues or food or surrounding medium and is recoverable from a culture without destruction of the producing agent. Classically has been defined as poisonous substance secreted by certain bacteria. The term has since been restricted to poison proteins that are antigenic (that is, they stimulate the formation of antibodies and formed by gram-positive bacteria.)
Toxins are formed within and excreted by the bacterial cell which itself is not toxic, and found in its immediate surroundings. Exotoxins are heat labile, and protein in nature. They are detoxified with retention of antigenicity by treatment with formaldehyde and are the most toxic substances known to man. Bacteria of the genus Clostridium are the chief producers of exotoxins. Such toxins are diptheria, botulism, tetanus and are all caused by bacteria.

ex’o•toxic (adj.)

Compare with endotoxin.


  • The American College Dictionary (Random House) ©1949
  • Webster's New World Dictionary of the American Language (College Edition) ©1955
  • Funk and Wagnalls Standard Dictionary, Comprehensive International Edition ©1976
  • Encyclopedia and Dictionary of Medicine, Nursing and Allied Health ©1978
  • Encyclopedia Britannica Micropedia ©1984
  • The American Heritage Dictionary, Second College Edition ©1985
  • Further Reading

  • Bacterial Protein Toxins, © Kenneth Todar, PhD
  • Bacterial Pathogenesis
  • Exotoxins
  • Microbial Mechanisms of Pathogenicity
  • Bacterial Toxigenesis, Food Toxicology, Instructor: Gregory Möller, Ph.D., University of Idaho
  • Bacterial Pathogenesis
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