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6.2: The Ability to Produce Harmful Exotoxins: An Overview

Skills to Develop

  1. Define exotoxin and list three types of exotoxins.
  2. State the major way the body defends itself against exotoxins.

Exotoxins (def) are toxins, often proteins in nature, secreted from a living bacterium but also released upon bacterial lysis. In addition, some bacteria use various secretion systems such as the type 3 secretion system to inject toxins directly into human cells. (As learned earlier, the lipopolysaccharide or LPS portion of the Gram-negative bacterial cell wall is known as endotoxin (def), a PAMP that can initiate an excessive inflammatory response in the host. It was originally called endotoxin because it was located within the Gram-negative cell wall as opposed to being secreted from bacteria as in the case of exotoxins.)

Not all exotoxins are necessarily produced to harm humans. Some may be designed to play a role in bacterial physiology, such as resisting bacteriophages, regulating cellular function, or quorum sensing. Other toxins may be produced primarily to target protozoa, insects, and smaller animals and harming human cells becomes an accidental side effect.

There are three main types of exotoxins:

  1. superantigens (Type I toxins);
  2. exotoxins that damage host cell membranes (Type II toxins); and
  3. A-B toxins and other toxin that interfere with host cell function (Type III toxins).

The body's major defense against exotoxins is the production of antitoxin antibodies. Once the antibody binds to the exotoxin, the toxin can no longer bind to the receptors on the host cell membrane.

We will now look at each of these three types of exotoxins.

Summary

  1. Exotoxins are toxins, often protein in nature, secreted from a living bacterium.
  2. Some bacteria use various secretion systems to inject toxins directly into human cells.
  3. There are three main types of exotoxins: superantigens (type I toxins); exotoxins that damage host cell membranes (type II toxins); and A-B toxins and other toxin that interfere with host cell function (type III toxins).
  4. The body's major defense against exotoxins is the production of antitoxin antibodies. Once the antibody binds to the exotoxin, the toxin can no longer bind to the receptors on the host cell membrane.

Questions

Study the material in this section and then write out the answers to these questions. Do not just click on the answers and write them out. This will not test your understanding of this tutorial.

  1. List three types of exotoxins.
    1. (ans)
    2. (ans)
    3. (ans)
  2. Define exotoxin. (ans)
  3. The body's major defense against exotoxins is _______________________________________________. (ans)

 


Contributors

  • Dr. Gary Kaiser (COMMUNITY COLLEGE OF BALTIMORE COUNTY, CATONSVILLE CAMPUS)