toxin

Examples of toxin in the following topics:

• Paralysis-Causing Bacterial Neurotoxins

  • In 1973, Alan Scott used botulinum toxin type A (BTX-A) in monkey experiments.
  • The heavy chain of the toxin is particularly important for targeting the toxin to specific types of axon terminals.
  • The toxin must get inside the axon terminals to cause paralysis.
  • Following the attachment of the toxin heavy chain to proteins on the surface of axon terminals, the toxin can be taken into neurons by endocytosis.
  • The light chain of the toxin has protease activity.

• Toxins

  • Some of the major types of toxins include, but are not limited to, environmental, marine, and microbial toxins.
  • Microbial toxins may include those produced by the microorganisms bacteria (i.e. bacterial toxins) and fungi (i.e. mycotoxins).
  • Mycotoxins are the classes of toxins produced by fungi.
  • The most potent toxin is AFB1 and it is associated with carcinogenic effects.
  • Describe the major toxin types (bacterial toxins and mycotoxins) and their mechanisms of action

• Diphtheria

  • The toxin can cause damage to the heart that affects its ability to pump blood or the kidneys' ability to clear wastes.
  • Diphtheria toxin is produced by C. diphtheriae only when it is infected with a bacteriophage that integrates the toxin-encoding genetic elements into the bacteria.
  • This signals the cell to internalize the toxin within an endosome via receptor-mediated endocytosis.
  • Inside the endosome, the toxin is split by a trypsin-like protease into its individual A and B fragments.
  • Corynebacterium diphtheriae produces toxins that can affect the skin by causing skin lesions, as shown here.

• Botulism

  • Botulism is a rare, but sometimes fatal, paralytic illness caused by botulinum toxin.
  • This toxin is a protein produced under anaerobic conditions by the bacterium Clostridium botulinum.
  • Botulinium toxin is one of the most powerful known toxins: about one microgram is lethal to humans.
  • Three main modes of entry for the toxin are known.
  • The bacterium then releases the toxin into the intestine, which is absorbed into the bloodstream.

• Staphylococcal Food Poisoning

  • Staphylococcal toxins are a common cause of food poisoning, as they can be produced in improperly-stored food.
  • Foodborne disease can also be caused by a large variety of toxins that affect the environment such as pesticides or medicines in food and naturally toxic substances such as poisonous mushrooms or reef fish.
  • Staphylococcus is a Gram-positive bacteria which includes several species that can cause a wide variety of infections in humans and other animals through infection or the production of toxins.
  • Staphylococcal toxins are a common cause of food poisoning, as they can be produced in improperly-stored food.
  • Toxins for bacterial infections are delayed because the bacteria need time to multiply.

• Human Health and Biodiversity

  • Maintaining biodiversity ultimately helps maintain of human health; many medicines are derived from plants and, recently, animal toxins.
  • Most plants produce secondary plant compounds, which are toxins used to protect the plants from insects and other animals that eat them, but some of which also work as medicines.
  • By 2007, the FDA had approved five drugs based on animal toxins to treat diseases such as hypertension, chronic pain, and diabetes.
  • Other toxins under investigation come from mammals, snakes, lizards, various amphibians, fish, snails, octopuses, and scorpions.

• Direct Damage

  • Upon the use of host nutrients for its own cellular processes, the bacteria may also produce toxins or enzymes that will infiltrate and destroy the host cell.
  • Examples of bacteria that will damage tissue by producing toxins, include, Corynebacterium diphtheriae and Streptococcus pyogenes.
  • It produces a toxin, diphtheria toxin, which alters host protein function.
  • The toxin can then result in damage to additional tissues including the heart, liver, and nerves.

• Genetically Modified Organisms (GMOs)

  • Bt toxin has to be ingested by insects for the toxin to be activated.
  • Insects that have eaten Bt toxin stop feeding on the plants within a few hours.
  • After the toxin is activated in the intestines of the insects, death occurs within a couple of days.
  • Modern biotechnology has allowed plants to encode their own crystal Bt toxin that acts against insects.
  • The crystal toxin genes have been cloned from Bt and introduced into plants.

• Peroxisomes

  • Peroxisomes neutralize harmful toxins and carry out lipid metabolism and oxidation reactions that break down fatty acids and amino acids.
  • Like miniature sewage treatment plants, peroxisomes neutralize harmful toxins so that they do not cause damage in the cells.

• Scarlet Fever

  • Scarlet fever is caused by an erythrogenic toxin, a substance produced by the bacterium Streptococcus pyogenes (group A strep. ) when it is infected by a certain bacteriophage.
  • Exotoxin A (speA) is probably the best studied of these toxins.
  • It is carried by the bacteriophage T12, which integrates into the Streptococcal genome, from where the toxin is transcribed.