Toxins

Toxins are harmful compounds that are produced and released by a variety of microorganisms and other organisms. Toxins can be fast-acting and, because they are already pre-formed, do not require the growth of a microorganism in the host. The illness and death that result from exposure to a variety of toxins make their detection a central part of forensic science.

Toxins are the main disease-causing factor for a number of bacteria. Some examples include Coryne-bacterium diphtheriae (diptheria), Vibrio cholerae (cholera), Bacillus anthracis (anthrax), Clostridium botulinum (botulism), certain strains of Escherichia coli (hemolytic uremic syndrome), and Staphylococcus aureus (toxic shock syndrome).

Certain species of these bacteria are of particular concern in biological warfare and biological terrorism. As the events of 2001 in the United States demonstrated, powdered preparations of Bacillus anthracis spores were easily delivered to a target through the mail. The dispersal of the spores in the air and the inhalation of the spores can cause a form of anthrax that develops quickly and, without treatment, is almost always fatal. The bacteria in the genus Clostridium also form spores. Additionally, during the 1990s, a strain of Staphylococcus aureus emerged that is resistant to almost all known antibiotics.

Bacterial toxins have a wide variety of activity. Some toxins damage the cell walls of host cells, either by dissolving the wall or by chemically punching holes through the wall. Examples of such toxins are the alpha toxin of Clostridium perfringens, hemolysin of Escherichia coli, and streptokinase of Streptococcus pyogenes. The damage to the host cells allows the bacteria to spread rapidly through the host. This can cause an overwhelming infection.

Other bacterial toxins kill host cells by stopping the manufacture of protein in host cells, or by degrading the proteins. Examples of protein blockers include exotoxin A of Pseudomonas aeruginosa and the Shiga toxins produced by both Escherichia coli and Shigella dysenteriae. Protein degrading toxins include those produced by Bacillus anthracis and Clostridium botulinum

Still other toxins stimulate an immune response of the host that is so strong that it can damage the host. The toxic shock syndrome associated with Staphylococcus aureus results from a host hyperimmune response to three of the bacterial proteins.

Other microorganisms also produce toxins. Marine microorganisms called dinoflagellates can produce toxins when they grow in species of shellfish. Eating the toxic shellfish can cause serious illness.

Some species of mold produce aflatoxin. Aspergillus flavus and Aspergillus parasiticus are aflatoxin-producing molds. The toxin is especially a concern when potatoes are contaminated. Ingestion of the contaminated potatoes can cause serious, even fatal illness.

Ricin is a toxin that is produced by the castor bean. It is the third most deadly toxin that is known, after the toxins produced by Clostridium botulinum and Clostridium tetani. The symptoms of ricin toxin include nausea, muscle spasms, severe lung damage, and convulsions. These symptoms appear within hours, and, without treatment, death from pulmonary failure can result within three days. There is no vaccine or antidote for ricin toxin.

Some toxins that are capable of causing much harm are also a source of protection. Because of its potency, a toxin cannot be used protectively in its unaltered form. Toxins can be altered, however, so that they do not produce the undesirable effects, but still stimulate the immune system to produce antibodies to a critical part of the toxin molecule. The weakened version of a toxin is called a toxoid.

The anthrax vaccine that is currently licensed for use contains two toxoids in addition to other immune stimulating molecules. The immune response will produce antibodies to the two toxins of the anthrax bacterium.