Exotoxin

Toxins are powerful pathogenicity factors produced by certain bacteria, fungi, animals, and plants which mediate drastic interactions of these pathogens on the organism host.

Exotoxins can be single polypeptides or heteromeric protein complexes that act on different parts of the cells. At the cell surface, they may insert into the membrane to cause damage, bind to receptors to initiate their uptake, or facilitate interactions with other cell types.

A specific bacterial pathogen may produce a single exotoxin or multiple exotoxins. Each exotoxin possesses a unique mechanism of action, which is responsible for the elicitation of a unique pathology.

Exotoxin can be found in both Gram positive and Gram-Negative bacteria. Exotoxins have a significant and sometimes the primary role as the disease-causing virulence factor,

There are three main types of exotoxins and they are often classified by their mode of action on animal cells:
•Type I (membrane acting) toxins bind surface receptors and stimulate transmembrane signals, and include the super-antigenic toxins.
•Type II (membrane damaging) exotoxins that damage host cell membranes
•Type III (intracellular effector) toxins translocate an active enzymatic component into the cell and modify an intracellular target molecule.

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.
Exotoxin

Endotoxins

Endotoxin was first described by Richard Pfeiffer as a heat-stable, cell-associated material isolated from Vibrio cholerae which induced toxic reactions in guinea-pigs.

Endotoxins are components of the outer membrane of nearly all gram-negative bacteria. Their structure has been characterized by a variety of biophysical and analytical techniques.

They fall into the category of lipopolysaccharides because they consist of a polysaccharide chain linked to a lipid moiety referred to as lipid A.

Lipid A represents the hydrophobic component of lipopolysaccharides which locates in the outer leaflet of the outer membrane, while core sugars and O-antigen repeats are displayed on the surface of bacteria. Lipid A is known to be responsible for the toxic effects of infections with Gram-negative bacteria.

Despite being essential for bacterial survival, as they shield the bacterium from cellular host defense strategies, bile acids and hydrophobic antibiotics, lipopolysaccharides play a prominent role in the infected host during severe infections, trauma, and shock.

The inhaled endotoxin has been associated with many pulmonary diseases. Endotoxin has been thought to be responsible for the adverse health effects after inhalation of organic dusts.

Some inhalation studies showed that endotoxin can cause fever, cough, dyspnea, headache, nose and throat irritation, diffuse aches, nausea, shortness of breath & chest tightness, acute air flow obstruction, and airway inflammation.

Endotoxin is widely present in the environment, including dust, animal waste, foods, and other materials generated from, or exposed to, Gram-negative bacterial products.
Endotoxins