Entry of toxins into the cells:

Toxins are poisonous substances produced by certain microbes. And the ability to produce toxins by which many pathogens produce disease is known as “toxigenesis”. Toxins may be carried far from the site of invasion by the blood or lymph. Various toxins may cause fever, cardiovascular disturbances, diarrhea, and shock. They can inhibit protein synthesis, destroy blood vessels, and disrupt the nervous system. Most of the toxins are bacterial origin whereas some toxins are also produced by some fungi as a competitive resource. The toxins, named mycotoxins, deter other organisms from consuming the food colonised by the fungi.

In response to the presence of a toxin, the body produces antibodies called antitoxins, which will combine with the toxin and make it harmless. The active toxins are treated by heat or expose to chemicals such as formaldehyde. This makes them harmless but still able to trigger the immune response that causes the production of antibodies. The inactivated toxins are called toxoids, and are used for vaccinations. Diphtheria and tetanus vaccines are prepared this way.

Bacterial Toxins:

There are two main types of bacterial toxins, lipopolysaccharides, which are associated with the cell wall of Gram-negative bacteria, and proteins, which are released from bacterial cells and may act at tissue sites removed from the site of bacterial growth. The cell-associated toxins are referred to as endotoxins and the extracellular diffusible toxins that are secreted by bacteria are referred to as exotoxins. However, in some cases, exotoxins are only released by lysis of the bacterial cell. Exotoxins are usually proteins, minimally polypeptides that act enzymatically or through direct action with host cells and stimulate a variety of host responses.

The production of the toxin is specific to a particular bacterial species that produces the disease associated with the toxin (e.g. only Clostridium tetani produces tetanus toxin; only Corynebacterium diphtheriae produces the diphtheria toxin). Usually, virulent strains of the bacterium produce the toxin while nonvirulent strains do not, and the toxin is the major determinant of virulence (e.g. tetanus and diphtheria).

Usually the site of damage caused by a toxin indicates the location for activity of that toxin. Some protein toxins have very specific cytotoxic activity. For example, tetanus and botulinum toxins attack only neurons. But some toxins (as produced by staphylococci, streptococci, clostridia, etc.) have fairly broad cytotoxic activity and cause nonspecific death of various types of cells or damage to tissues, eventually resulting in necrosis. Bacterial protein toxins are strongly antigenic. Protein exotoxins are inherently unstable. In time they lose their toxic properties but retain their antigenic ones.