Endotoxin is ... Exotoxins and endotoxins

One of the kingdoms of living nature includes single-celled living organisms, allotted to the Department of Bacteria. Most of their species produce special chemical compounds - exotoxins and endotoxins. Their classification, properties and effects on the human body will be studied in this article.

What are toxins?

Substances (mainly protein or lipopolysaccharide nature) released by the bacterial cell into the intercellular fluid after its death are bacterial endotoxins. If a living prokaryotic organism produces poisonous substances in a host cell, then in microbiology such compounds are called exotoxins. They exert a destructive effect on the tissues and organs of man, namely: inactivate the enzymatic apparatus at the cellular level, disrupt the metabolism. Endotoxin is a poison that has a damaging effect on living cells, and its concentration can be very small. In microbiology, about 60 compounds isolated by bacterial cells are known. Let us consider them in more detail.

Lipopolysaccharide nature of bacterial poisons

Scientists have found that endotoxin is a product of the splitting of the outer membrane of gram-negative bacteria. It is a complex consisting of a complex carbohydrate and a lipid, interacting with a specific type of cellular receptors. This compound consists of three parts: lipid A, oligosaccharide molecule and antigen. It is the first component, getting into the bloodstream, causing the most damaging effect, accompanied by all signs of severe poisoning: dyspeptic phenomena, hyperthermia, lesions of the central nervous system. Infection of the blood with endotoxins is so rapid that septic shock develops in the body .

Another structural element entering into endotoxin is an oligosaccharide containing heptose - C ₇ H ₁₄ O ₇ . Entering the bloodstream, the central disaccharide can also cause an intoxication of the body, but in a lighter form than when the lipid A enters the bloodstream.

Effects of endotoxin on the human body

The most common consequences of the action of bacterial poisons on cells are thrombohemorrhagic syndrome and septic shock. The first type of pathology arises from the entry into the blood of substances - toxins that reduce its coagulability. This leads to numerous injuries of organs consisting of connective tissue - parenchyma, such as, for example, the lungs, liver, kidneys. In their parenchyma there are multiple hemorrhages, and in severe cases - bleeding. Another kind of pathology that results from the action of bacterial poisons is a septic shock. It leads to violations of blood and lymph circulation, the consequences of which are violations of the transportation of oxygen and nutrients to vital organs and tissues: the brain, lungs, kidneys, liver.

A person has a dramatic increase in life-threatening symptoms, such as a rapid drop in blood pressure, hyperthermia and rapidly developing acute cardiovascular insufficiency. Urgent medical intervention (carrying out hormonal and antibiotic therapy) stops the action of endotoxin and quickly removes it from the body.

Distinctive features of exotoxins

Before we find out the specifics of this kind of bacterial poisons, we recall that endotoxin is one of the components of the lysate of the cell wall of a dead gram-negative bacterium. Exotoxins are synthesized by living prokaryotic cells: both gram-positive and gram-negative. In terms of chemical structure, they are exclusively proteins with a low molecular weight. We can say that the main clinical manifestations that arise in the process of infectious diseases are caused precisely by the damaging effect of exotoxins, which are formed due to the metabolism of the bacterium itself.

Microbiological studies have shown a higher virulence of this species of bacterial poisons, compared with endotoxins. The causative agents of tetanus, pertussis, diphtheria produce poisonous substances of protein nature. They have a thermolability and are destroyed by heating in the range of 70 to 95 degrees Celsius for 12-25 minutes.

Types of exotoxins

The classification of this type of bacterial poison is based on the principle of their effect on the structure of the cell. For example, distinguish membronotoxins, they destroy the shell of the host cell or disrupt the diffusion and active transport of ions passing through the membrane bilayer. There are also cytotoxins. These are poisons that act on the cell's hyaloplasm and violate the assimilation and dissimilation reactions taking place in the cellular metabolism. Other compounds - poisons "work", like enzymes, for example, hyaluronidase (neurominidase). They suppress the work of the human immune system, that is, inactivate the production of B lymphocytes, monocytes and macrophages in the lymph nodes. So proteases destroy protective antibodies, and lecithinase cleaves lecithin, which is part of the nerve fibers. This leads to disruption of bio-impulses, and, consequently, to a decrease in the innervation of organs and tissues.

Cytotoxins can act as detergents, and the integrity of the lipid layer of the host cell membrane is destroyed. Moreover, they are capable of destroying both individual cells of the organism and their associates - tissues, causing the formation of biogenic amines, which are products of metabolic reactions and manifesting toxic properties.

The mechanism of action of bacterial poisons

Microbiological studies have established that endotoxin is a complex structure containing 2 molecular centers. The first attaches a poisonous substance to a specific cell receptor, and the second, by splitting its membrane, gets directly into the cell's hyaloplasm. In it, the toxin blocks the metabolic reactions: the biosynthesis of proteins occurring in the ribosomes, the synthesis of ATP molecules, carried out by mitochondria, the replication of nucleic acids. The high virulence of bacterial peptides, from the point of view of the chemical structure of their molecules, is explained by the fact that some toxin loci are masked by the spatial structure of substances in the cell, such as neurotransmitters, hormones and enzymes. This allows the toxin to "bypass the cell defense system" and rapidly penetrate into its cytoplasm. Thus, the cell is unarmed before the bacterial infection, as it loses the ability to form its own protective substances: interferon, gamma globulins, antibodies. It should be noted that the properties of endotoxins and exotoxins are similar in that both types of bacterial poisons affect specific cells of the body, that is, they have high specificity.