One of the kingdoms of living nature includes unicellular living organisms, allocated to the department of Bacteria. Most of their species produce special chemical compounds - exotoxins and endotoxins. Their classification, properties and influence on the human body will be studied in this article.
What are toxins
Substances (mainly of a protein or lipopolysaccharide nature) released by a bacterial cell into the intercellular fluid after its death are bacterial endotoxins. If a living prokaryotic organism produces toxic substances into the host cell, then in microbiology such compounds are called exotoxins. They have a destructive effect on human tissues and organs, namely: they inactivate the enzymatic apparatus at the cellular level, disrupt 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 secreted by bacterial cells are known. Consider them in more detail.
Lipopolysaccharide nature of bacterial poisons
Scientists have found that endotoxin is a cleavage product of the outer membrane of Gram-negative bacteria. It is a complex consisting of a complex carbohydrate and lipid that interacts with a specific type of cell receptor. Such a compound consists of three parts: lipid A, an oligosaccharide molecule, and an antigen. It is the first component, entering the bloodstream, that causes the greatest damaging effect, accompanied by all the signs of severe poisoning: dyspeptic symptoms, hyperthermia, lesions of the central nervous system. Blood poisoning with endotoxins occurs so rapidly that septic shock develops in the body.
Another structural element included in endotoxin is an oligosaccharide containing heptose – C7H14O7 . Entering the bloodstream, the central disaccharide can also cause intoxication of the body, but in a milder form than if lipid A enters the blood.
Consequences of the influence of endotoxins on the human body
The most common effects of bacterial poisons on cells are thrombohemorrhagic syndrome and septic shock. The first type of pathology occurs due to the entry into the blood of substances - toxins that reduce its coagulability. This leads to numerous damage to organs consisting of connective tissue - the parenchyma, such as, for example, the lungs, liver, kidneys. In their parenchyma, multiple hemorrhages occur, and in severe cases, bleeding. Another type of pathologyresulting from the action of bacterial poisons is septic shock. It leads to impaired blood and lymph circulation, the consequences of which are violations of the transport of oxygen and nutrients to vital organs and tissues: the brain, lungs, kidneys, liver.
A person has a sharp increase in life-threatening symptoms, such as a rapid drop in blood pressure, hyperthermia and rapidly developing acute cardiovascular failure. Urgent medical intervention (hormonal and antibiotic therapy) stops the action of endotoxin and quickly removes it from the body.
Distinctive features of exotoxins
Before clarifying the specifics of this type of bacterial poisons, let us recall that endotoxin is one of the components of the cell wall lysate 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 small molecular weight. It can be said that the main clinical manifestations that occur in the process of infectious diseases are caused precisely by the damaging effect of exotoxins, which are formed as a result of the metabolism of the bacterium itself.
Microbiological studies have proven a higher virulence of this type of bacterial poisons compared to endotoxins. The causative agents of tetanus, whooping cough, diphtheria produce poisonoussubstances of a protein nature. They have thermolability and are destroyed when heated in the range of 70 to 95 degrees Celsius for 12-25 minutes.
Types of exotoxins
The classification of this type of bacterial poisons is based on the principle of their effect on cell structures. For example, membrane toxins are distinguished, they destroy the host cell membrane 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 hyaloplasm of the cell and disrupt the assimilation and dissimilation reactions that occur in cellular metabolism. Other compounds - poisons "work" like enzymes, for example, hyaluronidase (neurominidase). They suppress the work of the human immune system, that is, they inactivate the production of B lymphocytes, monocytes and macrophages in the lymph nodes. So proteases destroy protective antibodies, and lecithinase breaks down lecithin, which is part of the nerve fibers. This leads to a violation of the conduction of bioimpulses, and, as a result, to a decrease in the innervation of organs and tissues.
Cytotoxins can act as detergents, destroying the integrity of the lipid layer of the host cell membrane. Moreover, they are able to destroy both individual cells of the body and their associates - tissues, causing the formation of biogenic amines, which are products of metabolic reactions and exhibit toxic properties.
Mechanism of action of bacterial poisons
Microbiological studies have established that endotoxin is a complexstructure containing 2 molecular centers. The first attaches a poisonous substance to a specific cell receptor, and the second, splitting its membrane, enters directly into the cell hyaloplasm. In it, the toxin blocks metabolic reactions: protein biosynthesis occurring in ribosomes, ATP synthesis carried out by mitochondria, and nucleic acid replication. The high virulence of bacterial peptides, in terms of the chemical structure of their molecules, is explained by the fact that some toxin loci masquerade as the spatial structure of substances in the cell, such as neurotransmitters, hormones, and enzymes. This allows the toxin to “bypass the cellular defense system” and rapidly penetrate into its cytoplasm. Thus, the cell is unarmed against a 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 act on specific cells of the body, that is, they have high specificity.
