One of the kingdoms of wildlife includes unicellular living organisms isolated in 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 of a protein or lipopolysaccharide nature) secreted by a bacterial cell into the intercellular fluid after its death are bacterial endotoxins. If a living prokaryotic organism produces toxic substances in 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 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 secreted by bacterial cells are known. Let's 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 lipid, interacting with a specific type of cell receptor. Such a compound consists of three parts: lipid A, oligosaccharide molecule and antigen. It is the first component that enters the bloodstream that causes the most damaging effect, accompanied by all the signs of severe poisoning: dyspeptic symptoms, hyperthermia, lesions of the central nervous system. Infection of blood with endotoxins occurs so rapidly that septic shock develops in the body.
Another structural element involved in endotoxin is an oligosaccharide containing heptose - C 7 H 14 O 7 . Entering the bloodstream, the central disaccharide can also cause intoxication of the body, but in a milder form than if lipid A enters the bloodstream.
The effects 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 - parenchyma, such as, for example, the lungs, liver, kidneys. In their parenchyma, multiple hemorrhages occur, and in severe cases - bleeding. Another type of pathology resulting from the action of bacterial poisons is septic shock. It leads to impaired blood and lymph circulation, the consequences of which are disorders in the transport of oxygen and nutrients to vital organs and tissues: the brain, lungs, kidneys, and liver.
Life-threatening symptoms increase sharply in a person, 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 finding out the specifics of this type of bacterial poisons, we 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. From the point of view of the chemical structure, they are exclusively proteins with a small 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 proved a higher virulence of this type of bacterial poisons, compared with endotoxins. The causative agents of tetanus, pertussis, diphtheria produce toxic substances of a protein nature. They have thermal stability and are destroyed when heated in the range from 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 influence on cell structures. For example, they distinguish membranotoxins, they destroy the membrane 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 hyaloplasm and disrupt the assimilation and dissimilation reactions that occur in cellular metabolism. Other compounds - poisons “work” as enzymes, for example, hyaluronidase (neurominidase). They suppress the functioning 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 the lecithin, which is part of the nerve fibers. This leads to a violation of the bio-impulses, and, as a result, to a decrease in the innervation of organs and tissues.
Cytotoxins can act as detergents, with the destruction of the integrity of the lipid layer of the membrane of the host cell. Moreover, they are capable of destroying 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.
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 toxic substance to a specific cell receptor, and the second, splitting its membrane, enters directly into the cell’s hyaloplasm. In it, the toxin blocks metabolic reactions: protein biosynthesis that occurs in the ribosomes, the synthesis of ATP molecules carried out by mitochondria, and 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 cellular defense system" and rapidly penetrate its cytoplasm. Thus, the cell is unarmed before 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.