Bacterial endotoxins. GPM.1.2.4.0006.15 Bacterial endotoxins Which microorganisms contain endotoxins

Table of contents of the topic "Pathogenicity of microorganisms. Virulence.":
1. Pathogenicity of microorganisms. Pathogenic microorganisms. Pathogenic microbes.
2. Opportunistic microorganisms. Opportunistic microbes. Opportunistic pathogens. Non-pathogenic microorganisms.
3. Obligate parasites. Facultative parasites. Random parasites. Pathogenicity. What is pathogenicity?
4. Virulence. What is virulence? Virulence criteria. Lethal dose (DL, LD). Infectious dose (ID).
5. Genetic control of pathogenicity and virulence. Genotypic reduction in virulence. Phenotypic reduction in virulence. Attenuation.
6. Factors of pathogenicity of microorganisms. Factors of pathogenicity of microbes. Ability to colonize. Adhesion. Factors of colonization.
7. Capsule as a factor of pathogenicity of microorganisms. Inhibiting enzymes of microbes as pathogenicity factors. Invasiveness of microorganisms.
8. Toxigenicity of microorganisms. Toxins. Partial toxins. Cytolysins. Protoxins.
9. Exotoxins. Exotoxins of microorganisms. Classification of exotoxins. Groups of exotoxins.

To a certain extent, toxigenic microorganisms (actively secreting toxins) are opposed by pathogenic bacteria that have toxic substances that weakly diffuse into the environment and are called (at the suggestion of R. Pfeiffer) endotoxins.

Endotoxins- integral components of the cell wall of gram-negative bacteria; most of them are released only after the death of the bacterial cell. They are represented by a complex of proteins, lipid and polysaccharide residues. All groups of the molecule are responsible for the manifestation of the biological effect endotoxin.

The biological activity resembles that of some inflammatory mediators; endotoxemia usually accompanied by fever caused by the release of endogenous pyrogens from granulocytes and monocytes. If a significant amount of endotoxin enters the bloodstream, it is possible endotoxin shock, usually ending in the death of the patient.

Bacterial endotoxins exhibit a relatively weak immunogenic effect, and immune sera are not able to completely block their toxic effects. Some bacteria can simultaneously synthesize exotoxins and release (when they die) endotoxins (for example, toxigenic Escherichia coli and Vibrio cholerae).

Exoenzymes

Important pathogenicity factors should be considered exoenzymes(for example, lecithinase, hyaluronidase, collagenase, etc.), disrupting the homeostasis of cells and tissues, which leads to their damage. The ability to form exoenzymes largely determines the invasiveness of bacteria - the ability to penetrate mucous membranes, connective tissue and other barriers. For example, hyaluronidase breaks down hyaluronic acid, which is part of the intercellular substance, which increases the permeability of various tissues. This enzyme is synthesized by bacteria of the genera Clostridium, Streptococcus, Staphylococcus, etc. Neuraminidase facilitates overcoming the mucus layer, penetration into cells and distribution in intercellular spaces. Neuraminidase is secreted by cholera vibrios and diphtheria bacillus; it is also part of the influenza virus. Bacterial enzymes that decompose antibiotics should also be included in this group.

Superantigens

Some toxins (for example, Dick's toxin of streptococci or enterotoxin of staphylococci) can act as superantigens, causing polyclonal activation of various lymphocyte clones. Polyclonal activation is accompanied by hypersecretion of lymphokines with the development of cytokine-mediated intoxication.

Endotoxins are found only in gram-negative bacteria. They are represented by lipopolysaccharides and associated proteins. The peculiarity of endotoxins is that they are heat stable and are released from bacterial cells after their destruction. Endotoxins, unlike exotoxins, do not have specific action. Their toxicity and pyrogenicity are caused by lipid A, which is part of LPS and has a similar structure in different gram-negative bacteria. The pyrogenic effect of endotoxins is not associated with their direct effect on the thermoregulatory centers of the brain. They induce the release of some pyrogenic substance from polymorphonuclear leukocytes. Endotoxins are inflammatory agents; they increase capillary permeability and have a destructive effect on cells. Their inflammatory and pyrogenic effects are nonspecific. The variety of manifestations of endotoxin poisoning is due not only to LPS itself, but also to the release of numerous biologically active compounds, the synthesis of which it induces in humans and animals (histamine, serotonin, prostaglandins, leukotrienes, etc., more than 20 in total). These substances cause disorders in various organs and tissues.

All three components of LPS - lipid A, the polysaccharide core and its side chain of repeating sugars - have pronounced antigenic properties. LPS stimulates the synthesis of interferons, activates the complement system along the classical pathway, has a mitogenic effect on lymphocytes, as well as an allergenic effect. Its toxic properties, unlike exotoxins, are not removed by treatment with formaldehyde, and LPS is not converted into toxoid.

Exotoxins. They are produced by both gram-positive and gram-negative bacteria. In Gram-positive bacteria, exotoxins are actively secreted through the CM and cell wall into the environment using special secretion systems. In gram-negative bacteria (Vibrio cholerae, toxigenic E. coli, Salmonella), some exotoxins (enterotoxins) are synthesized only under certain conditions directly in the infected organism and are often stored in the cytoplasm, released from the cell only after its destruction.

All known bacterial exotoxins are proteins, among them there are heat-labile and heat-stable ones. Their main properties are associated with the protein nature of exotoxins: they have a high potency (the strongest toxins in nature are of microbial origin), high selectivity and associated specificity of action (the picture of tetanus in laboratory animals is the same, both when they are infected with the pathogen and its exotoxin), which they manifest after a certain latent period. Exotoxins are strong antigens, and some are even superantigens. They induce the formation of antibodies in the body, i.e. antitoxins, which neutralize their effect. When treated with formalin, exotoxins are neutralized and converted into toxoids. Toxoids are devoid of toxic properties, but retain their ability to induce the synthesis of antitoxins, therefore they are widely used to create artificial immunity against diphtheria, tetanus, botulism and other diseases.

Toxigenesis involves the production of toxins by pathogenic bacteria. This is one of the main methods of delivering diseases and diseases caused by bacteria. 2 categories of toxins that lead to various infections and diseases; endotoxins and exotoxins, and they differ depending on their chemical nature. Endotoxins are bacterial toxins composed of lipids (lipopolysaccharides), while exotoxins are composed of proteins.

What are endotoxins?

Endotoxins are lipopolysaccharides produced by gram-negative bacteria. Endotoxins are bound by cells and are produced only when cells are lysed. Entotoxins are present in the outer membrane of the cell wall in Gram bacteria. Endotoxins are also called lipopolysaccharides and are present in E coli, Shigella, Salmonella, Pseudomonas, Haemophilus influenza, Neisseria and Vibrio cholerae cells. Endotoxins are usually secreted by bacterial development due to the actions of certain antibiotics or by the action of phagocytic digestion.

Endotoxins exhibit less activity and are not very active on their substrate. They are heat resistant. The outer wall of bacteria is impermeable to large molecules and molecules that cannot dissolve in water and protect themselves from the external environment.

These toxins are part of this protective activity. It acts on the host during colonization. In addition, endotoxins exhibit weak antigenicity.

What are exotoxins?

Exotoxins are toxins that are released extracellularly as the body develops. Exotoxins are contagious toxins that spread from the site of infection to other parts of the body and cause damage. They are soluble proteins that act as enzymes. The exotoxin is capable of causing damage to the host by destroying cells or disrupting normal cellular metabolism. Exotoxins are very potent and can cause harm to the host. Exotoxins are released due to their rapid growth or during cell lysis. Both gram+ and gram-bacteria produce exotoxins.

Exotoxins are more toxic than endotoxins and differ from certain strains of bacteria. Exotoxins cause diseases specific only to this infection. Eg. Clostridium tetani produces tetanus toxin. There are 3 main categories of exotoxins: enterotoxins, neurotoxins and cytotoxins. These types indicate the location of the activity. Enterotoxic activity can be observed in the gastrointestinal tract. Neurotoxins exert their functions on neurons, and cytotoxins disrupt the functioning of the host cell. Some of the health disorders caused by exotoxins include cholera, tetanus and diphtheria. The antigenicity of exotoxins is quite high. Exotoxins trigger the immune system and secrete antitoxins to nullify the toxin.

exotoxin

Metabolic product of a developing cell.

disease

endotoxins

Urinary tract infections, typhoid fever, meningococcal meningitis, coronary artery disease, neonatal necrotizing enterocolitis, Crohn's disease and ulcerative colitis, cystic fibrosis, meningococcemia, sepsis with gram-negative rods, hemorrhagic shock

Exotoxins

Gas gangrene, Scarlet fever, Diphtheria, Botulism, tetanus, antibiotic-associated diarrhea, skin skin syndrome.

Summary of Endotoxins vs. Exotoxins

The differences between endotoxins and exotoxins are given below:

Comparison table for endotoxins and exotoxins

The term "pyrogen" comes from the Greek "pyreto" - fever. Pyrogens are substances that can cause an increase in body temperature. Pyrogenic reaction can cause substances of very different nature and origin. Pyrogens include gram-negative bacteria and their toxins, gram-positive bacteria and their toxins, viruses and their metabolic products, as well as steroids, etc. In the field of quality control of injectable drugs, bacterial endotoxins, which are fragments of the outer wall of gram-negative bacteria.

Gram-negative bacteria have a bilayer cell wall that surrounds the cytoplasmic membrane. The first layer is a very thin (1 nm thick) non-lipid membrane consisting of peptidoglycan. It is also called glycopeptide or mucopeptide. This is a complex matrix containing polysaccharide chains linked to each other by cross-links of short peptide chains. The second layer of the cell wall is a lipid membrane with a thickness of 7.5 nm. It is on this outer membrane that endotoxins (lipopolysaccharides) are located. Endotoxin molecules provide structural integrity and are responsible for many physiological functions, including determining the pathogenic and antigenic properties of bacteria. Structurally, the endotoxin molecule is divided into three parts - Lipid A, Core And O-specific chain.

O-specific chain Core Lipid A
Lipid A consists of disaccharide, phosphate and fatty acids. Fatty acids that make up Lipid A can be saturated or unsaturated. Most often, Lipid A contains acids: palmitic, lauric, glutamic, meristic. The Lipid A region is the most constant region of the LPS molecule, and its structure is similar in many bacteria.
O-specific chain lipopolysaccharides are built from repeating oligosaccharides. The most common sugars that make up the O-specific chain are glucose, galactose, and rhamnose. This part of the molecule gives it hydrophilic properties, due to which LPS is highly soluble in water. The polysaccharide part is the most variable part of the LPS molecule. This fragment of the molecule is often called the O-antigen, since it is responsible for the antigenic activity of gram-negative bacteria.
Core- the central part of the molecule that binds the O-antigen to Lipid A. Formally, the structure of the core is divided into external and internal parts. The inner part of the core usually contains residues of L-glycero-O-mannoheptose and 2-keto-3-deoxyoctonic acid (KDO). KDO contains 8 carbon atoms and is found almost nowhere else in nature.
In addition to lipopolysaccharides, the outer wall of gram-negative bacteria also includes proteins (the outer membrane is ¾ LPS, and only ¼ is protein components). These proteins, together with LPS, form protein-lipopolysaccharide complexes of different sizes and molecular weights. It is these complexes that are called bacterial endotoxins. The purified preparations that are used as standards are devoid of peptide fragments and represent a pure preparation of lipopolysaccharide. However, the term “bacterial endotoxins” is applied equally well to natural endotoxins that appear in solution as a result of bacterial destruction and to pure LPS preparations.
The outer wall of one gram-negative bacterium can contain up to 3.5 million LPS molecules. After her death, they all end up in solution. Endotoxins of gram-negative bacteria remain biologically active molecules even after the death of the bacteria. The endotoxin molecule is temperature stable and easily withstands the autoclave sterilization cycle. The small size of endotoxin molecules allows them to easily pass through membranes used to sterilize solutions (0.22 microns). Therefore, endotoxins may be present in finished dosage forms, even those produced under aseptic conditions and undergoing final sterilization.
Bacterial endotoxins are extremely active (strong) pyrogens. For the development of a febrile attack, the presence of bacterial endotoxins in the infusion solution at a concentration of 1 ng/ml (about 10 EU/ml) is sufficient. Other pyrogens are less active, and for the development of a pyrogenic response their concentration must be 100-1000 times higher. Typically, the terms “pyrogens” and “endotoxins” are used interchangeably and, although not all pyrogens are endotoxins, the most significant are the endotoxins of gram-negative bacteria.