Bacteriophages: modern aspects of application, prospects for the future
Gaining more and more fans among doctors, pushing antibiotics into the background. Once upon a time, the advent of antibiotics completely changed the way doctors think about treatment. Previously hopeless patients began to recover, treatment algorithms were extremely simplified, mortality fell sharply ... Miracles! Magic Medicines! But the enthusiastic attitude did not last long. Too many problems started to arise.
The enemy of my enemy is my friend
Now the "slippery" issues of antibiotic therapy are known to everyone. The action of antibiotics is accompanied by:
Destruction of the necessary, "useful", intestinal microflora and mucous membranes;
Active growth of new strains of bacteria resistant to them;
emergence side effects at the expense systemic action drugs.
In this regard, the search for fundamentally different drugs for the treatment of bacterial infections. And then bacteriophages came to the fore.
Bacteriophages are viruses that selectively infect bacterial cells. The virus attaches to the cell wall of the bacterium and injects its genetic material into the cell. As a result, the synthesis of new viruses begins, and then lysis occurs. bacterial cell and the release of 200-1000 new phages that infect other bacteria. When all the bacteria of the pathogenic strain are destroyed, the bacteriophages are eliminated from the body without a trace. Many bacteriophages are highly specific, and each strain of the virus infects only a certain type of bacteria, without affecting other microorganisms and body cells. This provides a significant reduction in the number of side effects.
Thus, to the undoubted advantages use of bacteriophages can be attributed:
High safety profile, allowing them to be used in patients of any age, from newborns to very old people;
Reducing the risk of developing resistant strains of bacteria;
The possibility of their combination with any other drugs, including antibiotics.
Perhaps the only thing that limits the use of bacteriophages is their selectivity, because of which, before treatment, it is necessary to clarify the nature of the pathogen and its sensitivity to various types bacteriophages. Such an analysis is by no means carried out everywhere and takes certain time, but the improvement of diagnostic systems allows us to hope that this problem can be resolved soon.
From theory to practice
Exist different types bacteriophages: monophages, aimed at the destruction of only one type of bacteria, and polyphages, acting simultaneously on several types of pathogenic bacteria. Since bacteriophages are extremely in demand in almost all areas of medicine, from surgery and gynecology to neonatology and ENT practice, the release of bacteriophages in various forms. They are used for oral administration reg os, in the form of enemas, applications, irrigations, for introduction into the cavity of wounds, vagina, uterus, nose, sinuses, as well as for introduction into drained cavities - abdominal, pleural, Bladder, renal pelvis. The duration of the course depends on clinical indications and can be 7-20 days. Safe, efficient and reliable bacteriophages are exactly the weapon that is so necessary in the fight against pathogenic bacteria.
Not only medicine
Progress in molecular biology and biotechnology has made it possible to use bacteriophages not only for treatment, but also for other purposes. In the United States, for example, bacteriophages are used as a safe preservative for food products. Added to foods, bacteriophages prevent the growth of unwanted bacteria.
Interesting Facts
The discovery of bacteriophages occurred in 1894, when the British bacteriologist Ernest Hankin noticed that the Indian rivers Ganges and Jumna had significant antibacterial activity, which completely disappeared after boiling. He suggested that there is some substance in the water that kills bacteria. The name "bacteriophage" ("eater of bacteria"), these viruses received in 1917 from the French scientist Felix d'Herelle, who discovered "an invisible microbe that infects the dysentery bacillus." Clarification of the nature of this "invisibility" became possible only after the advent of electron microscopy.
№ 10-2013
Photo taken with electron microscope,
shows the process of fixing bacteriophages (coliphages T1) on the surface of the bacterium E. coli.
At the end of the 20th century, it became clear that bacteria undoubtedly dominate the Earth's biosphere, accounting for more than 90% of its biomass. Each species has many specialized types of viruses. According to preliminary estimates, the number of bacteriophage species is about 10 15 . To understand the scale of this figure, we can say that if every person on Earth discovers one new bacteriophage every day, then it will take 30 years to describe all of them.
Thus, bacteriophages are the least studied creatures in our biosphere. Most of the bacteriophages known today belong to the order Caudovirales - tailed viruses. Their particles have a size of 50 to 200 nm. Tail different lengths and form ensures the attachment of the virus to the surface of the host bacterium, the head (capsid) serves as a repository for the genome. Genomic DNA encodes the structural proteins that form the "body" of the bacteriophage and the proteins that ensure the multiplication of the phage inside the cell during infection.
We can say that a bacteriophage is a natural high-tech nanoobject. For example, phage tails are a "molecular syringe" that pierces the wall of a bacterium and injects its DNA into the cell as it contracts. From this point on, the infectious cycle begins. Its further stages consist of switching the bacterial life mechanisms to serving the bacteriophage, multiplying its genome, building multiple copies of viral envelopes, packaging virus DNA in them, and, finally, destruction (lysis) of the host cell.
A bacteriophage is not a living being, but a molecular nanomechanism created by nature.
The tail of a bacteriophage is a syringe that pierces the wall of a bacterium and injects viral DNA,
which is stored in the head (capsid), inside the cell.
In addition to the constant evolutionary competition of defense mechanisms in bacteria and attack in viruses, the reason for the current balance can be considered as the fact that bacteriophages specialized in their infectious action. If available large colony bacteria, where the next generations of phages will find their victims, then the destruction of bacteria by lytic (killing, literally - dissolving) phages proceeds quickly and continuously.
If there are not enough potential victims or external conditions are not very suitable for efficient reproduction of phages, then phages with a lysogenic developmental cycle gain an advantage. In this case, after the introduction of the phage DNA into the bacterium, it does not immediately trigger the mechanism of infection, but for the time being it exists inside the cell in a passive state, often invading the bacterial genome.
In this state of the prophage, the virus can exist for a long time, going through cell division cycles together with the bacterium's chromosome. And only when the bacterium enters an environment favorable for reproduction, the lytic cycle of infection is activated. At the same time, when phage DNA is released from the bacterial chromosome, neighboring regions of the bacterial genome are often captured, and their contents can later be transferred to the next bacterium, which the bacteriophage infects. This process (gene transduction) is considered the most important means transfer of information between prokaryotes - organisms without cell nuclei.
How bacteriophage works
All these molecular subtleties were not known in the second decade of the twentieth century, when "invisible infectious agents that destroy bacteria" were discovered. But even without the electron microscope, which was used for the first time in the late 1940s to obtain images of bacteriophages, it was clear that they are capable of destroying bacteria, including pathogens. This property was immediately demanded by medicine.
The first attempts to treat dysentery with phages, wound infections, cholera, typhoid and even plague were carried out carefully enough, and the success looked quite convincing. But after the start of mass production and the use of phage preparations, euphoria turned into disappointment. About what bacteriophages are, how to produce, purify and use them dosage forms very little was known. Suffice it to say that, according to the results of a test undertaken in the United States in the late 1920s, bacteriophages proper were not found in many industrial phage preparations.
The problem with antibiotics
The second half of the twentieth century in medicine can be called the “era of antibiotics”. However, Alexander Fleming, the discoverer of penicillin, warned in his Nobel lecture that microbial resistance to penicillin arises rather quickly. For the time being, antibiotic resistance has been offset by the development of new types of antimicrobial drugs. But since the 1990s, it has become clear that humanity is losing the “arms race” against microbes.
Guilty in the first place uncontrolled use antibiotics not only for therapeutic, but also for preventive purposes, and not only in medicine, but also in agriculture, Food Industry and life. As a result, resistance to these drugs began to develop not only in pathogenic bacteria, but also in the most common microorganisms living in soil and water, making them "conditional pathogens".
These bacteria thrive in medical institutions, populating plumbing, furniture, medical equipment, sometimes even disinfectant solutions. In people with weakened immune systems, which are the majority in hospitals, they cause severe complications.
No wonder the medical community is sounding the alarm. In 2012, WHO Director-General Margaret Chan issued a statement predicting the end of the era of antibiotics and humanity's defenselessness against infectious diseases. However, practical possibilities combinatorial chemistry - the foundations of pharmacological science - are far from being exhausted. Another thing is that the development antimicrobial agents- a very expensive process that does not bring such profits as many other drugs. So the horror stories about “superbugs” are more of a warning that encourages people to look for alternative solutions.
Bacteriophages and immunity
Since there are a myriad of bacteriophages in nature and they constantly enter the human body with water, air and food, the immune system simply ignores them. There is even a hypothesis about the symbiosis of bacteriophages in the intestine, which regulates intestinal microflora. It is possible to achieve some kind of immune reaction only with prolonged administration into the body. large doses phages.
But in this way, you can achieve an allergy to almost any substance. Finally, it is very important that bacteriophages are inexpensive. The development and production of a drug consisting of precisely selected bacteriophages with fully decoded genomes, cultivated according to modern biotechnological standards on certain bacterial strains in chemically pure media and highly purified, is orders of magnitude cheaper than modern complex antibiotics.
This makes it possible to quickly adapt phage therapeutic preparations to changing sets of pathogenic bacteria and to use bacteriophages in veterinary medicine, where expensive medicines not economically justified.
In the medical service
The revival of interest in the use of bacteriophages seems quite logical - natural enemies bacteria to treat infections. Indeed, during the decades of the “era of antibiotics”, bacteriophages actively served science, not medicine, but fundamental molecular biology. Suffice it to mention the decoding of the "triplets" genetic code and the DNA recombination process. Enough is now known about bacteriophages to reasonably select phages suitable for therapeutic purposes.
Bacteriophages have many advantages as potential drugs. First of all, there are a myriad of them. Although changing the genetic apparatus of a bacteriophage is also much easier than that of a bacterium, and even more so in higher organisms, That is unnecessary. You can always find something suitable in nature. It's about rather, about selection, fixing the properties in demand and reproduction of the necessary bacteriophages.
This can be compared with the breeding of dog breeds - sledding, guard, hunting, hounds, fighting, decorative ... All of them remain dogs, but are optimized for a certain type of action, necessary to a person. Secondly, bacteriophages are strictly specific, that is, they destroy only a certain type of microbes without inhibiting normal microflora person.
Thirdly, when a bacteriophage finds a bacterium that it must destroy, it life cycle starts to multiply. Thus, the question of dosage becomes not so acute. Fourth, bacteriophages do not cause side effects. All cases allergic reactions when using therapeutic bacteriophages were caused either by impurities from which the drug was not sufficiently purified, or by toxins released during mass death bacteria. The last phenomenon, the "Herxheimer effect", is often observed with the use of antibiotics.
Two sides of the coin
Unfortunately, medical bacteriophages also have many shortcomings. The most important problem stems from the advantage of the high specificity of phages. Each bacteriophage infects a strictly defined type of bacteria, not even a taxonomic species, but a number of narrower varieties, strains. Relatively speaking, as if guard dog she began to bark only at two-meter-tall thugs dressed in black raincoats, and did not react at all to a teenager in shorts climbing into the house.
Therefore, it is not uncommon for current phage preparations to fail. effective application. A drug made against a specific set of strains and perfectly curing streptococcal tonsillitis in Smolensk, may be powerless against all signs of the same sore throat in Kemerovo. The disease is the same, caused by the same microbe, and streptococcus strains in different regions are different.
For the most effective use of bacteriophage, it is necessary accurate diagnosis pathogenic microbe, up to strain. The most common diagnostic method now - culture inoculation - takes a lot of time and does not provide the required accuracy. Quick Methods- typing with polymerase chain reaction or mass spectrometry - are being introduced slowly due to the high cost of equipment and higher requirements for the qualifications of laboratory assistants. Ideally, the selection of phage components of the drug could be done against the infection of each individual patient, but this is expensive and unacceptable in practice.
Another important disadvantage phages - their biological nature. In addition to the fact that bacteriophages require special conditions storage and transportation, such a method of treatment opens up a lot of speculation on the topic of "foreign DNA in a person." And although it is known that a bacteriophage, in principle, cannot infect a human cell and introduce its DNA into it, change public opinion not easy.
From the biological nature and rather large, in comparison with low-molecular drugs (the same antibiotics), the size follows the third limitation - the problem of delivering the bacteriophage into the body. If a microbial infection develops where the bacteriophage can be applied directly in the form of drops, spray or enema - on the skin, open wounds, burns, mucous membranes of the nasopharynx, ears, eyes, large intestine - then there are no problems.
But if the infection occurs in the internal organs, the situation is more complicated. Cases of successful treatment of infections of the kidneys or spleen with ordinary oral intake bacteriophage preparations are known. However, the mechanism of penetration of relatively large (100 nm) phage particles from the stomach into the bloodstream and into internal organs is poorly understood and varies greatly from patient to patient. Bacteriophages are also powerless against those microbes that develop inside cells, such as tuberculosis and leprosy. Through the wall human cell bacteriophage can't get through.
It should be noted that to oppose the use of bacteriophages and antibiotics in medical purposes it does not follow. With their joint action, a mutual strengthening of the antibacterial effect is observed. This allows, for example, to reduce the doses of antibiotics to values that do not cause pronounced side effects. Accordingly, the mechanism of development of resistance in bacteria to both components combined medicine almost impossible.
Arsenal expansion antimicrobials gives more degrees of freedom in the choice of treatment methods. Thus, the scientifically substantiated development of the concept of using bacteriophages in antimicrobial therapy is promising direction. Bacteriophages serve not so much as an alternative, but as a complement and enhancement in the fight against infections.
Practical use phages. Bacteriophages are used in the laboratory diagnosis of infections during the intraspecific identification of bacteria, i.e., the determination of the phagovar (phage type). To do this, the phage typing method is used, based on the strict specificity of the action of phages: drops of various diagnostic type-specific phages are applied to a cup with a dense nutrient medium seeded with a "lawn" of a pure culture of the pathogen. The phage phage of a bacterium is determined by the type of phage that caused its lysis (the formation of a sterile spot, "plaque", or "negative colony", phage). The phage typing technique is used to identify the source and ways of spreading the infection (epidemiological marking). Isolation of bacteria of the same fagovar from different patients indicates a common source of their infection.
Phages are also used to treat and prevent a number of bacterial infections. They produce typhoid, salmonella, dysentery, pseudomonas, staphylococcal, streptococcal phages and combined preparations(coliproteic, pyobacteriophages, etc.). Bacteriophages are prescribed according to indications orally, parenterally or topically in the form of liquid, tablet forms, suppositories or aerosols.
Bacteriophages are widely used in genetic engineering and biotechnology as vectors for obtaining recombinant DNA.
Bacteriophage preparations used in practice are a filtrate of a broth culture of the corresponding microbes lysed by a phage, containing living phage particles, as well as dissolved bacterial antigens released from bacterial cells during their lysis. The resulting preparation - a liquid bacteriophage should look like a completely clear liquid yellow color greater or lesser intensity.
For therapeutic and prophylactic purposes, phages can be produced in the form of tablets with an acid-resistant coating. Tableted dry phage is more stable during storage and convenient to use. One tablet of dry bacteriophage corresponds to 20-25 ml liquid preparation. The shelf life of the dry and liquid preparation is 1 year. Liquid bacteriophage should be stored at a temperature of + 2 +10 C, dry - no higher than +1 ° C, but it can be stored in a refrigerator at a negative temperature.
The bacteriophage taken orally remains in the body for 5-7 days. As a rule, taking a bacteriophage is not accompanied by any reactions or complications. There are no contraindications for admission. They are used in the form of irrigations, rinses, lotions, tampons, injections, and also injected into the cavities - abdominal, pleural, articular and bladder, depending on the location of the pathogen.
Diagnostic phages are produced both in liquid and dry form in ampoules. Before starting work, the dry bacteriophage is diluted. If the titer, tr, DRT (working titer dose) is indicated on the ampoules, it is used in the phage lizability test (Otto method) to identify bacteria, if the phage type is indicated, then for phage typing - to determine the source of infection.
The action of a bacteriophage on a microbial culture in a liquid medium and on a dense medium
Otto's Method (Falling Drop)
Make a dense sowing lawn of the crop under study. 5-10 minutes after sowing, a liquid diagnostic phage is applied to the dried surface of the nutrient medium. The dish is tilted slightly so that the drop of phage spreads over the surface of the agar. The cup is placed in a thermostat for 18-24 hours. The result is accounted for total absence culture growth at the site of phage droplet application.
Experiment on a liquid nutrient medium
Do sowing of the studied culture in two test tubes with a liquid medium. A diagnostic bacteriophage is added in a loop into one test tube (“O”). After 18-20 hours in a test tube where the bacteriophage was not added (“K”), a strong clouding of the broth is observed - the seeded culture has grown. The broth in the test tube, where the bacteriophage was added, remained transparent due to the lysis of the culture under its influence.
Phage typing of bacteria
According to the spectrum of action, the following bacteriophages are distinguished: polyvalent, lysing related types of bacteria; monovalent, lysing bacteria a certain kind; typical, lysing individual types (variants) of bacteria.
For example, one strain of pathogenic staphylococcus can be lysed by several types of phages; therefore, all typical phages (24) and strains of pathogenic staphylococci are combined into 4 groups.
The phage typing method has great importance for epidemiological research, as it allows to identify the source and ways of spreading pathogens. For this purpose, the phagovar isolated from the pathological material is determined. pure culture on dense nutrient media using typical diagnostic phages.
The fagovar of microorganism culture is determined by the type of phage that caused its lysis. The isolation of bacteria of the same fagovar from different subjects indicates the source of infection.
Due to their destructive (lytic) effect on bacteria, phages can be used for therapeutic purposes. preventive purpose at various diseases(dysentery, cholera, various purulent-inflammatory diseases, etc.). Sets of standard phages, including international ones, are used for phage typing of pathogens of a number of diseases (cholera, typhoid fever, salmonellosis, diphtheria, staphylococcal and other diseases). Bacteriophages are also used in genetic engineering as vectors that transfer DNA segments; natural transfer of genes between bacteria through certain phages (transduction) is also possible. As a rule, such patients are prescribed antibiotics. But due to the fact that constantly mutating bacteria acquire resistance to antibiotics, their effectiveness is last years weakened. The attention of researchers was attracted by bacteriophages - viruses that devour bacteria. Unlike antibiotics, which destroy both harmful and healthy microflora organism, bacteriophages are selective, only pathogenic bacteria. How do bacteriophages work in the body? They penetrate only certain cells and interact with their DNA, creating a lysogenic or lytic effect. By acting on microbes in the lytic type, bacteriophages destroy them, which allows them to multiply rapidly. The lysogenic type is the penetration of the phage genome into the bacterial genome, their synthesis and further transition from one generation to another. Information about bacteriophages appeared more than a century back when using them to treat staphylococcus aureus. Currently, they are widely used for the prevention and treatment of intestinal, staphylococcal, streptococcal, typhoid and many other infections. modern medicine is looking for methods that do not use live bacteriophages, but enzymes that act on pathogenic bacteria by lysing. Their application can be in the form of a nasal or oral spray, toothpaste, food, food additives. The effectiveness of the use of bacteriophages consists in the absence of contraindications and complications, compatibility with other drugs, active effect on antibiotic-resistant microbes. Due to these properties, bacteriophages are evaluated as drugs of the future for successful infection control.
The most important advantages of phage therapy are high sensitivity pathogenic microflora to bacteriophage, the possibility of initial use of small doses of bacteriophage, compatibility with all types of traditional antibiotic therapy, the absence of contraindications to phage prophylaxis and phage therapy. It has been established that in nature there are no microorganisms that are absolutely resistant to bacteriophage. It is important that bacteriophage reproduction is possible only in the presence of bacteria sensitive to it. After the death of the last microbial cell in the focus of an infectious lesion, it stops its vigorous activity and is completely eliminated from the body.
Due to the observed decrease therapeutic action antibiotic preparations of bacteriophages are used in clinical practice as an alternative to antibiotics and in combination with the latter. Bacteriophage preparations are not inferior to antibacterial drugs in terms of efficiency, stimulate local factors of specific and nonspecific immunity and do not cause side toxic and allergic reactions. Bacteriophages are administered orally, and are also used for irrigation of wounds, for injection into drained cavities - abdominal, pleural, sinus, middle ear, abscesses, wounds, uterus, bladder. With oral and aerosol application, as well as when applied to the surface of mucous membranes, bacteriophages penetrate into the blood and lymph and are excreted through the kidneys, sanitizing the urinary tract.
At present, interest in phage therapy has been renewed in surgery, urology, ophthalmology, and traumatology.
Therapeutic and prophylactic preparations of bacteriophages are composed of polyclonal virulent bacteriophages with a wide range of action, which are also active against bacteria resistant to antibiotics. They are produced in liquid form, in tablets with an acid-resistant coating, in the form of suppositories, ointments, liniments.
Bacteriophage preparations are a sterile filtrate of bacterial phagolysates, they are administered orally, topically for irrigation of wounds and mucous membranes, introduction into the cavity of the uterus, bladder, ear, paranasal sinuses, as well as in drained cavities - abdominal, pleural, and also in the cavity of abscesses after removal of exudate.
Bacteriophages are able to quickly penetrate into the blood and lymph and are excreted through the kidneys with urine. As shown in our studies, after ingestion of 30 ml of bacteriophage, phage particles are found in the urine after 2 hours, and their maximum concentration in the urine is reached 6-8 hours after ingestion.
The activity of therapeutic and prophylactic bacteriophages against pathogens of purulent-septic and enteric diseases is quite high - from 72% to 90%, including against strains of hospital origin, characterized by multiple resistance to antibiotics. Compliance of bacteriophage preparations with the modern athiological structure of pathogens is achieved by their constant adaptation to circulating strains due to the renewal of phage races and production bacterial stamps. This feature favorably distinguishes phages from other antimicrobial preparations - antibiotics, eubiotics or vaccines, where production strains or producer strains, or the synthesized substance are not subject to any modifications. Such plasticity of bacteriophage preparations ensures the continuation of the primary phage resistance of pathogens.
Benefits of bacteriophage preparations
The advantages of bacteriophage preparations include a narrow specificity of action, which, unlike antibiotics, does not cause inhibition of normal microflora. Proven stimulant effect staphylococcal bacteriophage on bifidobacteria - essential component intestinal microbiocenosis. Use of bacteriophages for treatment infectious diseases stimulates factors of specific and nonspecific immunity, which is especially effective for the treatment of chronic inflammatory diseases against the background of immunosuppressive states, bacteriocarrier.
Experimental work and long clinical observations the impossibility of transmission of plasmids of resistance to antibiotics and toxigenicity by therapeutic and prophylactic preparations of bacteriophages, because they are polyclonal complexes of virulent bacteriophages, has been proved.
In Russia, CIS countries, Poland, France, Spain, bacteriophages are widely used in medicine and veterinary medicine. Extensive experience has been accumulated in the use of bacteriophages in the treatment intestinal infections: high clinical efficacy of phage therapy for acute and chronic dysentery, salmonellosis, accompanied by sanitation of carriers. The high epidemiological effectiveness of the prophylactic use of dysentery, typhoid and salmonella bacteriophages has been proven. The use of bacteriophages has shown good results in the treatment of diseases caused by opportunistic bacteria, dysbacteriosis, purulent lesions skin, ENT - organs, musculoskeletal system, genitourinary system, systems of the circulatory and respiratory organs, including in newborns and children of the first year of life.
An important condition that ensures the effectiveness of treatment with phage preparations is a certain phage sensitivity of the pathogen.
The long experience of phage therapy at the Research Institute of Urology is clear; As a result of the adaptation of commercial bacteriophages to the hospital strains circulating in the urological clinic at NPO Biofag, the phage sensitivity of the strains increased by 15% and was at or above the level of sensitivity to the most modern foreign antibiotics. Against the background of long-term use of bacteriophages in a hospital, no formation of phage resistance was observed among hospital strains, while resistance to antibiotics decreased. The clinical efficacy of phage therapy was observed in 92% of cases, often exceeding the results of antibiotic therapy. Absence of contraindications and complications in the use of bacteriophage preparations, the possibility of their use in combination with other medicines, including with antibiotics, activity against antibiotic-resistant strains and adaptation of bacteriophages to modern pathogens - all this makes it possible to evaluate bacteriophage preparations as a highly effective and promising means of emergency treatment of purulent-septic and enteric infections. However, phages, these "natural orderlies", can be used not only for treatment, but also for the prevention of infectious diseases. They can be prescribed to pregnant women, nursing mothers and children of any age, including premature babies. The main condition for their successful application is to test the isolated culture for sensitivity to the corresponding phage. An amazing pattern was noted: unlike antibiotics, the sensitivity of clinical strains of microorganisms to bacteriophages is stable and tends to increase, which can be explained by enrichment medical preparations new races of phages. In addition to medical applications, bacteriophages are widely used in veterinary medicine; especially effective staphylococcal bacteriophage in the treatment of mastitis in cows. Bacteriophage preparations are prescribed orally for diseases internal organs or locally, directly on the lesion. The action of the phage is manifested already 2-4 hours after its introduction (which is especially important in intensive care). Bacteriophages penetrate into the blood, lymph and are excreted through the kidneys, sanitizing the urinary tract.
Thus, bacteriophages use:
In veterinary medicine for:
prevention and treatment bacterial diseases birds and animals;
treatment of purulent-inflammatory diseases of the mucous membranes of the eyes, oral cavity;
prevention of purulent-inflammatory complications in burns, wounds, surgical interventions;
In genetic engineering:
for transduction - the natural transfer of genes between bacteria;
as vectors that transfer sections of DNA;
using phages, it is possible to construct directed changes in the genome of the host DNA;
In the food industry:
mass-scale phage-containing agents are already processing ready-to-eat meat and poultry products;
bacteriophages are used in the production of food products from meat, poultry, cheeses, plant products, etc.;
Bacteriophages, application in medicine.
Bacteriophages. Application in medical practice.
Bacteriophages are bacterial viruses capable of specifically penetrating into bacterial cells, reproducing them and causing lysis.
They are found wherever bacteria exist - in soil, water, intestinal tract person. All are inherent in the phage biological features that are characteristic of viruses.
Phage morphology:
Phages differ in shape - filamentous, spherical, cubic, phages having a head and a tail (reminiscent of a spermatozoon).
Sizes are small, medium and large.
Large phages, consisting of a head and a tail, are most complex. The head is shaped like an icosahedron. The head is connected with the process with the help of a collar and an umbrella. Inside the process there is a hollow cylindrical rod that communicates with the head, from the outside the process has a protein sheath capable of contraction, the caudal process ends in a hexagonal basal plate with short spikes, from which filamentous fibril structures extend. The plate and spikes contain lysozyme. The process has 6 villi, which provide tight attachment phage to bacterial cell. There may be phages with a non-shrinking sheath, phages with short processes, phages with a process analog, and phages without a process.
Phage resistance: Phages tolerate temperatures of 50-60°C. Withstand freezing, perish at a temperature of 70 ° C. They are not affected by such poisons as cyanide, fluoride, as well as chloroform and phenol. Phages are well preserved in sealed ampoules, but they can be destroyed by boiling, the action of acids, and UV irradiation.
The mechanism of interaction of phages with a microbial cell:
According to the interaction, virulent and temperate phages are distinguished.
Virulent phages - they enter the bacterial cell, reproduce and cause lysis of the bacteria.
There are a number of features for phages with a process and a contracting sheath:
These phages are adsorbed on the surface of the bacterial cell with the help of fibrils of the process in the presence of the corresponding receptors. Then the ATP-ase enzyme is activated, which leads to a contraction of the sheath of the caudate process and the introduction of a hollow rod into the cell. An enzyme, lysozyme, is involved in the process of piercing the cell walls.
The phage DNA passes through the hollow stem of the outgrowth and is injected into the cell. The capsid and process remain on the cell surface. Then the phage protein and nucleic acid are reproduced inside the cell. The next stage is the assembly and formation of mature phage particles. Final stage: cell lysis and release of mature phage particles from it. Lysis can take place both from the inside - there is a rupture of the cell wall and the release of mature phages into the external environment and from the outside - the phages make many holes in the cell wall through which the contents of the cell flow out, with such lysis the phage does not multiply.
Temperate phages - do not lyse all cells in the population, enter into symbiosis with some of the cells, as a result of which the phage DNA is integrated into the cell chromosome. In this case, the phage genome is called a prophage.
The prophage becomes a part of the cell chromosome and during its reproduction it replicates synchronously with the cell genome without causing its lysis and is transmitted to the offspring.
The phenomenon of symbiosis of a microbial cell with a prophage is called lysogeny.
And the culture of bacteria containing prophage is lysogenic, this name reflects the ability of the prophage to spontaneously or under the influence of factors environment move into the cytoplasm and behave like a virulent phage lysing bacteria. Upon transition to a virulent form, a temperate phage can capture a part of the chromosome of a bacterial cell and, upon lysis, be transferred to another.
According to the spectrum of action, phages are divided into:
1. Polyvalent - lyse related bacteria (Salmonella phage lyses only Salmonella).
2. Species (monophages) - lyse bacteria of only one species.
3. Type-specific - selectively lyse individual variants of bacteria within a species (pathogen Staphylococcus aureus - 33 sets).
Practical use:
Phage preparations are used for the treatment and prevention of infections and their diagnosis. The action of phages is based on their strict specificity; production strains and corresponding bacterial cultures are used to obtain a phage preparation.
Release forms: liquid, dry, in the form of tablets, aerosols, suppositories. Introduced into the body parenterally, enterally and locally. Used for therapeutic and prophylactic purposes in various diseases (dysentery, cholera, various purulent - inflammatory diseases).
Phage diagnostics: the principle of diagnostics is based on the joint cultivation of test cultures with known and unknown phages, a positive result is considered in the presence of bacterial cell lysis. Lysis can be observed on liquid and solid nutrient media. On liquid nutrient media, clarification of the bacterial suspension appears, and on dense ones, areas of lack of growth are formed.
Phage typing: determination of the type variant of a species using a set of type phages. Typhoid phages, cholera diagnostic phages, salmonella phages, and dysenteric phages are produced. Phage typing is necessary when conducting an epidemiological analysis of the disease and in order to establish the source and routes of transmission. By detecting a phage, the content of the corresponding microorganisms is judged.
