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Bacteriophages, also known as phages, are a group of viruses capable of infecting and multiplying within bacterial cells and which, when they leave, promote their destruction.
Bacteriophages are present in different environments, and can be isolated from water, soil, food products and even other microorganisms. Although it can also be present in the body, mainly in the skin, in the oral cavity, in the lungs and in the urinary and gastrointestinal systems, bacteriophages do not cause diseases or changes in the human body, because they have a preference for prokaryotic cells, that is, less evolved, such as bacteria.
In addition, they are able to stimulate the body's immune response, so that they cannot act on the microorganisms responsible for the proper functioning of the organism, in addition to having high specificity in relation to their host, that is, the pathogenic microorganism. Thus, the bacteria that are part of the microbiome are not destroyed due to the positive relationship established between the bacteriophages and the immune system.
Characteristics of the bacteriophage
Bacteriophages are viruses that can be found in different environments, including the human body, however they do not cause changes or diseases as they do not have specificity for the cells that make up the body. Other characteristics of the bacteriophage are:
- They are formed by a capsid, which is a structure formed by proteins whose function is to protect the genetic material of the virus;
- They may have different types of genetic material, such as double stranded DNA, single stranded DNA or RNA;
- In addition to being able to be differentiated in terms of their genetic composition, bacteriophages can also be differentiated by the structure of the capsid;
- They are unable to multiply outside a host, that is, they need to be in contact with a bacterial cell for replication to occur, and for this reason they may also be known as "bacterial parasites";
- They have high specificity for the host, which are bacterial cells.
The classification of bacteriophages is still being studied, however, some properties can be useful for differentiation and classification of bacteriophages, such as type of genetic material, morphology, genomic characteristics and physical-chemical characteristics.
How happens the lytic and lysogenic cycles
The lytic and lysogenic cycles are cycles of multiplication of the bacteriophage when in contact with the bacterial cell and can be differentiated according to the behavior of the virus.
Lytic cycle
The lytic cycle is one in which, after the injection of the bacteriophage's genetic material into the bacterial cell, replication and formation of new bacteriophages takes place, which when they leave destroy the bacterial cell. So, in general, the cycle happens as follows:
- Adsorption: the bacteriophage sticks to the membrane of the susceptible bacterial cell through the membrane receptors;
- Entry or penetration: the genetic material of the bacteriophage enters the bacterial cell;
- Replication: this genetic material coordinates the synthesis of proteins and other DNA molecules, if it is a DNA bacteriophage;
- Assembly: new bacteriophages are formed and the replicated DNA is packaged with the aid of the synthesized proteins, giving rise to the capsid;
- Lysis: the bacteriophage formed leaves the bacterial cell, promoting its destruction.
Lysogenic cycle
In the lysogenic cycle, the genetic material of the bacteriophage is incorporated into that of the bacterium, however this process may represent only the silencing of virulence genes of the bacterium, in addition to being a reversible process. This cycle happens as follows:
- Adsorption: the bacteriophage adsorbs to the bacterial membrane;
- Entry: the genetic material of the bacteriophage enters the bacterial cell;
- Integration: there is the integration of the genetic material of the bacteriophage with that of the bacterium, becoming known as a profago;
- Division: the recombined material, the profago, divides according to the bacterial division.
The profagus is not active, that is, its genes are not expressed and, therefore, do not result in negative changes for bacteria and it is a fully reversible process.
Due to the fact that bacteriophages interact with the genetic material of the bacterium and can promote its destruction, these viruses can be used in the study to develop new strategies to combat multi-resistant infections.
What is phage therapy
Phage therapy, also known as phage therapy, is a type of treatment that uses bacteriophages to fight bacterial infections, especially those caused by multi-resistant microorganisms. This type of treatment is safe, since bacteriophages only have activity against pathogenic bacteria, preserving the person's normal microbiota.
Although this type of therapy has been described for years, it is only now that it has gained prominence in the literature due to the increase in the number of bacteria that do not respond to conventional treatment with antibiotics.
However, despite being a favorable technique, phage therapy has some limitations. Each type of bacteriophage is specific to a specific bacterium, so these phages could not be used in isolation to fight infections caused by various microorganisms, but in this case a "phage cocktail" could be formulated according to the microorganisms identified as responsible for the infection. In addition, mainly due to the lysogenic cycle, bacteriophages can promote the transfer of resistance genes to the bacterium, rendering the treatment ineffective.