- Characteristics of the bacteriophage
- How happens the lytic and lysogenic cycles
- What is Phage Therapy
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, which is why it is a reason for study to develop new strategies to fight infections multiresistant.
Bacteriophages are present in several 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 cells 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, the so-called microbiome or microbiota, in addition to having high specificity in relation to its 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 several environments, including the human body, however they do not cause changes or diseases as they do not have specificity for prokaryotic cells, which are 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 bacteriophage; They may have different types of genetic material, such as double stranded DNA, single stranded DNA or RNA; In addition to being differentiated as to 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 there to be replication, and therefore they can 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
Lytic and lysogenic cycles concern the behavior of bacteriophages when in contact with the bacterial cell. 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. On the other hand, in the lysogenic cycle, the genetic material of the bacteriophage is incorporated into that of the bacterium, however this process can only represent the silencing of virulence genes of the bacterium, in addition to being a reversible process.
Bacteriophages can have only one or both cycles. In general, the lytic cycle occurs 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.
On the other hand, the lysogenic 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 to the bacteria and it is a fully reversible process.
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 is gaining 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, making treatment ineffective.
