Phage therapy is the therapeutic use of select lytic bacteriophages to biocontrol specific strains of bacteria. It is a mechanism for eliminating specific bacteria from a microbiome. The microbiome is the collection of all microbes, such as bacteria, fungi, viruses, and their genes, that naturally live on our bodies and inside us.
What is a Phage?
Phages (bacteriophages) are viruses that only infect bacteria. Lytic bacteriophages lyse (the disintegration of a cell by rupture of the cell wall or membrane) bacteria. Phage Therapy is the therapeutic use of lytic bacteriophages to biocontrol a population of specific bacteria in a targeted microbiome — for example in the bladder, a non-healing wound, a vessel containing farmed fish or Salmonella in poultry.
Bacteriophage or phage are ubiquitous in the environment – they are everywhere on the planet. Higher life forms live in harmony with phages. Bacteriophages are extremely diverse. There are more genetically unique bacteriophages in the environment than all of the other plant and animal species on earth combined. But phages are also narrow spectrum. This means that, in the majority of cases, a given phage can only kill a very narrow range of strains of a given species of bacteria. If a phage has the correct anatomy (the receptors in the “feet” of the phage) to allow it to attach to a given strain of bacteria, it is said the strain of bacteria is sensitive to the phage. If the receptors can not interlock with the cell wall and thus infect and kill the bacteria, the bacteria is said to be resistant to the phage.
How Do Bacteriophages Work?
In the video to the right a bacterium is sensitive to a bacteriophage. The phage attaches to the cell wall, deposits its DNA, replicates itself by consuming the cell’s cytoplasm and nucleus, and then breaks the cell wall – clearly killing the host bacterium. This is called the lytic cycle and it can occur many times over until that specific strain of bacteria that populates the particular microbiome has been eliminated. All other strains / species of surrounding bacteria that are resistant remain unharmed by the surrounding phages.
Bacteriophages are nature’s natural population control for bacteria, there is a constant microscopic war going on between phages and bacteria – and this keeps the population of bacteria on the planet under control. The video to the right illustrates how a lytic phage attaches to the cell wall of the bacterial host, then inserts its DNA into the cell. The phage replicates itself may ties over then releases a lytic enzyme that causes the cell to rupture and release the progeny phages into the environment.