A bacteriophage is a virus which infects bacteria. These viruses typically cause their hosts to die as a result of infection, which makes bacteriophages of great interest to the medical community and to scientists who cultivate bacteria. In industries where bacteria are harnessed to perform tasks such as the fermentation of foods or the production of useful chemicals, contamination with bacteriophages is a major source of concern, as the viruses can bring a process to a complete halt.
Humans have been aware of the action of bacteriophages for centuries. Many observers noted historically that consuming water from certain places seemed to confer protection against disease. This water was teeming with bacteriophages which could attack the bacteria causing the disease, although these observers were not aware of this fact. Over time, people began to wonder what it was about waters such as those found in the River Ganges that provided protection from disease, and bacteriophages were discovered.
These viruses can contain DNA or RNA, along with proteins which can match to specific receptors on target bacteria. Because their receptors are customized to match up with particular proteins, bacteriophages generally infect only closely related bacteria, leaving others alone because they lack the ability to infect them. When a bacteriophage finds a bacterium with proteins which match its receptors, it can insert DNA or RNA into the bacterium and direct the organism to start producing replicas of the virus.
In the process of replicating the bacteriophage, many bacteria will experience lysis, in which they break up or dissolve, literally exploding as they become overloaded with viruses. Others may be able to survive the replication process, but they will eventually be prone to other problems which inhibit reproduction, effectively killing off the bacteria.
Phage therapy, or deliberate introduction of bacteriophages to the bodies of patients with bacterial infections, has been suggested in some regions of the world as a method which could be used to treat disease. Treatment with phages could also potentially address the issue of antibiotic resistance, as a bacteriophage can still lock on to a bacterium which has developed resistance to antibiotic medications.
These tiny viruses appear to be among the most common viruses in the world, and they can be found everywhere. This is perhaps not surprising, since bacteria can also be found everywhere, and the ability to prey on bacteria would ensure that a bacteriophage had a steady supply of victims.