A liquid that is cloudy from bacteria will become clear again when bacteriophages destroy all cells present. However, bacteriophages do not always kill their host, at least not immediately. Like all infectious organisms, bacteriophages could never make their host extinct, for they are dependent on their host bacteria to survive. See our display on infectious bacterial diseases . Indeed, phage therapy has been used in the past to cure infectious diseases, especially in Eastern Europe and Russia, and research is continuing.
Bacteriophages are important tools in bacteriological research.
They can be used as vehicles to introduce DNA into a bacteria. Phages don't mind to take along foreign DNA when they insert their own DNA into a bacterial cells. Microbiologists can make use of this. The formation of mutations in a bacterial population can be nicely demonstrated with bacteriophages.