A bacteriophage (informally, phage) is a virus that infects and replicates within bacteria. The term is derived from 'bacteria' and the Greek φαγεῖν phagein "to devour". Bacteriophage are composed of proteins that encapsulate a DNA or RNA genome, and may have relatively simple or elaborate structures. Their genomes may encode as few as four genes, and as many as hundreds of genes. Phage replicate within bacteria following the injection of their genome into the cytoplasm. Bacteriophage are among the most common and diverse entities in the biosphere.
Phages are widely distributed in locations populated by bacterial hosts, such as soil or the intestines of animals. One of the densest natural sources for phages and other viruses is sea water, where up to 9×108 virions per milliliter have been found in microbial mats at the surface, and up to 70% of marine bacteria may be infected by phages. They have been used for over 90 years as an alternative to antibiotics in the former Soviet Union and Eastern Europe, as well as in France. They are seen as a possible therapy against multi-drug-resistant strains of many bacteria.
Read more about Bacteriophage: Classification, History, Phage Therapy, Replication, Genome Structure, In The Environment, Role in Food Fermentation, Other Areas of Use, Model Bacteriophages, Cultural References