Phage therapy, viral phage therapy, or phagotherapy is the therapeutic use of bacteriophages for the treatment of pathogenic bacterial infections. This therapeutic approach emerged at the beginning of the 20th century but was progressively replaced by the use of antibiotics in most parts of the world after the Second World War. Bacteriophages, known as phages, are a form of virus that attach to bacterial cells and inject their genome into the cell. The bacteria's production of the viral genome interferes with its ability to function, halting the bacterial infection. The bacterial cell causing the infection is unable to reproduce and instead produces additional phages. Phages are very selective in the strains of bacteria they are effective against.
An electron micrograph of bacteriophages attached to a bacterial cell. These viruses are the size and shape of coliphage T1.
Frederick Twort
Félix d'Hérelle, discoverer of phage therapy
Phage in action on cultured Bacillus anthracis
A bacteriophage, also known informally as a phage, is a virus that infects and replicates within bacteria and archaea. The term was derived from "bacteria" and the Greek φαγεῖν, meaning "to devour". Bacteriophages are composed of proteins that encapsulate a DNA or RNA genome, and may have structures that are either simple or elaborate. Their genomes may encode as few as four genes and as many as hundreds of genes. Phages replicate within the bacterium following the injection of their genome into its cytoplasm.
Bacteriophage T2, a member of the Myoviridae due to its contractile tail
Félix d'Herelle conducted the first clinical application of a bacteriophage
George Eliava pioneered the use of phages in treating bacterial infections
In this electron micrograph of bacteriophages attached to a bacterial cell, the viruses are the size and shape of coliphage T1