Bacteriphages were described by Frederick Twort in 1915 and Felix d’Hérelle in 1917. D’Hérelle named them bacteriophages because they were able to lyse bacteria on the surface of agar plates. Phage research in the 1930s through 1950s led to the discovery of a large number of key concepts in biology and virology.
Bacteriophages, or phages, are viruses whose hosts are bacterial cells. Like all viruses, phages are metabolically inert in their extracellular form, and they reproduce by insinuating themselves into the metabolism of the host.
The mechanisms by which phage virions infect their host cells vary among the different types of phages, but they all result in delivery of the phage genome into the cytoplasm of the bacterial host, where it interacts with the cellular machinery to carry the phage life cycle forward. The result of infection can be, and often is, total destruction for the cell.
Bacterial cells can undergo one of two types of infections by viruses known as lytic and lysogenic infections (Figure 9). In E. coli, lytic infections are caused by a group seven phages known as the T-phages, while lysogenic infections are caused by the phage lambda. There are many similarities between bacteriophages and animal cell viruses. Thus, bacteriophage is viewed as model systems for animal cell viruses.