Theory

Bacteriophages, the viruses that infect bacteria, were discovered independently by Frederick W. Twort in 1915 and Félix d’Hérelle in 1917. The word bacteriophage was first coined by d’Hérelle, meaning "bacteria eater."

Phages are typically composed of a nucleic acid core (either DNA or RNA) surrounded by a protein coat that protects the genetic material. Bacteriophages exist in two forms: lytic and lysogenic.

In the lytic cycle, phages multiply within the host cell and eventually cause its death by lysis.

In the lysogenic cycle, the phage DNA integrates into the host genome and remains dormant, without causing immediate harm to the host cell.

Preparation of phage stocks is a vital step in Phage biology. In a bacterial culture, the phage suspension multiplies by taking bacterial cell machinery and lyse the cells eventually by releasing new phage particles. As a result, the medium contains a high concentration of phage particles. Lysed bacterial cell debris and unlysed cells are removed by centrifugation. Chloroform is also used along with phage dilution buffer to lyse the remaining cells and finally getting a solution of phage called phage lysate. Like preparation, conservation of bacteriophage stock is also a crucial step in phage biology. The most applicable method for long term storage of phage stock is placing them in SM buffer at 4oC. SM buffer or SM phage diluents which contains gelatin, Chloroform and Mg2+ are used for routine manipulation of phage stocks. The gelatin used in SM buffer helps to stabilize the phage particles while storage. Chloroform maintains the sterility of phage stock by hindering bacterial growth without causing any harm to phage