- Bacteriophages (phages) are the most abundant micro organisms in our environment and are present in significant numbers in water and foods of various origins.
- Phages are harmless to humans, animals and plants. Humans are routinely exposed to bacteriophages at high levels through food and water without adverse effect.
- Phages can be regarded as the natural enemies of bacteria, and therefore are logical organic agents for the control of food borne bacterial pathogens, such as Listeria.
- On fresh and processed meat and meat products, more than 108 viable phages per gram are often present, and high numbers of phages are routinely consumed with our food.
- Phages do not change the organoleptics of food products
- Phages are also normal commensals of humans and animals, and are especially abundant in the gastrointestinal tract.
- A bacteriophage (from 'bacteria' and Greek phagein, 'to eat') is a virus which infects and kills only bacteria.
- The term bacteriophage is commonly used in its shortened form, "phage".
- Typically, phages consist of an outer protein hull enclosing genetic material. The genetic material is usually double-stranded DNA between 5 and 500 kilo base pairs long.
- Phages are usually between 20 and 200 nm in size. A phage is approximately 100 times smaller than a typical bacterium.
- Phages are highly specific (do not cross species or genus boundaries), and will not affect:
(a) desired bacteria in foods (e.g., starter cultures)
(b) commensals in the gastrointestinal tract
(c) accompanying bacterial flora in the environment.
- Phages are generally composed entirely of proteins and nucleic acids, their eventual breakdown products consist exclusively of amino acids and nucleic acids. Thus, they are not xenobiotics and do not leave an ecological footprint
PHAGES - THE LYTIC CYCLE ( ≈ 20 min)
Phages are chemically attracted to a specific bacterial host. This attraction is extremely specific, which enables the use of lytic phage in a variety of applications without risk to humans, animals, and “non-target” bacteria. When a phage encounters its specific target bacterium, it attaches itself to the cell wall of the bacterium using its tail fibres. Once a phage attaches to the bacterium, it penetrates the cell wall of the bacterium and its DNA is drawn into the bacterium, effectively taking over the cell and destroying the bacterium’s ability to function or replicate.
When the replication of phage weakens the cell wall structure and exceeds the available space within the bacterium cell, the cell wall bursts (lyses) and new phages are released into the environment. In the absence of target bacteria, the phages break down into common biological particles that are naturally absorbed back into the environment.
view animation of bacteriophage T4 infection of its host
Source: Leiman PG, Chipman PR, Kostyuchenko VA, Mesyanzhinov VV, Rossmann MG, Cell. 2004 Aug 20;118(4):419-29.