Introduction to bacteriophage

The term bacteriophage is derived from the Greek term phage- meaning " to devour". A bacteriophage is also known as a phage - a  virus that infects and replicates within the bacteria. Structurally, these organisms are composed of a capsule of protein surrounding the  DNA or RNA genome and they are highly virulent. There are approximately 1031 bacteriophages on the earth. They distribute so densely, that there may be up to 9x108 virions per ML of water. They were discovered by Frederick W.Twort and Felix d. Herelle.

Table Of Content

1. Introduction to bacteriophage

2. The life cycles of phage

3. Structure of a typical bacteriophage

4. Phage therapy

5. Clinical applications of bacteriophages


The life cycles of phage

Like any other eukaryotic viruses, a typical phage undergoes 2 phases of reproduction namely, lytic stage and the lysogenic phase. A lytic phase of the cycle is an active and productive phase that synthesizes new phage particles whereas, the lysogenic cycle is a 'silent' phase. During the lysogenic phase, the genome of the phages silently gets integrated with the host chromosome.  In the initial phage of reproduction, it will first come in contact with a bacterial cell that contains an encoding receptor which is complementary to the phage anti-receptor. After the cell contact has been established through receptors, they either undergo replication or establish a state of 'silence.


Structure of a typical bacteriophage

Phages have a capsid that is attached to a tail structure. Both the head and tail encompass phage-encoded proteins. There is linear double-stranded DNA containing T4 and P1 within in a capsid that is attached to a tail. The T4 capsid is an elongated icosahedron with an elaborate tail structure. Tail structure also includes a collar at the base of the head and a rigid tail core surrounded by a contractile sheath. There is a hexagonal base plate to hold the core and sheath. The base plate is attached to the tail plate. At the tail end, there are minute and sickly hair-like structures called spikes or tail fibres. Spikes help in creating a communication with the host cells.


Diagram showing bacteriophage anatomy Free Vector


Phage therapy

As we already know that bacteriophages undergoes lytic phase during which they break the surface of bacteria. Keeping this feature of macrophages in mind, doctors use this for treating some infections. They can be bactericidal (kills the bacteria)by disrupting the bacterial metabolism that causes the bacterium to lyse/destruct. Many bacterial infections were treated by phage therapy through lytic bacteriophages. Phage therapy carries some advantages over the traditional antibiotic therapy. They can be very effective in certain conditions but, bacteria can also develop resistance to phages over a period of time. However, it is an easy and convenient way of killing bacteria in the short run.  


Phage therapy


Clinical applications of bacteriophages

Many experiments have proved that bacteriophages can be used in a wide number of clinical situations. Severe burns infected by several bacterial colonies can be destroyed by using bacteriophages. The food industry has seen a devastating effect because of food pathogens but these bacteriophages have proved to be the best in killing the food pathogens. Foot ulcers and cuts, wounds can also be treated by using phages.





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