Bacteriophage, or phages, are viruses that infect and replicate within bacteria. They have a protein coat that encapsulates either DNA or RNA and a tadpole shape with a hexagonal head and cylindrical tail. Phages have two life cycles: the lytic cycle kills the host bacterium to release new phages, while the lysogenic cycle incorporates the phage genome into the host genome without killing the cell. Phage therapy uses bacteriophages to treat bacterial infections and has advantages over antibiotics like host specificity and reduced risk of resistance development.

1. BACTERIOPHAGE

2. INTRODUCTION
Bacteriophage (bacteria-eater), as the name suggests, are the viruses that
infect and replicate within bacteria. They are commonly called a phage.
They are found everywhere. They contain DNA or RNA in their genome,
which is encapsulated in a protein coat. They also infect archaea.
Bactericidal activity of bacteriophage was first observed in 1896 by Ernest
Hanbury Hankin in the water of river Ganges, which could kill cholera
bacteria.William Twort discovered bacteriophage in 1915.
D’Hérelle termed them as ‘bacteriophage’ in 1917, as they showed the
ability to kill bacteria.
There are several types of phage virus, which infect only certain bacteria
specifically.
They act in the same way as antibiotics by disrupting the cell wall of

3. STRUCTURE AND MORPHOLOGY
• Tadpole shaped
• Hexagonal head
• cylindrical tail
• Head: nucleic acid (dsDNA)
surrounded by protein coat or
capsid; 28-100 nm size
• Tail: hollow core, surrounded by
contractile sheath and terminal
base plate 5

4. LIFE CYCLE OF BACTERIOPHAGE
THE LYTIC CYCLE INVOLVES THE REPRODUCTION OF VIRUSES USING A HOST CELL TO
MANUFACTURE MORE VIRUSES; THE VIRUSES THEN BURST OUT OF THE CELL. THE
LYSOGENIC CYCLE INVOLVES THE INCORPORATION OF THE VIRAL GENOME INTO THE
HOST CELL GENOME, INFECTING IT FROM WITHIN
LYTIC CYCLE:

5. LYSOGENIC CYCLE:

6. PHAGE THERAPY
• Phage therapy, viral phage therapy, or phagotherapy is the therapeutic use of
bacteriophages for the treatment of pathogenic bacterial infections.
• Advantages include reduced side effects and reduced risk of the bacterium
developing resistance
• Bacteriophages are much more specific than antibiotics. They are typically
harmless not only to the host organism but also to other beneficial bacteria,
such as the gut microbiota, reducing the chances of opportunistic infections.
• Phages tend to be more successful than antibiotics where there is a biofilm
covered by a polysaccharide layer, which antibiotics typically cannot penetrate.
• Phage therapy has many potential applications in human medicine as well as
dentistry, veterinary science, and agriculture. If the target host of a phage
therapy treatment is not an animal, the term “biocontrol” (as in phage-
mediated biocontrol of bacteria) is usually employed, rather than “phage