An overview of bacteriophage and its multiplication.

1. MULTIPLICATION OF
BACTERIOPHAGES
~ BY FALGUNI AGRAWAL

2. What are Viruses ?
They are obligatory intracellular
parasites which contains :-
1. Single type of nucleic acid
either DNA or RNA
2. A protein coat which itself
could be enveloped or not.
3. Multiplies inside living cell
by using the synthesizing
machinery of host cell.
4. Synthesizes specialized
structures that can transfer
viral nucleic acid to other
cells.

3. Introduction
What Are Bacteriophages ?
• Bacteriophages are obligatory
intracellular parasites.
• They were first observed by Twort
and d’Herelle.
• Bacteriophages are complex viruses.
• Only carries genetic information for
replication and synthesis.
• At present over 5000 bacteriophages
have been studied. T-even bacteriophage

4. Multiplication Of Bacteriophages
1. Lytic Cycle
• Example - T-even bacteriophage
• Host Cell – E.coli
• Virions of this bacteriophage are large,
complex, and non enveloped with a
characteristic head and tail.
• Length of DNA – 6% of that
contained in host cell.
• Occurs in 5 distinct stages –
Attachment, Penetration,
Biosynthesis, Maturation and Release
T-even bacteriophage
infecting E.coli

7. 2. Lysogenic cycle
• Example – lambda bacteriophage
• Host Cell – E.coli
• It has a temperate life cycle that allows it
either to undergo lytic cycle or else
lysogenic cycle.
•The virus particle consists of a head and a
tail that can have tail fibres.
•The genome contains 48,490 base pairs of
double-stranded, linear DNA.
•Occurs in 5 distinct stages – Attachment,
Entry, circularization of viral DNA,
Prophage formation, Cell divison.

9. Three important results of
Lysogeny
1. Lysogenic cells are immune to reinfection by the
same phage
2. Phage conversion – for eg: Cornybacterium
diptheria that causes diptheria.
3. Specialized transduction can be possible.

10. Growing Bacteriophages in
laboratory
• They can be grown either in:
a) suspensions of bacteria in liquid media
b) Bacterial cultures on solid media(Plaque Method)
• In plaque method –
Bacteriophages mixed with host bacteria + melted agar
After several Multiplication cycles, the area surrounding the original virus is
destroyed
Area of lysis formed is called a plaque
Each plaque begins with single viral particle
The concentration of these viruses is given as plaque-forming units.

11. Significance Of Bacteriophages
1. Virulent Phage 2. Temperate Phage
* Phage typing * Toxin production
* Phage therapy * Transduction
* Cloning Vector

12. Advantages and Disadvantages of using
Bacteriophages over Antibiotics
Advantages
1. Very specific
2. Replicates at the site of infection
3. Safe(no reports of serious adverse effects)
4. Active against antibiotic-resistant bacteria
Disadvantages
1. Additional research required
2. Development of Phage resistance and Phage neutralizing antibodies.
3. Not accessible to intracellular pathogens
4. Difficult to administer
5. Can transfer toxic genes between bacteria.

13. References
1. Microbiology by – Tortora Funke Case, IX
edition, Pearson Education
2. Bacteriophage : Genetics and Molecular Biology
by Stephen Mc Grath and Douwe van Sinderen,
Caister Academic Press, July 2007.

14. THANK YOU