This document discusses bacteriophages (phages), viruses that infect bacteria. It covers the composition and structure of phages, how they infect host cells through adsorption and nucleic acid injection, and their multiplication cycles of either the lytic or lysogenic pathways. The document also discusses phage typing, which uses specific phages to identify and differentiate bacterial pathogens, and applications of phages in areas like diagnostics, therapeutics, biocontrol, and more.

1. Bacteriophage, Phage
Typing and Application
By:- Zebene A.

2. Out line of the presentation
 Introduction
 Composition and Structure of Bacteriophages
 Infection of Host Cells
 Phage Multiplication Cycle
 A. Lytic or Virulent Phages
 B. Lysogenic or Temperate Phage
 Phage Typing
 Application of Bacteriophages
 Reference

3. Introduction
 Bacteriophage
 Virus that infects bacteria.
 Obligate intracellular parasites that multiply
inside bacteria by making use of some or all of
the host biosynthetic machinery.
 Twort and d'Herelle in 1915 and 1917
 broth cultures of certain intestinal bacteria could
be dissolved by addition of a bacteria-free filtrate
obtained from sewage.

4. Diversity
 There are at least 12 distinct groups of
bacteriophages
 which are very diverse structurally and
genetically;
 the best known ones are the common phages
of E.coli:T4(lytic phage )&Lambda
Phage(Lysogenic phage)
 Phage Diversity.docx

5. Composition and Structure of Bacteriophage
A. Composition
 They all contain nucleic acid and protein.
 Depending upon the phage, the nucleic acid can
be either DNA or RNA but not both.
 Complexity vary from 3-5 average size gene
products code for over 100 gene
 The nucleic acids of phages often contain
unusual or modified bases.
 These modified bases protect phage nucleic acid
from nucleases that break down host nucleic acids
during phage infection.

6. B. Structure
Bacteriophages come in many different sizes and
shapes.
 Size - T4 is among the largest phages; it is
approximately 200 nm long and 80-100 nm wide.
Other phages are smaller. Most phages range in size
from 24-200 nm in length.
 Head or Capsid -All phages contain a head
structure which can vary in size and shape.
 Head acts as the protective covering for the
nucleic acid.

7.  Tail-Many but not all phages have tails
attached to the phage head.
 Is a hollow tube through which the nucleic
acid passes during infection.
 size of the tail can vary
 E.g. Complex phages like T4
 The tail is surrounded by a contractile sheath
which contracts during infection of the bacterium
 At the end the tail have a base plate and one or
more tail fibers involved in the binding of the
phage to the bacterial cell.

8. Structure of Enterbacteriacae
phage/Bacteriophage T4

9. Infection of Host Cells
A. Adsorption
 Mediated by the tail fibers or by some analogous
structure on those phages that lack tail fibers and it is
reversible.
 The tail fibers attach to specific receptors on the
bacterial cell and the host specificity of the phage
 The nature of the bacterial receptor varies for
different bacteria(proteins on the outer surface of the
bacterium, LPS, Pili, and lipoprotein)

10. B. Irreversible attachment
 The attachment of the phage to the bacterium via
the tail fibers is a weak one and is reversible.
 Irreversible binding of phage to a bacterium is
mediated by one or more of the components of the
base plate.
 Phages lacking base plates have other ways of
becoming tightly bound to the bacterial cell.

11. C. Sheath Contraction
 The irreversible binding of the phage to the
bacterium results in the contraction of the
sheath (for those phages which have a sheath)
and the hollow tail fiber is pushed through the
bacterial envelope.
D. Nucleic Acid Injection
 The DNA/RNA ejected to the bacterial cell
through the hollow tube
 The remainder of the phage remains on the
outside of the bacterium

12. Phage Multiplication Cycle
 Based on the multiplication cycle /event occur
during replication:-
A. Lytic or Virulent Phages
B. Lysogenic or Temperate Phage

13. A. Lytic or Virulent Phages
 Lytic or virulent phages are phages which can
only multiply on bacteria and kill the cell by
lysis at the end of the life cycle.
 Life cycle
 1. Eclipse period
 2. Intracellular Accumulation Phase
 3. Lysis and Release Phase

14. Lytic cycle

15. B. Lysogenic cycle/Temperate
 Either multiply via the lytic cycle or enter a
quiescent state in the cell
 In this quiescent state most of the phage genes are
not transcribed
 Phage DNA in the repressed state is called a
prophage because it is not a phage but it has
the potential to produce phage.
 The cell harboring a prophage is termed a
lysogen.

16. Events Leading to Lysogeny:-The Prototype
Phage: Lambda
1. Circularization of the phage chromosome
2. Site-specific recombination
3. Repression of the phage genome
 A phage coded protein, called a repressor, is
made which binds to a particular site on the phage
DNA, called the operator, and shuts off
transcription of most phage genes except the
repressor gene.

17. What determines whether the virus takes
Lytic or Lysogenic cycle?
 Determined by the concentration of the
repressor and another phage protein
called cro in the cell.
 If a promoter of repressor gene called C I
dominates the phage will progress to
lysogenic.
 If the an operator gene called cro dominates
the phage will progress to lytic cycle.

18. Events Leading to Termination
of Lysogeny
 Anytime a lysogenic bacterium is exposed to
adverse conditions, the lysogenic state can be
terminated. This process is called induction
 Adverse conditions lead to the production of
proteases (rec A protein) which destroy the
repressor protein.
 This in turn leads to the expression of the phage
genes, reversal of the integration process and lytic
multiplication

19. General cycle In the lysogeny

20.  Used for identification and differentiating of
bacterial pathogen.
 Specific bacteriophage isolated is mixed with
known bacterial pathogen
 The lysis due to viral infection of the
bacterium is specific and important in
identification of the host.
Phage Typing

21. Plaque assay/Assay for Lytic Phage
 Lytic phages are enumerated by a plaque
assay
 A plaque is a clear area which results from the
lysis of bacteria.
 Each plaque arises from a single infectious
phage.
 The infectious particle that gives rise to a
plaque is called a pfu (plaque forming unit).

22. Application of Bacteriophages
 Model for animal virus transformation
 Lysogeny is a model system for virus
transformation of animal cells
 Bacteriophage-based Diagnostics and Phage
Typing
 Phage as vehicles for vaccine delivery
 Phage display
 A molecular technique used in synthesizing
polypeptides with novel characteristics.

23. Cont’d
 Phage Therapy
 Can any phage be used for developing
therapeutic phage preparation?
 Environmental Applications
 Bio control for dangerous bacteria

24. Reference
1. Microbiology byte [Internet].[Last updated 2010, cited 2013]
http://www.microbiologybytes.com/virology/Phages.html
2. University of South Carolina School of Medicine: Microbiology and Immunology on
line [Internet].[Last updated 2010, cited 2013] Available from
http://pathmicro.med.sc.edu/mayer/phage.htm
3. Kenneth Todar.The Microbial WorldLectures in Microbiology by Kenneth Todar
PhD University of Wisconsin-Madison Department of Bacteriology [Internet].
[Last updated 2012, cited 2013] Available from
http://textbookofbacteriology.net/themicrobialworld/Phage.html
4. Madigan, Martinko, Stahl, Clark. Brock Biology of Microorganisms 13thEdition:
Virus and Virology: Pearson Education .Inc; 2008.
5. Elisabeth Kutter, Alexander Sulakvelidze. Bacteriophage Biology and Application:
CRC Press; 2005.
6. Irshad Ul Haq, Waqas Nasir Chaudhry, Maha Nadeem Akhtar, Saadia Andleeb and
Ishtiaq Qadri. Bacteriophages and their implications on future biotechnology: a
review. Virology Journal 2012; 9(9);1-8
7. Filippov AA, Sergueev KV, Nikolich MP (2013) Bacteriophages against Biothreat
Bacteria: Diagnostic, Environmental and Therapeutic Applications. J Bioterr Biodef
2013, S3 : 1-8.