These slides are covering multiple aspects of Bacteriophages including History Classification Replication Plaque Assay Transduction Phage Therapy and pahge types.

1. By:
Zoqia Tariq and group
University of Gujrat

2. Contents
 Introduction
 History
 Classification
 Replication
 Plaque Assay
 Transduction
 Phage Therapy

3. Definition
 A bacteriophage (informally, phage) is a virus that
infects and replicates within a bacterium.
 The term is derived from "bacteria" and the Greek
word phagein, "to devour".

4. Structure of
Bacteriophage
.

5. History
 In 1896, Ernest Hanbury Hankin reported that
something in the waters of the Ganges and Yamuna rivers
in India had marked antibacterial action
against cholera and could pass through a very fine
porcelain filter.
 In 1915, British bacteriologist Frederick Twort,
superintendent of the Brown Institution of London,
discovered a small agent that infected and killed bacteria

6. Classification and Composition of
bacteriophages
 At present over 5000
bacteriophages have been
studied by electron
microscopy and can be
divided into 13 virus
families.

7. Genome structure 15091560-052
 They all contain nucleic acid and protein.
 Depending upon the phage, necleic acid can be either
DNA or RNA but not both.
 The nucleic acid of phages often contain unusual or
modified bases which protect phage nucleic acid from
nucleases that break down host nucleic acids during phage
infection.
 Simple phages may have 2 to 5 genes while complex
phages may have over 100 genes.

8. Genome Structure
Head, capsid, tail
fiber etc.

9. Replication
 Bacteriophages may have a lytic cycle or a lysogenic
cycle, and a few viruses are capable of carrying out both.
 Lytic Cycle: bacterial cells are broken open and destroyed
after immediate replication of the virion.
 In contrast, the lysogenic cycle does not result in
immediate lysing of the host cell. Those phages able to
undergo lysogeny are known as temperate phages.
 Their viral genome will integrate with host DNA and
replicate along with it relatively harmlessly, or may even
become established as a plasmid.

10. Replication
 Adsorption or Attachment
The lytic cycle begins with a collision between T-phage
virion and a susceptible host cell i.e. Escherichia coli. The
process of attachment of a virion on the host cell surface is
called adsorption.

11. Continue
 Penetration or Injection
The tail fibers of virion bend to bring the spikes and basal
plate in contact with the surface of bacterial wall. The tail
sheath contracts so that the hollow tail core (inner tube)
penetrates the bacterial wall and injects the viral genome
into the cytoplasm.

12. Continue
 Synthesis of proteins and nucleic acid
Within minutes, bacterial ribosomes start translating viral
mRNA into protein. For RNA-based phages, RNA
replicase is synthesized early in the process. Proteins
modify the bacterial RNA polymerase so it preferentially
transcribes viral mRNA.

13. Conti,…
 Virion assembly and Maturation
The capsid proteins assemble to form empty head and
a condensed viral DNA is packed inside it. Finally the
separately assembled tail joins to head to form a
daughter or progeny virion. Bacteriophage
components assemble and phages fully develop. The
whole process takes about 15 minutes.

14. Conti,...

15. Continue,…
 Release of virions
During assembly of progeny virions, the bacterial cell
becomes spherical. The phage enzymes weaken the cell
wall which ultimately burst or lyse to release about 100-
200 progeny virions.

16. Continue,…
 Lysogenic Cycle:
The phages that exhibit lysogenic cycle are called
temperate phages or non-virulent phages. For
example, λ phages attacking E. coli, during lysogenic
cycle, the phage DNA integrates into the bacterial
DNA and is now called as prophage. The host
bacterium containing prophage is called a lysogenic
bacterium or lysogen.

17. Replication
overview
Lytic and
Lysogenic
Cycle of a
bacteriophage

18. Plaque Assay
 The plaque assay, routinely used for determinations,
invaluable in quantitative analysis during mutational and
recombinational studies of bacteriophages.
 During infection of bacteria, enormous quantities of
bacteriophages may be obtained for investigation. Often,
more than 10-10 viruses are produced per milliliter of
culture medium.

19. Plaque Assay
.

20. Transduction
 A process by which a virus transfers genetic material from
one bacterium to another.
 Viruses called bacteriophages are able to infect bacterial
cells and use them as hosts to make more viruses.
 After multiplying, these viruses assemble and occasionally
remove a portion of the host cell's bacterial DNA. Later,
when one of these bacteriophages infects a new host cell,
this piece of bacterial DNA may be incorporated into the
genome of the new host.

21. Types of Transduction
 There are two types of transduction:
i. Generalized
ii. Specialized
 In generalized transduction, the bacteriophages can pick
up any portion of the host's genome.
 In specialized transduction, the bacteriophages pick up
only specific portions of the host's DNA.
 Scientists have taken advantage of the transduction
process to stably introduce genes of interest into various
host cells using viruses.

22. Transduction
Generalized
transduction

23. What is phage therapy?
 Phage therapy is the therapeutic use of bacteriophages
in order to treat pathogenic bacterial infections
 This method is still used for the treatment of a variety
of bacterial and poly-microbial biofilm infections
 But it has not yet been approved in Georgia
 It has many applications in human medicine as well as
dentistry, veterinary science, and agriculture
 Bacteriophages are more specific than antibiotics.
 They have a high therapeutic index
 Now-a-days phages are also used to kill food
poisoing bacteria e.g Listeria.

24. Use of phage therapy in history
 Previously, phage therapy was used to treat
Anthrax
Bubonic plague
Cholera
Dysentery
Enteritis
Gas gangerene
Gastrointestinal infections
Gonorrhea

25. Continued...
Meningitis
Staphylococcal skin diseases e.g. boils, carbuncles,
furuncles etc.
Tuberculosis
Thyroid fever
Lung and upper respiratory tract infections
Several bacterial infections e.g. mastoid infections,
vaginitis etc.

26. Advantages Of Phage Therapy
Over Antibiotics
 Phage therapy is effective against multidrug-resistant
pathogenic bacteria
 It has high specificity to target only bacterial species
 It can rapidly respond to appearances of phage resistant
mutants.
 The cost of developing a phage system is cheaper than
developing a new antibiotic
 Unlike antibiotics, side effects are uncommon because phages
as well as their products do not effect eukaryotic cells.
 They also replicate at the site of infection

27. Use Of Phage Therapy In Food
Industary
 Phage therapy controls the growth of Campylobacter and
Salmonella on chicken skin, Samonella eneritidis in
cheese, Listeria monocytogenes on meat and on fresh-cut
fruits
 It controls the presence of biofilms in food processing
environments i.e used to control the growth of L.
Monocytogenes
 Hence, useful to provide hygeinic foods including meat
and poultry products.

28. Phage Therapy In Agriculture And
Fisheries
 Phage therapy controls the fish pathogens
 It is used in food and livestock markets in order to avoid
contamination of food products with pathogenic bacteria
like L. Monocytogenes, Salmonella on cut vegetables
and fruits and the pathogenic Escherichia coli O157 : H7.

29. 15091560-054
Advantages of bacteriophages
 Phages can be used as bio control agents in agriculture and
petroleum industry.
 Phages are used as vehicles for vaccines both DNA and
protein, for the detection of pathogenic bacterial strain, as
display system for many proteins and antibodies.
 Bacteriophages are diverse group of viruses which are easily
manipulated and therefore they have potential uses in
biotechnology, research, and therapeutics.
 They have been proposed as alternatives to antibiotics for many
antibiotic resistant bacterial strains.
 Phages are very specific and do not harm the useful bacteria
that live in and on the body.

30. Continued…
 Phages are also excellent as food bio preservation agents since
they are reported to lyse hosts at temperatures as low as 1°C,
limiting growth of pathogenic and spoilage bacteria on
refrigerated foods.
 Reduction of colonization on foods (bio control) during
industrial food processing can be accomplished by applying
phages directly on food surfaces.
 Application of phages to poultry has been successful to prevent
fatal respiratory infections in broiler chickens.
 Phages can be administered orally, incorporated in drinking
water or food to control Salmonella and Campylobacter in
poultry, or by spray to target avian pathogenic E. coli in
poultry

31. Disadvantages of Bacteriophages
 There are no internationally recognized studies that prove the
efficacy of phages in humans.
 Bacteria can also become resistant to phages.
 Bacteria have a type of ‘immune system’ that destroys the
hereditary material of some penetrating phages. Only suitable
phages can conquer this ‘immune system.
 Infections whose agents are hidden in the interior of human
cells may be inaccessible to phages.
 Phages are more difficult to administer than antibiotics. A
physician needs special training in order to correctly prescribe
and use phages.
 In comparison to chemical molecules, phages are complex
organisms that can transfer toxin genes between bacteria.

32. Continued…
 Phages that are injected into the bloodstream are
recognized by the human immune system. Some of them
are quickly excreted and, after a certain period, antibodies
against the phages are produced by the body. For this
reason, it appears that one type of phage can only be used
once for intravenous treatment.
 In comparison to chemical molecules, phages are
relatively large. For this reason, the sites in the body that
can be reached by them must be carefully clarified.

33. Viroids and Prions:
 Viruses, viroids, and prions are all a cellular pathogens.
They are not within any kingdom and carry their own
significant characteristics.
 Obligate intracellular parasite – require a host to cause
damage
 Filterable – small enough to be filtrated
 Contains an outer protein coat and inner genome
 Has only one kind of nucleic acid (RNA or DNA, but
never both)
 Lacks metabolic abilities

34. Continued…
Viroids:
 These are very small, circular RNA (may appear linear),
and infectious in plants. They do not contain a capsid.
 A virion contains a protein coating called a capsid, which
surrounds the core of the virus containing the nucleic acid.
 Some virions also contain an envelope which is made up
of a phospholipid membrane.
Prions:
 Prions are proteinaceous infective particles. Prions do not
contain nucleic acid.
 Prions infect animals and is responsible for a number of
diseases that affect the brain and other neural tissue

35. .