bacteriophage-22033mdkmkdmmdk1174042.pdf

bacteriophage-22033mdkmkdmmdk1174042.pdf

1. Bacteriophage

2. Real Image of T4 bacteriophage
via electron microscope

3. Bacteriophage
from the greek phagein, meaning "to eat“
Eaters or destroyers of bacteria
First described in 1915

4. Viruses infecting a bacterium

5. BACTERIOPHAGE
Viruses that infect and parsitized bacteria
is known as bacteriophage.
It was discovered by Frederick.W.Twort in
Great Britian (1915) and Felix d’ Herelle in
France(1917).
D’ Herelle coined the term bacteriophage
meaning ‘bacterial eater’ to describe the
agent’s bacteriocidal activity. He observed
lysis of a broth culture of a dysentry
bacillus.

6. Phages are very simple in structure,
consisting merely of aDNA (or occasionally
ribonucleic acid (RNA)) molecule carrying a
number of genes, surrounded by a protective
coat or capsid made up of protein
molecules.
They can undergo two life cycle
Lytic cycle
Lysogenic cycle

7. Structure of Bacteriophage
•Most of the phages are tadpole-
shaped.
•Phage head:hexagonal in shape,
composed of coat protein and genome in
the core
•Genome: dsDNA codes for enzymes
and proteins necessary to replicate more
viruses
•Tail Sheath: hollow core covered with
a contractile sheath. DNA travels from
head to bacteria through sheath
•Tail fiber:helps anchor the phage on the
cell membrane
•Examples are Lambda phage, M13
phage, T4,T7 phage, P1 phage etc.

8. CHARECTERSTICS OF BACTERIOPHAGES
•Hostspecificity:theyhavehighhost
specificity.
•Theyarefilterablethroughfilters.
•Lyticphagecauseslysisofbacteria.
•Theyaresensitivetoheat.
•Theircommonesthabitalisintestinal
bacterialfloraofmanandanimal.

9. PHAGE LIFE CYCLE: LYTIC VS LYSOGENIC
Phagereplicatesbylyticlifecycle
(virulentphage)
•Non-integrationofphagegeneticmaterial
•Intracellularmultiplicationofthephageendsin
lysisofhostbacterium.
Phagereplicatesbylysogeniclifecycle
(temperatephages(prophages))
•Integrationofphagegeneticmaterialinto
bacterialgenome.
•Phagereplicateswithbacteriacausingnoharm
tothehostcell

10. Adsorption by LyticBacteriophage
The bacteriophage binds to specific
receptors on the bacterial cell wall.
Tail conformation changes/contracts
terminal base plate penetrates cell wall

11. An electron micrographof bacteriophages attached to a bacterial cell. These
viruses are the size and shape of coliphage T1

13. Cycle of events in Bacteriophageinfecting
a Bacterial Cell

14. Penetration
•The bacteriophage injects its genome into
the bacterium's cytoplasm

15. Synthesis of phage component
•Phage-coded enzymes shut down host’s DNA, RNA, protein synthesis.
•Intially, early proteins, including specific enzymes, necessary for
synthesis of phage components are synthesized. During this phase, phage
are not detectable also known as eclipse phase.
•Late functions include the subsequent synthesis of other proteins and
assembly of the nucleocapsid.
-MATURATION
After this the protein subunits of phage head, and tail and phage DNA
assembles to form infective phage particle

16. Phage Release
• A bacteriophage-coded enzyme break down the
peptidoglycan in the bacterial cell wall causing osmotic
lysis.

18. Attachment:
Phage attaches
to host cell.
Penetration:
Phage pnetrates
host cell and
injects its DNA.
Biosynthesis:
Transcription/
Translation and
Viral
chromosome
replication
1
2
3
Bacterial
cell wall
Bacterial
chromosome
Capsid DNA
Capsid
Sheath
Tail fiber
Base plate
Pin
Cell wall
Tail
Plasma membrane
Sheath contracted
Tail core
LyticLifecycle of a BacteriophageI

19. 4Maturation/Assembly:
Viral components are
assembled into
virions.
Tail
5 Release:
Host cell lyses and
new virions are
released.
DNA
Capsid
Tail fibers
LyticLifecycle of a BacteriophageII

20. LYSOGENIC CONVERSION
The prophageconfers certain new properties to
lysogenicbacterium.
Examples: of Lysogenicconversion
* Corynebacterium diphtheria produces the toxin of
diphtheria only when it is infected by the phage β. In this case, the
gene that codes for the toxin is carried by the phage, not the
bacteria.
* Vibriocholera is a non-toxic strain that can become toxic,
producing cholera toxin, when it is infected with the phage CTXφ.
* Clostridium botulinumcauses botulism.
* Streptococcus pyogenescauses scarlet fever.
* Shiga toxin
* Tetanus

21. BacteriophagesSignificance
•Phage typing: Used as
epidemiological markers to
identify reservoir of infection.
•Phage therapy: acts as
bacteriocidal agent.
•Acts as a carriers of genes from
one bacterium to another known
as transduction.
•Confers the property of toxin
production in some bacteria.
•Used in studying host-parasite
relationships.

22. TRANSDUCTION
•DNA may be transferred by a
bacteriophage to a bacteria in a
process called transduction.

23. •Phagetypingisusedasepidemiologicalmarkerto
identifydifferentbacterialstrainsthatare
biochemicallyserologicallyidenticaland
indistinguishablefromeachother.
•Suchbacterialstrainsaredifferentiatedbyusing
typespecificbacteriophage.
•Thetechniquehasmostextensivelybeenused
forthedetectionofMycobacteriumtuberculosis,
E.coli,Pseudomonas,Salmonella,Listeria,and
Campylobacterspecies

24. Bacteriophagesin Medicine
•Bacteriophages,orphages,bytheir
verynature,theycanbeconsidered
aspotentialantibacterialagents.
•Overthepastdecadeortwo,theidea
ofphagetherapy,i.e.theuseoflytic
bacteriophagesforboththe
prophylaxisandthetreatmentof
bacterialinfections,hasgained
specialsignificance.
•thisleadstotheriseinthe
prevalenceofhighlyantibiotic-
resistantbacterialstrains.

25. Phage Therapy
•Phages were discovered
to be anti-bacterial
agents and were used
throughout the 1940s in
the Soviet Union for
treating bacterial
infections. They had
widespread use including
treating soldiers in the
Red Army. However, they
were abandoned for
general use in the west.
25

26. S.aureusinfection
Treated with phage
impregnated pad
Improvement in wound healing

27. Limitations of phage therapy
1.Emergenceofbacterialstrainsresistantto
particularphages.Theemergenceofphage–
resistantbacterialmutantswasobservedand
thephenomenonwassuggestedtobea
potentialproblemofphagetherapy
(Summers,1999;d’Herelle,1930)