bacteriophage is a type of virus that infects bacteria. In fact, the word "bacteriophage" literally means "bacteria eater," because bacteriophages destroy their host cells. All bacteriophages are composed of a nucleic acid molecule that is surrounded by a protein structure
2. DEFINITION
• Bacteriophage, also called phage or
bacterial virus, group of viruses that
infect bacteria
• more than 10³¹ bacteriophages
3. HISTORY
• Frederick W. Twort in
Great Britain (1915) –
Staph col – degen.
• Félix d’Hérelle in France
(1917) – dysentry
• D’Hérelle coined the
term bacteriophage,
meaning “bacteria eater”
• (Phagein) - "to devour"
Félix d’Hérelle
Frederick W. Twort
4. INTRODUCTION
• Wide distribution
• Faeces, sewage, Natural
water
• Study – Virus host
interaction
• Transduction
• Phage conversion
• Phage typing – Id bacteria
5.
6. CLASSIFICATION
• International Committee
on Taxonomy of Viruses
(ICTV) according to
morphology and nucleic
acid.
• Nineteen families
• 2 families have RNA
genomes
• 5 families – envelope
• 8 families with DNA
genomes - circular
genomes
• 9 (DNA) - linear
genomes
8. MORPHOLOGY
• Tadpole
• Hexagonal Head
• Cylindrical tail
• Head –
– Tightly packed core of
ds DNA
– Surrounded by Protein
coat / Capsid
• Tail –
– hollow core
– Contractile sheath
surr
– Terminal base plate –
attached prongs /
fibres
• Spherical / filamentous
• ss DNA / RNA
9.
10.
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12.
13. LIFE CYCLE
LYTIC PHASE
• Virulent
• Intracellular
multiplication
• Bacterial host – lysis
• Release of progeny
virions
LYSOGENIC PHASE
• Temperate
• Phage DNA combines
with host s DNA
• Replicating together
• No harm to host
17. ADSORPTION
• Attaches to bacterial surface to
area having complimentary
receptors to its base plate
• Rapid – minutes
• Location of bacterial Rs – cell
wall / Flagella / Pili
• Protoplasts – Not infected
( Transfection )
18. PENETRATION
• Lysozyme on tail makes hole on surface
• Hollow core pierces the cell wall
• Contractile tail sheath propels nucleic acid in bacteria
• Initiates synthesis of daughters
• Empty head and tail remain outside – GHOST
19.
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22. SYNTHESIS OF PHAGE COMPONENTS
• First synthesised – Early proteins
• Enzymes – manufacture of complex molecules
– phage specific
• Late proteins – Head and Tail
23. ASSEMBLY
• DNA of daughter phage – Packed into head
• Tail is added
MATURATION
• The previous process and conversion to
infective stage
24. RELEASE
• Lysis of bacterial cell
• Phage enzymes
• Bacteria becomes spherical during replication of
Phage
• Defective cell wall
• ECLIPSE PHASE – Entry to first intracellular
phage formation
25.
26.
27. LYSOGENIC CYCLE
• Symbiotic Relationship
• Enters the bacterial cell
• Integrated in bacterial chromosome
• Prophage
• Replicates synchronously with host
DNA
• Lysogeny
• Bacterial host metabolism -
UNAFFECTED
28. • Lysogenic / Phage conversion –
– Prophage confers new properties to bacteria
– ? - synthesis of new proteins
– Eg – toxin production in Diptheria by beta
phage
• During repeated multiplication – lysogenic phage
may be excised from host chromosome – initiates
– Lytic cycle – SPONTANEOUS INDUCTION
OF PROPHAGE
31. TRANSDUCTION
• Carrier of genes between 2 bacteria
• 2 Types
– Restricted – genes common to bacteria
– Generalised – Any
• Plasmid mediated drug resistance - MRSA
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33.
34. PHAGE ASSAY
Zone of lysis after incubation – Plaques
Size, shape, nature – characteristic for different phages
36. PHAGE TYPING
Specificity of Phage bacterium interaction - Id and Typing of Bacteria
Adaption of Host – after serial passage in host becomes specific for
that host
