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Bacteriophage

Bacteriophage. Bacteriophage (Phage). Definition : viruses that infect bacteria (twort & d’Herelle 1917) Significance Models for animal cell viruses Gene transfer in bacteria Medical applications Identification of bacteria - phage typing Treatment and prophylaxsis???.

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Bacteriophage

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  1. Bacteriophage

  2. Bacteriophage (Phage) • Definition : viruses that infect bacteria (twort & d’Herelle 1917) • Significance • Models for animal cell viruses • Gene transfer in bacteria • Medical applications • Identification of bacteria - phage typing • Treatment and prophylaxsis???

  3. Bacteriophage - Morphology • Tadpole shaped • Hexagonal head (ds DNA) • Tail: hollow core with contractile sheath • Base plate: tail fibers

  4. Head/Capsid Contractile Sheath Tail Tail Fibers Base Plate Composition and Structure

  5. Infection of Host Cells • Irreversible attachment • Adsorption • LPS for T4 • Sheath Contraction • Nucleic acid injection

  6. Bacteriophage:The Lytic Cycle • Attachmentto cell surface receptors (chance encounter – no active movement) • Penetration– only genome enters • Biosynthesis–Production of phage DNA and proteins • Maturation– assembly to form intact phage • Releasedue to phage induced lysozyme production

  7. Lytic Cycle of a Bacteriophage 1 2 3

  8. Lytic Cycle of a Bacteriophage 4

  9. Assay for Lytic Phage Phage • Plaque assay • Method • Plaque forming unit (pfu) • Measures infectious particles Bacteria + Phage

  10. Lysogenic cycle • Phage DNA integrates into bacterial chromosome • Integrated genome: PROPHAGE • Bacterium carrying the prophage: LYSOGENIC bacterium • Super infection immunity: a lysogenic bacterium is resistant to re-infection by the same or related phages • Lysogenic phage can become lytic

  11. Lysogenic Cycle of a Bacteriophage

  12. Significance of Lysogeny • Model for animal virus transformation • Lysogenic or phage conversion • Definition: A change in the phenotype of a bacterial cell as a consequence of lysogeny • Modification of Salmonella O antigen • Toxin production by Corynebacterium diphtheriae

  13. Significance/ uses of bacteriophages • Phage typing: to classify bacteria • Epidemiological investigation to know the relatedness b/w strains of same species • S.aureus • Vi Ag typing of S.typhi • Vibriocholerae • C.diphtheria

  14. Phage assay • When virulent phages are spread over the lawn culture of susceptible bacteria areas of clearing/ lysis called PLAQUES are seen around growth of each phage

  15. 4. Phage therapy • Lytic phages can kill bacteria: treatment of bacterial infections: burn & wound infections • Used in diagnosis: identification of M.tuberculosis • Used as vectors for cloning in recombinant DNA technology • TRANSDUCTION: Temperate phages vehicles for transferring genes from one bacterium to another: antibiotic resistance genes • Eg: In S.aureus plasmids encoding B-lactamases are transferred by transduction

  16. 6. CODE FOR TOXINS: phage genome codes for the following bacterial toxins: • Diphtheria toxin • Cholera toxin • Verocytotoxin of EHEC • Botulinum toxin C & D 7. Alter antigenic properties of bacteria

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