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vsv7

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Transcript

  • 1. Bacteriophage
  • 2. Bacteriophage (Phage)
    • Definition - Obligate intracellular parasites that multiply inside bacteria by making use of some or all of the host biosynthetic machinery
    • Significance
      • Models for animal cell viruses
      • Gene transfer in bacteria
      • Medical applications
        • Identification of bacteria - phage typing
        • Treatment and prophylaxsis???
  • 3. Medical Applications of Phage
    • “ I strongly believe phage could become an effective antibacterial tool” - Carl Merril, Chief of the Laboratory of Biochemical Genetics, National Institute of Mental Health, NIH.
    • “ It might be another string on the bow, such that when (conventional antibiotics) fail, here’s something that has a chance of working. But it’s not going to be a panacea” - Joshua Lederberg, Sackler Foundation Scholar at The Rockefeller University
    Reassessment of Medicinal Phage Spurs Companies to Study Therapeutic Uses American Society for Microbiology News 64:620-623, 1998
  • 4. Medical Applications of Phage
    • Exponential Biotherapies (Rockville, MD)
      • Vancomycin resistant Enterococcus facium and Streptococcus pneumoniae
    • Phage Therapeutics (Bothell, WA)
      • Staphylococcus aureus and Staphylococcus epidermidis
    • Intralytix, Inc. (Baltimore, MD)
      • Salmonella in meat and poultry
    • Biopharm Ltd. (Tblisi, Georgia)
      • Infections associated with burns
    • University of Idaho
      • Escherichia coli O157:H7 in cattle
    Reassessment of Medicinal Phage Spurs Companies to Study Therapeutic Uses. American Society for Microbiology News 64:620-623, 1998. Phages eyed as agents to protect against harmful E. coli. American Society for Microbiology News 65:666-667, 1999.
  • 5. Bacteriophage
    • T 4
    • Lambda (  )
  • 6. Composition and Structure
    • Composition
      • Nucleic acid
        • Genome size
        • Modified bases
      • Protein
        • Protection
        • Infection
    • Structure (T 4 )
      • Size
      • Head or capsid
      • Tail
    Tail Tail Fibers Base Plate Head/Capsid Contractile Sheath
  • 7. Infection of Host Cells
    • Irreversible attachment
    • Adsorption
      • LPS for T4
    • Nucleic acid injection
    • Sheath Contraction
  • 8. Types of Bacteriophage
    • Lytic or virulent phage: Phage that can only multiply within bacteria and kill the cell by lysis. ( e.g., T 4 )
  • 9. Lytic Phage Multiplication Cycle
    • Eclipse
      • Early genes
      • Phage DNA synthesis
      • Late genes
    • Intracellular accumulation
    • Lysis and Release
    Total Phage Extracellular Phage Eclipse Intracellular accumulation phase Time after Infection Number of Infectious Particles Lysis
  • 10. Assay for Lytic Phage
    • Plaque assay
      • Method
      • Plaque forming unit (pfu)
      • Measures infectious particles
    Bacteria Phage + Phage
  • 11. Types of Bacteriophage
    • Lysogenic or temperate phage: Phage that can either multiply via the lytic cycle or enter a quiescent state in the bacterial cell. ( e.g.,  )
      • Expression of most phage genes repressed
      • Prophage
      • Lysogen
  • 12. Events Leading to Lysogeny
    • Circularization of the phage chromosome
      • Cohesive ends
    Lygase Closed Circle Cohesive Ends Linear Double Stranded Opened Circle
  • 13. Events Leading to Lysogeny
    • Site-specific recombination
      • Phage coded enzyme
    • Repression of the phage genome
      • Repressor protein
      • Specific
      • Immunity to superinfection
    gal bio gal bio gal bio
  • 14. Termination of Lysogeny
    • Induction
      • Adverse conditions
    • Role of proteases
      • recA protein
      • Destruction of repressor
    • Excision
    • Lytic growth
    • Gene expression
    gal bio gal bio gal bio gal bio
  • 15. Lytic vs Lysogenic Cycle?
    • Role of repressor
    • Role of cro gene product
    • Role of proteases
  • 16. 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