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Bacteriophage
 

Bacteriophage

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    Bacteriophage Bacteriophage Presentation Transcript

    • Bacteriophage
    • 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???
    • 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
    • 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.
    • Bacteriophage
      • T 4
      • Lambda (  )
    • 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
    • Infection of Host Cells
      • Irreversible attachment
      • Adsorption
        • LPS for T4
      • Nucleic acid injection
      • Sheath Contraction
    • Types of Bacteriophage
      • Lytic or virulent phage: Phage that can only multiply within bacteria and kill the cell by lysis. ( e.g., T 4 )
    • 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
    • Assay for Lytic Phage
      • Plaque assay
        • Method
        • Plaque forming unit (pfu)
        • Measures infectious particles
      Bacteria Phage + Phage
    • 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
    • Events Leading to Lysogeny
      • Circularization of the phage chromosome
        • Cohesive ends
      Lygase Closed Circle Cohesive Ends Linear Double Stranded Opened Circle
    • 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
    • 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
    • Lytic vs Lysogenic Cycle?
      • Role of repressor
      • Role of cro gene product
      • Role of proteases
    • 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