Bacteriophage

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Bacteriophage
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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???

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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, heres
  something that has a chance of working. But its
  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 64620-623, 1998
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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 O157H7 in cattle

Reassessment of Medicinal Phage Spurs Companies
to Study Therapeutic Uses. American Society for
Microbiology News 64620-623, 1998. Phages eyed
as agents to protect against harmful E. coli.
American Society for Microbiology News
65666-667, 1999.
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Bacteriophage

• T4
• Lambda (?)

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Composition and Structure

• Composition
• Nucleic acid
• Genome size
• Modified bases
• Protein
• Protection
• Infection

• Structure (T4)
• Size
• Head or capsid
• Tail

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Infection of Host Cells

• Adsorption
• LPS for T4

• Irreversible attachment

• Sheath Contraction

• Nucleic acid injection

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Types of Bacteriophage

• Lytic or virulent phage Phage that can only
  multiply within bacteria and kill the cell by
  lysis. (e.g., T4)

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Lytic Phage Multiplication Cycle

• Eclipse
• Early genes
• Phage DNA synthesis
• Late genes
• Intracellular accumulation
• Lysis and Release

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Assay for Lytic Phage
Phage

• Plaque assay
• Method
• Plaque forming unit (pfu)
• Measures infectious particles

Bacteria

Phage
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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

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Events Leading to Lysogeny

• Circularization of the phage chromosome
• Cohesive ends

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Events Leading to Lysogeny

• Site-specific recombination
• Phage coded enzyme

• Repression of the phage genome
• Repressor protein
• Specific
• Immunity to superinfection

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Termination of Lysogeny

• Induction
• Adverse conditions
• Role of proteases
• recA protein
• Destruction of repressor

• Gene expression

• Excision

• Lytic growth

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Lytic vs Lysogenic Cycle?

• Role of repressor
• Role of cro gene product
• Role of proteases

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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