Bacteriophage Bacteriophage Phage Definition Obligate intracellular parasites that

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 O 157: H 7 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 Head/Capsid • Genome size • Modified bases – Protein • Protection • Infection • Structure (T 4) – Size – Head or capsid – Tail Contractile Sheath Tail Fibers Base Plate

Infection of Host Cells • Adsorption – LPS for T 4 • Irreversible attachment • Sheath Contraction • Nucleic acid injection

Types of Bacteriophage • Lytic or virulent phage: Phage that can only multiply within bacteria and kill the cell by lysis. (e. g. , T 4)

• Eclipse – Early genes – Phage DNA synthesis – Late genes • Intracellular accumulation • Lysis and Release Number of Infectious Particles Lytic Phage Multiplication Cycle Total Phage Eclipse Extracellular Phage Intracellular accumulation phase Time after Infection Lysis

Assay for Lytic Phage • Plaque assay – Method – Plaque forming unit (pfu) – Measures infectious particles Bacteria + 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 Cohesive Ends Lygase Linear Double Stranded Opened Circle Closed Circle

Events Leading to Lysogeny • Site-specific recombination – Phage coded enzyme gal • Repression of the phage genome – Repressor protein – Specific – Immunity to superinfection bio gal bio

Termination of Lysogeny • Induction – Adverse conditions • Role of proteases bio gal – rec. A protein – Destruction of repressor • Gene expression • Excision • Lytic growth 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