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 • T4 • Lambda ()

6. Head/Capsid Contractile Sheath Tail Tail Fibers Base Plate Composition and Structure • Composition • Nucleic acid • Genome size • Modified bases • Protein • Protection • Infection • Structure (T4) • Size • Head or capsid • Tail

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

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

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

10. Assay for Lytic Phage Phage • Plaque assay • Method • Plaque forming unit (pfu) • Measures infectious particles Bacteria + 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. Cohesive Ends Lygase Linear Double Stranded Closed Circle Opened Circle Events Leading to Lysogeny • Circularization of the phage chromosome • Cohesive ends

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

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

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