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19. Bacteriophages and their role in Microbiology.pptx
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- 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 ofPhage “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
- 4. Medical Applications ofPhage 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
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- 6. Composition and Structure Composition ◦Nucleic acid ◦ Genome size ◦ Modified bases ◦ Protein ◦ Protection ◦ Infection • Structure (T4) – Size – Head or capsid – Tail Tail Tail Fibers Base Plate Head/Capsid Contractile Sheath
- 7. Infection of HostCells Irreversible attachment • Adsorption – LPS for T4 • Nucleic acid injection • Sheath Contraction
- 8. Types of Bacteriophage Lyticor virulent phage: Phage that can only multiply within bacteria and kill the cell by lysis. (e.g., T4)
- 9. Lytic Phage MultiplicationCycle 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 LyticPhage • Plaque assay – Method – Plaque forming unit (pfu) – Measures infectious particles Bacteria Phage + Phage
- 11. Types of Bacteriophage Lysogenicor temperate phage: Phage that can either multiply via the lytic cycle or enter a quiescent state in the bacterial cell. ◦ Expression of most phage genes repressed ◦ Prophage ◦ Lysogen
- 12. Events Leading toLysogeny Circularization of the phage chromosome ◦ Cohesive ends Lygase Closed Circle Cohesive Ends Linear Double Stranded Opened Circle
- 13. Events Leading toLysogeny 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 gal bio gal bio gal bio gal bio • Gene expression
- 15. Significance of Lysogeny Modelfor 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
- 16. Life Cycle ofBacteriophages T-Even Bacteriophages: Lytic Cycle Lytic: Cell bursts at end of cycle 1. Attachment or adsorption: Virus tail binds to specific receptors on the cell surface. 2. Penetration: Virus injects genetic material (DNA) into cell. Tail releases lysozyme, capsid remains outside. 3. Biosynthesis: Viral proteins and nucleic acids are made. Eclipse phase: No virions can be recovered from infected cells.
- 17. Lytic Cycle ofBacteriophage
- 18. 4. Maturation: Bacteriophagecapsids and DNA are assembled into complete virions. 5. Release: Bacteriophage virions are released from the cell. Plasma membrane breaks open and cell lyses. Burst time: Time from attachment to release of new virions (20-40 minutes). Burst size: Number of new phage particles that emerge from a single cell (50-200).
- 19. Lytic Cycle ofBacteriophage
- 20. Life Cycle ofBacteriophages Bacteriophage Lambda: Lysogenic Cycle 1. Attachment and Penetration: Virus tail binds to specific receptors on the cell surface and injects genetic material (DNA) into cell. 2. Circularization: Phage DNA circularizes and enters either lytic or lysogenic cycle. Lysogenic Cycle 3. Integration: Phage DNA integrates with bacterial chromosome and becomes a prophage. Prophage remains latent. 4. Excision: Prophage DNA is removed due to a stimulus (e.g.: chemicals, UV radiation) and initiates a lytic cycle.
- 21. Lysogenic versus LyticCycles of Bacteriophage