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BACTERIOPHAGE

BACTERIOPHAGE. Bacteriophage (Phage). Definition - Viruses that infect and multiply inside bacteria by making use of some or all of the host biosynthetic machinery. Figure Bacteriophage. Head/Capsid. Contractile Sheath. Tail. Tail Fibers. Base Plate. Composition and Structure.

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BACTERIOPHAGE

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  1. BACTERIOPHAGE

  2. Bacteriophage (Phage) • Definition - Viruses that infect and multiply inside bacteria by making use of some or all of the host biosynthetic machinery

  3. Figure Bacteriophage

  4. 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

  5. Each phage attaches to a specific cell surface molecule (usually a protein) and so only cells bearing that “receptor” can be infected by a given phage.

  6. Two Basic Types • Lytic phage: eg. T phage infect a bacterial cell DNA replication coat proteins expression host cell lysed to release the new phage

  7. The lytic growth cycle Figure 21-1

  8. 2. Temperate phage: eg. Phage λ Lysogeny —the phage genome integrated into the bacterial genome and replicated passively as part of the host chromosome, coat protein genes not expressed. The phage is called a prophage. Daughter cells are lysogens.

  9. Figure 21-2 The lysogenic cycle of a bacteriophage

  10. The lysogenic state can switch to lytic growth, called induction. Excision of the prophage DNA DNA replication Coat proteins expression Lytic growth

  11. Figure 16-24 Growth and induction of λ lysogen

  12. Progagate phage • Find a suitable host cell that supports the growth of the virus. • The mixture of viruses and bacteria are filtered through a bacterial-proof filter.

  13. Assay for Lytic Phage Phage • Plaque assay • Method • Plaque forming unit (pfu) • Measures infectious particles Bacteria + Phage

  14. This circle-of-death produces a hole or PLAQUE in a lawn of living cells. These plaques can be easily seen and counted so that the numbers of virus can be quantitated. As the viruses replicate and are released, they spread and infect the nearby cells.

  15. The Single-Step Growth Curve Latentperiod-the time lapse between infection and release of progeny. Burstsize-the number of phage released Bacteriophage Figure 21-4

  16. Therapy and prevention • Phage therapy is the application of bacteriophages to bacterial infections of humans (or other animals) reducing bacterial load • Phages can be delivered topically, orally, directly into body tissues, or systemically • To treat bacterial infections that do not respond to conventional antibiotics

  17. Therapeutic use of lyticbacteriophages • Phage therapy of staphylococcal infections (including MRSA) may be less expensive than antibiotic treatment • To control biofilms, form on the surfaces of embedded medical devices such as catheters.

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