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Bacteriophages

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Bacteriophages

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Bacteriophages

  1. 1. Bacteriophages Dr.T.V.Rao MD11/20/12 Dr.T.V.Rao MDs Undergraduate Series 1
  2. 2. What are Bacteriophages Viruses that attack bacteria were observed by Twort and dHerelle in 1915 and 1917. They observed that broth cultures of certain intestinal bacteria could be dissolved by addition of a bacteria-free filtrate obtained from sewage11/20/12 Dr.T.V.Rao MDs Undergraduate Series 2
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  4. 4. Bacteriophages under Electron Microscope11/20/12 Dr.T.V.Rao MDs Undergraduate Series 4
  5. 5. 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???11/20/12 Dr.T.V.Rao MDs Undergraduate Series 5
  6. 6. Bacteriophages: Definition & History  Bacteriophages are viruses that can infect and destroy bacteria.  They have been referred to as bacterial parasites, with each phage type depending on a single strain of bacteria to act as host.11/20/12 Dr.T.V.Rao MDs Undergraduate Series 6
  7. 7. BACTRIOPHAGES Like most viruses, bacteriophages typically carry only the genetic information needed for replication of their nucleic acid and synthesis of their protein coats.. They require precursors, energy generation and ribosomes supplied by their bacterial host cell.11/20/12 Dr.T.V.Rao MDs Undergraduate Series 7
  8. 8. Bacteriophages: Classification  At present, over 5000 bacteriophages have been studied by electron microscopy and can be divided into 13 virus families.11/20/12 Dr.T.V.Rao MDs Undergraduate Series 8
  9. 9. Bacteriophage  Bacteriophages make up a diverse group of viruses, some of which have complex structures, including double- stranded DNA.11/20/12 Dr.T.V.Rao MDs Undergraduate Series 9
  10. 10. Bacteriophage11/20/12 Dr.T.V.Rao MDs Undergraduate Series 10
  11. 11. Bacteriophage  Also known simply as a phage; a virus that attacks and infects bacteria. The infection may or may not lead to the death of the bacterium, depending on the phage and sometimes on conditions. Each bacteriophage is specific to one form of bacteria.11/20/12 Dr.T.V.Rao MDs Undergraduate Series 11
  12. 12. Composition and Structure  Composition − Nucleic acid Head/Capsid  Genome size  Modified bases Contractile Tail Sheath • Protein −Structure (T ) 4 Size Tail Fibers –  Protection – Head or Infection Base Plate capsid11/20/12 Dr.T.V.Rao MDs Undergraduate Series 12 – Tail
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  14. 14. Phage entering a bacterial cell11/20/12 Dr.T.V.Rao MDs Undergraduate Series 14
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  16. 16. Bacteriophage showing Lytic and lysogenic cycle11/20/12 Dr.T.V.Rao MDs Undergraduate Series 16
  17. 17. Bacteriophages: Virulence Factors Carried On Phage  Temperate phage can go through one of two life cycles upon entering a host cell. 1) Lytic: Is when growth results in lysis of the host and release of progeny phage. 2) Lysogenic: Is when growth results in integration of the phage DNA into the host chromosome or stable replication as a plasmid. Most of the gene products of the lysogenic phage remains dormant until it is induced to enter the lytic cycle.11/20/12 Dr.T.V.Rao MDs Undergraduate Series 17
  18. 18. Bacteriophages: Lysogenic Conversion  Some lysogenic phage carry genes that can enhance the virulence of the bacterial host.  For example, some phage carry genes that encode toxins.  These genes, once integrated into the bacterial chromosome, can cause the once harmless bacteria to release potent toxins that can cause disease.11/20/12 Dr.T.V.Rao MDs Undergraduate Series 18
  19. 19. Bacteriophages • Used for cloning foreign genes among other applications • Proteins and peptides are fused to the Capsid(surface) of the phage • The combination of the phage and peptide is known as a Fusion Protein11/20/12 Dr.T.V.Rao MDs Undergraduate Series 19
  20. 20. Bacteriophages • Used for cloning foreign genes among other applications • Proteins and peptides are fused to the Capsid(surface) of the phage • The combination of the phage and peptide is known as a Fusion Protein11/20/12 Dr.T.V.Rao MDs Undergraduate Series 20
  21. 21. Bacteriophages • Once these Phages are isolated and recovered they can be used to infect bacteria which will create a particle similar to a monoclonal antibody11/20/12 Dr.T.V.Rao MDs Undergraduate Series 21
  22. 22. Lytic and Lysogenic cycle11/20/12 Dr.T.V.Rao MDs Undergraduate Series 22
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  25. 25. Bacteriophages: Lysogenic Conversion Examples of Virulence Factors Carried by Phage Gene Bacterium Phage Phenotype Product Vibrio cholerae CTX phage cholerae toxin cholera lambda hemorrhagic Escherichia coli shigalike toxin phage diarrhea clostridial botulinum botulism (food Clostridium botulinum phages toxin poisoning) Corynebacterium corynephage diphtheria diphtheria diphtheriae beta toxin Streptococcus erythrogenic T12 scarlet fever pyogenes toxins11/20/12 Dr.T.V.Rao MDs Undergraduate Series 25
  26. 26. Lysogenic conversionIn some interactions between lysogenicphages and bacteria, lysogenic conversionmay occur. It is when a temperate phageinduces a change in the phenotype of thebacteria infected that is not part of a usualphage cycle. Changes can often involve theexternal membrane of the cell by making itimpervious to other phages or even byincreasing the pathogenic capability of thebacteria for a host.11/20/12 Dr.T.V.Rao MDs Undergraduate Series 26
  27. 27. Assay for Lytic Phage Phage•  Plaque assay Plaque assay  Method Method – Bacteria Plaque forming unit – +  Plaque forming (pfu) Phage unit (pfu) infectious Measures –  particles Measures infectious particles 11/20/12 Dr.T.V.Rao MDs Undergraduate Series 27
  28. 28. Lytic vsLysogenic Cycle 11/20/12 Dr.T.V.Rao MDs Undergraduate Series 28
  29. 29. Transduction11/20/12 Dr.T.V.Rao MDs Undergraduate Series 29
  30. 30. Transduction11/20/12 Dr.T.V.Rao MDs Undergraduate Series 30
  31. 31. Bacterial Bacterial Capsid DNA cell wall chromosome Capsid Sheath Tail fiber1 Attachment: Tail Base plate Phage Pin attaches to host cell. Cell wall Plasma membrane2 Penetration: Phage pnetrates host cell and injects its DNA. Sheath contracted Tail core3 Merozoites released into bloodsteam from liver may infect new red blood cells 11/20/12 Dr.T.V.Rao MDs Undergraduate Series 31 Figure 13.10.1
  32. 32. Tail DNA4 Maturation: Viral components are assembled Capsid into virions.5 Release: Host cell lyses and new virions Tail fibers are released. 11/20/12 Dr.T.V.Rao MDs Undergraduate Series 32 Figure 13.10.2
  33. 33. Examples: * Corynebacterium diphtheria produces the toxin of diphtheria only when it is infected by the phage β. In this case, the gene that codes for the toxin is carried by the phage, not the bacteria. * Vibrio cholerae is a non-toxic strain that can become toxic, producing cholera toxin, when it is infected with the phage CTXφ. * Clostridium botulinum causes botulism. * Streptococcus pyogenes causes scarlet fever. * Shiga toxin11/20/12 * Tetanus Dr.T.V.Rao MDs Undergraduate Series 33
  34. 34. Medical Applications of Phages “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 University11/20/12 Dr.T.V.Rao MDs Undergraduate Series 34
  35. 35.  The Programme Created by Dr.T.V.Rao MD for Undergraduate Learning in Developing Countries  Email  doctortvrao@gmail.com11/20/12 Dr.T.V.Rao MDs Undergraduate Series 35

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