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Bacteriophages and their general characteritics
- 2. DEFINITION • Bacteriophage, also called phage or bacterial virus, group of viruses that infect bacteria • more than 10³¹ bacteriophages
- 3. HISTORY • Frederick W. Twort in Great Britain (1915) – Staph col – degen. • Félix d’Hérelle in France (1917) – dysentry • D’Hérelle coined the term bacteriophage, meaning “bacteria eater” • (Phagein) - "to devour" Félix d’Hérelle Frederick W. Twort
- 4. INTRODUCTION • Wide distribution • Faeces, sewage, Natural water • Study – Virus host interaction • Transduction • Phage conversion • Phage typing – Id bacteria
- 6. CLASSIFICATION • International Committee on Taxonomy of Viruses (ICTV) according to morphology and nucleic acid. • Nineteen families • 2 families have RNA genomes • 5 families – envelope • 8 families with DNA genomes - circular genomes • 9 (DNA) - linear genomes
- 7. • Myoviridae • Contractile tail • Linear ds DNA • T4 phage (T even phage) – E. coli
- 8. MORPHOLOGY • Tadpole • Hexagonal Head • Cylindrical tail • Head – – Tightly packed core of ds DNA – Surrounded by Protein coat / Capsid • Tail – – hollow core – Contractile sheath surr – Terminal base plate – attached prongs / fibres • Spherical / filamentous • ss DNA / RNA
- 13. LIFE CYCLE LYTIC PHASE • Virulent • Intracellular multiplication • Bacterial host – lysis • Release of progeny virions LYSOGENIC PHASE • Temperate • Phage DNA combines with host s DNA • Replicating together • No harm to host
- 15. LYTIC CYCLE • Adsorption • Penetration • Synthesis of phage components • Assembly • Maturation • Release
- 17. ADSORPTION • Attaches to bacterial surface to area having complimentary receptors to its base plate • Rapid – minutes • Location of bacterial Rs – cell wall / Flagella / Pili • Protoplasts – Not infected ( Transfection )
- 18. PENETRATION • Lysozyme on tail makes hole on surface • Hollow core pierces the cell wall • Contractile tail sheath propels nucleic acid in bacteria • Initiates synthesis of daughters • Empty head and tail remain outside – GHOST
- 22. SYNTHESIS OF PHAGE COMPONENTS • First synthesised – Early proteins • Enzymes – manufacture of complex molecules – phage specific • Late proteins – Head and Tail
- 23. ASSEMBLY • DNA of daughter phage – Packed into head • Tail is added MATURATION • The previous process and conversion to infective stage
- 24. RELEASE • Lysis of bacterial cell • Phage enzymes • Bacteria becomes spherical during replication of Phage • Defective cell wall • ECLIPSE PHASE – Entry to first intracellular phage formation
- 27. LYSOGENIC CYCLE • Symbiotic Relationship • Enters the bacterial cell • Integrated in bacterial chromosome • Prophage • Replicates synchronously with host DNA • Lysogeny • Bacterial host metabolism - UNAFFECTED
- 28. • Lysogenic / Phage conversion – – Prophage confers new properties to bacteria – ? - synthesis of new proteins – Eg – toxin production in Diptheria by beta phage • During repeated multiplication – lysogenic phage may be excised from host chromosome – initiates – Lytic cycle – SPONTANEOUS INDUCTION OF PROPHAGE
- 30. SPONTANEOUS INDUCTION OF PROPHAGE • UV Rays • Hydrogen peroxide • Nitrogen Mustard • Lysogenic bacteria – Resistant to reinfection – Superinfection Immunity
- 31. TRANSDUCTION • Carrier of genes between 2 bacteria • 2 Types – Restricted – genes common to bacteria – Generalised – Any • Plasmid mediated drug resistance - MRSA
- 34. PHAGE ASSAY Zone of lysis after incubation – Plaques Size, shape, nature – characteristic for different phages
- 35. PHAGE ASSAY • Titrating the number of viable phages • Purification of phages
- 36. PHAGE TYPING Specificity of Phage bacterium interaction - Id and Typing of Bacteria Adaption of Host – after serial passage in host becomes specific for that host
- 37. APPLICATIONS
- 38. Intraspecies typing of bacteria
- 47. THANK YOU