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NAJRAN UNIVERSITY College of Medicine

NAJRAN UNIVERSITY College of Medicine. Microbiology &Immunology Course Lecture No. 20. By. Dr. Ahmed Morad Asaad Associate Professor of Microbiology. Bacteriophages

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NAJRAN UNIVERSITY College of Medicine

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  1. NAJRAN UNIVERSITY College of Medicine Microbiology &Immunology Course Lecture No. 20 By Dr. Ahmed MoradAsaad Associate Professor of Microbiology

  2. Bacteriophages Bacteriophages or phages are viruses which infect bacteria. The majority are DNA viruses. Each phage attacks only particular species or in many cases only certain strain within the species Structure It is composed of a polygonal head consisting of DNA surrounded by a thin protein membrane and a short straight tail consisting of protein as in this figure: However, spherical and filamentous phages had been reported

  3. Life cycle of bacteriophages Two cycles are known Vegetative cycle and lysogenic cycle 1- The vegetative cycle: *- The phage is called virulent phage *- The cycle contains these steps: - Attachment (adsorption) - Penetration - Eclipse phase - Replication - Assembly - Release

  4. 2- The lysogenic cycle: *- The phage is called temperate phage *- The cycle contains these steps: - Attachment (adsorption) - Penetration - Eclipse phase - The phage does not replicate but it will be integrated into the bacterial chromosome and remain latent for a period of time - This phage is now called prophage - The bacteria carrying prophage is called lysogen - The lysogen will not be lysed but grow and multiply with prophage as a part of the chromosome -The lysogen can acquire new properties - The prophage may revert to virulent phage and infected bacteria will be lysed

  5. Practical applications of bacteriophage 1- Bacteriophage typing 2- Classification of bacteria into phage groups 3- Phage lysogenic conversion 4- Phage therapy 5- A cloning vector

  6. Antiviral agents Classes A- Natural antiviral compounds (Interferon) Interferon is a natural substance that has antiviral properties. 1- Types of interferon - Interferon-α (IFN-α): with maximal antiviral activity - Interferon-ß (IFN-ß): with intermediate activity B- Synthetic antiviral agents Grouped according their point of action in the viral replication cycle into:

  7. 1- Nucleoside analogs: They block viral nucleic acid synthesis. e.g., acyclovir, ribavirin and zidovudin 2- Nucleotide analogs: They differ from nucleoside analogs by having an attached phosphate group. They can persist in cells for long periods of time. e.g., Cidofovir 3- Non nucleoside reverse transcriptase inhibitors: They bind to reverse transcriptase. e.g., Nevirapine 4- Protease inhibitors: They inhibit viral protease. e.g., Saquinavir 5- Other types: Amantidine and Rimantidine: Inhibit Influenza viruses by inhibiting viral uncoating Foscarnet: Inhibit viral polymerase in Herpes viruses and inhibit reverse transcriptase in HIV

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