Bacteriophage

Views:
 
     
 

Presentation Description

Powerpoint presentation for under graduate medical students

Comments

Presentation Transcript

Bacteriophage:

Bacteriophage Dr. Pendru Raghunath Reddy Assistant Professor Dept of Microbiology Dr. VRK Women’s Medical College

PowerPoint Presentation:

Bacteriophage Definition: Bacteriophages are viruses that infect and parasitise bacteria d’Herelle named the bacteriophage (Greek phagein, to eat) Phages occur widely in the environment such as sewage, faeces, soil and other natural sources of mixed bacterial growth

PowerPoint Presentation:

Morphology Bacteriophages that infect E. coli , called the T-even phages (T 2 , T 4 , T 6 ), have been extensively studied T-even phages are tadpole-shaped, possess a head and a tail Head Hexagonal in shape and consists of a tightly packed core of nucleic acid (double stranded DNA) enclosed by a protein coat, called a capsid The size of the head varies in different phages from 28 nm to 100 nm

PowerPoint Presentation:

Tail Tail Fibers Base Plate Head/Capsid Contractile Sheath 2. Tail It is composed of a hollow core surrounded by a contractile sheath, and a terminal base plate which has attached to prongs, tail fibres or both

PowerPoint Presentation:

Life cycle Phages exhibit two different types of life cycle Virulent or lytic cycle Temperate or lysogenic cycle Lytic cycle Replication of a virulent phage can be divided into five stages Adsorption Penetration Synthesis of phage components Maturation Release

PowerPoint Presentation:

Adsorption Phage attaches to a specific receptor site by means of tail fibres Adsorption is a specific process and depends on the presence of complementary chemical groups on the receptor sites and on the terminal base plate of the phage Infection cannot occur in the absence of adsorption The infection of a bacterium by the naked phage nucleic acid is known as ‘transfection’

PowerPoint Presentation:

Penetration

PowerPoint Presentation:

Virulent or lytic cycle of bacteriophage Eclipse phase The interval between the entry of the phage nucleic acid into the bacterial cell and the appearance of first infectious intracellular phage particle

PowerPoint Presentation:

Lysogenic cycle In lysogenic cycle, the bacteriophage nucleic acid becomes inserted into the bacterial chromosome. The integrated phage genome in this state is known as the ‘prophage’ The prophage behaves like a segment of the host chromosome and replicates synchronously with it. This phenomenon is called ‘lysogeny’ The bacterium that carries a prophage is known as a ‘lysogenic bacterium’ The prophage confers certain new properties on the lysogenic bacterium. This is known as ‘lysogenic conversion or phage conversion’ Bacteriophage that parasitise a bacterium without lysing it is known as ‘temperate phage’

Bacteriophages: Lysogenic Conversion:

Bacteriophages: Lysogenic Conversion Virulence factors coded by prophage Bacterium Phage Gene Product Medical importance Vibrio cholerae CTX phage cholerae toxin cholera Escherichia coli lambda phage shigalike toxin hemorrhagic diarrhea Clostridium botulinum CE β and DE β botulinum toxin botulism (food poisoning) Corynebacterium diphtheriae beta phage diphtheria toxin diphtheria Streptococcus pyogenes T12 erythrogenic toxins scarlet fever

Events Leading to Lysogeny:

Events Leading to Lysogeny Circularization of the phage chromosome Cohesive ends Lygase Closed Circle Cohesive Ends Linear Double Stranded Opened Circle

Events Leading to Lysogeny:

Events Leading to Lysogeny Site-specific recombination Phage coded enzyme Repression of the phage genome Repressor protein Immunity to superinfection gal bio gal bio gal bio

Termination of Lysogeny:

Termination of Lysogeny gal bio gal bio gal bio gal bio Occasionally integrated prophage may become excised from bacterial DNA and initiates lytic cycle and the daughter phage particles are released, which infect other bacteria and render them lysogenic This is known as ‘spontaneous induction of prophage’

PowerPoint Presentation:

Significance of phages Virulent phage Phage typing Phage therapy Phage display 2. Temperate phage Toxin production b) Antigenic property c) Transduction d) Cloning vector

PowerPoint Presentation:

Phage display

authorStream Live Help