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BACTERIOPHAGE
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Bacteriophage
• A bacteriophage (from 'bacteria and Greek φαγεῖν phagein "to devour") is any one of a number of viruses that infect bacteria. They do this by injecting genetic material, which they carry enclosed in an outer protein capsid. The genetic material can be ssRNA, dsRNA, ssDNA, or dsDNA ('ss-' or 'ds-' prefix denotes single-strand or double-strand) along with either circular or linear arrangement.
What are Bacteriophages
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Viruses that attack bacteria were observed by Twort and d'Herelle 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 sewage. The lysis of the bacterial cells was said to be brought about by a virus which meant a
"filterable poison ("virus" is Latin for "poison").
BACTRIOPHAGES
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Bacteriophages typically carry only the genetic information needed for replication of their nucleic acid and synthesis of their protein coats. When phages infect their host cell, the order of business is to replicate their nucleic acid and to produce the protective protein coat. But they cannot do this alone. They require precursors, energy generation and ribosomes supplied by their bacterial host cell.
Bacteriophage• Bacteriophages
make up a diverse group of viruses, some of which have complex structures, including double-stranded DNA.
BacteriophageBacteriophage• 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.
Bacteriophages: Classification
• At present, over 5000 bacteriophages have been studied by electron microscopy and can be divided into 13 virus families.
Double stranded DNA, Enveloped
Double stranded DNA,Non-enveloped
Myoviridae
Siphoviridae
Podoviridae
P2
T2
λ
P22
Tectiviridae PRD1
Corticoviridae PM2
Single-stranded DNA Inoviridae M13 & fd
Microviridae ΦX174 Leviviridae
Single strande
d RNAMS2
Lipothrixviridae
TTV1
Fuselloviridae SSV1Plasmaviridae
Double stranded RNA
phi666
Cystoviridae
RudiviridaeSIRV 1, 2
13 Bacteriophage families
13 Bacteriophage familiesCorticoviridae
icosahedral capsid with lipid layer, circular supercoiled dsDNA
Cystoviridaeenveloped, icosahedral capsid, lipids, three molecules of
linear dsRNA
Fuselloviridaepleomorphic, envelope, lipids, no capsid, circular
supercoiled dsDNA
Inoviridae genus(Inovirus/Plectrovirus)
long filaments/short rods with helical symmetry, circular ssDNA
Leviviridae quasi-icosahedral capsid, one molecule of linear ssRNA
Lipothrixviridae enveloped filaments, lipids, linear dsDNA
Microviridae icosahedral capsid, circular ssDNA
Myoviridae (A-1,2,3) tail contractile, head isometric
Plasmaviridaepleomorphic, envelope, lipids, no capsid, circular
supercoiled dsDNA
Podoviridae (C-1,2,3) tail short and noncontractile, head isometric
Rudiviridae helical rods, linear dsDNA
Siphoviridae (B-1,2,3) tail long and noncontractile, head isometric
Tectiviridaeicosahedral capsid with, linear dsDNA, "tail" produced for
DNA injection [email protected]/[email protected]
Bacteriophages• Morphology of the T series of Phages Name Plaque size Head (nm) Tail (nm) Latent period (min) Burst size
T1 medium 50 150 x 15 13 180
T2 small 65 x 80 120 x 20 21 120
T3 large 45 invisible 13 300
T4 small 65 x 80 120 x 20 23.5 300
T5 small 100 tiny 40 300
T6 small 65 x 80 120 x 20 25.5 200-300
T7 large 45 invisible 13 300
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.
Lysogenic conversion
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In some interactions between lysogenic phage's and bacteria, lysogenic conversion may occur. It is when a temperate phage induces a change in the phenotype of the bacteria infected that is not part of a usual phage cycle. Changes can often involve the external membrane of the cell by making it impervious to other phages or even by increasing the pathogenic capability of the bacteria for a host.
Examples: of Lysogenic conversion
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* Corynebacterium diphtheria 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 cholera 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 toxin * Tetanus [email protected]/
Bacteriophages: Lysogenic Conversion
Bacterium Phage Gene Product Phenotype
Vibrio cholerae CTX phage cholerae toxin cholera
Escherichia coli lambda phage shigalike toxin hemorrhagic
diarrhea
Clostridium botulinum clostridial phages
botulinum toxin
botulism (food poisoning)
Corynebacterium diphtheriae
corynephage beta
diphtheria toxin diphtheria
Streptococcus pyogenes T12 erythrogenic
toxins scarlet fever
Examples of Virulence Factors Carried by Phage
Bacteriophages Uses
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• 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 Protein
Bacteriophages causes Lysis of Bacteriophages causes Lysis of Infected CellsInfected Cells
• The T-phages, T1 through T7, are referred to as lytic phages because they always bring about the lysis and death of their host cell, the bacterium E. coli. T-phages contain double-stranded DNA as their genetic material. In addition to their protein coat or capsid (also referred to as the "head"), T-phages also possess a tail and some related structures
Genetic Engineering Genetic Engineering BacteriophagesBacteriophages
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• Different sets of genes are inserted into the genomes of multiple phages
• These separate phages will only display one protein, peptide, or antibody
• Collections of these phages can comprise Libraries
• These Libraries are exposed to selected targets and only some phages will interact with targets
Bacteriophages
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• Once these Phages are isolated and recovered they can be used to infect bacteria which will create a particle
similar to a monoclonal antibody
Bacteriophages• By taking gene segment of
antigens of antibodies and fusing them to the protein coat of phages, these phages will now express the anti-body in a fusion protein
• Phage Display Libraries of antigens can be created to create anti-body phage display libraries [email protected]/
Bacteriophages in Medicine• Bacteriophages, or phages, by their very nature,
they can be considered as potential antibacterial agents. Over the past decade or two, the idea of phage therapy, i.e. the use of lytic bacteriophages for both the prophylaxis and the treatment of bacterial infections, has gained special significance in view of a dramatic rise in the prevalence of highly antibiotic-resistant bacterial strains paralleled by the withdrawal of the pharmaceutical industry from research into new antibiotics
Phage Therapy• Phages were discovered
to be anti-bacterial agents and were used throughout the 1940s in the Soviet Union for treating bacterial infections. They had widespread use including treating soldiers in the Red Army. However, they were abandoned for general use in the west for several reasons:
Phage Therapy• Medical trials were
carried out, but a basic lack of understanding of phages made these invalid.
• Phage therapy was seen as untrustworthy, because many of the trials were conducted on totally unrelated diseases such as allergies and viral infections.
FDA Approves• In August 2006, the United States Food and Drug
Administration (FDA) approved LMP-102 (now List Shield) as a food additive to target and kill Listeria monocytogenes. LMP-102 was approved for treating ready-to-eat (RTE) poultry and meat products. In October of that year, following the food additive approval of LMP-102 by Intralytix, the FDA approved a product by EBI using bacteriophages on cheese to kill the Listeria monocytogenes bacteria, giving them GRAS status.
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