Bacteriophages

Dr.T.V.Rao MD

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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.

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What are Bacteriophages

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").

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BACTRIOPHAGES

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.

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Bacteriophage Bacteriophages

make up a diverse group of viruses, some of which have complex structures, including double-stranded DNA.

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Bacteriophage

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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.

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Bacteriophages: Classification

At present, over 5000 bacteriophages have been studied by electron microscopy and can be divided into 13 virus families.

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Double stranded DNA, Enveloped

Double stranded DNA,Non-enveloped

Myoviridae

Siphoviridae

Podoviridae

P2

T2

λ

P22

Tectiviridae PRD1

Corticoviridae PM2

Single-stranded DNA

InoviridaeM13 & fd

Microviridae ΦX174 Leviviridae

Single strande

d RNAMS2

Lipothrixviridae

TTV1

Fuselloviridae SSV1Plasmaviridae

Double stranded RNA

phi666

Cystoviridae

RudiviridaeSIRV 1, 2

13 Bacteriophage families

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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 injectionDr.T.V.Rao MD 10

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

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Cycle of events in Bacteriophage infecting a Bacterial Cell

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Phage entering a bacterial cellPhage entering a bacterial cell

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Lytic and Lysogenic cycleLytic and Lysogenic cycle

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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.

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Lysogenic conversion

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.

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Examples: of Lysogenic conversion

* 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

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Bacteriophages: Lysogenic Conversion

Examples of Virulence Factors Carried by Phage

Bacterium PhageGene

ProductPhenotype

Vibrio cholerae CTX phage cholerae toxin cholera

Escherichia colilambda phage

shigalike toxinhemorrhagic

diarrhea

Clostridium botulinumclostridial phages

botulinum toxin

botulism (food poisoning)

Corynebacterium diphtheriae

corynephage beta

diphtheria toxin

diphtheria

Streptococcus pyogenes

T12erythrogenic

toxinsscarlet fever

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Bacteriophages Uses• 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

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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

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Genetic Engineering Genetic Engineering BacteriophagesBacteriophages

• 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

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Bacteriophages

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Bacteriophages• Once these Phages are isolated and recovered they can be used to infect bacteria which will create a particle

similar to a monoclonal antibody

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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

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

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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:

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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.

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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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Programme created by Dr.T.V.Rao MD Programme created by Dr.T.V.Rao MD Medical and Paramedical Students in Medical and Paramedical Students in

the Developing World the Developing World Email

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