Bacteriophages Dr Amita Arya 1 Bacteriophage A bacteriophage
Bacteriophages Dr. Amita Arya 1
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 ss. RNA, ds. RNA, ss. DNA, or ds. DNA ('ss-' or 'ds-' prefix denotes single-strand or double-strand) along with either circular or linear arrangement. 2
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"). 3
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. 4
Bacteriophage Bacteriophages make up a diverse group of viruses, some of which have complex structures, including doublestranded DNA. 5
Bacteriophage 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. 6
13 Bacteriophage families Double stranded DNA, Non-enveloped P 2 Double stranded DNA, Enveloped SIRV 1, 2 Rudiviridae Myoviridae T 2 Plasmaviridae Fuselloviridae SSV 1 λ Tectiviridae TTV 1 PRD 1 Siphoviridae Lipothrixviridae P 22 Corticoviridae Podoviridae Single-stranded DNA Inoviridae M 13 & fd PM 2 Single stranded RNA Double stranded RNA MS 2 Microviridae ΦX 174 phi 666 Dr. T. V. Rao MDLeviviridae 79 Cystoviridae
Cycle of events in Bacteriophage infecting a Bacterial Cell 88
Phage entering a bacterial cell 99
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Lytic and Lysogenic cycle 111 1
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. 3) 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. 121 2
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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. 141 4
Examples: of Lysogenic conversion * 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 151 5
Bacteriophages: Lysogenic Conversion Examples of Virulence Factors Carried by Phage 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 T 12 erythrogenic toxins scarlet fever 161 6
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 171 7
Bacteriophages causes Lysis of Infected Cells The T-phages, T 1 through T 7, are referred to as lytic phages because they always bring about the lysis and death of their host cell, the bacterium E. coli. Tphages 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 181 8
Genetic Engineering Bacteriophages • • 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. T. V. Rao MD phages will interact wit. Drh targets 251 9
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 2 0
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 2 1
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 2 2
Phage Therapy Phages were discovered to be anti-bacterial agents and were used throughout the 1940 s 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: 2 3
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. 2 4
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-toeat (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. 2 5
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