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Encyclopedia > Phage

A phage (short for bacteriophage, from 'bacteria' and Greek phagein, meaning 'to eat') is a virus that infects bacteria. Like viruses that infect eukaryotes (plants, animals and fungi), phages display a variety of different compositions. Typically, they consist of an outer protein hull and the enclosed genetic material, which consists of double-stranded DNA of 5 to 650 kbp (kilo base pairs) in the vast majority of the phages known. The dimensions of a phage is on the order of 24 to 200 nm. Several phages sport a structure called a tail, which is used to inject the genetic material into the host. The human immunodeficiency virus (HIV) A bacteriophage virus A virus is a submicroscopic parasitic particle that infects cells in biological organisms. ... Infection is also the title of an episode of the television series Babylon 5, and the English title of the Japanese film Kansen. ... Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular, bacterium) are a major group of living organisms. ... Kingdoms Animalia - Animals Fungi Plantae - Plants Protista A eukaryote (IPA: ), also spelled eucaryote, is an organism with a complex cell or cells, in which the genetic material is organized into membrane-bound nucleus/nuclei. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Genetic material is the material used to store genetic information for a living organism. ... The general structure of a section of DNA Deoxyribonucleic acid (DNA) is a nucleic acid —usually in the form of a double helix— that contains the genetic instructions specifying the biological development of all cellular forms of life, and most viruses. ... In genetics, two nucleotides on opposite complementary DNA or RNA strands that are connected via hydrogen bonds are called a base pair (often abbreviated bp). ... A nanometre (American spelling: nanometer, symbol: nm) is 1. ...


Phages are ubiquitous and can be found in many reservoirs populated by bacteria, such as soil or the intestine of animals. One of the densest natural sources for phages is sea water, where up to 2.5×108 virions per cm3 have been found (see references). Subgroups Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular: bacterium) are a major group of living organisms. ...

Structural overview of bacteriophage
Structural overview of bacteriophage
Actual picture of Bacteriophages
Actual picture of Bacteriophages
A T4 type bacteriophage landing on a bacterium and preparing to inject their genetic material.
A T4 type bacteriophage landing on a bacterium and preparing to inject their genetic material.

Contents

Image File history File links Tevenphage. ... Image File history File links Tevenphage. ... Image File history File links The use of this file has been permitted by the owner. ... Image File history File links The use of this file has been permitted by the owner. ... Image File history File links Trialphage. ... Image File history File links Trialphage. ...


Life cycle

Phages infect only specific bacteria. It is unknown whether there is a phage for every species of bacteria as only a fraction of bacteria have been studied in this detail. Some phages are virulent, meaning that upon infecting a cell they immediately begin reproducing, and within a short time lyse (destroy) the cell, releasing new phages. Some phages (so-called temperate phages) can instead enter a relatively harmless state, either integrating their genetic material into the chromosomal DNA of the host bacterium (much like endogenous retroviruses in animals) or establishing themselves as plasmids. These endogenous phages, referred to as prophages, are then copied with every cell division together with the DNA of the host cell. They do not kill the cell, but monitor (via some proteins they code for) the status of their host. When the conditions of host worsen for instance due to increase in temperature or depletion of nutrients, the endogenous phages become active. They initiate the reproductive cycle resulting in the lysis of the host cell, thus pre-empting a possible demise of the bacterium. An example is phage λ of E. coli. Sometimes, prophages even provide benefit to the host bacterium while they are dormant, by adding new functions to the bacterial genome, a phenomenon called lysogenic conversion. A famous example is the conversion of a harmless strain of Vibrio cholerae by a phage into a highly virulent one, which causes cholera. Virulence is a term used to refer to either the relative pathogenicity or the relative ability to do damage to the host of an infectious agent. ... Lysis (Greek lusis from luein = to separate) is the reduction of symptoms of a disease the dissolving of cells osmotic lysis chemical lysis viral lysis a dialogue of Plato about friendship (philia) This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same... Figure 1: Chromosome. ... Genera Alpharetrovirus Betaretrovirus Gammaretrovirus Deltaretrovirus Epsilonretrovirus Lentivirus Spumavirus A retrovirus is a virus which has a genome consisting of two RNA molecules, which may or may not be identical. ... Figure 1: Schematic drawing of a bacterium with plasmids enclosed. ... This article or section does not cite its references or sources. ... Enterobacteria phage λ (lambda phage) is a temperate bacteriophage that infects Escherichia coli. ... Binomial name Escherichia coli T. Escherich, 1885 Escherichia coli (usually abbreviated to E. coli) is one of the main species of bacteria that live in the lower intestines of warm-blooded animals (including birds and mammals) and are necessary for the proper digestion of food. ... In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ... Lysogenic conversion is when a temperate phage induces a change in the phenotype of the bacteria infected that is not part of a usual phage cycle. ... Binomial name Vibrio cholerae Pacini 1854 Vibrio cholerae is a gram negative bacterium with a curved-rod shape that causes cholera in humans. ... Drawing of Death bringing the cholera, in Le Petit Journal. ...


Therapy

Main article: Phage therapy

Phages were tried as anti-bacterial agents after their discovery. However Antibiotics, upon their discovery, proved to be more practical. Research on phage therapy was largely discontinued in the West. Phage therapy has been used since the 1940s in the former Soviet Union as an alternative to antibiotics for treating bacterial infections. Phage therapy is an alternative to antibiotics, being developed for clinical use by many western research groups in Europe and the US. It has been extensively used and developed in the former Soviet Union. ... An antibiotic is a drug that kills or slows the growth of bacteria. ... A compass rose with west highlighted This article refers to the cardinal direction; for other uses see West (disambiguation). ... Phage therapy is an alternative to antibiotics, being developed for clinical use by many western research groups in Europe and the US. It has been extensively used and developed in the former Soviet Union. ... // Events and trends World War II was a truly global conflict with many facets: immense human suffering, fierce indoctrination, and the use of new, extremely devastating weapons such as the atomic bomb. ... An antibiotic is a drug that kills or slows the growth of bacteria. ...


The evolution of bacterial strains through natural selection that are resistant to multiple drugs has led some medical researchers to re-evaluate phages as alternatives to the use of antibiotics. Unlike antibiotics, phages adapt along with the bacteria, as they have done for millions of years, so a sustained resistance is unlikely. A specific type of phage often infects only one specific type of bacterium (ranging from several species, to only certain subtypes within a species), so one has to make sure to identify the correct type of bacteria, which takes about 24 h. Sometimes mixes of several strains of phage are used to create a more 'broad spectrum' cure. An added advantage is that no other (possibly benevolent) bacteria are attacked (it effectively works as a very narrow spectrum antibiotic). However, this is a disadvantage in infections with several different types of bacteria, which is often the case. But when an effective phage has been found, it will seek out the bacteria (being a biological agent) and continue to kill bacteria of that type until they are all gone: this is unlike the action of antibiotics, which are chemotherapeutical. Antibiotic resistance is the ability of a microorganism to withstand the effects of an antibiotic. ...


Phages work best when in direct contact with the infection, so they are best applied directly to an open wound, which rarely is applicable in the current clinical setting where infections occur systemic. Despite individual successes in the former USSR where other therapies had failed, many researchers studying infectious diseases question whether phage therapy will achieve any medical relevance. There have been no large clinical trials to test the efficacy of phage therapy yet, but research continues because of the rise of multiple antibiotic resistance. A problem, though, is that they are attacked by the body's immune system. Systemic Relating to, or affecting a particular body system; especially the nervous system. ... The immune system is the system of specialized cells and organs that protect an organism from outside biological influences. ...


Model bacteriophages

Following is a list of bacteriophages that are extensively studied:

Enterobacteria phage λ (lambda phage) is a temperate bacteriophage that infects Escherichia coli. ... A lysogen or lysogenic phage is a phage that does not go into a lytic cycle but instead either integrates into the host bacterias chromosome or lives as a stable plasmid within the host cell. ... Enterobacteria phage T4 is a phage that infects E. coli bacteria. ... Headline text this website sucks your mothers dickIn molecular biology, two nucleotides on opposite complementary DNA or RNA strands that are connected via hydrogen bonds are called a base pair (often abbreviated bp). ... A nanometre (American spelling: nanometer, symbol: nm) is 1. ... Bacteriophage T7 Capsid size The T7 capsid is spherical with an inner diameter of 55 nm. ... M13 is a filamentous bacteriophage composed of single stranded DNA (ssDNA 6407 nucleotides long) encapsulated in approximately 2700 copies of the major coat protein P8, and capped with 5 copies of two different minor coat proteins (P9, P6, P3) on the ends. ... A nanometre (American spelling: nanometer, symbol: nm) is 1. ...

See Also

  • Evergreen State College
  • Phage.org
  • Pittsburgh Bacteriophage Institute

  Results from FactBites:
 
Science Netlinks: Science Updates (848 words)
Phages could even be genetically engineered to attack a wider range of bacteria.
Another problem with phage is that you have to grow them in cultures of the same harmful bacteria that they're meant to fight.
Instead, phage were cultivated as the treatment of choice for decades after they fell from Western favor.
Phage Biotech Ltd. (1597 words)
Phage therapy is practiced routinely in the former Soviet Union as an alternative, combinatory, and complimentary form of treatment in conjunction with, or in lieu of, antibiotics.
Phages generally display a low chemotherapeutic index, particularly upon primary administration systemically or upon topical administration, and they are vastly more diverse in their potential to overcome bacterial resistance than known antibiotics also displaying comparatively low chemotherapeutic indices.
Phage therapy, as a clinical method, was rejected altogether in the West upon the discovery, immediate popularization, and wide-scale dissemination of penicillin in the early 1940s.
  More results at FactBites »

 
 

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