Agar: Difference between revisions
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:''Main article: [[Agar plate]]'' |
:''Main article: [[Agar plate]]'' |
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Nutrient agar is used throughout the world as a medium for the growth of [[bacteria]] and [[fungi]], but not [[virus]]es. |
Nutrient agar is used throughout the world as a medium for the growth of [[bacteria]] and [[fungi]], but not [[virus]]es. Though it is only known how to grow less than 1% of all bacteria that exist, the basic agar formula can be used to grow most of the [[microbe]]s, whose needs are known. More specific nutrient agars are available, because microbes can be picky. For example, blood agar, which is generally combined with horse blood, can be used to detect the presence of haemorrhagic micro-organisms such as E.coli O:157 H:7. The bacteria digest the blood, turning the plate clear. |
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Agarose is also used in Agarose [[gel electrophoresis]]. |
Agarose is also used in Agarose [[gel electrophoresis]]. |
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Revision as of 09:34, 22 December 2005
Agar is a galactose polymer (or agarose) obtained from the cell walls of some species of red algae or seaweed (Sphaerococcus euchema) and species of Gelidium, chiefly from eastern Asia and California. It is also known as Kanten, Agar-Agar, or Agal-Agal (Ceylon Agar).
Chemically, agar is a polymer made up of subunits of the sugar galactose; it is a component of the algae's cell walls. Dissolved in hot water and cooled, agar becomes gelatinous; its chief use is as a culture medium for microbiological work. Other uses are as a laxative, a vegetarian gelatin substitute — a thickener for soups, in jellies, ice cream and Japanese desserts such as anmitsu, as a clarifying agent in brewing, and for paper sizing fabrics.
Uses in microbiology
- Main article: Agar plate
Nutrient agar is used throughout the world as a medium for the growth of bacteria and fungi, but not viruses. Though it is only known how to grow less than 1% of all bacteria that exist, the basic agar formula can be used to grow most of the microbes, whose needs are known. More specific nutrient agars are available, because microbes can be picky. For example, blood agar, which is generally combined with horse blood, can be used to detect the presence of haemorrhagic micro-organisms such as E.coli O:157 H:7. The bacteria digest the blood, turning the plate clear.
Agarose is also used in Agarose gel electrophoresis.
Selective Media
Selective media is agar specially treated to apply a selective pressure to organisms growing on it -- for example, to select for salt-tolerant, gram-positive, or gram-negative bacteria.
Differential Media
Differential media includes an indicator that causes visible, easily detectable changes in the appearance of the agar gel or bacterial colonies in a specific group of bacteria. For example, EMB (Eosin Methylene Blue) agar causes E. Coli colonies to have a metallic green sheen, and MSA (Mannitol Salt Agar) turns yellow in the presence of mannitol fermenting bacteria.
Hysteresis
Hysteresis describes the phenomenon of the differing liquid-solid state transition temperatures that agar exhibits. Agar melts at 85 °C and solidifies from 32-40 °C.