Agar is a galactose polymer obtained from the cell walls of some species of red algae or seaweeds (Sphaerococcus Euchema ) and species of Gelidium , chiefly from eastern Asia and California. 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 sizing fabrics.

Uses in microbiology

Nutrient agar is used the world over as a medium for the growth of bacteria and fungi, but not viruses. The basic agar formula can be used to grow almost all microbes; however, other more specific nutrient agars are available, e.g., blood agar, which is generally combined with horse blood, and can be used to detect the presence of haemophoragic micro-organisms such as E.coli 0157 (the bacteria digest the blood, turning the plate clear).

See also

• Agarose
• Agar plate
• Rhodophyta
• Asepsis
• Microbiology