agar

A complex polysaccharide (a sulfated galactan) derived from seaweed (various red algae); used as a solidifying agent in culture media; it has the valuable property of melting at 100°C, but not solidifying until 49°C. [Bengalese]

- bile salt a. an a. medium containing lactose, peptone, sodium taurocholate, and neutral red, for the growth and isolation of Gram-negative rods.

- birdseed a. media prepared from Guizottia abyssinica seeds used in culturing and in the presumptive diagnosis of Cryptococcus neoformans.

- blood a. a mixture of blood, usually sheep or horse, and an a.-based medium used for the cultivation of many medically important microorganisms.

- Bordet-Gengou potato blood a. glycerine-potato a. with 25% of blood, used for the isolation of Bordetella pertussis.

- brain-heart infusion a. a medium used for the isolation of fastidious microorganisms, especially fungi.

- chocolate a. blood a. heated until the blood becomes brown or chocolate in color, used especially to isolate Haemophilus or Neisseria and other species for which unheated blood is inhibitory.

- cholera a. an alkaline a. medium for cultivating Vibrio cholerae.

- cornmeal a. a culture medium that is low in nutrients, used extensively in the study of yeastlike and filamentous fungi; it suppresses vegetative growth while stimulating sporulation of many species, and is widely used for producing the distinctive chlamydospores of Candida albicans.

- Czapek solution a. a culture medium used for the cultivation of fungus species and for identification of Aspergillus and Penicillium species. SYN: Czapek-Dox medium.

- EMB a. SYN: eosin-methylene blue a..

- Endo a. a medium containing peptone, lactose, dipotassium phosphate, a., sodium sulfite, basic fuchsin, and distilled water; originally developed for the isolation of Salmonella typhi, this medium is now most useful in the bacteriological examination of water; coliform organisms ferment the lactose, and their colonies become red and color the surrounding medium; non-lactose-fermenting organisms produce clear, colorless colonies against the faint pink background of the medium. SYN: Endo medium.

- eosin-methylene blue a. a. composed of peptone, lactose, and sucrose and containing eosin and methylene blue, used to distinguish between lactose-fermenting and non–lactose-fermenting Gram-negative bacteria. Echerichia sp. show a characteristic sheen. SYN: EMB a..

- MacConkey a. medium containing peptone, lactose, bile salts, neutral red, and crystal violet, used to identify Gram-negative bacilli and characterize them according to their status as lactose fermenters. Fermenters appear as pink colonies while nonfermenters are colorless.

- Mueller-Hinton a. medium containing beef infusion, peptone, and starch used primarily for the disk-a. diffusion method for antimicrobial susceptibility testing.

- Novy and MacNeal blood a. a nutrient a. containing two volumes of defibrinated rabbit's blood; suitable for the cultivation of a number of trypanosomes.

- nutrient a. a simple solid medium containing beef extract, peptone, a., and water; used for growing many common heterotrophic bacteria.

- oatmeal-tomato paste a. a special culture medium for the production of ascospore formation in the dermatophytes.

- potato dextrose a. a culture medium used extensively for the cultivation of fungi; especially good for development of conidia and other sporulating forms by which an organism is identified microscopically.

- rice-Tween a. a useful medium for the development of the chlamydospores in Candida albicans and for preparation of slide cultures for other forms of sporulation in other fungal species.

- Sabouraud a. a culture medium for fungi containing neopeptone or polypeptone a. and glucose, with final pH 5.6; it is the standard, most universally used medium in mycology and is the international reference. Modified Sabouraud a. (Emmons modification) with neutral pH and less glucose is better for pigment development in the colonies.

- Sabouraud dextrose a. a dextrose peptone medium that supports the growth of most pathogenic fungi.

- serum a. an enriched medium for cultivation of fastidious organisms; prepared by adding sterile serum to melted a..

- Thayer-Martin a. a Mueller-Hinton a. with 5% heat-hemolyzed sheep blood and antibiotics, used for transport and primary isolation of Neisseria gonorrhoeae and Neisseria meningitidis. SYN: Thayer-Martin medium.

- yeast extract a. a medium used to induce sporulation and reduce vegetative growth in the cultivation of fungi.

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Australian Group on Antimicrobial Resistance [study]

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agar 'äg-ər n

1) a gelatinous colloidal extractive of a red alga (as of the genera Gelidium, Gracilaria, and Eucheuma) used esp. in culture media or as a gelling and stabilizing agent in foods

2) a culture medium containing agar

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n.

an extract of certain seaweeds that forms a gel suitable for the solidification of liquid bacteriological culture media. Blood agar is nutrient agar containing 5-10% horse blood, used for the cultivation of certain bacteria or for detecting haemolytic (blood-destroying) activity.

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(agґahr) [Malay agar-agar] [NF] a mucilaginous complex sulfated polymer of galactose units, extracted from Gelidium cartilagineum, Gracilaria confervoides, and related red algae. It melts at 100°C and solidifies into a gel at 40°C, is not digested by most bacteria, and as a gel is used in the preparation of solid culture media for microorganisms, as a bulk laxative, in making emulsions, as a supporting medium in procedures such as immunodiffusion and electrophoresis, and as the principal component in reversible hydrocolloid dental impression material. See under culture medium for specific agars.