Nutrient Agar
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Nutrient agar is a general-purpose solid
medium Medium may refer to: Aircraft *Medium bomber, a class of warplane * Tecma Medium, a French hang glider design Arts, entertainment, and media Films * ''The Medium'' (1921 film), a German silent film * ''The Medium'' (1951 film), a film vers ...
supporting growth of a wide range of non- fastidious organisms. It typically contains ( mass/volume): * 0.5% peptone – this provides organic nitrogen * 0.3% beef extract/
yeast extract Yeast extracts consist of the cell contents of yeast without the cell walls; they are used as food additives or flavorings, or as nutrients for bacterial culture Growing media, media. They are often used to create savoury flavors and umami tast ...
– the water-soluble content of these contribute vitamins, carbohydrates, nitrogen, and salts * 1.5%
agar Agar ( or ), or agar-agar, is a jelly-like substance consisting of polysaccharides obtained from the cell walls of some species of red algae, primarily from " ogonori" and " tengusa". As found in nature, agar is a mixture of two components, t ...
– this gives the mixture solidity * 0.5%
sodium chloride Sodium chloride , commonly known as Salt#Edible salt, edible salt, is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. It is transparent or translucent, brittle, hygroscopic, and occurs a ...
– this gives the mixture proportions similar to those found in the
cytoplasm The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...
of most organisms *
distilled water Distilled water is water that has been purified by boiling it into vapor then condensing it back into liquid in a separate container. Impurities in the original water that do not boil below or near the boiling point of water remain in the origin ...
– water serves as a transport medium for the agar's various substances * pH adjusted to neutral (6.8) at . Nutrient broth has the same composition, but lacks agar. These ingredients are combined and boiled for approximately one minute to ensure they are mixed and then sterilized by autoclaving, typically at for 15 minutes. Then they are cooled to around and poured into Petri dishes which are covered immediately. Once the dishes hold solidified agar, they are stored upside down and are often refrigerated until used.
Inoculation Inoculation is the act of implanting a pathogen or other microbe or virus into a person or other organism. It is a method of artificially inducing immunity against various infectious diseases. The term "inoculation" is also used more generally ...
takes place on warm dishes rather than cool ones: if refrigerated for storage, the dishes must be rewarmed to room temperature prior to inoculation.


See also

* Plate count agar *
Bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...
*
Bacterial growth 250px, Growth is shown as ''L'' = log(numbers) where numbers is the number of colony forming units per ml, versus ''T'' (time.) Bacterial growth is proliferation of bacterium into two daughter cells, in a process called binary fission. Providi ...


References


Further reading

*Lapage S., Shelton J. and Mitchell T., 1970, Methods in Microbiology', Norris J. and Ribbons D., (Eds.), Vol. 3A, Academic Press, London. *MacFaddin J. F., 2000, Biochemical Tests for Identification of Medical Bacteria, 3rd Ed., Lippincott, Williams and Wilkins, Baltimore. *Downes F. P. and Ito K., (Ed.), 2001, Compendium of Methods for the Microbiological Examination of Foods, 4th Ed., American Public Health Association, Washington, D.C. *American Public Health Association, Standard Methods for the Examination of Dairy Products, 1978, 14th Ed., Washington D.C. Microbiological media {{Microbiology-stub