Nutrient Medium


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Nutrient Medium

 

a fluid or solid substance that is used in the laboratory or under industrial conditions for growing bacteria, yeasts, and microscopic fungi, as well as algae, protozoans, viruses, and cultures of plant or animal cells. Synthetic nutrient mediums supply specified proportions of necessary organic and inorganic compounds providing for carbon, nitrogen, phosphorus, sulfur, potassium, sodium, and trace elements. Examples of complex organic nutrient mediums are beef and peptone broth, wort, and milk.

A fluid medium may be solidified by adding 2-percent agar or 10-percent gelatin. Solid mediums are also prepared with pieces of potato or carrot, grains of rice or millet, coagulated horse serum, and pieces of internal organs of animals. All nutrient mediums are first sterilized in an autoclave. It was formerly believed that certain pathogenic bacteria could grow only on nutrient mediums that contain such physiological substances as blood, serum, and ascitic fluid. However, studies have shown that the majority of pathogenic microbes can grow on synthetic nutrient mediums that contain glucose and ammonium sulfate as sources of carbon and nitrogen and that also contain the essential vitamins, amino acids, purine and pyrimidine bases, and trace elements. Certain microorganisms, for example, the causative agent of syphilis—Treponema pallidum —have not yet successfully been grown on synthetic mediums.

Mediums can be suitable for all microorganisms, or they can be specially selected to create more favorable conditions for the growth of only certain species. The latter type are called selective mediums. For growing anaerobic microorganisms, substances that decrease oxidation-reduction potential can be added.

Selective nutrient mediums of known composition are used to elucidate a number of physiological properties of microorganisms. For example, mediums that do not contain nitrogenous compounds are used to isolate nitrogen-fixing bacteria. The capacity of a microorganism to reduce nitrates is examined on a fluid medium that contains nitrates and an indicator, which changes color when the medium becomes alkaline, that is, when there is a shift in pH. Fluid mediums that contain various carbohydrates or alcohols, in addition to an indicator that changes color with acidification, are poured into test tubes in the bottoms of which are placed tiny inverted test tubes; when the medium is acidified by microorganisms, the indicator changes color and the gas formed accumulates in the small test tubes.

Growth on beef and peptone gelatin may be accompanied by liquefaction of the gelatin, which indicates biosynthesis of proteolytic enzymes. Inoculations on blood agar are used to examine the hemolytic properties of a microorganism (see HEMOLYSIS). The ability of microorganisms to hydrolyze starch is tested by inoculation on potato agar and subsequent treatment of colonies or streaks with solutions that contain iodine. A positive test is indicated by the disappearance of the dark blue color that starch gives in the presence of iodine. Special-purpose nutrient mediums are used to identify pathogenic species of microorganisms. (See CULTURE and TISSUE CULTURE.)

A. A. IMSHENETSKII

References in periodicals archive ?
At this stage of bacteriological diagnosis, a culture of Mycobacterium grown inside the liquid nutrient medium in the form of diffused clouds cannot be differentiated into species by cultural-morphological features, and reseeding on a dense nutrient medium of Lowenstein-Jensen lengthens study periods up to 20 days, just like the direct seeding of the biomaterial by conventional method of TB diagnosis (control).
The results show the existence of significant differences in the average concentration of alkaloids in the stalks by the differences in the added concentration of Auxins and Cytokinins in the nutrient medium (F test significance value [less than or equal to] 0.
was cultivated on Bogdanov's modified nutrient medium with the 2 times increased maintenance of nitric components.
Optimization of LiP production in SSF: The LiP production process in SSF using wheat straw as substrate was optimized by varying different physical and nutritional factors such as particle size of substrate, basal nutrient medium, moisture level, inoculum size, additional carbon and nitrogen sources, and C: N ratio.
But Tisserat changed the way nutrient medium is applied to the shoots, modified the physical environment in which they are grown, and switched from Magenta vessels to larger growth chambers, which provide the tender shoots with much more space and media.
5 for 5-6 h; then 1 seedling was transplanted into a 1000-mL beaker containing 900 mL of liquid nutrient medium (pH 4.
When cultured on a nutrient medium, these bacteria form visible colonies.
Supplied in circular disks in a nutrient medium, Apligraf has an epidermal layer--formed by keratinocytes with a well-differentiated stratum corneum--and a dermal layer that contains human fibroblasts in a lattice made of bovine collagen.
The organisms were screened in a low nutrient medium to imitate the surface of fruits.
Because Petipa's heritage has been treated creatively by the Maryinsky Theatre, the great master has remained a friend and mentor of new generations, while his ballets have represented a nutrient medium and organic environment for Russian art.
In the wild state, this mold will grow on a nutrient medium in which sugar is the only significant organic compound.
Tissue culture The process of aseptically growing living tissue isolated from a living organism, plant or animal, on a nutrient medium.