Composition
Ingredients | Gms/Ltr. |
Agar | 15.00 |
Peptone | 5.00 |
Sodium chloride | 5.00 |
Beef extract | 3.00 |
* Dehydrated powder, hygroscopic in nature, store in a dry place in tightly- sealed containers 25°C and protected from direct Sunlight.
Instructions for use
Dissolve 28gms in 1000ml distilled water. Gently heat to boiling with gentle swirling and dissolve the medium completely. Sterilize by autoclaving at 15 psi (at 121°C) for 15 minutes. Cool to 45-500C and pour into sterile Petri plates.
Appearance: Light cream colour, very slightly opalescent
pH (at 25°C): 7.2 ± 0.2
Principle
NUTRIENT AGAR is used for less fastidious microorganisms as well as for permanent cultures (general purposes medium). The medium contains Beef extract and Peptone as sources of nitrogen, vitamins, amino acids and carbon for potential microorganism’s growth. Sodium chloride ensures osmotic balance. Thus, when adding blood, as supplement the blood cells will not rupture. Addition of 10% different biological fluids such as blood, serum and egg yolk makes it suitable for the cultivation of related fastidious organism. For eg., Pseudomonas aeruginosa produces a blue-green pigment, pyocyanin, which diffuses into the medium giving the plate a charactersitic colour. For growing specific bacteria culture, spread the bacteria on the plate using sterile swab or inoculating loop. The bacteria will grow and become visible in 24 – 48 hrs. It is generally used in the laboratory to prepare stock cultures of the bacteria.
Interpretation
Cultural characteristics observed after inoculating (103-105CFU/ml), on incubation at 30 – 35ºC for 18 – 72 hours.
Microorganisms | ATCC | Inoculum (CFU/ml) | Growth | Recovery rate | Appearance of colony |
Streptococcus pneumoniae | 12228 | 103-105 | Luxuriant | >= 70% | Cream |
Staphylococcus aureus | 25922 | 103-105 | Luxuriant | >= 70% | Light pale or yellow pigment |
Escherichia coli | 25923 | 103-105 | Luxuriant | >= 70% | Cream |
Reference
- M.A. Sagardoy, C.M. Salerno, Studies on heterotrophic bacteria in some Argentine soils, Anal. Edaf. Agrobiol. 42, 2069. (1984).
- M.L. Gray, HJ. Stafseth, F. Thorp, The use of potassium tellurite, sodium azide and acetic acide in a selective medium for the isolation of Listeria monocytogenes, J. Bact., 59, 443. (1950).
- Lapage .S, Shelton. T, Mitchell. T, Methods in Microbiology, J. Norris, D. Rippons (Eds.), Vol. 3A, Academic Press, London. (1970).
- J. MacFaddin. Media for Isolation-Cultivation-Identification-Maintainance of Medical Bacteria, Vol. l, Williams, Wilkins, Baltimore. (1985).
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