Nutrient Agar: Composition, Preparation and Uses

Nutrient Agar is a general purpose, nutrient medium used for the cultivation of microbes supporting growth of a wide range of non-fastidious organisms. Nutrient agar is popular because it can grow a variety of types of bacteria and fungi, and contains many nutrients needed for the bacterial growth.

Composition of Nutrient Agar

  • 0.5% Peptone

It is an enzymatic digest of animal protein. Peptone is the principal source of organic nitrogen for the growing bacteria.

  • 0.3% beef extract/yeast extract

It is the water-soluble substances which aid in bacterial growth, such as vitamins, carbohydrates, organic nitrogen compounds and salts.

  • 1.5% agar

It is the solidifying agent.

  • 0.5% NaCl

The presence of sodium chloride in nutrient agar maintains a salt concentration in the medium that is similar to the cytoplasm of the microorganisms.

  • Distilled water

Water is essential for the growth of and reproduction of micro-organisms and also provides the medium through which various nutrients can be transported.

  • pH is adjusted to neutral (7.4) at 25 °C.

Preparation of Nutrient Agar

1. Suspend 28 g of nutrient agar powder in 1 litre of distilled water.

2. Heat this mixture while stirring to fully dissolve all components.

3. Autoclave the dissolved mixture at 121 degrees Celsius for 15 minutes.

4. Once the nutrient agar has been autoclaved, allow it to cool but not solidify.

5. Pour nutrient agar into each plate and leave plates on the sterile surface until the agar has solidified.

6. Replace the lid of each Petri dish and store the plates in a refrigerator.

Uses of Nutrients Agar

1. It is frequently used for isolation and purification of cultures.

2. It can also be used as a means for producing the bacterial lawns needed for antibiotic sensitivity tests.  In actuality, antibiotic sensitivity testing is typically performed on media specially formulated for that purpose.

Four nutrient agar plates growing colonies of common Gram negative bacteria.
Four nutrient agar plates growing colonies of common Gram negative bacteria.
Source: Wikipedia

48 thoughts on “Nutrient Agar: Composition, Preparation and Uses”

    • It may depend on the manufacturer of the brand of nutrient agar you will use. But for all the ones i have worked with, it was specified that one one should use 28g/l which would mean 14g/500ml.

  1. Hello… I wonder that I can ask a question about my problems. I did subculture Bacteria Lignolytic, Selulotic and Cytophaga on Nutrient Broth. But the result the subculture turning into red. I suspected that subculture contain E.coli. I’m not sure about that.

  2. That % mean for 1000ml or 1l you need that particular amount of any substance,like peptone for Nam that is 5gm for 1000ml . Now if you have to prepare low amount of medium then you have to reduce the %. Here you mentioned for 1l media you have to add 1% malt extract for 500lm media it’ll be .5% of malt extract.. That’s how it works

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  5. Agar are come from huge agar plant know as kelps .are cooked with dilute acid and filtered the acidic liquid is neutralized and cooled so that agal gel is obtained

  6. For 1 L media we need 0.4% yeast extract, 1% malt extract, and 0.4% glucose.

    My question is: What does % mean?

  7. To prepare 1 L media we need yeast extract 0.4%. malt extract 1%, and glucose 0.4%.

    My question is: what does % mean?

  8. Sir I have used nutrient agar for fungus culture…. Before i use PDA for culture it was gud…. But i found lots of bacterial contamination in my Nutrient agar culture…. Does the composition of beef extract hampers the groeth of fungus and favours bacteria instead.

  9. Hello I have a question. If a leg wound is cultured and it is put on a nutrient agar, Selective agar and Differential Agar what are expected to show?

  10. Hi ! I streaked out from sweet potato steep water and I had both red colonies and white colonies that turned nutrient agar kind of green. Please what kind of organisms are these . They areboth staining gram positive

  11. Nutrient agar favored 4 Non fastidious bacteria
    Blood agar used to detect bacteria that produce enzymes to break apart the Red blood cells
    Mac conkey agar favored 4 gram – bacteria
    sabouraud agar favoured 4 fungi
    lowenstein jensen agar favored 4 mycobacterium tuberculosis
    salmonella shigella agar favored in the isolation of salmonella&shigella

  12. the compositon and funtions were helpful. but i dont really get the beef extract could you please explain more. you did a nice job. my name is Anie, 19yr old microbiology student, i’m currently in my 3rd year in Uni

  13. among the types of medias we have can somebody help me and tell me the kind of micro organism to which each media favour the growth
    eg nutrient agar favour the growth of …..

  14. Sir/Madam,
    Could u tell me what are the microbial techniques? Just list put techniques name so that i could learn it from basics.

    Thank you

    • Could u tell me what are the microbial techniques? Just list out the techniques name so that i could learn it from basics.

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