Nutrient Agar Media

Just like humans, microorganisms also require food for survival and growth. Naturally growing microbes get the necessary nutrients from their surrounding environment.

But when we culture them in a laboratory in order to identify the infectious agent or for research, quality control, or serological testing, we need to provide them with an artificial food source. This food is referred to as culture media or nutrient media.

One such medium is Nutrient Agar Media.

What is Nutrient Agar Media?

Nutrient agar media or NAM, is considered a general-purpose media that supports the growth of a wide range of organisms, including different bacteria and fungi. Because of its relatively simple formulation, it is considered to be a basal media.

NAM is a solid media due to the presence of agar. Agar gives a semi-solid and slightly rigid appearance to the media. On solid media, microorganisms exhibit their morphology and other features like pigmentation, haemolysis etc., in a better way.

For the above-mentioned reasons, research professionals highly prefer NAM for the cultivation, maintenance and enumeration of non-fastidious microbes either collected from sewage, soil, faeces, dairy or air samples.

The content aims to provide you with complete information about Nutrient Agar Media along with its composition, principle, preparation, uses and limitations.

Content: Nutrient Agar Media

1. Composition of Nutrient Agar Media
2. Nutrient Agar Media Principle
3. pH of Nutrient Agar
4. Materials required for NAM Preparation
5. Preparation of Nutrient Agar Media
6. How to prepare Nutrient Agar Media Alternatively?
7. Nutrient Agar Media Plates
8. Uses of Nutrient Agar Media
9. Limitations of Nutrient Agar Media
10. Frequently Asked Questions (FAQs)

Composition of Nutrient Agar Media

The media comprises some basic elements necessary for the growth of the microbes. The composition varies as per your required volume.

Reagent	For 100 ml	For 500 ml	For 1000 ml
Beef Extract	0.3 g	1.5 g	3.0 g
Peptone	0.5 g	2.5 g	5.0 g
NaCl	0.5 g	2.5 g	5.0 g
Agar	1.5 g	7.5 g	15.0 g

Apart from these components, various biological fluids like horse or sheep blood, egg yolk, serum etc., are also used as supplementary agents in the media. These agents provide extra enrichment to the growing culture.

If we use blood as a supplement in the media, then it is called blood agar.

Nutrient Agar Media Principle

NAM is a non-selective media which is ideal for the routine cultivation of microbes. This is because of its simple formulation that comprises only a few components.

The peptone added to the media is the enzymatic digest of animal proteins. It serves the role of primary source for amino acids, organics nitrogen, long-chained peptides etc.. It aids the proper growth of bacteria by fulfilling its protein demands.

The second one is beef or yeast extract that provides the carbohydrates, vitamins, organic nitrogen, trace minerals, other water-soluble substances and salts.

The third component is sodium chloride(NaCl), which maintains the osmotic equilibrium between the growing microbe and the medium. Besides, it has no nutritive value.

At last, the agar is added, which acts as a solidifying component. This solidification provides a stable solid platform for microbial culture.

pH of Nutrient Agar

The pH value of the nutrient media should range between 6.8 ± 2 at normal room temperature. You can use 1N HCL and 1N NaOH to adjust the pH level of the media.

Materials required for NAM Preparation

• Conical Flask
• Regents: beef extract, peptone, NaCl, agar.
• Spatula
• Measuring cylinder
• Sterile distilled water
• pH meter
• Weighing balance
• Magnetic stirrer and pellets
• Heating plate
• Sterile Petri plates

Preparation of Nutrient Agar Media

1. The quantity of the ingredients varies according to the desired volume of media (Here, we will make for 1000 ml of media).
2. Weigh all the components separately, including- Beef or yeast extract (3g), peptone (5g), NaCl (5g) and agar (15g).
3. Take a conical flask and pour 900 ml of autoclaved distilled water or deionized water into it.
4. Now, transfer all the ingredients except for agar into a conical flask.
5. With the help of a magnetic stirrer, dissolve the components.
6. Adjust the pH level to the desired value by adding HCl or NaOH accordingly.
   
7. Makeup the final volume of the media to 1000 ml by adding the required amount of sterile distilled water.
8. Now add the last component, i.e., agar, according to the volume medium. Here, add 15 gm of agar for 1000 ml.
9. Heat the suspension with continuous agitations so as to completely homogenize the agar and other ingredients. Take a quick boil until the hazy suspension becomes a transparent solution.
10. Seal the mouth of the flask with a cotton plug and then wrap with paper and a rubber band.
11. Keep the flask in an autoclave at 15 psi. at 121^o C for 15 minutes.
    

How to prepare NAM Alternatively?

1. Take 1000 ml of sterile distilled water.
2. To it, add 28 gm of dehydrated industrially prepared NAM powder.
3. Heat (boil) the suspension for homogenizing all the components. Remove the flask from the hot plate when the suspension becomes transparent.
4. Seal the flask and keep it for autoclaving.

Nutrient Agar Media Plates

After autoclaving, cool down the flask up to 40-45^o C.

1. You can prepare the NAM plates by pouring this cooled media onto the sterile Petri plates. For plating, take all the plating material to laminar airflow.
2. For pouring, slightly remove the cotton plug and hold it between the fingers. Now slightly open the Petri plate and bring it closer to the mouth of the flask.
3. Pour about 25 to 30 ml of the media into a plate.
4. Keep the Petri plate with the lid open in the laminar airflow to avoid the vapours.
5. After the solidification of the media, you can use the plates to inoculate desired microbial samples.

Storage of NAM

You can store the prepared Nutrient agar medium at 4^o C for further utilization. Irrespective of whether it contains antibiotics, you can use them for 1 to 2 months if you store them in a contamination-free zone.

Uses of Nutrient Agar Media

• The NAM is ideal for demonstration and teaching purposes where we require a generalized culture of various microorganisms.
• NAM supports the growth of many infectious pathogens and non-fastidious species. This factor greatly helps in diagnostic procedures.
• It also aids the production of a pure line of the culture for biochemical or serological testing.
• You can store NAM cultures for a prolonged period if kept in a contamination-free area.
• Best for culturing the microbial samples from sewage, air and soil.

Limitations of NAM

• There are high chances of overgrowth in the culture.
• Since it supports many of the bacteria and fungi; thus the culture often gets contaminated by undesirable microbes.
  
• Sometimes, you may not get the desired culture as all the microbes have different growth needs and development patterns.
• If you are using the industrially manufactured NAM powered, any type of carelessness like not sealing it properly can hamper your culture.

Frequently Asked Questions (FAQs)

Is Nutrient agar media a differential media, selective or non-selective media?

The Nutrient agar is a non-selective media that supports the growth of wide-range organisms.

What is the colour of NAM?

The natural colour of nutrient agar media is yellow or pale yellow.

Can all types of bacteria grow on Nutrient agar media?

No, not all. NAM does support the growth of a wide variety of bacteria and fungus, but that doesn’t mean that all bacteria can be cultured on it.