The Ultimate Guide To Nutrient Agar

Nutrient agar is known as a nutrient medium that is general purpose and typically used for the cultivation of all sorts of microbes which in turn, supports the bacterial growth of a variety of non-fastidious organisms.

The Ultimate Guide To Nutrient Agar

Nutrient agar can contribute to the growth of a variety of fungi and bacteria.

In this guide, we’ll be taking you through everything you need to know about nutrient agar from its composition, preparation, and uses, among other relevant information that you should know about. 

What Is Nutrient Agar?

Nutrient agar is known as a general-purpose medium that can support the growth of non-fibrous and non-fastidious organisms.

This means that it can contribute to the growth of all sorts of bacteria and fungi, meaning that the microorganisms will receive the nutrients they need to grow and survive. 

Nutrient agar contains various components that allow it to thrive easily and can easily be made and applied to various organisms. 

What Is In Nutrient Agar?

Nutrient agar has a particular composition that ensures that it can contribute to bacterial and fungi growth in all sorts of non-fastidious organisms. Each component has a different purpose, and it is essential that you learn about what each component does.

In this section, we’ll be delving into each component that can be found in nutrient agar and what its purpose is. Here are the various components found in nutrient agar:

0.3% Beef Extract Or Yeast Extract

The first thing that is found in nutrient agar is the beef extract or yeast extract. It is found in the smallest quantity as it only makes up 0.3% of the total nutrient agar.

The beef extract or yeast extract is a water-soluble substance that helps with bacterial growth. These bacteria can include carbohydrates, organic nitrogen compounds, salts, and vitamins among more. 

0.5% Peptone

Secondly, nutrient agar contains peptone with approximately 0.5% of the substance made up of peptone.

Peptone is an enzymatic digest of animal protein meaning that this is the main source of nitrogen for the bacterial growth, providing the bacteria with the energy it needs to grow. 

0.5% Sodium Chloride (NaCl)

Another component that makes up 0.5% of nutrient agar is sodium chloride. The sodium chloride provides the nutrient agar with its salt concentration that acts as a cytoplasm within the microorganism.

Sodium chloride is a gelatinous liquid that promotes healthy bacterial growth. 

1.5% agar

It is probably unsurprising to learn that the nutrient agar contains agar. Agar makes up approximately 1.5% of nutrient agar and works as the solidifying agent for the medium.

Solidifying agents help substances to grow and breathe. When it comes to plant tissues, agar is one of the most commonly found gelling agents thanks to its array of properties.

Distilled Water

The rest of the nutrient agar is made up of distilled water. This is essential because the water promotes healthy growth as well as the reproduction of microorganisms.

This allows various nutrients to travel throughout the material and allows the nutrient agar to grow and thrive. The distilled water should be adjusted to a neutral pH of 7.4 at a temperature of 25 °C.

Preparing Nutrient Agar

Knowing how to prepare nutrient agar will ensure that you are promoting healthy bacterial growth in whichever microorganism you are dealing with. 

In this section, we’ll be taking you through everything you need to do to ensure that you are preparing nutrient agar properly.

Before you get started, you need to make sure that you have everything you need to make the nutrient agar. Here are the components that you will need:

  • 28g nutrient agar powder (this should contain all the components discussed above, except for the distilled water)
  • 1 liter of distilled water

Here is the best way to thoroughly prepare nutrient agar:

1. Suspending The Nutrient Agar Powder

The first thing you need to do is suspend all the nutrient agar powder into the distilled water. What suspending means is that the powder will not dissolve in the water and should be left to freely move around the medium.

Therefore, don’t be surprised if you find that the nutrient agar powder does not mix in with the distilled water as this is supposed to happen. 

2. Heating The Mixture

The second thing you need to do is heat the mixture. This is the stage when the nutrient agar powder will begin to dissolve into the distilled water.

Make sure that you are stirring the mixture while it is heating to ensure that the nutrient agar powder is fully dissolved. 

3. Autoclaving The Dissolved Mixture

Now you need to autoclave the dissolved mixture. Make sure that you do this for 15 minutes at 121 degrees Celsius to ensure that it has been done correctly.

An autoclave is defined as a strong heated container that is primarily used for chemical reactions through high temperatures and pressures such as steam sterilization. 

4. Cooling The Mixture

Once the autoclaving stage has been completed, you need to give the mixture some time to cool. It’s important to make sure that the mixture is allowed to cool without solidifying as this will mean that you have to repeat the process all over again. 

5. Pouring The Nutrient Agar Onto The Plates 

When you are confident that the nutrient agar has cooled down sufficiently, you can now pour the nutrient afar onto the plates. When you have done this, make sure that the plates are left on a sterile surface, so the agar can solidify. 

6. Replacing The Lids Of The Petri Dishes

Lastly, make sure that you replace the lids from each Petri dish before storing the plates securely in a refrigerator to maintain their freshness. 

Nutrient Agar Uses And Benefits

Nutrient Agar Uses And Benefits

Now you know what nutrient agar consists of and how to prepare it, you may be thinking: well, what’s it even good for? Nutrient agar has plenty of uses within the scientific community that make it useful for all sorts of things. 

The American Public Health Association first published the formula in 1917, meaning that it has been widely used when cultivating bacteria across all kinds of materials including water, and feces, among other materials. 

What makes nutrient agar so effective is that it is devoid of any indicators, differential ingredients, selective agents, or enriching substances meaning that it provides better pigmentation expression, serotyping, and biochemical testing. 

Here are some of the main uses that nutrient agar has that you need to know about:

Cultivation Of Non-Fastidious Organisms

The first use that nutrient agar is known for is that it is used for the cultivation of non-fastidious organisms.

It is a general medium that can also provide routine cultivation for a variety of microorganisms from all sorts of environments including air, food, or water among others. 

Demonstrations And Teaching

If the nutrient agar does not contain any harmful substances, it can be used for demonstration and teaching purposes to show how the isolation of multiple microorganisms works.

Easy Preparation

Nutrient agar is incredibly easy to prepare thanks to its simple composition which means that it can be prepared in the simplest of setups and laboratories, provided that you have the correct equipment. 

Preserving Microorganisms

One of nutrient agar’s many uses is that it can be used to preserve microorganisms for a longer period of time, preventing contamination that can occur without any intervention. 

Purity Testing

Nutrient agar can be used to test the purity of a variety of materials before various biochemical tests and serological tests were developed. 

Bacterial Enumeration

Nutrient agar can be used for bacterial enumeration, especially when deriving it from environmental samples. Enumeration is when the number of bacteria in any given material is determined.

Determining the number of bacteria in any material can be helpful for all sorts of reasons and is something that researchers need to know when studying various diseases and are looking for a cure. 

Selective Toward Certain Fastidious Organisms

Lastly, nutrient agar boasts a selective process so if any biological fluids have been added to the organism, the nutrient agar can be selective towards certain fastidious organisms. 

Nutrient Agar Disadvantages And Limitations

Just as it’s important to learn about the various benefits and uses that come with using nutrient agar, you should also learn about the various disadvantages and limitations. This will give you a further understanding of how it works. 

There are some limitations and disadvantages that you need to know about as this ensures that you will know what to expect if you are conducting research using nutrient agar.

Here are some of the disadvantages you may encounter:

Unreliable Testing

Although nutrient agar is known for being non-selective toward non-fastidious organisms, it is critical to know that different materials and organisms may have different growth requirements.

This can affect the growth patterns in the medium and thus can result in unreliable testing results, especially during the isolation phase. 


Another limitation you need to be aware of is the high chances of contamination that can occur during the isolation phase.

This is because the nutrient media can promote the growth of all sorts of microorganisms, meaning that if you are researching a specific type of microorganism, the research may be compromised. 

Not Suitable For Cultivating Fastidious Organisms

One of the main disadvantages is that nutrient agar is not suitable for cultivating the majority of fastidious organisms.

This is because fastidious organisms may already have particular nutrient requirements that the nutrient agar cannot differentiate. 

Doesn’t Allow For Other Microorganisms

Nutrient agar does not tend to allow for the isolation of other microorganisms such as fungi as it is specifically engineered for bacterial isolation. This can be an issue if there are other microorganisms on the material.

Colony Morphologies

Nutrient agar may be subject to various colony morphologies that can make it difficult to distinguish without having to conduct a further microscopic examination.

If there is a risk of colony morphologies, it is best that you conduct your research in a well-equipped laboratory.

Frequently Asked Questions

What Bacteria Grow On Nutrient Agar?

The bacteria that grow on nutrient agar can vary as they provide the microorganisms with the food and water that they need as well as a suitable environment that allows them to grow and survive.

Therefore, the nutrient agar contains common bacteria such as Staphylococcus and Streptococcus as well as various fungi such as mold and yeast. 

What Is The Difference Between Agar And Nutrient Agar?

Although they both contain the word agar, there are differences between agar and nutrient agar.

The primary difference is that the nutrient agar contains agar powder, which is a solidifying agent that solidifies when exposed to room temperatures. However, the nutrient broth will remain in its liquid form. 

What Is The pH Of Nutrient Agar?

Nutrient agar is often used to check the purity of subcultures within water and dairy prior to the serological and biochemical tests.

When exposed to its optimum pH growth range, the nutrient agar should be between 6.6 and 7.0 meaning that it can be used in conjunction with non-fastidious organisms. 

What Is The Use Of Nutrient Media?

Nutrient media is a culture media that is used to maintain microorganisms for a longer period of time, whilst also cultivating fastidious and non-fastidious organisms that have been enriched with other materials.

Nutrient media can also be used to check purity levels before various biochemical tests or serological tests were developed, with the formula first being published by the American Public Health Association in 1917. 

Why Is Peptone Used In Culture Media?

Peptone is a key component of culture media, whilst only requiring a small amount to become effective.

Peptone is important because it provides the media substance with carbon and nitrogen, which is crucial when it comes to using cultural media. This is because the majority of organisms can utilize the amino acids found in Peptone.

What Is The Difference Between Protein And Peptone?

Protein and peptone are often used interchangeably, but they do have their differences. They have the same purpose as they provide the media with the energy and nutrients it needs to successfully isolate the bacteria.

However, the main difference between the two is their length and structure.

This is because protein is a polymer of amino acids that are linked by peptide bonds, while peptone is a water-soluble mixture of amino acids and polypeptides that are created by the partial hydrolysis of protein. 

Is Nutrient Agar Enriched?

Due to its nature of being a prepared medium, it is possible to enrich the nutrient agar or use it to enrich other materials.

Nutrient agar should have a 0.8% sodium chloride content with a pH of 6.0 meaning that it can be used to cultivate bacteria in slightly acidic conditions. 

Nutrient agar can be used as an enriched media when added with an extra 10% biological fluids such as blood, ascetic fluid, or serum.

This can be helpful when researching specific diseases, so scientists can better understand how the disease in question works, and in turn, help researchers look for a cure. 


In conclusion, nutrient agar is a nutrient medium that is used for the cultivation of a variety of non-fastidious organisms. Thanks to its ability to grow all sorts of fungi and bacteria, it is attributed to bacterial growth for the cultivation of microbes.

Understanding the various aspects of nutrient agar can help you to understand its importance and function as it has a variety of uses that are regularly overlooked.

Nutrient agar is made up of various components that each serve a specific purpose to promote healthy bacterial growth.

Just as nutrient agar has many benefits and uses, it’s also essential to understand that there are specific limitations that can impact your research.

Therefore, make sure that using nutrient agar is going to benefit your research rather than hinder it and do everything you can to reduce the amount of risk involved.

Jennifer Dawkins

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