Nutrient Agar Composition and Uses

In this nutrient agar composition and uses post we have briefly explained about nutrient agar principle, composition, appearances, storage, preparation, result, applications, and limitations.

Nutrient Agar Powder

Nutrient agar powder are fundamental culture media that are used to keep microorganisms alive, to cultivate fastidious organisms by enriching them with serum or blood, and to assess for purity before biochemical or serological tests.

Nutrient agar powder is useful for demonstration and teaching applications where cultures must survive for longer periods of time at room temperature without the risk of overgrowth that might occur with a more nutritional substrate.

This very simple formula has been kept and is still commonly employed in the microbiological evaluation of a wide range of materials, as well as being suggested by standard techniques.

It is one of the non-selective media used in ordinary microbe production. It can be used for the cultivation and enumeration of bacteria that are not very picky.

It is suitable for the culture of related fastidious organisms due to the addition of different biological fluids such as horse or sheep blood, serum, egg yolk, and so on.

Peptone, HM peptone B, and yeast extract give the nitrogen molecules, carbon, vitamins, and trace elements that bacteria require to flourish. The osmotic balance of the medium is maintained by sodium chloride.

Principle

Peptone is derived by the enzymatic digestion of proteinaceous sources such as meat, casein, gelatine, and other similar compounds. It provides nitrogen and is made up of pure amino acids or nitrogenous substances that the bacteria can use right away. Depending on the contents of peptone and the mode of digestion, different bacteria use it in different ways.

The beef extract is a water-soluble extract of the animal tissue that contains essential nutrients such as vitamins, carbohydrates, nitrogen, and salts for bacterial growth on the media.

By keeping the osmotic concentration of the media identical to that of bacterial cytoplasm, sodium chloride or common salt preserves osmotic equilibrium.

Agar is a type of complex carbohydrate derived from marine algae. It is a primary component of the culture media, which provides a stable growth environment. It is the component that bacteria do not consume since agar has no nutritional value. The temperatures at which agar gels and liquefies are 45°C and 95°C, respectively.

Distilled or sterile water is free of contaminants such as calcium, chlorine, and fluorine, and provides a pure water source that is necessary for bacteria to thrive and develop. It also serves as a conduit for numerous nutrients to enter bacterial cells.

Composition

Nutrient agar powder Ingredients Gms/Litre: Peptone: 5.000, Sodium chloride: 5.000, HM peptone: 1.500, Yeast extract: 1.500, Agar: 15.000, Final pH (at 25°C) 7.4±0.2.

Preparation

28.0 grams dissolved in 1000 mL pure/distilled water Bring to a boil to completely dissolve the medium. Autoclave at 15 lbs pressure (121°C) for 15 minutes to sterilise. Reduce the temperature to 45-50°C. The medium can be augmented with 5-10% blood or other biological fluids if desired. Pour into sterile Petri plates after thoroughly mixing.

Quality Control

The pH of the nutrient agar powder should be 6.8 to maintain the quality of the nutrient media and achieve the optimum outcomes. The finished nutrient agar powder should be a clear, uniform solution with no lumps or haziness.

Autoclave the nutrient agar powder media mixes until they are somewhat opalescent or light amber in colour. When using the plating method, always prepare a control or standard plate to compare the development of the culture plates to the control or standard plate.

Bacteria require a temperature of 35°C and a time period of 18-48 hours to incubate, depending on the type of bacteria and their growth requirements.

Storage

Store the prepared nutrient agar powder medium at 20-30°C in a firmly covered container between 10-30°C. Use before the label’s expiration date.

Due to the hygroscopic nature of the product, it should be stored dry after opening and tightly sealing the bottle to prevent lump development.

Lump development might occur if the product is not stored properly. Store in a dry, well-ventilated environment away from extremes of temperature and ignite sources. After each usage, carefully close the container. Use before the label’s expiration date.

Result

Nutrient agar

Escherichia coli (CFU-50-100) – good-luxuriant

Pseudomonas aeruginosa (CFU-50-100) – good-luxuriant

Salmonella Typhi (CFU-50-100) – good-luxuriant

Staphylococcus aureus (CFU-50-100) – good-luxuriant

Streptococcus pyogenes (CFU-50-100) – good-luxuriant

Salmonella Enteritidis (CFU-50-100) – good-luxuriant

Salmonella Typhimurium (CFU-50-100) – good-luxuriant

Yersinia enterocolitica (CFU-50-100) – good-luxuriant

Applications

1. Nutrient agar powder is widely used for culture isolation and purification. Nutrient agar powder can also be used to make the bacterial lawns that are required for antibiotic sensitivity tests.

2. Antibiotic sensitivity testing is usually done on medium that has been particularly developed for that purpose. Nutrient agar powder is a must-have standard media for producing organisms that aren’t picky.

3. Nutrient agar powder also necessary for subculturing and maintaining pure cultures. Nutrient agar powder is a conventional media that can be modified to act as an enriched, selective, or differential media.

4. Before performing any biochemical or serological assays, it provides a preliminary testing media that screens for the presence or absence of any hazardous bacteria.

5. Nutrient agar powder is utility extends beyond the aforementioned domains, as it also aids in the preparation of bacterial lawns for antibiotic sensitivity testing. It can also be used to perform bacteriological tests on a range of materials or samples.

Limitations

1. Different organisms may have different growth requirements, and their development patterns on the medium may vary. During isolation, this renders the medium highly unreliable.

2. Because nutrient media promotes the growth of a wide range of bacteria, the risk of contamination during isolation is substantial in nutrient agar powder media.

3. Nutrient agar powder media can’t be employed as a selective medium for the development of picky organisms with specific nutrient requirements.

4. Nutrient agar powder media is primarily used to isolate bacteria and does not allow for the isolation of other species such as fungi.

5. On nutritional agar, some microbes may have similar colony morphologies, making it difficult to identify between them without microscopic investigation.

Further Readings

Reference