Note: Nutrient agar and nutrient broth share almost the same media composition. The main difference between them is that the nutrient agar contains a solidifying agent, the agar powder that causes the medium to solidify at room temperature.
Summary :
◉ Overview
Nutrient agar is a general purpose medium suitable for the cultivation of a wide variety of nonfastidious microorganisms. The medium, with a relatively simplified composition, is used to subculture organisms for maintenance purposes or to check the purity of subcultures and for the enumeration of organisms in water, wastewater, urine, feces and other material.
Nutrient agar is devoid of indicator, selective agent, differential ingredients and enriching substances, therefore uses for better pigmentation expression, biochemical testing and even for serotyping.
Nutrient agar formula was first published by the American Public Health Association in 1917
Nutrient agar
◉ Composition of nutrient agar
◈ The composition can be adjusted to obtain optimal performance, for 1 liter of medium:
Composition of nutrient agar |
|
|---|---|
| Ingredients | Gram / liter |
| Tryptone | 5,0g |
| Meat extract | 1,0g |
| Yeast extract | 2,0 g |
| Sodium chloride | 5,0 g |
| bacteriological Agar | 12,0 g |
Dehydrated Nutrient Agar
◉ Preparation of nutrient agar
Dehydrated medium
- Suspend 28.0 grams in 1 litre of purified/distilled or deionized water.
- Heat to a boil to completely dissolve the medium.
- Sterilize by autoclaving at a pressure of 15 lb (121°C) for 15 minutes.
- After autoclaving, cool to 45-50°C.
- Pour nutritious agar into Petri dishes (until the agar is solidified).
- Keep boxes in the refrigerator at 2-8°C.
Prepared medium
Liquefy the agar (e.g.: bain marie), cool to 45-50°C and pour into Petri dishes. Let stand for at least 30 minutes.
Prepared nutrient agar
Note : Nutrient agar with 0.8% NaCl and pH 6.0 is used for the culture of bacteria requiring slightly acidic conditions. Nutrient media can be used as enriched media by the addition of 10% blood or other biological fluids such as ascetic fluid, serum, etc.
Pseudomonas in Nutrient agar
Serratia in Nutrient agar
◈ Some colonies may have characteristic pigmentation
- Not diffusible: Serratia: red, Staphylococcus aureus: golden yellow
- Diffuse: Pseudomonas aeruginosa: middle coloration in green
