Introduction
utrient broth is one of the most common and basic culture media used in microbiology laboratories. It provides the essential nutrients required for the growth of non-fastidious bacteria and serves as the foundation for many other enriched and specialized media.
Media Type
Type: Simple (basal) liquid medium
Purpose: Supports the growth of non-fastidious organisms such as Escherichia coli, Staphylococcus aureus, and Salmonella spp.
State: Liquid (broth form, without agar).
Example: Nutrient agar is derived from nutrient broth by adding agar (1.5–2%)
Composition & pH of Nutrient Broth
A standard nutrient broth contains:
| Component | Function |
|---|---|
| Peptone (5 g/L) | Source of amino acids, nitrogen |
| Beef extract (3 g/L) | Provides vitamins, minerals, growth factors |
| Sodium chloride (5 g/L) | Maintains osmotic balance |
| Distilled water | Solvent |
Sterilization
Nutrient broth is sterilized by autoclaving:
Temperature: 121°C
Pressure: 15 psi (1.05 kg/cm²)
Time: 15–20 minutes
This process ensures destruction of all vegetative bacteria and spores.
Preparation of Nutrient Broth
Weighing: Dissolve peptone (5 g), beef extract (3 g), and NaCl (5 g) in 1 liter of distilled water.
Mixing: Stir until completely dissolved.
pH Adjustment: Adjust final pH to 7.2–7.4.
Dispensing: Distribute into test tubes or flasks.
Sterilization: Autoclave at 121°C for 15 minutes.
Storage: Store at 2–8°C until use.
Uses of Nutrient Broth
General purpose medium for cultivation of non-fastidious bacteria.
Used for primary bacterial growth before sub-culturing on selective/differential media.
Helps in studying bacterial motility in liquid cultures.
Used in bacterial growth curve experiments.
Employed in biochemical tests (e.g., indole test preparation).
Serves as a stock culture medium for maintaining organisms.
Conclusion
Nutrient broth is the simplest and most widely used culture medium in microbiology. Its ease of preparation, ability to support a wide range of bacteria, and role in diagnostic and research microbiology make it an essential part of the laboratory
