Bacteria can be grown in nutrient agar using several methods, primarily plate cultures, slant cultures, and liquid cultures. The plate culture method is the most common approach.
Plate Cultures
- Preparation of Nutrient Agar:
- Prepare the nutrient agar according to the manufacturer's instructions. Typically, this involves dissolving the agar powder in distilled water and sterilizing it by autoclaving (usually at 121°C for 15 minutes).
- Pouring Plates:
- Allow the sterilized nutrient agar to cool slightly (around 50-55°C) before pouring it into sterile Petri dishes. Pour enough agar to create a layer about 4-5 mm thick.
- Solidification:
- Let the agar solidify completely at room temperature. This usually takes about 30-60 minutes.
- Inoculation:
- Sterilize an inoculating loop by flaming it in a Bunsen burner until it glows red-hot. Allow it to cool before use to avoid killing the bacteria.
- Pick up a small amount of bacteria from the source culture with the sterilized loop.
- Streak the bacteria onto the surface of the agar plate using a streaking pattern to dilute the bacteria. Common streaking methods include quadrant streaking, T-streaking, or continuous streaking. This helps to obtain isolated colonies.
- Incubation:
- Invert the inoculated Petri dish to prevent condensation from dripping onto the agar surface and affecting colony formation.
- Incubate the plate at the appropriate temperature for the bacteria being cultured (typically 37°C for many common bacteria) for the required duration (usually 24-48 hours).
- Observation:
- Observe the growth of bacterial colonies on the agar plate. Isolated colonies represent individual bacterial cells that have multiplied.
Slant Cultures
Slant cultures are used for the long-term storage of bacterial cultures.
- Preparation: Nutrient agar is prepared as described above and poured into test tubes.
- Slanting: Before the agar solidifies, the test tubes are placed at an angle to create a slanted surface.
- Inoculation: After solidification, the agar slant is inoculated by streaking bacteria onto its surface using a sterile loop.
- Incubation: The inoculated slant is incubated at the appropriate temperature until growth is visible.
Liquid Cultures
Liquid cultures involve growing bacteria in nutrient broth instead of nutrient agar.
- Preparation: Nutrient broth is prepared and sterilized.
- Inoculation: A small amount of bacteria is added to the broth.
- Incubation: The broth is incubated, often with shaking or aeration, to promote bacterial growth.
In summary, growing bacteria in nutrient agar typically involves sterilizing the media, pouring it into plates or tubes, inoculating with the desired bacteria, and incubating at an appropriate temperature to allow for growth and colony formation.
