B5 - practical bacteria growth

Growing Bacteria

  • Bacteria are grown in a substance called culture medium.

    • A culture medium contains necessary elements for bacterial growth, including:

    • Carbohydrates

    • Minerals

    • Proteins

    • Vitamins

  • The culture medium can exist in two common forms:

    • Nutrient broth solution

    • Agar jelly

  • On agar jelly plates, bacteria will form visible colonies on the surface of the jelly.

    • Bacteria will spread out to create an even coverage across the medium.

Practical Procedure for Making Agar Plates

  1. To create an agar plate, hot agar jelly is poured into a petri dish.

  2. Once the agar has cooled and set, use inoculating loops to transfer microorganisms to the culture medium.

    • Alternative tools include:

    • Sterile dropping pipette

    • Spreader

  3. The microorganisms will then multiply in the medium.

  4. In laboratory settings (e.g., schools), agar plates should not be kept above 25°C to prevent the growth of harmful pathogens.

  5. In industrial conditions, bacteria can be incubated at higher temperatures to promote faster growth.

Preventing Growth

  • Testing the action of antiseptics using cultures of bacteria involves the following steps:

  1. Place paper disks soaked in different antibiotics on an agar plate that has an even coverage of bacteria.

    • Ensure to leave space between the disks.

  2. The antibiotics should diffuse into the agar jelly.

  3. Antibiotic-resistant bacteria will remain unaffected by the antibiotics and continue to grow, while non-resistant bacteria will die off, resulting in a clear area on the agar where bacterial growth has ceased.

    • This clear area is referred to as the incubation zone.

  4. A control must be included in the experiment: a disk that has not been soaked in antibiotic but instead soaked in sterile water. This is necessary to observe the difference in growth patterns.

  5. Allow the experiment to sit for 48 hours at 25°C.

  6. The antibiotic that is most effective against the bacteria will show a larger incubation zone, indicating more significant bacterial death in that area.