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Observation of Bacteria from a Bathroom Glass

Experiment Metadata

ID: EXP-20250311-001

Author: Your Name

Date: 2025-03-12

Version: 1.0

License: CC BY-SA 4.0

Ongoing

Safety Status: Caution

Hazards:

Objective​

To demonstrate the presence of bacterial contamination on a used bathroom glass by culturing bacteria in a homemade growth medium.

Materials​

  • Cornstarch (Maïzena) or agar substitute
  • Water
  • Sugar
  • Salt
  • A clean, sterilized petri dish or container
  • Isopropyl alcohol (95%) for sterilization
  • Sterile cotton swab
  • Adhesive tape and plastic bag (for sealing the petri dish)
  • Bleach solution (for disposal)
  • Labels and markers
  • Gloves (nitrile or latex, EN 374-5 certified)

Procedure​

1. Preparation of Growth Medium​

  1. Mix 250mL of water, 1 tbsp cornstarch, 1 tsp sugar, and a pinch of salt.
  2. Heat the solution until it thickens into a gel.
  3. Pour the warm gel into the petri dish and let it solidify.

2. Collection of Sample​

  1. Sterilize hands and workspace with isopropyl alcohol.
  2. Use a sterile cotton swab to rub the inside of the bathroom glass.
  3. Gently streak the swab across the surface of the gel in a zigzag pattern.

3. Incubation​

  1. Close the petri dish and seal it with adhesive tape.
  2. Place the dish in a warm, dark place (25-35°C).
  3. Store it inside a sealed plastic bag to prevent contamination.
  4. Leave undisturbed for 48-72 hours.

4. Observation & Documentation​

  1. Observe growth without opening the container.
  2. Record color, shape, and size of colonies.
  3. Take photographs at 24h, 48h, and 72h intervals.

5. Disposal​

  1. Immerse the sealed petri dish in a bleach solution (1:10 dilution) for 30 minutes.
  2. Dispose of the petri dish and gloves safely in biohazard waste or a sealed bag.
  3. Disinfect the workspace with alcohol or bleach.

Safety Precautions​

  • Do not open the petri dish once bacteria have grown.
  • Always wear protective gloves and safety glasses.
  • Ensure proper ventilation when handling chemicals.
  • Dispose of bacterial cultures following biohazard protocols.

Conclusion​

This experiment visually demonstrates bacterial contamination from everyday objects, reinforcing the importance of proper hygiene.

References​

  • CDC Biosafety Guidelines (2023)
  • WHO Laboratory Safety Manual (2022)

Notes​

Label the petri dish with:

  • Experiment ID: EXP-20240312-001
  • Date of Inoculation
  • Warning: Do not open - Bacterial Culture Inside