Page:Bacteria, why do they make me sick?.pdf/51



“Growing microorganisms in Petri dishes”

Materials: • 1 envelope of plain unflavored gelatin • ½ liter of hot boiled water (2 ½ cups or 500 mL) • 1 beef bouillon cube • A 3 cups or 600 mL size bowl • 2 cups • Plastic or glass Petri dishes (You can also use short plastic boxes with lids) • 10 cm ruler

Dissolve the beef bouillon cube in 1/4 cup of water (50 mL). At the same time, dissolve the envelope of plain unflavored gelatin in 3/4 cup of water (150 mL). Stir both mixtures, dissolve and add 1 cup of water (200 mL).

Pour the resulting medium into the Petri dishes (or short plastic boxes with lids) until reaching 0.5 cm height (use the ruler to measure). Cover the Petri dishes and allow them to harden stored in a refrigerator. The content of the Petri dishes will be used in activities 2, 3, 4 and 5.