Are the bacteria grown on agar plates dangerous?

Most colonies from a hand swab are harmless bacteria that live naturally on your skin. However, never eat or inhale anything grown on agar. Always wash your hands after handling the plates and let a grown-up dispose of them sealed in a bag.

Why does agar solidify?

Agar is extracted from red algae (seaweed). It melts above 85°C and solidifies below 40°C, forming a gel. It stays solid at body temperature (37°C) while providing nutrients, making it perfect for growing bacteria.

How fast do bacteria multiply?

Under ideal conditions, many bacteria divide in two every 20 minutes. One single bacterium can theoretically become over a million in just 7 hours. This is why regular hand-washing is so important.

Why do different colonies look different colors?

Different species of bacteria produce different pigments and grow at different rates. The color, shape, and size of a colony are like a fingerprint that scientists use to identify the species.

Quizzy

Living Things

The Bacteria Zoo: Growing Invisible Monsters

April 8, 2026Ages 3–9

Q-bo's Answer

Bacteria are too small to see, but if we give them food (agar) and a warm bed, they multiply into big groups called colonies that look like colorful dots!

📖 Explanation

🎒 For Ages 6-9

Microbial Growth

Bacteria reproduce by dividing in half. One bacteria becomes two, two become four, and so on. On a nutrient-rich surface like agar, they grow so fast that within a few days, millions of them huddle together to form a 'colony' that you can see with your own eyes.

❓ Frequently Asked Questions

Are the bacteria grown on agar plates dangerous?: Most colonies from a hand swab are harmless bacteria that live naturally on your skin. However, never eat or inhale anything grown on agar. Always wash your hands after handling the plates and let a grown-up dispose of them sealed in a bag.
Why does agar solidify?: Agar is extracted from red algae (seaweed). It melts above 85°C and solidifies below 40°C, forming a gel. It stays solid at body temperature (37°C) while providing nutrients, making it perfect for growing bacteria.
How fast do bacteria multiply?: Under ideal conditions, many bacteria divide in two every 20 minutes. One single bacterium can theoretically become over a million in just 7 hours. This is why regular hand-washing is so important.
Why do different colonies look different colors?: Different species of bacteria produce different pigments and grow at different rates. The color, shape, and size of a colony are like a fingerprint that scientists use to identify the species.

Step 1 / 2

🧪 Where do Germs Live?

~120h

Test different surfaces—like your phone, a doorknob, or your unwashed hands—to see where the most bacteria live.

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📋 Steps

1
🧫 Swab the surface
Rub a clean cotton swab on a doorknob, then gently rub it in a zigzag pattern on the agar.
2
🌡️ Incubate and wait
Tape the lid shut and leave the plate in a warm, dark place for 3 to 5 days.

Watch the Video

Evolution of Bacteria on Mega-Plate (Kishony Lab)

The Bacteria Zoo: Growing Invisible Monsters