Potato dextrose agar facts for kids
Potato dextrose agar (often called "PDA") and potato dextrose broth (PDB) are special foods for tiny living things. Scientists use them to grow fungi (like molds and yeasts) and bacteria in a lab. These "foods" are made from potato juice and a type of sugar called dextrose. PDA is one of the most popular ways to grow fungi and bacteria.
Contents
What is Potato Dextrose Agar Made Of?
Potato dextrose agar is like a jelly that helps microbes grow. Here's what's usually in it:
- Water: About 1 liter (1000 ml) of water.
- Potatoes: It uses the juice from about 200 grams of potatoes. These potatoes are sliced, washed, and left unpeeled.
- Dextrose: About 20 grams of dextrose, which is a sugar that gives energy to the microbes.
- Agar powder: About 20 grams of agar powder. Agar is a natural jelly-like substance that makes the mixture solid.
- pH level: The final mixture needs to be slightly acidic, with a pH of about 5.6. This is good for growing fungi.
- Temperature: It's usually kept at about 25°C (77°F) when microbes are growing on it.
To make the potato juice, you boil about 200 grams of sliced potatoes in about 1 liter of clean water for 30 minutes. After boiling, the liquid is carefully poured out or strained through a cloth. More clean water is added until the total liquid is 1 liter. Then, 20 grams of dextrose and 20 grams of agar powder are mixed in.
How is PDA Made Safe?
After mixing, the liquid is put into a special machine called an autoclave. This machine uses high pressure and steam to heat the mixture to about 15 pounds per square inch (psi) for 15 minutes. This process makes sure that all unwanted germs are killed, so only the microbes you want to study will grow.
What is Potato Dextrose Broth?
Potato dextrose broth (PDB) is very similar to PDA. The main difference is that PDB does not have agar. This means PDB stays a liquid instead of turning into a jelly. Scientists use PDB to grow microbes in a liquid environment.
What Microbes Grow on PDB?
Many common microbes can grow well in potato dextrose broth. These include:
- Yeasts: Like Candida albicans (a common yeast) and Saccharomyces cerevisiae (baker's yeast, used to make bread and beer).
- Molds: Like Aspergillus niger (a common mold found on fruits and vegetables).
