Did you know that Julius Richard Petri was born today in 1852? He was a microbiologist and inventor. A microbiologist uses microscopes and magnifying lenses to study organisms that can’t be seen with just the human eye. Some of these organisms include bacteria, viruses, algae, and fungi. Julius Petri also invented the petri dish. A petri dish is a shallow glass or plastic dish filled with a special type of gelatin microorganisms can grow in. Scientists and doctors can inoculate or ‘plant’ microorganisms on a petri dish so they can cultivate, study, and identify them.
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Agar is a jelly-like material made from algae. Nutrients such as blood, carbohydrates, amino acids, dyes, or antibiotics are added depending on what microorganisms are being studied.
When adding microorganisms to a petri dish, scientists use a process called ‘streaking’. They take a sterilized stick, gather the microorganism, and then make a streak on the petri dish. Then they take a second sterilized stick and spread the planted microorganisms around the dish. This helps to prevent contamination.
Petri dishes can be reused if they are sterilized using an autoclave or exposed to very hot, dry air (about 160°C).