The Petri Dish!
Google is commemorating today the achievements of the scientist Julius Richard Petri with a Google Doodle that shows his invention – the Petri dish – in action.
Petri dishes are often used to make plates that are used for microbiology studies. The dish is partially filled with warm liquid containing agar, and a mixture of specific ingredients that may include nutrients, blood, salts, carbohydrates, dyes, indicators, amino acids and antibiotics. After the agar cools and solidifies, the dish is ready to receive a microbe-laden sample in a process known as inoculation or “plating.” For virus or phage cultures, a two-step inoculation is needed: bacteria are grown first to provide hosts for the viral inoculum.
Often, the bacterial sample is diluted on the plate by a process called “streaking”: a sterile plastic stick, or a wire loop which has been sterilized by heating is used to take the first sample, and make a streak on the agar dish. Then a fresh stick, or a newly-sterilized loop, passes through that initial streak, and spreads the plated bacteria onto the dish. This is repeated a third, and sometimes a fourth time, resulting in individual bacterial cells that are isolated on the plate, which then divide and grow into single “clonal” bacterial colonies.
Petri plates are sometimes incubated upside down (agar on top) to lessen the risk of contamination from settling airborne particles and to prevent water condensation from accumulating and disturbing the cultured microbes.
P&R Labpak supply a wide range of petri dishes – glass and disposable plastic in various diameters. If you need any, why not contact us?
We also supply various agars and media from all leading brands.