A 'Petri dish' (alternatively known as a 'Petri plate' or 'cell-culture dish') is a shallow transparent lidded dish that biologists use to culture cells, such as bacteria, fungi or small mosses. It is the most common type of culture plate. The Petri dish is one of the most common items in biology laboratories and has entered popular culture. The term is often written in lower case, especially in non-technical literature.

Penicillin, the first antibiotic, was discovered in 1929 when Alexander Fleming noticed that mold that had contaminated a bacterial culture in a 'Petri dish' had killed the bacteria all around it.

The container is named after the German bacteriologist Julius Richard Petri.

'Petri dishes' are usually cylindrical, mostly with diameters ranging from 30 to 200 mm (1.18 to 7.87 in), and a height to diameter ratio ranging from 1:10 to 1:4. Squarish versions are also available.

'Petri dishes' are widely used in biology to cultivate microorganisms such as bacteria, yeasts, and molds. It is most suited for organisms that thrive on a solid or semisolid surface. The culture medium is often an agar plate, a layer a few mm thick of agar or agarose gel containing whatever nutrients the organism requires (such as blood, salts, carbohydrates, amino acids) and other desired ingredients (such as dyes, indicators, and medicinal drugs).

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