page_title: Petri dish
section_title: Microbiology
hierarchical_section_title: Petri dish / Uses / Microbiology
caption_attribution_description: English: An agar plate with microorganisms isolated from a deep-water sponge.
context_page_description: A Petri dish is a shallow transparent lidded dish that biologists use to hold growth medium in which cells can be cultured, originally, cells of bacteria, fungi and small mosses. The container is named after its inventor, German bacteriologist Julius Richard Petri. 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.
context_section_description: 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). The agar and other ingredients are dissolved in warm water and poured into the dish and left to cool down.  Once the medium solidifies, a sample of the organism is inoculated ("plated").
  The dishes are then left undisturbed for hours or days while the organism grows, possibly in an incubator.  They are usually covered, or placed upside-down, to lessen the risk of contamination from airborne spores. 
  Virus or phage cultures require that a population of bacteria be grown in the dish first, which then becomes the culture medium for the viral inoculum. 
  While Petri dishes are widespread in microbiological research, smaller dishes tend to be used for large-scale studies in which growing cells in Petri dishes can be relatively expensive and labor-intensive.
caption: A Petri dish with bacterial colonies on an agar-based growth medium
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