Petri dishes are used as research plates 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 that is grown acts like a host for the viral inoculum. The bacterial sample is diluted on the plate in a process called "
streaking": a sterile plastic stick, or a wire loop which is sterilized by heating, is used to collect a sample, and then to make a streak on the dish with the agar. This process may be repeated multiple times using the same dish with a fresh stick or sterilized loop, and results in individual bacterial cells that are isolated on the plate, which then are capable to divide and grow into single
clonal bacterial colonies. Petri plates can be incubated upside down (agar on top), which can help lessen the risk of contamination from airborne particles containing microbes settling and to decrease and prevent the chance of condensation from water accumulating and disturbing the microbes being cultured. Scientists had long been growing cells in natural and synthetic matrix environments to elicit
phenotypes that are not expressed on conventionally rigid substrates. Unfortunately, growing cells either on or within soft matrices can be an expensive, labor-intensive, and impractical undertaking. The basic design of the Petri dish has not changed since being created by Petri in 1887. It was a challenge to keep dishes free of dust and extra bacteria that could collect and alter samples; heavy bell jars used for this purpose having proved ineffective, six years later Petri created a transparent plate slightly larger than the dish, which served as a transparent lid. After running the Göbersdorf sanatorium, he became the director of the Museum of Hygiene in Berlin in the year 1886. == Works ==