Growth medium

A growth medium or culture medium is a solid or liquid or semi-solid designed to support the growth of microorganisms or cells, or small plants like the moss Physcomitrella patens. Different types of media are used for growing different types of cells.

The two major types of growth media are those used for cell culture, which use specific cell types derived from plants or animals, and microbiological culture, which are used for growing microorganisms, such as bacteria or fungi. The most common growth media for microorganisms are nutrient broths and agar plates; specialized media are sometimes required for microorganism and cell culture growth. Some organisms, termed fastidious organisms, require specialized environments due to complex nutritional requirements. Viruses, for example, are obligate intracellular parasites and require a growth medium containing living cells.

The most common growth media for microorganisms are nutrient broths (liquid nutrient medium) or LB medium (lysogeny broth). Liquid media are often mixed with agar and poured via a sterile media dispenser into Petri dishes to solidify. These agar plates provide a solid medium on which microbes may be cultured. They remain solid, as very few bacteria are able to decompose agar (the exception being some species in the genera: Cytophaga, Flavobacterium, Bacillus, Pseudomonas, and Alcaligenes). Bacteria grown in liquid cultures often form colloidal suspensions.

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