A culture medium is a solid or liquid preparation that can support growth. It contains nutrient material that can aid in growth and proliferation of a microbial colony. Culture media are used in laboratories for controlled growth of bacteria, yeast, animal cells or plant cells. They are generally differentiated as media for microorganic culture and media for cell culture that involves growing animal and plant cell types.
The most basic types of culture media used are for bacterial or yeast cultures. These can either be liquid broth medium or a solid agar medium. The liquid broth is used to culture yeast or suspended colonies of bacteria while the solid agar medium is used for culturing a surface adherent layer of bacteria.
There are two main classifications of culture media namely defined and undefined. An undefined culture medium contains a basic source of aminoacids and nitrogen which are the essential requirements for growth of microorganisms. Common examples of the constituents are beef and yeast extracts. The exact composition and percentage of the individual amino acid or nitrogen providing source is unknown and this is used for basic culture and maintenance of strains. An undefined medium is also called a basal or complex medium. In addition to the aminoacid and nitrogen source it also contains a source for glucose, water and other essential salts.
A defined culture medium or synthetic medium is one that contains salts and a glucose source and other components based on the requirements of culture. It contains no yeast or animal extracts. Each of the components used are accurately weighed and the percentage known.
There also exists differential culture media that contain specific indicator compounds to track the presence or absence of particular substances during growth.
Minimal culture media are used to grow wild type strains of bacteria to eliminate or isolate on strains of interest from a combination of colonies. These media are very basic and contain no amino acids and use only a carbon source and salts. Selective or enriched culture media are used for isolation.