Selective liquid media for microbiology

A selective medium is a medium that allows the selection of one or more types of microorganisms. These microorganisms will be the only ones able to grow on or in the medium while all the others will be inhibited. Selectivity is achieved in several ways. For example, organisms that can use a given sugar are easily selected by making this sugar the only source of carbon in the medium. On the other hand, selective inhibition of certain types of microorganisms can be achieved by adding dyes, antibiotics, salts or specific inhibitors that affect the metabolism or enzyme systems of the organisms.

Differential media are used to differentiate between closely related organisms or groups of organisms. Due to the presence of certain dyes or chemicals in the media, the organisms produce characteristic changes or growth patterns that are used for identification or differentiation. A variety of selective and differential media are used in medical, diagnostic and water pollution laboratories, as well as food and dairy laboratories.