Introductory Microbiology

Types of media

• Many special media are needed to facilitate recognition, enumeration and isolation of certain types of bacteria. To meet these needs, the microbiologist has available numerous media which, on the basis of their application or function, consistency and nature may be classified as follows.

Selective media
These media provide nutrients that enhance the growth and predominance of a particular type of bacterium and do not enhance other types of organisms that may be present. For instance, a medium in which cellulose is the only carbon source will specifically select for or enrich the growth of cellulose utilizing organisms when it is inoculated with a soil sample containing many kinds of bacteria. e.g.,Eosine methylene blue agar

Differential media
Certain reagents or supplements, when incorporated into culture media, may allow differentiation of various kinds of bacteria. For example, if a mixture of bacteria is inoculated into a blood containing agar medium (blood agar), some of the bacteria may hemolyze (destroy) the red blood cells, others do not thus one can distinguish between hemolytic and non-hemolytic bacteria on the same medium. e.g., Congored yeast extract mannitol agar

Assay media
Media of prescribed composition are used for the assay of vitamins, amino acids and antibiotics. Media of special composition are also available for testing disinfectants.