Specialized media are widely employed for the isolation and identification of microorganisms, testing the antibiotic sensitivities, analysis of water and food, industrial microbiology, and other activities. Although all microorganisms need sources of energy, nitrogen, carbon, phosphorus, sulfur, and various minerals, the exact composition of a satisfactory medium will rely on the species one is trying to identify and cultivate because nutritional requirements vary so greatly among the microorganisms.
Knowledge of microorganism’s normal habitat is often useful in selecting a suitable culture medium because its nutrient requirements reflect its natural surroundings. A medium is used to select and growing specific microorganisms or to help identifying a particular species. In these cases, the function of the medium also depends on its composition. In addition to nutrients necessary for the growth of all bacteria, special-purpose media contain one or more chemical compounds that are essential for their functional specificity.