Selective medium refers to the medium designed according to the special nutritional needs of microorganisms or their resistance to certain chemical and physical factors. Its function is to make the inferior bacteria in the mixed bacteria sample become the dominant bacteria, thus improving the screening efficiency of the bacteria. For example, a culture medium with cellulose as the sole carbon source can be dispersed into microorganisms that decompose cellulose. When dispersing yeast and mold, appropriate amount of penicillin, tetracycline or streptomycin can be added to inhibit the growth of bacteria and actinomycetes.

Identification medium is a kind of culture medium, in which an indicator which can react with the colorless metabolites of the target bacteria is added, so that the colony of the target bacteria can be easily found from the approximate colony only by distinguishing the colors with naked eyes. This culture medium is generally used to identify different microorganisms. For example, EMB is a lactose producing group of eosin and methylene blue. Escherichia coli decomposes lactose and breeds a large number of mixed acids, which can be stained by acid eosin, which combines with methylene blue, and the colonies are dyed deep purple, and green metals can also be seen from the light emitted from the colony appearance.