What is selective media in microbiology?

Selective media are utilized to encourage the growth of particular microorganisms while inhibiting the growth of others. For example, if a microorganism has the ability to resist the effects of a specific antibiotic (e.g ampicillin) that antibiotic can be incorporated into the growth medium. This inclusion acts to prevent the growth of cells, which lack resistance to the ampicillin, permitting only resistant microorganisms to multiply on the selective medium.