An enrichment culture is a medium with specific and known qualities that favors the growth of a particular microorganism. The enrichment culture's environment will support the growth of a selected microorganism, while inhibiting the growth of others. Lourens Bass Becking succinctly summarized enrichment cultures' abilities when he said "everything is everywhere; the environment selects." Enrichment cultures are similar to selective growth mediums however, enrichment cultures are used to increase the small number of a desired organism to detectable levels. They are used because these targeted bacteria may be easy to miss on other cultures where they would not grow in populations large enough to be detectable. Enrichment cultures are often used for soil and fecal samples.
The microbiologist (and botanist) Martinus Beijerinck is credited with developing the first enrichment cultures. Sergei Winogradsky also experimented on bacteria using different cultures.
High salt concentration will select for halophiles. High temperatures will select for thermophiles.
Selenite broth is used to selectively isolate Salmonella species. Alkaline Peptone Water is used for the cultivation of vibrio. Both these examples are clinically relevant for clinical microbiology relating to stool samples.