EnrichmentMedium

An enrichment medium is a type of microbiological culture medium formulated to favor the growth of particular microorganisms when they are present in low numbers or stressed, by providing nutrients and conditions that support their replication while suppressing competing flora. Unlike selective media, which primarily inhibit non-target organisms, enrichment media are designed to amplify the target organism to detectable levels and are often followed by subculture onto selective or differential media for isolation.

Design and operation of enrichment media can vary. They may be non-selective basals enriched with nutrients to revive stressed cells, or they may include selective components such as inhibitors or antibiotics to suppress competing microbes. Conditions such as pH, salt concentration, temperature, and atmospheric requirements are frequently adjusted to favor the target organism. Some protocols begin with a pre-enrichment step in a non-selective broth, followed by transfer to an enrichment broth that provides a growth advantage to the organism of interest.

Applications commonly arise in clinical, environmental, and food microbiology. Enrichment is used to enhance detection of pathogens or low-abundance microbes in complex samples, after which isolates are obtained by plating on selective or differential media. The approach increases sensitivity and can improve diagnostic yield, but it may also bias the recovered population toward organisms best adapted to the enrichment conditions. Enrichment work requires careful interpretation and confirmatory testing to identify the target organism accurately.

See also: culture methods, selective media, differential media, enrichment culture.