Magnetic beads coated with specific antibodies pull a substance out of a sample. Once the beads have interacted with the analyte of interest, a magnetic particle separator pulls them out of the sample. It often serves as an enrichment stage in the isolation and detection of microorganisms — food microbiologists use it to concentrate pathogens such as Salmonella or E. coli O157 from complex foods before detection. By pulling targets out of interfering matrices, it dramatically improves the sensitivity of downstream tests.