Bacteriocin inhibition zones from overlaid producer colonies, deferred antagonism spots, or patch-plate isolations. Panel A, representative bacteriocin inhibition zones obtained with “sandwich overlay” plates of food enrichment samples overlaid with Listeria monocytogenes 39-2 indicator lawns. Panel B, deferred antagonism assay of culture spots overlaid with Staphylococcus aureus ATCC 12600. Panel C, patch plate of Serratia plymuthica POT-1 (left) overlaid with S. aureus ATCC 12600 and an inhibition zone from Serratia ficaria CCEL-1 (right) against Salmonella Typhimurium H3380 used as a primary indicator screen.