A new medium is described for the isolation of Listeria spp. from foods and
environmental samples. It is based on a modified Oxford medium in which 3,
4-cyclohexenoesculetin-beta -D-glucoside replaces aesculin. Positive coloni
es are intensely black with the advantage that the pigment does not diffuse
into the medium. The medium, when tested alongside the US Department of Ag
riculture (spiked samples) and Food and Drug Administration (naturally cont
aminated samples) isolation procedures, performed significantly better than
the current formulations (34% more confirmed positives from naturally cont
aminated samples) with a reduction of 1 d in the assay time for most sample
s.