The Neogen Petrifilm Environmental Listeria Plate is a sample-ready culture medium containing selective agents, nutrients, a cold-water-soluble gelling agent, and a chromogenic indicator that facilitates Listeria colony detection. The Petrifilm Environmental Listeria Plates were designed to analyze environmental samples. This plate is designed to analyze environmental samples and help increase the efficiency of monitoring plant sanitation. The Petrifilm Environmental Listeria Plate provides results in just 26 to 30 hours. The presence of indicator Listeria such as Listeria innocua provides evidence that environmental conditions are suitable for the occurrence of Listeria monocytogenes . The Petrifilm Environmental Listeria Plate detects the majority of environmental Listeria , consisting of Listeria monocytogenes , Listeria innocua , and Listeria welshimeri . L. ivanovii , L. grayi /murrayi and L. seeligeri grow but do not form typical colonies.