Petrifilm TM Environmental Listeria Plate for the Rapid Enumeration of Listeria from Environmental Surfaces

Accurate and rapid detection of Listeria is of significant interest to the food industry. The 3MTM PetrifilmTM Environmental Listeria Plate has been developed in order to provide a Listeria result from environmental samples within 27 to 31 hours. This study compared the Petrifilm Plate method with ISO 11290-2 using PALCAM agar for detection and enumeration of Listeria. Studies of 88 strains demonstrated that the Petrifilm Environmental Listeria Plate has an inclusivity (sensitivity) of 98% and an exclusivity (specificity) of 100% when compared to ISO 11290-2. When comparing colony counts of the strains tested, a paired t-test showed that there was no significant difference between counts on the Petrifilm Plate method and the ISO method (p>0.05). Three different surfaces and nine different collection devices were tested using both methods. The surfaces were artificially inoculated with Listeria and background microbiota. Both sponges and swabs were used as collection devices. After a 60 to 75 minute repair step in buffered peptone water at room temperature (23.7°C), the samples were plated onto Petrifilm Plates and onto PALCAM agar plates. Results showed that, on average, the Petrifilm Plate method was not statistically different (p>0.05) from the ISO method for enumeration of Listeria.