Petrifilm Environmental Listeria Plate detects the following Listeria species as red-violet colonies: Listeria monocytogenes, Listeria innocua and Listeria welshimeri, but does not differentiate these organisms from one another.
A repair broth (5 mL of buffered peptone water) is added to the collected environmental sample and allowed to remain at room temperature for 1 hour. This short repair step is not an enrichment step. Three milliliters (3 mL) of the sample is pipetted onto the 3M Petrifilm Environmental Listeria Plate and the plate is then incubated for 26-30 hours.
The 3M Petrifilm Environmental Listeria Plate method may be used as a qualitative, quantitative or semi-quantitative test:
- A qualitative interpretation may be desired if a yes/no answer is sufficient and appropriate
- A quantitative interpretation may be desired if different actions will be taken based upon the number present
- A semi-quantitative interpretation may be desired if different actions will be taken depending on the relative level present, and/or if recording actual numbers is not desirable.
The assigned category (e.g., high, medium and low, or unacceptable, marginal and acceptable) is dependent upon your sampling location and your individual plant standard.