PetrifilmTM system
Using the PetrifilmTM system (3M Company, St. Paul, MN, EUA), the EB (Enterobacteriaceae) plates were inoculated with 1.0 mL of each of the dilutions and gently and evenly spread with a plastic spreader over the plate growth surface of the 20 cm2 plates. The plates were incubated with the transparent side facing upward in a laboratory incubator at 35 °C for 24 hours. According to the instructions of the manufacturer, red colonies with or without gas production and/or yellow zone are considered positive for Enterobacteriaceae (Kornacki and Johnson, 2001).