Purpose: The purpose of this study was to compare recovery of Listeria inoculated onto sponges hydrated with HC or neutralizing buffer (NB) dosed with low or high levels of sanitizer.
Methods: Polyurethane sponges pre-hydrated with 10 ml of HC or NB were dosed with low level (0.6 - 0.8 mg) or high level (3 mg) of a quaternary ammonium, chlorine, or mixed acid sanitizer. The sponges were inoculated with approximately 800 cells of a Listeria cocktail (containing two strains of L. monocytogenes and 1 strain each of L. innocua and L. ivanovii), placed into refrigeration and shipped to 9 participating laboratories. Detection was performed 72 hours after inoculation using commercial immunodiagnostic or molecular amplification kits.
Results: Listeria-positive results were obtained with all 81 sponges hydrated with HC and dosed with no, low or high levels of sanitizer. For sponges hydrated with NB, Listeria-positive results were obtained with all 27 sponges receiving no sanitizer, 22 out of 27 sponges receiving low level, and 16 out of 27 sponges receiving high level of sanitizer. NB sponges dosed with low and high levels of chlorine or mixed acid sanitizer produced the Listeria-negative results.
Significance: Sampling devices used in environmental monitoring programs must maintain the viability of target organisms until samples are processed in the laboratory, even if residual sanitizer is present. HC was better than NB at maintaining the viability of Listeria for 72 hours at refrigerated temperatures in the presence of chlorine and mixed acid sanitizers.