Effect of a bacteriophage cocktail in combination with modified atmosphere packaging in controlling Listeria monocytogenes on fresh-cut spinach

Abstract

A Listeria monocytogenes-specific bacteriophage cocktail was evaluated for its activity against a nalidixic acid-resistant L. monocytogenes (Lm-NalR) isolate on fresh-cut spinach stored under modified atmosphere packaging at various temperatures. Pieces (~2 × 2 cm2) of fresh spinach inoculated with 4.5 log CFU/cm2 Lm-NalR were sprayed with the phage cocktail (6.5 log plaque-forming units [PFU]/cm2) or a control. The samples were stored at 4°C or 10°C for up to 14 d in sealed packages filled with either atmospheric air (AA) or modified atmosphere (MA). At 4°C under AA, the phages significantly (P ≤ 0.05) lowered the Lm-NalR populations on spinach, compared to control-treated inoculated samples, by 1.12 and 1.51 log CFU/cm2 after 1 and 14 d, respectively. At 4°C under MA, Lm-NalR was significantly reduced by 1.95 log CFU/cm2 compared to control leaves after both 1 and 14 d. At 10°C under AA, the phages significantly reduced Lm-NalR by 1.50 and 2.51 log CFU/cm2 after 1 and 14 d compared to the control. Again at 10°C under MA, the phages significantly reduced Lm-NalR by 1.71 and 3.24 log CFU/cm2 compared to control after 1 and 14 d, respectively. The results support the potential of lytic bacteriophages in effectively reducing populations of L. monocytogenes on freshcut leafy produce, under both AA and MA conditions.