Application of Bacteriophage Cocktail in Leafy Greens to Control Salmonella enterica in Produce Wash Water

Introduction: Produce is responsible for 46% of all foodborne illnesses in the USA, of which leafy greens is a leading contributor. Salmonella enterica causes 19,000 hospitalizations each year, and has been associated with produce. Presently, chlorine based sanitizers are recommended for disinfection of produce, but organic matter interferes with its activity. Bacteriophage treatments are an all-natural and target specific alternative method for pathogen inactivation. 

Purpose: The objective of this study was to determine the impact of organic matter on the efficacy of bacteriophage and subsequent reduction of S. enterica in romaine lettuce. 

Methods: To examine the impact of organic matter, simulated wash water was made by blending, straining, and diluting romaine lettuce into solution with turbidities of 0, 25, 50, and 100 NTU. Bacteriophage activity was measured after incubation with wash water solutions for 0, 30, 60, and 300 min at 20°C. To examine bacteriophage efficacy against S. enterica, 9 log CFU/ml of S. enterica was added to 0 and 100 NTU solutions and incubated with 9 log PFU/ml bacteriophage for 0 and 135 min at 37°C. 

Results: All incubation studies with bacteriophage and organic load levels yielded no statistical differences (P < 0.05). In 100 NTU romaine lettuce solutions with bacteriophage and S. enterica, bacteriophage grew 1.84 + 0.12 PFU/ml, the 0 NTU control grew 1.36 + 0.12 log PFU/ml.  S. enterica was reduced 1.81 + 0.07 log CFU/ml in control solutions and 1.79 + 0.10 log CFU/ml in 100 NTU solutions within 135 min. 

Significance: Results show that unlike chlorine, bacteriophage remain viable in wash water with high organic load.  Bacteriophage also delivered a reduction in pathogen load that is comparable to those reported for chlorine. Our data suggests that bacteriophage treatments represent a potential alternative to chlorine for on-farm disinfection of produce.