Effect of Sequential Treatment of Plasma Activated Water and Bacteriophage on Decontamination of Salmonella Typhimurium in Lettuce

Abstract

AbstractEnsuring food safety measures are essential to minimize the risk of foodborne diseases linked to raw food products. Here, we investigated the efficacy of an innovative approach for the control of Salmonella Typhimurium found in fresh produces. Plasma activated water (PAW) and bacteriophages are emerging effective and valuable alternative methods for microbiological decontamination. The efficacy of PAW and a lytic bacteriophage (109 PFU/mL), both separately and sequentially, against S. Typhimurium in fresh produce was investigated. S. Typhimurium (105–107 CFU/g) were inoculated on lettuce leaves and treated with PAW, S. Typhimurium phage SK-T2 or their combination. PAW or bacteriophage inactivated S. Typhimurium, on lettuce leaves at different initial populations, by 2.90–3.46 or 1.45–3.25 log CFU/g, respectively. After sequential treatments of PAW and bacteriophage, S. Typhimurium populations, initially applied at ~ 105 CFU/g reduced by 4.47 log CFU/g, but when the order of application was changed (i.e., bacteriophage followed by PAW), the combination synergistically decreased the Salmonella numbers below the detection limit of the method used for the enumeration (i.e., < 101 CFU/g). At the high-level inoculum (~ 7 log CFU/g), consecutive treatments of PAW and phage decreased the S. Typhimurium population by 3.28 log CFU/g, and a reduction of 6.20 log CFU/g was achieved after reversing the order of treatment. Regardless of the bacterial inoculum level, sequential applications of bacteriophage and PAW resulted in a higher level of inactivation. This study proved that the bacteriophage–PAW combination constitutes a promising alternative approach to the conventional washing process in fresh produce wash waters in the food industry. Graphical Abstract