Sensitivity of Foodborne Pathogens in Sterile and Vegetable Wash-off Water to Sanitizers and Microbiome Shift in Wash-off Water

Fresh produce harbors large and diverse microbes and is a known vehicle for a number of recent foodborne outbreaks. The survival and proliferation of bacterial pathogens might be strongly influenced by the produce microbiota. However, the impact of native microflora of vegetables on the sensitivity of foodborne pathogens to commonly used sanitizers during washing has not been well explored. In addition, the sensitivity and shift of bacterial communities in wash water during produce processing is unclear. In this study, we investigated the effect of chlorine (ClO-) and peracetic acid (PAA) on the shift of foodborne pathogens and microbial flora from spinach and lettuce in water. Free chlorine resulted in higher reduction levels of foodborne pathogens in sterile and wash-off water of both spinach and lettuce than PAA at the same concentration, however, PAA was not significantly depleted after treatment. Viable but not culturable cells after sanitation were detected by microscopy, qPCR and 16S rDNA amplicon sequencing. The sensitivity of foodborne pathogens to sanitizers were significantly higher in sterile water than in wash-off water, which might be influenced by the organic matter and contextual microbial communities from produce. Most of the ClO- and PAA resistant bacteria in spinach and lettuce wash-off water were gram positive, such as Bacillus and Brevibacterium spp., while several ClO- resistant Pseudomonas spp. were also isolated from lettuce wash-off water. This study can benefit the mitigation strategies of foodborne pathogens and spoilage bacteria during produce processing.