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Fresh produce, as a known or suspected source of multiple foodbome outbreaks, harbors large populations of diverse microorganisms, which are partially released into wash water during processing. However, the dynamics of bacterial communities in wash water during produce processing is poorly understood. In this study, we investigated the effect of chlorine (FC) and peracetic acid (PAA) on the microbiome dynamics in spinach and romaine lettuce rinse water. Treatments with increasing concentrations of sanitizers resulted in convergence of distinct microbiomes. The resultant sanitizer resistant microbiome showed dominant presence by Bacillus sp., Arthrobacter psychrolactophilus, Cupriavidus sp., and Ralstonia sp. Most of the FC and PAA resistant bacteria isolated from spinach and lettuce rinse water after sanitation were gram positive spore forming species including Bacillus, Paenibacillus, and Brewbacillus spp., while several PAA resistant Pseudomonas spp. were also isolated from lettuce rinse water. Inoculation of foodbome pathogens altered the microbiome shift in spinach rinse water under PAA treatment, but not in lettuce rinse water or FC treated samples. These inoculated foodbome pathogens were not isolated among the sanitizer resistant strains. U.S. Department of Agriculture (USDA) National Institute of Food and Agriculture (NIFA) Specialty Crop Research Initiative [2016-51181-25403] This study was partially supported by a research grant from U.S. Department of Agriculture (USDA) National Institute of Food and Agriculture (NIFA) Specialty Crop Research Initiative, Award No. 2016-51181-25403. Public domain – authored by a U.S. government employee

Between 2000 and 2010 the Eastern Shore of Virginia was implicated in four Salmonella outbreaks associated with tomato. Therefore, a multi-year study (2012-2015) was performed to investigate presumptive factors associated with the contamination of Salmonella within tomato fields at Virginia Tech's Eastern Shore Agricultural Research and Extension Center. Factors including irrigation water sources (pond and well), type of soil amendment: fresh poultry litter (PL), PL ash, and a conventional fertilizer (triple superphosphate - TSP), and production practices: staked with plastic mulch (SP), staked without plastic mulch (SW), and non-staked without plastic mulch (NW), were evaluated by split-plot or complete-block design. All field experiments relied on naturally occurring Salmonella contamination, except one follow up experiment (worst-case scenario) which examined the potential for contamination in tomato fruits when Salmonella was applied through drip irrigation. Samples were collected from pond and well water; PL, PL ash, and TSP; and the rhizosphere, leaves, and fruits of tomato plants. Salmonella was quantified using a most probable number method and contamination ratios were calculated for each treatment. Salmonella serovar was determined by molecular serotyping. Salmonella populations varied significantly by year; however, similar trends were evident each year. Findings showed use of untreated pond water and raw PL amendment increased the likelihood of Salmonella detection in tomato plots. Salmonella Newport and Typhimurium were the most frequently detected serovars in pond water and PL amendment samples, respectively. Interestingly, while these factors increased the likelihood of Salmonella detection in tomato plots (rhizosphere and leaves), all tomato fruits sampled (n = 4800) from these plots were Salmonella negative. Contamination of tomato fruits was extremely low (< 1%) even when tomato plots were artificially inoculated with an attenuated Salmonella Newport strain (10(4) CFU/mL). Furthermore, Salmonella was not detected in tomato plots irrigated using well water and amended with PL ash or TSP. Production practices also influenced the likelihood of Salmonella detection in tomato plots. Salmonella detection was higher in tomato leaf samples for NW plots, compared to SP and SW plots. This study provides evidence that attention to agricultural inputs and production practices may help reduce the likelihood of Salmonella contamination in tomato fields.