Agricultural Practices Influence Contamination and Survival in Pre-harvest Tomato Production.

Between 2000 and 2010 the Eastern Shore of Virginia was implicated in four outbreaks associated with tomato. Therefore, a multi-year study (2012-2015) was performed to investigate presumptive factors associated with the contamination of 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 contamination, except one follow up experiment (worst-case scenario) which examined the potential for contamination in tomato fruits when 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. was quantified using a most probable number method and contamination ratios were calculated for each treatment. serovar was determined by molecular serotyping. 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 detection in tomato plots. 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 detection in tomato plots (rhizosphere and leaves), all tomato fruits sampled ( = 4800) from these plots were negative. Contamination of tomato fruits was extremely low (< 1%) even when tomato plots were artificially inoculated with an attenuated Newport strain (10 CFU/mL). Furthermore, was not detected in tomato plots irrigated using well water and amended with PL ash or TSP. Production practices also influenced the likelihood of detection in tomato plots. 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 contamination in tomato fields.