Hydroponic nutrient solution temperature impacts Tulane virus persistence over time

Abstract

Abstract Controlled environment agriculture (CEA), or indoor agriculture, encompasses non-traditional farming methods that occur inside climate-controlled structures (e.g., greenhouses, warehouses, high tunnels) allowing for year-round production of fresh produce such as leaf lettuce. However, recent outbreaks and recalls associated with hydroponically grown lettuce contaminated with human pathogens have raised concerns. Few studies exist on the food safety risks during hydroponic cultivation of leaf lettuce; thus, it is important to identify contributing risk factors and potential mitigation strategies to prevent foodborne transmission via hydroponically-grown produce. In this study, the persistence of Tulane virus (TV), a human norovirus surrogate, in hydroponic nutrient solution at 15°C, 25°C, 30°C, and 37°C was determined over a duration of 21 days to mimic the time from seedling to mature lettuce. Tulane virus persisted throughout the 21-day study period at 15, 25, and 30°C compared to 37°C where TV persistence was limited five days. The mean log reduction for TV was 0.86, 1.80, 2.87, and ³3.77 log PFU/mL at 15°C, 25°C, 30°C, and 37°C, respectively, at the end of the 21-day period. The decimal reduction values (D-values) of TV indicate longer persistence in hydroponic nutrient solution at 15°C compared to 25°C, 30°C, and 37°C with D-values of 28.5, 15.0, 8.2, and 2.3 days, respectively. This study aids in identification of possible food safety risks associated with hydroponic systems and aid in developing risk management strategies to reduce foodborne outbreaks, fresh produce recalls, and economic losses.