Purpose: This study aims to evaluate the capability of the huNoV surrogate (murine norovirus (MNV)) internalized from roots to edible tissues of microgreens, and virus survival in re-circulated water without disinfection.
Methods: After kale and mustard seeds growing on hydroponic pads (7-days, harvest at days 8 - 12), edible tissues (10 g) were cut 1 cm above the pads followed by collecting two pieces (3 × 3 cm2) of pads containing only roots. Samples were collected from a newly contaminated system (circulated water inoculated with 3.54 ± 0.49 log PFU/ml MNV on Day 8), and from a previously contaminated system (upon harvest completion, a new set of microgreens was grown without disinfection). Samples were quantified by plaque assay and real-time RT-PCR, and data (3 replicates/3 samples each) were analyzed by ANOVA on JMP.
Results: The behavior of MNV was similar in kale and mustard microgreens (P > 0.05). Constant high levels of viral RNA were present in edible tissues (2.18 to 2.79 log copies/g) and roots (3.35 to 4.16 log copies/cm2) from days 8 - 12; relatively low levels (1.49 to 0.83 log PFU/g and 1.19 to 0.20 log PFU/cm2) of infectious viruses were found with a decreasing trend over time. Cross-contamination occurred easily; MNV remained infectious in previously contaminated hydroponic systems for up to 12 days (2.26 to 1.00 PFU/ml), and was translocated in edible tissues (1.10 to 1.61 PFU/g) via roots (0.34 to 0.71 PFU/cm2). An uninocuated control system remained negative over the sampling period.
Significance: Viruses could be re-circulated in water, taken up through roots, and transferred to edible tissues. Ease of contamination shown here reinforced the need for proper sanitation.