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P1-100 Inactivation of Human Norovirus and Its Surrogates on Alfalfa Seeds by Aqueous Ozone

Monday, August 4, 2014
Exhibit Hall D (Indiana Convention Center)
Qing Wang, University of Delaware, Newark, DE
Sarah Markland, University of Delaware, Wilmington, DE
Kalmia Kniel, University of Delaware, Newark, DE
Introduction: Alfalfa sprouts have been associated with numerous foodborne outbreaks, where seed contamination was identified as the source. There is a gap in knowledge regarding viral contamination of seeds since human norovirus is a leading cause of produce-associated outbreaks. Many studies have been conducted investigating the effectiveness of aqueous ozone on bacterial-contaminated seeds, yet little is known about viruses. 

Purpose: This study assessed aqueous ozone for the disinfection of alfalfa seeds contaminated with human norovirus (huNoV) and huNoV surrogates. The inactivation of viruses without food matrix was also investigated. 

Methods: Alfalfa seeds were inoculated with huNoV GII, Tulane virus (TV) and murine norovirus (MNV); viruses without food matrix/inoculated seeds were soaked in deionized water containing 6.25 ppm aqueous ozone with agitation at 22°C for 30s, 1, 5, 15, or 30 min. Sodium thiosulfate (5%) was added post-treatment to quench residual ozone; samples were collected, and seed viruses eluted with Hank’s Balanced Salt Solution. Viruses were quantified by real-time RT-PCR and plaque assay; inoculated seeds soaked in agitated water without ozone were included as controls.

Results: Aqueous ozone resulted in inactivation of MNV and TV infectivity from 1.66 ± 1.11 to 5.60 ± 1.11 log PFU/g seeds; for all treatment times significantly higher reductions were observed for MNV (P < 0.05). Viral genomes were relatively resistant with reduction of 1.03 ± 0.54 to 3.00 ± 0.14 log genomic copies/g seeds; reduction of TV was similar to that of huNoV, whereas the MNV had significantly greater reductions in genomic copies (P < 0.05). Similar trends were observed in ozone-treated viruses without food matrix, with significantly higher levels of inactivation (P < 0.05), especially with reduced levels of infectivity for MNV and TV. 

Significance: Significant inactivation by aqueous ozone indicates that ozone can be an alternative treatment for seeds. The behavior of TV similar to huNoV makes it a promising surrogate.

Back to: Poster Session - Applied Laboratory Methods, Produce, Low-water Activity, Beverages and Water
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