Human norovirus (NoV) is the leading cause of foodborne disease in the United States, and epidemiological studies have shown that fresh produce is one of the major vehicles for the transmission of human NoV. However, the mechanisms of norovirus contamination and persistence in fresh produce are poorly understood. The objective of this study is to determine whether human NoV surrogates, murine norovirus (MNV-1) and Tulane virus (TV), can attach and become internalized and disseminated in strawberries grown in soil. The soil of growing strawberry plants was inoculated with MNV-1 and TV at a level of 10 8 PFU/plant. Leaves and berries were harvested over a 14-day period, and the viral titer was determined by plaque assay. Over the course of the study, 31.6% of the strawberries contained internalized MNV-1, with an average titer of 0.81 ؎ 0.33 log 10 PFU/g. In comparison, 37.5% of strawberries were positive for infectious TV, with an average titer of 1.83 ؎ 0.22 log 10 PFU/g. A higher percentage (78.7%) of strawberries were positive for TV RNA, with an average titer of 3.15 ؎ 0.51 log 10 RNA copies/g as determined by realtime reverse transcriptase quantitative PCR (RT-qPCR). In contrast, no or little virus internalization and dissemination were detected when TV was inoculated into bell peppers grown in soil. Collectively, these data demonstrate (i) virally contaminated soils can lead to the internalization of virus via plant roots and subsequent dissemination to the leaf and fruit portions of growing strawberry plants and (ii) the magnitude of internalization is dependent on the type of virus and plant.H uman norovirus (NoV) is the major cause of nonbacterial gastroenteritis, contributing to over 95% of the cases of nonbacterial acute gastroenteritis and an estimated 58% of all foodborne illnesses reported annually in the United States (1-4). In recent years, fresh produce has been identified as a leading cause of foodborne illness in the United States (3, 5, 6). Human NoV alone accounts for over 40% of the fresh produce-related illnesses reported each year in the United States (1, 2, 4-8). Human NoV has been attributed to outbreaks in many diverse types of produce, including fresh cut fruit, lettuce, tomatoes, melons, salads, green onions, strawberries, blueberries, raspberries, and salsa, as well as many others (5-7, 9-15). Human NoV is resistant to common disinfectants, has a low infectious dose, and is highly stable in the environment, which contributes to the high prevalence of foodborne outbreaks associated with the virus and its presence and persistence in food commodities (3,16,17).Foods can become contaminated with human NoV at any point from farm to fork, including production, processing, and preparation. Infected food handler contamination and exposure to fecally contaminated water are thought to be the most frequent modes of human NoV contamination of foods (2, 5, 10, 18). The use of irrigation water that is contaminated with fecal matter is considered a significant cause of viral contamination in soft b...
Human norovirus (NoV) is a major cause of fresh produce-associated outbreaks and human NoV in irrigation water can potentially lead to viral internalization in fresh produce. Therefore, there is a need to develop novel intervention strategies to target internalized viral pathogens while maintaining fresh produce quality. In this study electron beam (E-beam) and gamma radiation were evaluated for efficacy against a human NoV GII.4 strain and Tulane virus (TV). Virus survival following ionizing radiation treatments was determined using direct quantitative reverse transcriptase PCR (RT-qPCR), the porcine gastric mucin magnetic bead (PGM-MB) binding assay followed by RT-qPCR, and plaque assay. In simple media, a high dose of E-beam treatment was required to completely abolish the receptor binding ability of human NoV (35.3kGy) and TV (19.5-24.1kGy), as assessed using the PGM-MB binding assay. Both human NoV and TV were more susceptible to gamma irradiation than E-beam, requiring 22.4kGy to achieve complete inactivation. In whole strawberries, no human NoV or TV RNA was detected following 28.7kGy of E-beam treatment using the PGM-MB binding assay. Overall, human NoV and TV are highly resistant to ionizing radiation and therefore the technology may not be suitable to eliminate viruses in fresh produce at the currently approved levels. In addition, the PGM-MB binding assay is an improved method to detect viral infectivity compared to direct RT-qPCR.
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