Internalization and dissemination of human norovirus and Tulane virus in fresh produce is plant dependent

Recycling composted human feces as biofertilizer for crop production: Assessment of soil and lettuce plant tissue contamination by Escherichia coli and human adenovirus

Using waste from sewage systems, particularly human excreta, could save resources and increase soil fertility, contributing to nutrient management. However, because of the pathogenic content in human feces, this resource can pose health risks to farmers and consumers. Therefore, this work analyzed the behavior of the microorganisms: Escherichia coli ATCC13706 and human adenovirus (HAdV-2) in the soil and the internal part of the plant tissue during the vegetative stage after applying spiked composted human feces as biofertilizer. In a greenhouse, we simulated the application of the biofertilizer in lettuce cultivation by spiking three concentrations of E. coli (6.58, 7.31, and 8.01 log10 CFU.g-1) and HAdV-2 (3.81, 3.97, and 5.92 log10 PFU.g-1). As a result, we achieved faster decay in soil at higher concentrations of E. coli. We estimated linear decay rates of -0.07279, -0.09092, and -0.115 days, corresponding to T90s of 13.7, 11.0, and 8.6 days from higher to smaller concentrations of E. coli, respectively. The estimated periods for the inactivation of 4 logarithmic units of E. coli bacteria in soil are longer than the cultivation period of lettuce for all concentrations studied. Concerning the bacterial contamination in plants, we found E. coli in the internal part of the leaves at the highest concentration tested during the first three weeks of the experiment. Furthermore, HAdV-2 was found in roots at a stable concentration of 2-2.3 log10 PFU.g-1 in five of the six samples analyzed. Therefore, bacterial infection could pose a risk, even if fresh greens are washed before consumption, especially for short-term cultures. Regarding viral infection, a positive result in the roots after disinfection may pose a risk to root and tubercule vegetables. These discoveries highlight the importance of conducting comprehensive evaluations of hygiene practices in incorporating organic amendments in crops, explicitly aiming to minimize the risk of post-contamination.

A comprehensive examination of microbial hazards and risks during indoor soilless leafy green production

Produce grown under controlled environment agriculture (CEA) is often assumed to have a reduced risk of pathogen contamination due to the low chance of exposure to outdoor contaminant factors. However, the 2021 outbreak and numerous recalls of CEA-grown lettuce and microgreens demonstrate the possibility of pathogen introduction during indoor production when there is a failure in the implementation of food safety management systems. Indoor production of commercial leafy greens, such as lettuce and microgreens, is performed across a range of protective structures from primitive household setups to advanced and partially automatized growing systems. Indoor production systems include hydroponic, aquaponic, and aeroponic configurations. Hydroponic systems such as deep water culture and nutrient film technique comprised of various engineering designs represent the main system types used by growers. Depending on the type of leafy green, the soilless substrate, and system selection, risk of microbial contamination will vary during indoor production. In this literature review, science-based pathogen contamination risks and mitigation strategies for indoor production of microgreens and more mature leafy greens are discussed during both pre-harvest and post-harvest stages of production.

Internalization of Salmonella in Leafy Vegetables during Postharvest Conditions

The consumption of fresh produce is increasing due to its role in promoting a healthy and balanced diet. However, this trend is accompanied by increased foodborne disease cases associated with pathogens such as Escherichia, Listeria, and Salmonella. Previous studies provided evidence that the internalization of foodborne pathogens in fresh produce may be a potential contamination route and may pose a public health risk. This study investigates the combination effects of storage temperature and humidity on Salmonella internalization in six types of leafy greens (iceberg lettuce, romaine lettuce, red lettuce, green onion, spinach, and kale) during the storage stage. The results indicated that temperature plays a critical role in Salmonella internalization, with higher concentrations observed in samples stored at 25 °C compared to those stored at 7 °C. The mean concentration of internalized Salmonella in the iceberg lettuce sample was the highest and that in the green onion sample was the lowest (iceberg lettuce > red lettuce > romaine lettuce > spinach > kale > green onion). Mist conditions also had an impact on internalization. The group treated with mist showed an increase in Salmonella internalization of about 10-30% rather than the group without mist treatment. This research emphasizes the importance of understanding the factors influencing bacterial internalization in fresh produce and highlights the need for proper storage conditions to minimize the risk of contamination and ensure food safety.

Persistence and transfer of Tulane virus in a microgreen cultivation system

Microgreens are niche salad greens which have increased in popularity among consumers in recent years. Due to similarities with sprouts and leafy greens-both attributed to numerous foodborne disease outbreaks-characterization of the food safety risks associated with microgreen production is warranted. The present study aimed to determine the fate and persistence of a human norovirus (HuNoV) surrogate, Tulane virus (TV), within a microgreen production system. Initially, the persistence of TV in two types of microgreen soil-free cultivation matrix (SFCM)-BioStrate® (biostrate) and peat-was determined. On day 0, water containing 7.6 log PFU of TV was applied to SFCM in growing trays, and the trays were maintained under microgreen growth conditions. TV persisted throughout the 10-day observation in biostrate and peat with overall reductions of 3.04 and 1.76 log plaque forming units (PFU) per tray, respectively. Subsequently, the transfer of TV to microgreen edible tissue was determined when planted on contaminated SFCM. Trays containing each type of SFCM were pre-inoculated with 7.6 log PFU of TV and equally divided into two areas. On day 0, sunflower (SF) or pea shoot (PS) seeds were planted on one-half of each tray, while the other half was left unplanted to serve as a control. The microgreens were harvested on day 10, and SFCM samples were collected from planted and unplanted areas of each tray. No TV were detected from the edible portion of either type of microgreen, yet TV were still present in the SFCM. TV concentrations were significantly lower in the root-containing planted area compared with the unplanted area for both biostrate (P = 0.0282) and peat (P = 0.0054). The mean differences of TV concentrations between unplanted and planted areas were 1.22 and 0.51 log PFU/g for biostrate and peat, respectively. In a subsequent investigation, TV transfer from day 7 inoculated SFCM to microgreens edible portion was not detected either. Overall, this study characterized the viral risk in a microgreen production system, which will help to understand the potential food safety risk related to HuNoV and to develop preventive measures.

Peracetic Acid Sanitation on Arugula Microgreens Contaminated with Surface-Attached and Internalized Tulane Virus and Rotavirus

Hydroponic production of vegetables is becoming more common, especially in regions with unfavorable climate for year-round crop production. However, if viruses are present in the hydroponics feed water, then there is a chance that infectious viruses will be internalized into the tissues of hydroponically grown vegetables. When this happens, surface sanitization of postharvest vegetables may not be effective because the sanitizer cannot disinfect the internalized viruses. In this study, we determined if the effectiveness of peracetic acid (PAA), a sanitizer used in the vegetable industry, is affected by the location of viruses (produce surface or interior tissue) in microgreen arugula. Either internally or externally contaminated hydroponically grown microgreen arugula was then treated with PAA at either 30 or 80 ppm for up to 3 min. The PAA disinfection efficacy was higher when the RV was on the arugula surface (approximately 5-log₁₀ in PFU after 3 min of exposure), instead of the arugula interior (1.5-log₁₀ in PFU after 3 min of exposure). However, PAA disinfection efficacy of TV was not dependent on the virus location in arugula. For both internalized TV and RV, the disinfection efficacy was less than 2-log₁₀ in PFU using all the tested PAA concentrations and exposure times examined here. Thus, both the type and location of virus in fresh vegetables may influence the virus disinfection of postharvest vegetables. Therefore, the optimization of sanitation for postharvest fresh vegetables is needed to reduce foodborne viral infection risks.

SARS-CoV-2 from Urban to Rural Water Environment: Occurrence, Persistence, Fate, and Influence on Agriculture Irrigation. A Review

The novel coronavirus disease (COVID-19), originating from China, has rapidly crossed borders, infecting people worldwide. While its transmission may occur predominantly via aerosolization of virus-laden droplets, the possibility of other routes of contagion via the environment necessitates considerable scientific consideration. SARS-CoV-2 viral RNA has been detected in the feces of infected persons, and studies also have reported its occurrence in wastewater and surface water bodies. Therefore, water may be a possible route of virus outbreaks. Agricultural irrigation is the largest use of water globally, accounting for 70% of water use worldwide. Ensuring adequate water quality within irrigation practices is fundamental to prevent harm to plants and soils, maintain food safety, and protect public health. This review aims to gather information on possible SARS-CoV-2 transmission routes within urban and rural water environments, looking into the detection, persistence, and fate of SARS-CoV-2. Based on published literature, the effect of current treatment technologies in wastewater treatment plants (WWTPs) on SARS-CoV-2 inactivation has also been investigated. Preliminary research efforts that concentrated on SARS-CoV-2 indicate that the risk of virus transmission from the aquatic environment may currently be non-existent, although a few studies have reported the presence of SARS-CoV RNA in soils, whereas there are still no studies on the detection of SARS-CoV-2 in crops.

Effects of Weather and Environmental Factors on the Seasonal Prevalence of Foodborne Viruses in Irrigation Waters in Gyeonggi Province, Korea

This study aimed to investigate the prevalence of foodborne viruses in reservoirs (an important resource of irrigation water) and its correlation with environmental and weather factors. From May 2017 to November 2018, we visited ten reservoirs and a river in the Anseong region of South Korea and collected a total of 192 samples in accordance with the environment protection agency guidelines. We recorded the weather factors (temperature, humidity, and accumulated precipitation) and investigated the surrounding environment factors (livestock, fishing site, the catchment area of reservoirs, etc.). Our research results show that from the river and reservoirs, the detection rates of human norovirus GII, adenovirus, rotavirus, human norovirus GI, and astrovirus were 27.1, 10.4, 10.4, 4.16, and 3.1%, respectively. Their viral load ranged from -1.48 to 1.55 log₁₀ genome copies/l. However, hepatitis A virus was not detected in any irrigation water sample. Although no sampling was performed in winter, foodborne viruses and male-specific coliphages were frequently found during spring (40.78%) and autumn (39.47%). Interestingly, the significant correlation between the accumulative precipitation and the number of detected norovirus and adenovirus was confirmed by linear regression analysis. Furthermore, when the accumulative precipitation ranged from 20 to 60 mm, it significantly affected the viral load and prevalence. Among the environmental factors, recreational facilities such as fishing sites and bungalow fishing spots were identified as contamination sources by correlation analysis. Our research results confirmed the correlations between environmental contamination factors in the reservoir and weather factors with the prevalence of foodborne viruses in the reservoir. These facilitates the assessment of potential foodborne virus contamination during crop irrigation. In addition, predictive models including environmental and weather factors should be developed for monitoring and controlling the safety of irrigation waters in reservoirs.

UV Inactivation of Rotavirus and Tulane Virus Targets Different Components of the Virions

Enteric viruses are shed in fecal material by humans and other animals and are common contaminants in wastewater and surface water. Wastewater treatment plants often disinfect this effluent with low-pressure and medium-pressure UV lamps, which emit 254-nm and 220- to 280-nm irradiation, respectively. It is not known whether this treatment is efficacious against enteric viruses or how such treatments may inactivate these enteric viruses. This study examined UV disinfection for two enteric viruses: rotavirus (RV) (strain OSU with double-stranded RNA and a three-layer capsid) and Tulane virus (TV) (a cultivable surrogate for human norovirus with single-stranded RNA and a single-layer capsid). Viruses were treated with UV irradiation at 220 or 254 nm under conditions relevant to wastewater stabilization ponds, whose water is often used for irrigation. TV was susceptible to 220- or 254-nm UV at similar levels. It appears that UV irradiation inactivated TV by mutagenizing both its genome and capsid binding proteins. RV was more susceptible to UV at 220 nm than to UV at 254 nm. UV irradiation of RV at either 220 or 254 nm resulted in a virus that retained its ability to bind to its host cell receptor. After 220-nm treatment, the VP7 segment of the RV genome could not be amplified by PCR, suggesting that this treatment mutagenized the viral genome. However, this correlation was not observed when UV at 254 nm was used. Thus, RV and TV, with different genome and capsid contents, are targeted by UV irradiation in different ways.IMPORTANCE UV irradiation is becoming common for disinfection in water treatment plants, but little is known about the effectiveness of this treatment for enteric RNA viruses. Here, we observed that 220-nm UV irradiation was efficacious against rotavirus (RV) and Tulane virus (TV). UV irradiation at 254 nm inactivated TV to a greater extent than RV. Additional assays showed that UV irradiation compromised different portions of the RV and TV life cycles. UV irradiation decreased the binding of TV to its host receptor and mutagenized the TV genome. UV irradiation at 220 nm appeared to allow RV-host receptor interaction but halted RV genome replication. These findings provide knowledge about the disinfection of waterborne viruses, information that is important for the safe reuse or release of treated wastewater.

Multi-phased internalization of murine norovirus (MNV) in Arabidopsis seedlings and its potential correlation with plant defensive responses

Norovirus is a highly infectious human pathogen that causes acute foodborne diseases worldwide. As global diet patterns have begun to incorporate a higher consumption of fresh agricultural products, the internalization of norovirus into plants has emerged as a potential threat to human health. Here, we demonstrated that murine norovirus (MNV1) was internalized into Arabidopsis in multiple phases, and this internalization was correlated with Arabidopsis innate immunity responses. Under hydroponic conditions, continuous treatment of MNV1 retarded root growth and facilitated flower development of Arabidopsis without causing necrotic lesions. Examination of viral titers and RNA levels revealed that MNV1 was internalized into Arabidopsis in at least three different phases. In response to MNV1 treatment, the Arabidopsis defensive marker PR1 (a salicylic acid signaling marker) was transiently up-regulated at the early stage. PDF1.2, a jasmonic acid signaling marker, exhibited a gradual induction over time. Noticeably, Arabidopsis RNS1 (T2 ribonuclease) was rapidly induced by MNV1 and exhibited anti-correlation with the internalization of MNV1. Exposure to recombinant Arabidopsis RNS1 protein reduced the viral titers and degraded MNV1 RNA in vitro. In conclusion, the internalization of MNV1 into Arabidopsis was fluctuated by mutual interactions that were potentially regulated by Arabidopsis immune systems containing RNS1.

Key characteristics of foods with an elevated risk for viral enteropathogen contamination

Viral enteropathogens are one of the leading causative agents of foodborne illnesses in both the United States and the European Union. While human noroviruses and hepatitis A virus cause the vast majority of outbreaks and illnesses, there are handful of human enteric viruses that contribute to sporadic outbreaks worldwide including astrovirus, sapovirus, rotavirus, enterovirus and Aichi virus. In addition, hepatitis E virus is increasingly being recognized as an emerging zoonotic threat within the food supply. This review aims to briefly describe the primary human enteric viruses of concern with respect to foodborne transmission. Next, we focus on the contamination and persistence of these viruses within three high-risk food commodities-leafy greens, soft red fruits and bivalve mollusks. As opposed to detailing the specific routes by which these foods can be contaminated with enteric viruses, we have chosen to focus on their persistence and specific interactions within the food itself. Therefore, the processes of attachment and internalization of the viruses in foods have been emphasized. Looking forward, the implications of these specific interactions of human enteric viruses with leafy greens, soft red fruits and bivalve mollusks are briefly considered within the context of future prevention and control strategies.

Potential of Human Norovirus Surrogates and Salmonella enterica Contamination of Pre-harvest Basil (Ocimum basilicum) via Leaf Surface and Plant Substrate

Fresh produce has been identified as an important vehicle for foodborne pathogen transmission and fresh culinary herbs have occasionally been associated with human pathogens and illness. In this study, the fate of human NoV surrogates [murine norovirus 1 (MNV-1) and Tulane virus (TV)] and three strains of Salmonella enterica on pre-harvest basil (Ocimum basilicum) was investigated. The persistence after contamination via either leaf surface or plant substrate was tested respectively. After 3 days, both MNV-1 and TV on pre-harvest leaves were at non-detectable levels (>5.5-log reduction for MNV-1 and >3.3-log reduction for TV). The three Salmonella strains showed consistent reductions of 3- to 4-log. At day 6 and 9, all the tested samples showed low levels of infectivity which were close or below the detection limits (1.7-log PFU/sample leaf for MNV-1 and TV, 0.7-log CFU/sample leaf for Salmonella) except for S. Thompson FMFP 899, one out of three samples showed to maintain present at exceptional high levels (day 6: 5.5-log CFU/sample leaf; day 9: 6.7-log CFU/sample leaf). Possibilities of microbial internalization into the edible parts of basil via the roots was demonstrated with both MNV-1 and S. enterica Thompson FMFP 899. The infectivity of internalized MNV-1 and S. enterica both decreased to non-detectable levels within 9 days after inoculation. Moreover, it should be noticed that very high microbial inoculation was used in the experimental set-up (8.46-log PFU/ml of MNV-1, 8.60-log CFU/ml of S. enterica), which is abnormal in the real-life expected contamination scenario. Within the tested scenarios in this study, S. enterica contaminated on the adaxial leaf surface of basil plants while in growth, and remained/reached a high population of over 6-log CFU/sample leaf after 9 days in one out of three samples, thus showed the highest potential for causing foodborne infection.

Tissue Distribution and Visualization of Internalized Human Norovirus in Leafy Greens

Lettuce has been implicated in human norovirus (HuNoV) outbreaks. The virus is stable on the leaf surface for at least 2 weeks; however, the dynamics of virus internalization have not been fully investigated. The purpose of this study was to assess the internalization and distribution of HuNoV and two surrogate viruses, porcine sapovirus (SaV) and Tulane virus (TV), in lettuce and spinach. Viral inoculations through the roots of seedlings and the petiole of leaves from mature plants were performed, and the viruses were tracked on days 1 and 6 post-root inoculation and at 16 h and 72 h post-petiole inoculation. Confocal microscopy was used to visualize root-internalized HuNoV. In both lettuce and spinach, (i) HuNoV was internalized into the roots and leaves at similar RNA titers, whereas surrogate viruses were more restricted to the roots, (ii) all three viruses were stable inside the roots and leaves for at least 6 days, and (iii) HuNoV disseminated similarly inside the central veins and leaf lamina, whereas surrogate viruses were more restricted to the central veins. Infectious TV, but not SaV, was detectable in all tissues, suggesting that TV has greater stability than SaV. HuNoV was visualized inside the roots' vascular bundle and the leaf mesophyll of both plants. In conclusion, using surrogate viruses may underestimate the level of HuNoV internalization into edible leaves. The internalization of HuNoV through roots and cut leaves and the dissemination into various spinach and lettuce tissues raise concerns of internal contamination through irrigation and/or wash water.IMPORTANCE Human noroviruses are the leading cause of foodborne outbreaks, with lettuce being implicated in the majority of outbreaks. The virus causes acute gastroenteritis in all age groups, with more severe symptoms in children, the elderly, and immunocompromised patients, contributing to over 200,000 deaths worldwide annually. The majority of deaths due to HuNoV occur in the developing world, where limited sanitation exists along with poor wastewater treatment facilities, resulting in the contamination of water resources that are often used for irrigation. Our study confirms the ability of lettuce and spinach to internalize HuNoV from contaminated water through the roots into the edible leaves. Since these leafy greens are consumed with minimal processing that targets only surface pathogens, the internalized HuNoV presents an added risk to consumers. Thus, preventive measures should be in place to limit the contamination of irrigation water. In addition, better processing technologies are needed to inactivate internalized viral pathogens.

Selected Viruses Detected on and in our Food

PURPOSE OF REVIEW

The purpose of this review is to provide an update on recent literature and findings concerning selected foodborne viruses. Two groups of viruses were selected: (a) the most important viruses contaminating food, based on numbers of publications in the last 5 years and (b) viruses infecting sources of food that might have an impact on human health.

RECENT FINDINGS

Important foodborne viruses such as norovirus, hepatitis A and rotavirus are usually "only" contaminating food and are detected on the surface of foodstuffs. However, they are threats to human public health and make up for the majority of cases. In contrast, the meaning of viruses born from within the food such as natural animal and plant viruses is still in many cases unknown. An exception is Hepatitis E virus that is endemic in pigs, transmitted via pork meat and is recognised as an emerging zoonosis in industrialised countries.

SUMMARY

Even though the clinical meaning of "new" foodborne viruses, often detected by next generation sequencing, still needs clarification, the method has great potential to enhance surveillance and detection particularly in view of an increasingly globalised food trade.