The Basis of Peracetic Acid Inactivation Mechanisms for Rotavirus and Tulane Virus under Conditions Relevant for Vegetable Sanitation

Hydroponic Nutrient Solution Temperature Impacts Tulane Virus Persistence over Time

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 concentration of infectious 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. The mean log PFU reduction for TV was 0.86, 1.80, 2.87, and ≥ 3.77 log10 at 15 °C, 25 °C, 30 °C, and 37 °C, respectively, at the end of the 21-day period. Similarly, average decimal reduction values (D-values) of TV at 15 °C, 25 °C, 30 °C, and 37 °C were 48.0, 11.3, 8.57, and 7.02 days, respectively. This study aids in the (i) identification of possible food safety risks associated with hydroponic systems specifically related to nutrient solution temperature and (ii) generation of data to perform risk assessments within CEA leaf lettuce operations to inform risk management strategies for the reduction of foodborne outbreaks, fresh produce recalls, and economic losses.

Human intestinal enteroids and predictive models validate the operational limits of sanitizers used for viral disinfection of vegetable process wash water

Vegetables are globally associated with a considerable number of foodborne outbreaks caused by viral infections, specifically human norovirus. In fresh produce industry, washing represents a critical step for food safety as process wash water (PWW) needs to be maintained at appropriate microbial quality to prevent water-mediated cross-contamination. This study aimed to explore the disinfection efficacy of chlorine (free chlorine, FC), chlorine dioxide (ClO2) and peracetic acid (PAA) in PWW against infectious human norovirus and Tulane virus (TV). First, we tested the extent of TV inactivation in baby leaf, bell pepper, and vegetables mix PWW and monitored the viral decay by cell culture. Then, inactivation kinetics were defined for infectious human norovirus exposed to FC, ClO2 and PAA in baby leaves PWW using the human intestinal enteroids (HIE) system. Finally, kinetic inactivation models were fitted to TV reduction and decay of sanitizers to aid the implementation of disinfection strategies. Results showed that >8 log10 human norovirus and 3.9 log10 TV were inactivated by 20 ppm FC within 1 min; and by 3 ppm ClO2 in 1 min (TV) or 5 min (norovirus). PAA treatment at 80 ppm reduced ca. 2 log10 TV but not completely inactivated the virus even after 20 min exposure, while 5 min treatment prevented norovirus replication in HIE. TV inactivation in PWWs was described using an exponential decay model. Taking these data together, we demonstrated the value of applying the HIE model to validate current operational limits for the most commonly used sanitizers. The inactivation kinetics for human norovirus and TV, along with the predictive model described in this study expand the current knowledge to implement post-harvest produce safety procedures in industry settings.

Underlying the mechanisms of pathogen inactivation and regrowth in wastewater using peracetic acid-based disinfection processes: A critical review

Peracetic acid (PAA) disinfection is an emerging wastewater disinfection process. Its advantages include excellent pathogen inactivation performance and little generation of toxic and harmful disinfection byproducts. The objective of this review is to comprehensively analyze the experimental data and scientific information related to PAA-based disinfection processes. Kinetic models and modeling frameworks are discussed to provide effective tools to assess pathogen inactivation efficacy. Then, the efficacy of PAA-based disinfection processes for pathogen inactivation is summarized, and the inactivation mechanisms involved in disinfection and the interactions of PAA with conventional disinfection processes are elaborated. Subsequently, the risk of pathogen regrowth after PAA-based disinfection process is clearly discussed. Finally, to address ecological risks related to PAA-based disinfection, its impact on the spread of antibiotic-resistant bacteria and the transfer of antibiotic resistance genes (ARGs) is also assessed. Among advanced PAA-based disinfection processes, ultraviolet/PAA is promising not only because it has practical application value but also because pathogen regrowth can be inhibited and ARGs transfer risk can be significantly reduced via this process. This review presents valuable and comprehensive information to provide an in-depth understanding of PAA as an alternative wastewater disinfection technology.

Bacteria and Virus Inactivation: Relative Efficacy and Mechanisms of Peroxyacids and Chlor(am)ine

Peroxyacids (POAs) are a promising alternative to chlorine for reducing the formation of disinfection byproducts. However, their capacity for microbial inactivation and mechanisms of action require further investigation. We evaluated the efficacy of three POAs (performic acid (PFA), peracetic acid (PAA), and perpropionic acid (PPA)) and chlor(am)ine for inactivation of four representative microorganisms (Escherichia coli (Gram-negative bacteria), Staphylococcus epidermidis (Gram-positive bacteria), MS2 bacteriophage (nonenveloped virus), and Φ6 (enveloped virus)) and for reaction rates with biomolecules (amino acids and nucleotides). Bacterial inactivation efficacy (in anaerobic membrane bioreactor (AnMBR) effluent) followed the order of PFA > chlorine > PAA ≈ PPA. Fluorescence microscopic analysis indicated that free chlorine induced surface damage and cell lysis rapidly, whereas POAs led to intracellular oxidative stress through penetrating the intact cell membrane. However, POAs (50 μM) were less effective than chlorine at inactivating viruses, achieving only ∼1-log PFU removal for MS2 and Φ6 after 30 min of reaction in phosphate buffer without genome damage. Results suggest that POAs' unique interaction with bacteria and ineffective viral inactivation could be attributed to their selectivity toward cysteine and methionine through oxygen-transfer reactions and limited reactivity for other biomolecules. These mechanistic insights could inform the application of POAs in water and wastewater treatment.

Inactivation of foodborne viruses by novel organic peroxyacid-based disinfectants

Viruses are responsible for most enteric foodborne illnesses worldwide. The foods most frequently involved are fresh fruits and vegetables since they undergo little or no processing. Washing with a chemical disinfectant is a convenient way of inactivating viruses on foods. Peracetic acid, widely used as a disinfectant in the food industry, has the drawback of leaving a strong odor and is ineffective alone against some foodborne viruses. In this study, four disinfectants, namely per levulinic acid with or without sodium dodecyl sulfate, peracetic acid and a commercial peracetic acid-based disinfectant were tested on murine norovirus 1 (MNV-1), hepatitis A virus (HAV), and hepatitis E virus (HEV). Disinfectant concentrations were 50, 80, 250, 500, and 1000 mg l^-1 and contact times were 0.5, 1, 5, and 10 min. Under these conditions, per levulinic acid supplemented with 1% SDS reduced MNV-1 infectious titer by 3 log cycles vs. 2.24 log cycles by peracetic acid within 0.5 min. On stainless steel at 80 ppm, only peracetic acid produced 3-log reductions within 0.5 min. None of these peroxyacids was able to reduce infectious titers of HAV or HEV by even 2 log cycles at any concentration or time-tested. This study will guide the development of new chemical formulas that will be more effective against major foodborne viruses and will have less impact on food quality and the environment.

Inactivation and genome damage of rotavirus and a human norovirus surrogate by monochloramine treatment and sequential application with UV

The inactivation efficacy by monochloramine for disinfecting gastroenteritis-causing rotaviruses (RV) and Tulane viruses (TV), a surrogate for noroviruses, were evaluated in this study. In addition, the strategies for improving the disinfection efficiency of monochloramine by raising the temperature and sequentially implementing UV irradiation were investigated. The results showed that monochloramine was more effective in the inactivation of TV than RV. Additionally, the inactivation rate constants of RV and TV by monochloramine at 35 °C were improved approximately by 46% and 100%, respectively, compared to those at 25 °C. Moreover, applying UV irradiation before monochloramine enhanced the inactivation efficacy of RV and TV by 63% and 72% compared to monochloramine alone (UV: 6 mJ/cm², NH₂Cl: 60 ppm × min). Furthermore, the synergistic effect was observed during the RV inactivation by the sequential process. Especially, higher than 0.5 log₁₀ reductions of RV VP1 genome contributed to the synergistic effect in sequential treatment, while less than 0.1 log₁₀ reductions of RV VP1 genome were observed during UV alone (13 mJ/cm²) or monochloramine alone (94 ppm × min). The genome damage might be the primary mechanism of generating synergy in sequential treatment for the inactivation of RV. By comparison, no synergistic effect was discovered for the inactivation of TV due to high susceptibility to monochloramine and UV. The findings on the inactivation efficacy and mechanism for improvement will contribute to a wide application of monochloramine for virus inactivation in water treatment and distribution systems.

Inactivation Mechanism and Efficacy of Grape Seed Extract for Human Norovirus Surrogate

Proper disinfection of harvested food and water is critical to minimize infectious disease. Grape seed extract (GSE), a commonly used health supplement, is a mixture of plant-derived polyphenols. Polyphenols possess antimicrobial and antifungal properties, but antiviral effects are not well-known. Here we show that GSE outperformed chemical disinfectants (e.g., free chlorine and peracetic acids) in inactivating Tulane virus, a human norovirus surrogate. GSE induced virus aggregation, a process that correlated with a decrease in virus titers. This aggregation and disinfection were not reversible. Molecular docking simulations indicate that polyphenols potentially formed hydrogen bonds and strong hydrophobic interactions with specific residues in viral capsid proteins. Together, these data suggest that polyphenols physically associate with viral capsid proteins to aggregate viruses as a means to inhibit virus entry into the host cell. Plant-based polyphenols like GSE are an attractive alternative to chemical disinfectants to remove infectious viruses from water or food. IMPORTANCE Human noroviruses are major food- and waterborne pathogens, causing approximately 20% of all cases of acute gastroenteritis cases in developing and developed countries. Proper sanitation or disinfection are critical strategies to minimize human norovirus-caused disease until a reliable vaccine is created. Grape seed extract (GSE) is a mixture of plant-derived polyphenols used as a health supplement. Polyphenols are known for antimicrobial, antifungal, and antibiofilm activities, but antiviral effects are not well-known. In studies presented here, plant-derived polyphenols outperformed chemical disinfectants (i.e., free chlorine and peracetic acids) in inactivating Tulane virus, a human norovirus surrogate. Based on data from molecular assays and molecular docking simulations, the current model is that the polyphenols in GSE bind to the Tulane virus capsid, an event that triggers virion aggregation. It is thought that this aggregation prevents Tulane virus from entering host cells.

Design of SARS-CoV-2 Variant-Specific PCR Assays Considering Regional and Temporal Characteristics

Monitoring the prevalence of SARS-CoV-2 variants is necessary to make informed public health decisions during the COVID-19 pandemic. PCR assays have received global attention, facilitating a rapid understanding of variant dynamics because they are more accessible and scalable than genome sequencing. However, as PCR assays target only a few mutations, their accuracy could be reduced when these mutations are not exclusive to the target variants. Here we introduce PRIMES, an algorithm that evaluates the sensitivity and specificity of SARS-CoV-2 variant-specific PCR assays across different geographical regions by incorporating sequences deposited in the GISAID database. Using PRIMES, we determined that the accuracy of several PCR assays decreased when applied beyond the geographic scope of the study in which the assays were developed. Subsequently, we used this tool to design Alpha and Delta variant-specific PCR assays for samples from Illinois, USA. In silico analysis using PRIMES determined the sensitivity/specificity to be 0.99/0.99 for the Alpha variant-specific PCR assay and 0.98/1.00 for the Delta variant-specific PCR assay in Illinois, respectively. We applied these two variant-specific PCR assays to six local sewage samples and determined the dominant SARS-CoV-2 variant of either the wild type, the Alpha variant, or the Delta variant. Using next-generation sequencing (NGS) of the spike (S) gene amplicons of the Delta variant-dominant samples, we found six mutations exclusive to the Delta variant (S:T19R, S:Δ156/157, S:L452R, S:T478K, S:P681R, and S:D950N). The consistency between the variant-specific PCR assays and the NGS results supports the applicability of PRIMES. IMPORTANCE Monitoring the introduction and prevalence of variants of concern (VOCs) and variants of interest (VOIs) in a community can help the local authorities make informed public health decisions. PCR assays can be designed to keep track of SARS-CoV-2 variants by measuring unique mutation markers that are exclusive to the target variants. However, the mutation markers may not be exclusive to the target variants because of regional and temporal differences in variant dynamics. We introduce PRIMES, an algorithm that enables the design of reliable PCR assays for variant detection. Because PCR is more accessible, scalable, and robust for sewage samples than sequencing technology, our findings will contribute to improving global SARS-CoV-2 variant surveillance.

Selected Mechanistic Aspects of Viral Inactivation by Peracetic Acid

Peracetic acid (PAA) is an alternative to traditional wastewater disinfection as it has a high oxidation potential without producing chlorinated disinfection byproducts. Reports have shown the effectiveness of PAA to reduce waterborne viruses, but the mechanism of inactivation is understudied. This study evaluated PAA consumption by amino acids and nucleotides that are the building blocks of both viral capsids and genomes. Cysteine (>1.7 min^-1) and methionine (>1.2 min^-1) rapidly consumed PAA, while cystine (1.9 × 10^-2 min^-1) and tryptophan (1.4 × 10^-4 min^-1) reactions occurred at a slower rate. All other amino acids and nucleotides did not react significantly (p < 0.05) with PAA during experiments. Also, PAA treatment did not result in significant (p < 0.05) reductions of purified RNA from MS2 bacteriophage and murine norovirus. Data in this study suggest that PAA effectively inactivates viruses by targeting susceptible amino acids on capsid proteins and does not readily damage viral genomes. Knowledge of virus capsid structures and protein compositions can be used to qualitatively predict the relative resistance or susceptibility of virus types to PAA. Capsid structures containing a higher total number of target amino acids may be more susceptible to PAA reactions that damage structural integrity resulting in inactivation.