Recognition of Histo-Blood Group Antigen-Like Carbohydrates in Lettuce by Human GII.4 Norovirus

The attachment factors and attachment receptors of human noroviruses

Human noroviruses (HuNoVs) are the leading etiological agent causing the worldwide outbreaks of acute epidemic non-bacterial gastroenteritis. Histo-blood group antigens (HBGAs) are commonly acknowledged as cellular receptors or co-receptors for HuNoVs. However, certain genotypes of HuNoVs cannot bind with any HBGAs, suggesting potential additional co-factors and attachment receptors have not been identified yet. In addition, food items, such as oysters and lettuce, play an important role in the transmission of HuNoVs. In the past decade, a couple of attachment factors other than HBGAs have been identified and analyzed from foods and microbiomes. Attachment factors exhibit potential as inhibitors of viral binding to receptors on host cells. Therefore, it is imperative to further characterize the attachment factors for HuNoVs present in foods to effectively control the spread of HuNoVs within the food chain. This review summarizes the potential attachment factors/receptors of HuNoVs in humans, foods, and microbiome.

Interactions between human norovirus and intestinal microbiota/microbes: A scoping review

Human norovirus (HuNoV) is an important foodborne virus, which causes non-bacterial acute gastroenteritis and is associated with a high disease burden. Recently, researchers have focus on the interaction between HuNoV and intestinal microbiota/microbes and engaged in studies investigating the implications of this interaction on HuNoV infection. However, the interaction mechanism and the implication of this interaction on host remain obscure. Current scoping review aimed to systematically investigate the interaction between HuNoV and intestinal microbiota, as well as their implication on HuNoV or HuNoV related symptoms. We found that HuNoV could bind to intestinal microbes and affect the intestinal microbial composition, diversity, and microbial gene expression. In reverse, intestinal microbes could affect HuNoV infectivity, although demonstrating contradictory effects (i.e., promote or inhibit HuNoV replication). These contradictory effects existed among microbes, in part, could be attributed to the differences among microbes (histo-blood group antigens and/or other small molecule substances). Results of current scoping review could assist in the selection and isolation of potential microbial candidates to prevent and/or alleviate HuNoV related symptoms.

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.

Common and Potential Emerging Foodborne Viruses: A Comprehensive Review

Human viruses and viruses from animals can cause illnesses in humans after the consumption of contaminated food or water. Contamination may occur during preparation by infected food handlers, during food production because of unsuitably controlled working conditions, or following the consumption of animal-based foods contaminated by a zoonotic virus. This review discussed the recent information available on the general and clinical characteristics of viruses, viral foodborne outbreaks and control strategies to prevent the viral contamination of food products and water. Viruses are responsible for the greatest number of illnesses from outbreaks caused by food, and risk assessment experts regard them as a high food safety priority. This concern is well founded, since a significant increase in viral foodborne outbreaks has occurred over the past 20 years. Norovirus, hepatitis A and E viruses, rotavirus, astrovirus, adenovirus, and sapovirus are the major common viruses associated with water or foodborne illness outbreaks. It is also suspected that many human viruses including Aichi virus, Nipah virus, tick-borne encephalitis virus, H5N1 avian influenza viruses, and coronaviruses (SARS-CoV-1, SARS-CoV-2 and MERS-CoV) also have the potential to be transmitted via food products. It is evident that the adoption of strict hygienic food processing measures from farm to table is required to prevent viruses from contaminating our food.

Pseudomonas composti isolate from oyster digestive tissue specifically binds with norovirus GII.6 via Psl extracellular polysaccharide

Oysters are recognized as important vectors for human norovirus transmission in the environment. Whether norovirus binds to bacteria in oyster digestive tissues (ODTs) remains unknown. To shed light on this concern, ODT-54 and ODT-32, positive for histo-blood group antigen (HBGA) -like substances, were isolated from ODTs and identified as Pseudomonas composti and Enterobacter cloacae, respectively. The binding of noroviruses (GII.4 and GII.6 P domains) to bacterial cells (ODT-32 and ODT-54; in situ assay) as well as extracted extracellular polysaccharides (EPSs; in vitro assay) was analyzed by flow cytometry, confocal laser scanning microscopy, ELISA, and gene knock-out mutants. ODT-32 bound to neither GII.4 nor GII.6 P domains, while ODT-54 specifically binds with GII.6 P domain through Psl, an exopolysaccharide encoded by the polysaccharide synthesis locus (psl), identified based on gene annotation, gene transcription, Psl specific staining, and ELISAs. These findings attest that ODT bacteria specifically bind with certain norovirus genotypes in a strain-dependent manner, contributing to a better understanding of the transmission and enrichment of noroviruses in the environment.

Impact of water reuse on agricultural practices and human health

Climate change is altering the habits of the population. Extensive drought periods and overuse of potable water led to significant water shortages in many different places. Therefore, new water sources are necessary for usage in applications where the microbiological and chemical water quality demands are less stringent, as for agriculture. In this study, we planted, germinated, and grew vegetables/fruits (cherry tomato, lettuce, and carrot) using three types of potential waters for irrigation: secondary-treated wastewater, chlorine-treated wastewater, and green wall-treated greywater, to observe potential health risks of foodstuff consumption. In this study the waters and crops were analyzed for three taxonomic groups: bacteria, enteric viruses, and protozoa. Enteric viruses, human Norovirus I (hNoVGI) and Enterovirus (EntV), were detected in tomato and carrots irrigated with secondary-treated and chlorine-treated wastewater, in concentrations as high as 2.63 log genome units (GU)/g. On the other hand, Aichi viruses were detected in lettuce. Bacteria and protozoa remained undetected in all fresh produce although being detected in both types of wastewaters. Fresh produce irrigated with green wall-treated greywater were free from the chosen pathogens. This suggests that green wall-treated greywater may be a valuable option for crop irrigation, directly impacting the cities of the future vision, and the circular and green economy concepts. On the other hand, this work demonstrates that further advancement is still necessary to improve reclaimed water to the point where it no longer constitutes risk of foodborne diseases and to human health.

Effect of Direct Viral-Bacterial Interactions on the Removal of Norovirus From Lettuce

Norovirus (NoV) is the main non-bacterial pathogen causing outbreaks of gastroenteritis and is considered to be the leading cause of foodborne illness. This study aims to determine whether lettuce-encapsulated bacteria can express histo-blood group antigen (HBGA)–like substances to bind to NoV and, if so, to explore its role in protecting NoV from disinfection practices. Fifteen bacterial strains (HBGA-SEBs) were isolated from the lettuce microbiome and studied as they were proved to have the ability to express HBGA-like substances through indirect ELISA detection. By using attachment assay, HBGA-SEBs showed great abilities in carrying NoVs regarding the evaluation of binding capacity, especially for the top four strains from genera Wautersiella, Sphingobacterium, and Brachybacterium, which could absorb more than 60% of free-flowing NoVs. Meanwhile, the direct viral–bacterial binding between HBGA-like substance-expressing bacteria (HBGA-SEB) and NoVs was observed by TEM. Subsequently, results of simulated environmental experiments showed that the binding of NoVs with HBGA-SEBs did have detrimental effects on NoV reduction, which were evident in short-time high-temperature treatment (90°C) and UV exposure. Finally, by considering the relative abundance of homologous microorganisms of HBGA-SEBs in the lettuce microbiome (ca. 36.49%) and the reduction of NoVs in the simulated environments, we suggested putting extra attention on the daily disinfection of foodborne-pathogen carriers to overcome the detrimental effects of direct viral–bacterial interactions on the reduction of NoVs.

Reduction of Norovirus Surrogates Alone and in Association with Bacteria on Leaf Lettuce and Tomatoes During Application of Aqueous Ozone

Retail foodservice establishments (FSE) frequently utilize washes with sanitizing agents during fresh produce preparation. This study evaluated the efficacy of ozonated water on the inactivation of viruses, bacteria, and viruses in association with bacteria on produce surfaces. Boston bibb lettuce (BB) and cherry tomatoes were spot inoculated with viruses (murine norovirus (MNV) and MS2 bacteriophage), bacteria (Enterobacter cloacae and Bacillus cereus), or MNV associated with E. cloacae or B. cereus. Following inoculation, produce was held at 4 °C for 90 min (virus, virus + bacteria) or 24 h (virus, bacteria) prior to treatment. A batch wash ozone sanitation system (BWOSS) was prepared with ice (3-5 °C) and 0.5 ppm initial ozone concentration or no ozone. Produce samples were treated for 40 min with an ozonated water (0.86-0.99 ppm) or water-only wash with samples taken every 10 min. Samples were processed for microbial recovery, and plaque forming units (PFU) and colony forming units remaining on the produce were determined. Although microbial reductions of 99 to 99.99% were achieved during ozone treatments, few statistically significant differences (P > 0.1) were detected when comparing the ozonated water to water-only wash. Notably, a significant difference (P = 0.009) in log reduction of MNV + bacteria and MNV alone on BB was observed after 40 min ozonated water wash. Specifically, MNV with B. cereus achieved a 1-log greater reduction (2.60 log PFU/ml) compared to MNV alone (1.63 log PFU/ml). Overall, washing produce in ozonated water did not significantly increase microbial inactivation compared to water alone under the conditions presented here. Variables impacting ozone wash effectiveness should be considered when implementing produce wash sanitation systems within FSE.

Adhesion of Norovirus to Surfaces: Contribution of Thermodynamic and Molecular Properties Using Virus-Like Particles

The aim of the study was to assess human norovirus and feline calicivirus (FCV) surface free energy, hydrophobicity, and ability to interact with fresh foods and food-contact surfaces. Virus-like particles (VLPs) of human norovirus (GI.1 and GII.4) and FCV were produced, purified, and analyzed for their surface free energy, hydrophobicity, and the total interfacial free energy of interaction [Formula: see text] with lettuce, strawberry, polyethylene, and stainless steel. GII.4 VLPs were further tested for adhesion at different pH, ionic strengths, and temperature. All the VLPs and the test materials showed low surface energies, as well as hydrophobic characters except for GI.1. Nearly all [Formula: see text] values were propitious for spontaneous adhesion. GII.4 VLPs adsorbed almost indifferently to stainless steel, polyethylene, and lettuce. Isoelectric point and high temperature generally promoted adhesion while ionic strength effect was surface-dependant. According to this study, all the materials assessed are of low-energy and hydrophobic nature except GI.1 VLPs. Interfacial free energies of interaction were favorable for spontaneous adhesion ([Formula: see text] < 0) of all VLPs to the test materials, except for GI.1 VLPs to both stainless steel and straweberry. It is also found that norovirus adhesion is more sensitive to physicochemical conditions than to surface character itself.

Complete genome sequence of the Pseudomonas oleovorans strain ODT-83 isolated from oyster

A bacterial strain ODT-83 is isolated from oysters, which is capable of adsorbing norovirus (NoV) via histo-blood group antigen-like (HBGA-like) substances. To better understand its genetic background associated with the production of HBGA-like substances, the genome of the ODT-83 was completely sequenced and analyzed. The ODT-83 only contains one circular chromosome, with a length of 5,384,159 bp. Both the 16S rRNA gene phylogeny and the average nucleotide identity (ANI) analyses confirm that the ODT-83 is a new Pseudomonas oleovorans strain. The whole genome encodes a total of 5037 predicted open reading frames (ORFs), 66 tRNA genes and 12 rRNA genes. Two gene clusters are detected on the genome, which are involved in the synthesis of polysaccharides of alginate and Pel, respectively. These results lay the foundation for further research on the interaction between the P. oleovorans strain ODT-83 and NoV.

Interaction between norovirus and Histo-Blood Group Antigens: A key to understanding virus transmission and inactivation through treatments?

Human noroviruses (HuNoVs) are a main cause of acute gastroenteritis worldwide. They are frequently involved in foodborne and waterborne outbreaks. Environmental transmission of the virus depends on two main factors: the ability of viral particles to remain infectious and their adhesion capacity onto different surfaces. Until recently, adhesion of viral particles to food matrices was mainly investigated by considering non-specific interactions (e.g. electrostatic, hydrophobic) and there was only limited information about infectious HuNoVs because of the absence of a reliable in vitro HuNoV cultivation system. Many HuNoV strains have now been described as having specific binding interactions with human Histo-Blood Group Antigens (HBGAs) and non-HBGA ligands found in food and the environment. Relevant approaches to the in vitro replication of HuNoVs were also proposed recently. On the basis of the available literature data, this review discusses the opportunities to use this new knowledge to obtain a better understanding of HuNoV transmission to human populations and better evaluate the hazard posed by HuNoVs in foodstuffs and the environment.

Culturable bacteria resident on lettuce might contribute to accumulation of human noroviruses

Human noroviruses (HuNoVs) are the primary non-bacterial pathogens causing acute gastroenteritis worldwide. Attachment and invasion of HuNoVs are thought to involve histo-blood group antigens (HBGAs). Romaine lettuce, which is usually consumed raw, is a common food-related vehicle for HuNoVs transmission. This study investigated the possibility that bacteria resident on the surface of lettuce leaves contribute to norovirus adherence to this food. To test this hypothesis, bacteria were isolated from romaine lettuce and screened to evaluate whether they produced any polysaccharides with structures resembling HBGAs. Twenty-seven bacterial isolates were screened and 18, belonging to 13 different genera, were found to produce HBGAs-like polysaccharides that were recognized by monoclonal antibodies specific to type A, B, H and Lewis a, b, x and y. One bacterial isolate, belonging to the genus Pseudomonas was further investigated because it produced polysaccharides with the widest range of HBGA types, including type B, H and Lewis a, b and x. The Pseudomonas HBGAs-like polysaccharides were found to be extracellular and their production was enhanced when the bacteria were cultured in oligotrophic medium. HuNoVs capture assays revealed that GI.1, GI.8, and GII.2, GII.3, GII.4, GII.6, GII.12, GII.17 genotypes can be bind to Pseudomonas HBGAs-like polysaccharides. The direct evidence of bacterial production HBGAs-like polysaccharides demonstrates one possible mechanism driving accumulation of HuNoVs on lettuce.

Apoptosis and autophagy as a turning point in viral–host interactions: the case of human norovirus and its surrogates

Human gastroenteritis viruses are amid the major causes of disease worldwide, responsible for more than 2 million deaths per year. Human noroviruses play a leading role in the gastroenteritis outbreaks and the continuous emergence of new strains contributes to the significant morbidity and mortality. Many aspects of the viral entry and infection process remain unclear, including the major response of the host cell to the virus, which is the trigger of several programmed cell death related mechanisms. In this review, we assessed apoptosis and autophagy at various stages in the infection process to provide better understanding of the viral–host interaction. This brings us closer to fully understanding how noroviruses work, thus allowing the development of specific antiviral therapies.

Characterization of a Histo-Blood Group Antigen-like Substance in Romaine Lettuce That Contributes to Human Norovirus Attachment

Human noroviruses (HuNoVs) are among the main pathogens causing acute nonbacterial gastroenteritis. Histo-blood group antigens (HBGAs) are widely accepted receptors for HuNoV specific binding. HBGA-like substances in produce are also considered as the critical ligands for capture of HuNoVs. However, the composition of viral ligands from food substrates remains unknown. In this study, an oligosaccharide (H2N2F2) was captured and isolated from romaine lettuce extract by a bacterial surface display system. Using electrospray ionization mass spectrometry and tandem mass spectrometry, it was shown that H2N2F2 was most likely to be a chimera of type A, H, and Lewis a HBGAs. The composition was consistent with our ELISA results using a panel of monoclonal antibodies against HBGAs. Our results revealed a possible interaction mechanism between HuNoVs and romaine lettuce. Better understanding of the interaction of HuNoVs with easily contaminated produce will ultimately aid in the control of and reduction in disease outbreaks.

Human Norovirus Histo-Blood Group Antigen (HBGA) Binding Sites Mediate the Virus Specific Interactions with Lettuce Carbohydrates

Lettuce is often implicated in human norovirus (HuNoV) foodborne outbreaks. We identified H-like histo-blood group antigens (HBGAs) on lettuce leaves as specific binding moieties for virus-like particles (VLPs) of HuNoV GII.4/HS194/2009 strain. The objective of this study was to determine whether HuNoV-lettuce binding is mediated through the virus HBGA binding sites (HBS). Toward this objective, VLPs of historical HuNoV GII.4 strains (1987, 1997, 2002, 2004 and 2006) with known natural mutations in their HBS, two newly generated VLP mutants of GII.4/HS194/2009 (D374A and G443A) and a VLP mutant (W375A) of GI.1/Norwalk/1968 along with its wild type VLPs, which displays distinct HBS, were investigated for their binding to lettuce. ELISA revealed that historical GII.4 strains binding to lettuce was dependent on their HBGAs profiles. The VLP mutants D374A and G443A lost binding to HBGAs and displayed no to minimal binding to lettuce, respectively. The VLPs of GI.1/Norwalk/1968 strain bound to lettuce through an H-like HBGA and the binding was inhibited by fucosidase digestion. Mutant W375A which was previously shown not to bind to HBGAs, displayed significantly reduced binding to lettuce. We conclude that the binding of HuNoV GII.4 and GI.1 strains to lettuce is mediated through the virus HBS.

Characterization of conditions for bacteria-human norovirus capsid P protein complex (BPC) binding to and removal from Romaine lettuce extract

Norovirus is a very contagious virus that causes acute gastroenteritis. Contaminated produce is a main vehicle for dissemination of human noroviruses (HuNoVs). As HuNoVs could bind to bacteria effectively, it is highly possible that produce could be contaminated by bacteria-HuNoVs complex. In this study, we used a bacterial-surface-display system to express genogroup I (GI) or genogroup II (GII) HuNoV capsid protein (P protein) on the surface of bacteria. The bacteria-P protein complex (BPC) was used to characterize the conditions for binding to Romaine lettuce extract and removal of the bound BPCs. We demonstrated both GI and GII BPCs could bind to extract from leaf (LE) and vein (VE) effectively. Carbohydrates in LE and VE were involved in GI BPCs binding, and both carbohydrates and proteins were involved in GII BPCs binding. Saliva from both type A and O secretors could completely block binding of both BPCs to LE and VE. Saliva from type B secretors only partially blocked binding of GII but not GI BPCs to LE and VE. However, LE- and VE-bound BPCs could not be reversely removed by washing solution containing free HBGAs from saliva. The binding of GI BPCs to LE and VE was enhanced when pH was below pI (6.1) of GI and reduced when pH was above pI of GI (p < 0.05). The optimal binding for GII BPCs to LE and VE occurred at pI (6.4) of GII. All LE- or VE-bound BPCs could be reversely removed by washing with low (3.0-5.0) or high (9.0-10.0) pH buffer. The effect of ionic strength (NaCl and MgCl2, from zero to 100 g/L) on binding of BPCs to LE and VE was tested. The optimal ionic strength for binding of BPCs to LE and VE was 10.0 g/L (GI) and 5.0 g/L (GII) for NaCl, and 5.0 g/L for MgCl2. LE- and VE-bound BPCs could be reversely removed by washing with high ionic solutions. All LE- or VE- bound BPCs could be released when washed with NaCl concentrations of above 75.0 g/L (GI) and 25.0 g/L (GII), or with MgCl2 concentrations of above 75.0 g/L (GI) and 50.0 g/L (GII). Binding of BPCs to LE and VE was inhibited in the presence of Tween-80 (nonionic surfactant) as low as 0.05% (v/v). All LE- and VE-bound BPCs could be reversed by Tween-80 concentrations over 0.1% (v/v). The study provided important parameters for BPCs binding to and removal from lettuce extract.

Specific Interactions between Human Norovirus and Environmental Matrices: Effects on the Virus Ecology

Human norovirus is the major cause of non-bacterial epidemic gastroenteritis. Human norovirus binds to environmental solids via specific and non-specific interactions, and several specific receptors for human norovirus have been reported. Among them, histo-blood group antigens (HBGA) are the most studied specific receptor. Studies have identified the presence of HBGA-like substances in the extracellular polymeric substances (EPS) and lipopolysaccharides (LPS) of human enteric bacteria present in aquatic environments, gastrointestinal cells, gills, and palps of shellfish, and cell walls, leaves, and veins of lettuce. These HBGA-like substances also interact with human norovirus in a genotype-dependent manner. Specific interactions between human norovirus and environmental matrices can affect norovirus removal, infectivity, inactivation, persistence, and circulation. This review summarizes the current knowledge and future directions related to the specific interactions between human norovirus and HBGA-like substances in environmental matrices and their possible effects on the fate and circulation of human norovirus.

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.

Microgreens-A review of food safety considerations along the farm to fork continuum

The food safety implications of microgreens, an emerging salad crop, have been studied only minimally. The farm to fork continuum of microgreens and sprouts has some overlap in terms of production, physical characteristics, and consumption. This review describes the food safety risk of microgreens as compared to sprouts, potential control points for microgreen production, what is known to date about pathogen transfer in the microgreen production environment, and where microgreens differ from sprouts and their mature vegetable counterparts. The synthesis of published research to date may help to inform Good Agricultural Practices (GAPs) and Good Handling Practices (GHPs) for the emerging microgreen industry.

A Bacterial Surface Display System Expressing Cleavable Capsid Proteins of Human Norovirus: A Novel System to Discover Candidate Receptors

Human noroviruses (HuNoVs) are the dominant cause of food-borne outbreaks of acute gastroenteritis. However, fundamental researches on HuNoVs, such as identification of viral receptors have been limited by the currently immature system to culture HuNoVs and the lack of efficient small animal models. Previously, we demonstrated that the recombinant protruding domain (P domain) of HuNoVs capsid proteins were successfully anchored on the surface of Escherichia coli BL21 cells after the bacteria were transformed with a plasmid expressing HuNoVs P protein fused with bacterial transmembrane anchor protein. The cell-surface-displayed P proteins could specifically recognize and bind to histo-blood group antigens (HBGAs, receptors of HuNoVs). In this study, an upgraded bacterial surface displayed system was developed as a new platform to discover candidate receptors of HuNoVs. A thrombin-susceptible “linker” sequence was added between the sequences of bacterial transmembrane anchor protein and P domain of HuNoV (GII.4) capsid protein in a plasmid that displays the functional P proteins on the surface of bacteria. In this new system, the surface-displayed HuNoV P proteins could be released by thrombin treatment. The released P proteins self-assembled into small particles, which were visualized by electron microscopy. The bacteria with the surface-displayed P proteins were incubated with pig stomach mucin which contained HBGAs. The bacteria-HuNoV P proteins-HBGAs complex could be collected by low speed centrifugation. The HuNoV P proteins-HBGAs complex was then separated from the recombinant bacterial surface by thrombin treatment. The released viral receptor was confirmed by using the monoclonal antibody against type A HBGA. It demonstrated that the new system was able to capture and easily isolate receptors of HuNoVs. This new strategy provides an alternative, easier approach for isolating unknown receptors/ligands of HuNoVs from different samples including mammalian cell lines, oysters, and fresh produce.

Bacterial Surface-Displayed GII.4 Human Norovirus Capsid Proteins Bound to HBGA-Like Molecules in Romaine Lettuce

Human Noroviruses (HuNoVs) are the main cause of non-bacterial gastroenteritis. Contaminated produce is a main vehicle for dissemination of HuNoVs. In this study, we used an ice nucleation protein mediated surface display system to present the protruding domain of GII.4 HuNoV capsid protein on bacterial surface and used it as a new strategy to explore interaction between HuNoV protein and receptor candidates from romaine lettuce. The surface-displayed HuNoV proteins were confirmed on the surface of the transformed bacteria by an immunofluorescence assay. The distribution patterns of the surface-displayed HuNoV proteins in romaine lettuce were identified through a confocal immunofluorescence assay. The surface-displayed HuNoV proteins could be found in the stomata, and the surfaces of vein and leaf of romaine lettuce. The surface-displayed HuNoV proteins could be captured by an ELISA assay utilizing extract from leaf (LE) or vein (VE). The binding of the surface-displayed HuNoV proteins to LE or VE could be competitively blocked by histo-blood group antigens from human saliva. In addition, the binding of the surface-displayed HuNoV proteins to LE or VE could also be attenuated by heat denaturation of lettuce proteins, and abolished by oxidation of lettuce carbohydrates. The results indicated that histo-blood group antigen-like molecules in LE or VE were involved in the binding of the surface-displayed HuNoV proteins to romaine lettuce. All data demonstrated that the surface-displayed HuNoV proteins could be utilized in a new and simple system for investigation of the interaction between the HuNoVs and their candidate ligands.