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

Virus Association with Bacteria and Bacterial Cell Components Enhance Virus Infectivity

The transmission and infection of enteric viruses can be influenced by co-existing bacteria within the environment and host. However, the viral binding ligands on bacteria and the underlying interaction mechanisms remain unclear. This study characterized the association of norovirus surrogate Tulane virus (TuV) and murine norovirus (MNV) as well as the human enteric virus Aichi virus (AiV) with six bacteria strains (Pantoea agglomerans, Pantoea ananatis, Bacillus cereus, Enterobacter cloacae, Exiguobacterium sibiricum, Pseudomonas spp.). At room temperature, the viruses bound to all bacteria in strain-dependent rates and remained bound for at least 2 h. The virus association with two gram-positive bacteria B. cereus and E. sibiricum was less efficient than gram-negative bacteria. Next, the bacterial envelope components including lipopolysaccharides (LPS), extracellular polymeric substances (EPS), and peptidoglycan (PG) from selected strains were co-incubated with viruses to evaluate their effect on virus infectivity. All the tested bacteria components significantly increased virus infection to variable degrees as compared to PBS. The LPS of E. coli O111:B4 resulted in the greatest increases of infection by 0.19 log PFU for TuV as determined by plaque assay. Lastly, bacterial whole cell lysate of B. cereus and E. cloacae was examined for their impact on the infectivity of MNV and TuV. The co-incubation with whole cell lysates significantly increased the infectivity of TuV by 0.2 log PFU but not MNV. This study indicated that both the individual bacteria components and whole bacterial cell lysate can enhance virus infectivity, providing key insights for understanding virus-bacteria interaction.

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.

Protective Effect of Select Bacterial Species Representative of Fresh Produce on Human Norovirus Surrogates Exposed to Disinfecting Pulsed Light

Contamination of berries and leafy greens with human norovirus (HuNoV) is a major cause of outbreaks of epidemic gastroenteritis worldwide. Using murine norovirus type 1 (MNV-1) and Tulane virus, we studied the possible extension of HuNoV persistence by biofilm-producing epiphytic bacteria on fresh produce. Nine bacterial species frequently found on the surface of berries and leafy greens (Bacillus cereus, Enterobacter cloacae, Escherichia coli, Kocuria kristinae, Lactobacillus plantarum, Pantoea agglomerans, Pseudomonas fluorescens, Raoultella terrigena, and Xanthomonas campestris) were evaluated for the ability to form biofilms in the MBEC Assay Biofilm Inoculator and in 96-well microplates. The biofilm-forming bacteria were further tested for binding MNV-1 and Tulane virus and the ability to protect them against loss of capsid integrity upon exposure to disinfecting pulsed light at a fluence of 11.52 J/cm2. Based on viral reductions, MNV-1 did not benefit from attachment to biofilm whereas Tulane virus was significantly more resistant than the control when attached to biofilms of E. cloacae (P ≤ 0.01), E. coli (P ≤ 0.01), K. kristinae (P ≤ 0.01), P. agglomerans (P ≤ 0.05), or P. fluorescens (P ≤ 0.0001). Enzymatic dispersion of biofilm and microscopic observations suggest that the biofilm matrix composition may contribute to the virus resistance. Our results indicate that direct virus-biofilm interaction protects Tulane virus against disinfecting pulsed light, and that HuNoV on fresh produce therefore might resist such treatment more than suggested by laboratory tests so far. IMPORTANCE Recent studies have shown that bacteria may be involved in the attachment of HuNoV to the surface of fresh produce. Because these foods are difficult to disinfect by conventional methods without compromising product quality, nonthermal nonchemical disinfectants such as pulsed light are being investigated. We seek to understand how HuNoV interacts with epiphytic bacteria, particularly with biofilms formed by bacterial epiphytes, with cells and extracellular polymeric substances, and to determine if it thus escapes inactivation by pulsed light. The results of this study should advance understanding of the effects of epiphytic biofilms on the persistence of HuNoV particle integrity after pulsed light treatment and thus guide the design of novel pathogen control strategies in the food industry.

Identification of Potential Proteinaceous Ligands of GI.1 Norovirus in Pacific Oyster Tissues

Human norovirus (HuNoV) is the leading foodborne pathogen causing nonbacterial gastroenteritis worldwide. The oyster is an important vehicle for HuNoV transmission, especially the GI.1 HuNoV. In our previous study, oyster heat shock protein 70 (oHSP 70) was identified as the first proteinaceous ligand of GII.4 HuNoV in Pacific oysters besides the commonly accepted carbohydrate ligands, a histo-blood group antigens (HBGAs)-like substance. However the mismatch of the distribution pattern between discovered ligands and GI.1 HuNoV suggests that other ligands may exist. In our study, proteinaceous ligands for the specific binding of GI.1 HuNoV were mined from oyster tissues using a bacterial cell surface display system. Fifty-five candidate ligands were identified and selected through mass spectrometry identification and bioinformatics analysis. Among them, the oyster tumor necrosis factor (oTNF) and oyster intraflagellar transport protein (oIFT) showed strong binding abilities with the P protein of GI.1 HuNoV. In addition, the highest mRNA level of these two proteins was found in the digestive glands, which is consistent with GI.1 HuNoV distribution. Overall the findings suggested that oTNF and oIFT may play important roles in the bioaccumulation of GI.1 HuNoV.

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.

Soluble extracellular polymeric substance (SEPS) of histo-blood group antigen (HBGA) expressing bacterium Sphingobacterium sp. SC015 influences the survival and persistence of norovirus on lettuce

Foodborne norovirus (NoV) outbreaks linked to leafy greens are common due to a lack of efficient strategies to prevent NoV spread from contaminated surfaces. We previously found that Sphingobacterium sp. SC015 in lettuce phyllosphere expresses histo-blood group antigen (HBGA)-like substances in soluble extracellular polymeric substances (SEPS) that contribute to NoV adherence on lettuce. Here, we extracted SEPS from bacterium SC015 (SEPS-SC015), analyzed their chemical composition, and examined their roles in the survival and protection of NoV and surrogates [murine norovirus (MNV-1) and Tulane virus (TuV)] on lettuce. Presence of SEPS-SC015 significantly increased survival and persistence of human NoV (HuNoV), MNV-1, and TuV at days 7 and 14, compared with virus alone. HuNoV, TuV, and MNV-1 seeded with SEPS-SC015 were more resistant to heat (70 °C, 2 min) than these viruses alone. SEPS-SC015 also increased viral resistance to sodium hypochlorite inactivation by treatment with 30 and 300 ppm bleach at 26 °C for 10 min. However, SEPS-SC015 was not effective at protecting these viruses under UV inactivation. Binding of TuV to SC015 bacteria and SEPS-SC015, visualized using transmission electron microscopy, suggests that protection might be related to direct interaction between SEPS-SC015 and viral particles. This study provides important insights that will help inform strategies to improve food safety.

The Role of Histo-Blood Group Antigens and Microbiota in Human Norovirus Replication in Zebrafish Larvae

Human norovirus (HuNoV) is the major agent for viral gastroenteritis, causing >700 million infections yearly. Fucose-containing carbohydrates named histo-blood group antigens (HBGAs) are known (co)receptors for HuNoV. Moreover, bacteria of the gut microbiota expressing HBGA-like structures have shown an enhancing effect on HuNoV replication in an in vitro model. Here, we studied the role of HBGAs and the host microbiota during HuNoV infection in zebrafish larvae. Using whole-mount immunohistochemistry, we visualized the fucose expression in the zebrafish gut for the HBGA Lewis X [Le^X, α(1,3)-fucose] and core fucose [α(1,6)-fucose]. Costaining of HuNoV-infected larvae proved colocalization of Le^X and to a lower extent core fucose with the viral capsid protein VP1, indicating the presence of fucose residues on infected cells. Upon blocking of fucose expression by a fluorinated fucose analogue, HuNoV replication was strongly reduced. Furthermore, by comparing HuNoV replication in conventional and germfree zebrafish larvae, we found that the natural zebrafish microbiome does not have an effect on HuNoV replication, contrary to earlier reports about the human gut microbiome. Interestingly, monoassociation with the HBGA-expressing Enterobacter cloacae resulted in a minor decrease in HuNoV replication, which was not triggered by a stronger innate immune response. Overall, we show here that fucose has an essential role for HuNoV infection in zebrafish larvae, as in the human host, but their natural gut microbiome does not affect viral replication. IMPORTANCE Despite causing over 700 million infections yearly, many gaps remain in the knowledge of human norovirus (HuNoV) biology due to an historical lack of efficient cultivation systems. Fucose-containing carbohydrate structures, named histo-blood group antigens, are known to be important (co)receptors for viral entry in humans, while the natural gut microbiota is suggested to enhance viral replication. This study shows a conserved mechanism of entry for HuNoV in the novel zebrafish infection model, highlighting the pivotal opportunity this model represents to study entry mechanisms and identify the cellular receptor of HuNoV. Our results shed light on the interaction of HuNoV with the zebrafish microbiota, contributing to the understanding of the interplay between gut microbiota and enteric viruses. The ease of generating germfree animals that can be colonized with human gut bacteria is an additional advantage of using zebrafish larvae in virology. This small animal model constitutes an innovative alternative to high-severity animal models.

Docking-based generation of antibodies mimicking Cry1A/1B protein binding sites as potential insecticidal agents against diamondback moth (Plutella xylostella)

BACKGROUND

Broad use of insecticidal Cry proteins from Bacillus thuringiensis in biopesticides and transgenic crops has resulted in cases of practical field resistance, highlighting the need for novel approaches to insect control. Previously we described an anti-Cry1Ab idiotypic-antibody (B12-scFv) displaying toxicity against rice leafroller (Cnaphalocrocis medinalis) larvae, supporting the potential of antibodies for pest control. The goal of the present study was to generate insecticidal antibodies against diamondback moth (Plutella xylostella) larvae.

RESULTS

Four genetically engineered antibodies (GEAbs) were designed in silico from B12-scFv using three-dimensional (3D) structure and docking predictions to alkaline phosphatase (ALP) as a Cry1Ac receptor in P. xylostella. Among these GEAbs, the GEAb-dV_L antibody consisting of two light chains had overlapping binding sites with Cry1A and Cry1B proteins and displayed high binding affinity to P. xylostella midgut brush border membrane (BBM) proteins. Proteins in BBM identified by pull-down assays as binding to GEAb-dV_L included an ABC transporter and V-ATPase subunit A protein. Despite lacking the α-helical structures in Cry1A that are responsible for pore formation, ingestion of GEAb-dV_L disrupted the P. xylostella larval midgut epithelium and resulted in toxicity. Apoptotic genes were activated in gut cells upon treatment with GEAb-dV_L .

CONCLUSION

This study describes the first insecticidal GEAb targeting P. xylostella by mimicking Cry proteins. Data support that GEAb-dV_L toxicity is associated to activation of intracellular cell death pathways, in contrast to pore-formation associated toxicity of Cry proteins. This work provides a foundation for the design of novel insecticidal antibodies for insect control. © 2021 Society of Chemical Industry.

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.

Oyster Heat Shock Protein 70 Plays a Role in Binding of Human Noroviruses

Human noroviruses (HuNoVs) are important foodborne pathogens causing acute gastroenteritis. Oysters are an important vehicle for the transmission of HuNoVs. Histo-blood group antigen (HBGA)-like substances are considered the primary ligands for bioaccumulation of HuNoVs in oyster tissues. In this study, proteinaceous ligands for specific binding of HuNoVs were mined from oyster tissues using a bacterial cell surface display system. The macromolecular target was captured and identified in proteomic analysis. The distribution of viral particles, oyster heat shock protein 70 (oHSP 70), and type A HBGA (positive control) in oyster tissue was investigated by multiplex immunofluorescence assays after artificial contamination with HuNoVs (GII.4). Our results demonstrated that oHSP 70 is a candidate vital ligand for specific binding of HuNoVs in oyster tissues. In addition, P proteins (GI.1 and GII.4) and viral particles (GI.1 and GII.4) were captured by recombinant oHSP 70 in an enzyme-linked immunosorbent assay with a sample signal/negative signal of 7.8, 6.3, 17.0, and 8.8, respectively. The findings suggested that oHSP 70 plays an important role in the binding of these foodborne viruses. IMPORTANCE Human noroviruses (HuNoVs) are the most important pathogen for nonbacterial epidemic gastroenteritis cases. Foodborne transmission plays an important role in HuNoVs infection. Oysters, filter-feeding epibenthic bivalves, can be contaminated by fecal discharge in harvest water. A new proteinaceous ligand for HuNoVs other than HBGA is identified in oyster tissues. The significance of our research is in identifying and verifying the ligands in oyster tissues for HuNoV binding. Our data will allow a better understanding of HuNoV attachment in and transmission by oysters, leading to the control of undesired foodborne disease.