Efficacy of a disinfectant containing silver dihydrogen citrate against GI .6 and GII .4 human norovirus

Machine Learning and Imputation to Characterize Human Norovirus Genotype Susceptibility to Sodium Hypochlorite

Human norovirus (HuNoV) is the leading cause of foodborne illness in the developed world and a major contributor to gastroenteritis globally. Its low infectious dose and environmental persistence necessitate effective disinfection protocols. Sodium hypochlorite (NaOCl) bleach is a widely used disinfectant for controlling HuNoV transmission via contaminated fomites. This study aimed to evaluate the susceptibility of HuNoV genotypes (n = 11) from genogroups I, II, and IV to NaOCl in suspension. HuNoV was incubated for 1 and 5 min in diethyl pyrocarbonate (DEPC) treated water containing 50 ppm, 100 ppm, or 150 ppm NaOCl, buffered to maintain a pH between 7.0 and 7.5. Neutralization was achieved by a tenfold dilution into 100% fetal bovine serum. RNase pre-treatment followed by RT-qPCR was used to distinguish between infectious and non-infectious HuNoV. Statistical methods, including imputation, machine learning, and generalized linear models, were applied to process and analyze the data. Results showed that NaOCl reduced viral loads across all genotypes, though efficacy varied. Genotypes GI.1, GII.4 New Orleans, and GII.4 Sydney were the least susceptible, while GII.6 and GII.13 were the most susceptible. All NaOCl concentrations above 0 ppm were statistically indistinguishable, and exposure duration did not significantly affect HuNoV reduction, suggesting rapid inactivation at effective concentrations. For instance, some genotypes were completely inactivated within 1 min, rendering extended exposure unnecessary, while other genotypes maintained the initial concentration at both 1 and 5 min, indicating a need for longer contact times. These findings underscore the critical role of HuNoV genotype selection in testing disinfection protocols and optimizing NaOCl concentrations. Understanding HuNoV susceptibility to NaOCl bleach informs better disinfection strategies, aiding public health and food safety authorities in reducing HuNoV transmission and outbreaks.

Evaluation of cytotoxicity of 3.8 % SDF and BioAKT solutions on the viability of dental pulp stem cells

Introduction

Nonsurgical endodontic therapies have evolved from classic endodontic therapies to regenerative endodontic treatments (RETs) in recent years. In context of the cytotoxic activity of the most commonly used endodontic irrigant, NaOCl, newer endodontic irrigating solutions should be tested for its effective use in RETs. The aim of this trial was to examine and assess the cytotoxic response of 3.8 % SDF and BioAKT irrigating solutions on the viability of DPSCs.

Methods

The viability of DPSCs cultivated in 5.25 % NaOCl, 3.8 % SDF & BioAKT at dilutions of 1:100,1:20 &1:10 were evaluated through MTT assay after 10 min, 60 min and 24 h incubation, detection of apoptosis and ALP activity after 7,14 & 21-days incubation. A two-way analysis of variance (ANOVA) with post hoc Turkey HSD was performed to determine significant differences between the specimens tested.

Results

When compared to the control at all time periods, all test specimens at varied dilutions (1:100, 1:20, and 1:10) caused no cytotoxic effects. The maximum number of live cells and ALP activity was observed with DPSCs cultivated in BioAKT followed by 3.8 % SDF and 5.25 % NaOCl at all time intervals.

Conclusion

Different doses of 3.8 % SDF and BioAKT solution revealed encouraging outcomes when compared to 5.25 % NaOCl in terms of viability, proliferation and long-term ALP functioning potential when cultivated in DPSCs.

Antiviral Natural Products, Their Mechanisms of Action and Potential Applications as Sanitizers and Disinfectants

Plant extracts, natural products and plant oils contain natural virucidal actives that can be used to replace active ingredients in commercial sanitizers and disinfectants. This review focuses on the virucidal mechanisms of natural substances that may exhibit potential for indoor air and fomite disinfection. Review of scientific studies indicates: (1) most natural product studies use crude extracts and do not isolate or identify exact active antiviral substances; (2) many natural product studies contain unclear explanations of virucidal mechanisms of action; (3) natural product evaluations of virucidal activity should include methods that validate efficacy under standardized disinfectant testing procedures (e.g., carrier tests on applicable surfaces or activity against aerosolized viruses, etc.). The development of natural product disinfectants requires a better understanding of the mechanisms of action (MOA), chemical profiles, compound specificities, activity spectra, and the chemical formulations required for maximum activity. Combinations of natural antiviral substances and possibly the addition of synthetic compounds might be needed to increase inactivation of a broader spectrum of viruses, thereby providing the required efficacy for surface and air disinfection.

The Effect of Water Hardness and pH on the Efficacy of Peracetic Acid and Sodium Hypochlorite against SARS-CoV-2 on Food-Contact Surfaces

Sodium hypochlorite (NaOCl) and peracetic acid (PAA) are commonly used disinfectants with a maximum recommended concentration of 200 ppm for food-contact surfaces. The objectives of this study were to assess the effect of pH and water hardness on NaOCl and PAA efficacy against SARS-CoV-2 on stainless steel (SS). The two disinfectants were prepared at 200 ppm in water of hardness 150 or 300 ppm with the final pH adjusted to 5, 6, 7, or 8. Disinfectants were applied to virus-contaminated SS for one minute at room temperature following the ASTM E2197 standard assay. SARS-CoV-2 infectivity was quantified using TCID50 assay on Vero-E6 cells. In general, increasingly hard water decreased the efficacy of NaOCl while increasing the efficacy of PAA. Hard water at 300 ppm significantly increased virus log reduction with PAA at pH 8 by ~1.5 log. The maximum virus log reductions were observed at pH 5 for both NaOCl (~1.2 log) and PAA (~2 log) at 150 and 300 ppm hard water, respectively. In conclusion, PAA performed significantly better than NaOCl with harder water. However, both disinfectants at 200 ppm and one minute were not effective (≤3 log) against SARS-CoV-2 on contaminated food-contact surfaces, which may facilitate the role of these surfaces in virus transmission.

Use of a silver-based sanitizer to accelerate Escherichia coli die-off on fresh-cut lettuce and maintain produce quality during cold storage: Laboratory and pilot-plant scale tests

Outbreaks and product recalls involving romaine and iceberg lettuce are frequently reported in the United States. Novel technologies are needed to inactivate pathogens without compromising product quality and shelf life. In this study, the effects of a process aid composed of silver dihydrogen citrate, glycerin, and lactic acid (SGL) on Escherichia coli and Listeria monocytogenes concentrations on lettuce immediately after washing and during cold storage were evaluated. Sensory and quality attributes of fresh-cut iceberg lettuce were also evaluated. Laboratory results indicated that application of SGL solution for 30 s as a first step in the washing process resulted in a 3.15 log reduction in E. coli O157:H7 immediately after washing. For E. coli O157:H7 a significant difference between SGL treatment and all other treatments was maintained until day 7. On day zero, SGL led to a 2.94 log reduction of L. monocytogenes. However, there was no significant difference between treatments with or without SGL regardless of storage time. Pilot-plant results showed that samples receiving SGL spray followed by chlorinated flume wash exhibited a greater reduction (1.48 log) in nonpathogenic E. coli populations at the end of shelf life than other treatments (p < 0.05). Additional pilot plant tests were conducted to investigate the hypothesis that SGL residues could continue to impact microbial survival on the final washed lettuce. Results show that pathogens introduced subsequent to flume washing of lettuce pretreated with SGL solution were not affected by antimicrobial residues. The final quality and shelf life of flume washed lettuce were also unaffected by pretreatment with SGL. In conclusion, the results of this study demonstrate that this new technology has the potential to accelerate E. coli die-off on fresh-cut lettuce during cold storage and improve product safety, while not affecting quality throughout the shelf life of the finished products.

Efficacy of an alcohol-based surface disinfectant formulation against human norovirus

Aim

To evaluate the anti‐noroviral efficacy of PURELL® surface sanitizer and disinfectant spray (PSS, an alcohol‐based formulation) using human norovirus GII.4 Sydney [hNoV, by RT‐qPCR and human intestinal enteroid (HIE) infectivity assay] and its cultivable surrogate, Tulane virus (TuV, infectivity assay), compared to sodium hypochlorite (NaOCl) solutions.

Methods and Results

PSS efficacy was evaluated in suspension and on surfaces [stainless steel (SS)] using ASTM methods. Results were expressed as log₁₀ reduction (LR) of genome equivalent copy number (GEC, for hNoV, assayed by RT‐qPCR) and plaque forming units (PFU, for TuV, per infectivity assay). In suspension, PSS achieved a 2.9 ± 0.04 LR hNoV GEC irrespective of contact time (30 or 60 s) and soil load (2.5% or 5%). Under all treatment conditions, infectious TuV could not be recovered following exposure to PSS, corresponding to the assay limit of detection (3.1–5.2 log₁₀ PFU). Infectious hNoV could not be detected in the HIE model after exposure to PSS. On SS and 2.5% soil, PSS produced a 3.1 ± 0.1 LR hNoV GEC, comparable to 500 ppm NaOCl for 60 s. With 5.0% soil, PSS produced a 2.5 ± 0.2 LR hNoV GEC, which was similar to 1000–5000 ppm NaOCl for 60 s.

Conclusions

PSS showed high anti‐hNoV efficacy by RT‐qPCR and in in vitro (TuV) and ex vivo (HIE) infectivity assays and performed similar to 1000–5000 ppm NaOCl for a 60‐s contact time on SS with added soil.

Significance and Impact of Study

hNoV remains a significant cause of morbidity globally, partly due to its resistance to numerous surface disinfectants. RT‐qPCR results from this study indicate PSS efficacy against hNoV is comparable to NaOCl efficacy. Infectivity assays leveraging TuV and the HIE model for hNoV support and confirm loss of virus infectivity. Collectively, these results indicate the product’s ability to inactivate hNoV quickly, which could be beneficial in settings having elevated risk for hNoV transmission.

Evaluation of Cytotoxicity and Antibacterial Activity of a New Class of Silver Citrate-Based Compounds as Endodontic Irrigants

In the present study, the cytotoxicity and the antimicrobial activity of two silver citrate-based irrigant solutions were investigated. Cytotoxicity of various concentrations (0.25%, 0.5%, 1%, 2.5%, 5%) of both solutions (BioAKT and BioAKT Endo) was assessed on L-929 mouse fibroblasts using the MTT assay. For the quantitative analysis of components, an infrared (I.R.) spectroscopy was performed. The minimum inhibitory and minimal bactericidal concentrations (M.I.C. and M.B.C., respectively) were ascertained on Enterococcus faecalis strain ATCC 4083. For biofilm susceptibility after treatment with the irrigating agent, a minimum biofilm eradication concentration (M.B.E.C.) and confocal laser scanning microscope (C.L.S.M.) assays were performed. Quantification of E. faecalis cell biomass and percentage of live and dead cells in the biomass was appraised. Normality of data was analyzed using the D’Agostino & Pearson’s test and the Shapiro–Wilk test. Statistical analysis was performed using one-way analysis of variance (ANOVA) and Tukey’s test. Both silver citrate solutions showed mouse fibroblasts viability >70% when diluted to 0.25% and 0.5%. Conversely, at higher concentrations, they were extremely cytotoxic. F.T.-IR spectroscopy measurements of both liquids showed the same spectra, indicating similar chemical characteristics. No substantial contrast in antimicrobial activity was observed among the two silver citrate solutions by using broth microdilution methods, biofilm susceptibility (MBEC-HTP device), and biomass screening using confocal laser scanning microscopy (C.L.S.M.) technique. Both solutions, used as root canal irrigants, exhibited significant antimicrobial activity and low cytocompatibility at dilutions greater than 0.5%.

Efficacy of novel aqueous photo-chlorine dioxide against a human norovirus surrogate, bacteriophage MS2 and Clostridium difficile endospores, in suspension, on stainless steel and under greenhouse conditions

AIMS

The efficacy of a novel photochemical method for generating chlorine dioxide (photoClO₂ ) was evaluated against human noroviruses (HuNoV) surrogate, bacteriophage MS2, and Clostridium difficile endospores.

METHODS AND RESULTS

Chlorine dioxide was generated by mixing 1% sodium chlorite with 10 parts-per-million (ppm) Eosin Y and irradiating with a photo-activator-excitable light. PhotoClO₂ efficacy was assessed against bacteriophage MS2 and C. difficile endospores in suspension, on hard surfaces and greenhouse conditions under soiled and unsoiled conditions. The estimated effective photoClO₂ produced and consumed was 20·39 ± 0·16 ppm at a rate of 8·16 ppm per min in a 1% sodium chlorite solution. In suspension, MS2 phage was reduced by 3·35 and >5·10 log₁₀ PFU per ml in 120 and 90 min, with and without soil, respectively. At the same time, when dried on stainless steel surface, MS2 phage was reduced by >4·53 log₁₀ PFU per carrier in 30 min under both conditions. On the other hand, C. difficile endospores in suspension were reduced by 2·26 and 3·65 log₁₀ CFU per ml in 120 min with and without soiling, respectively. However, on stainless steel surface, maximal reductions of the C. difficile endospores were 0·8 and 1·5 log₁₀ CFU per carrier with and without soiling, respectively, and a maximal reduction of 2·97 log₁₀ CFU per carrier under greenhouse conditions at 24 h.

CONCLUSIONS

Overall, photoClO₂ showed promise as a technology to control HuNoV contamination on environmental surfaces but requires further optimization and testing against C. difficile endospores.

SIGNIFICANCE AND IMPACT OF THE STUDY

Results from this investigation will serve as a model for how to generate and quantify photoClO₂ and how to appropriately evaluate this new class of disinfectants against environmentally resilient pathogens: viruses and bacterial endospores.

Efficacy of alcohol-based hand sanitizers against human norovirus using RNase-RT-qPCR with validation by human intestinal enteroid replication

Successful human norovirus (HuNoV) cultivation in stem cell‐derived human intestinal enteroids (HIE) was recently reported. The purpose of this study was to evaluate the anti‐HuNoV efficacy of two alcohol‐based commercial hand sanitizers and 60% ethanol by suspension assay using RNase‐RT‐qPCR, with subsequent validation of efficacy by HuNoV cultivation using the HIE model. In suspension, when evaluated by RNase‐RT‐qPCR, 60% ethanol resulted in less than one log₁₀ reduction in HuNoV genome equivalent copies (GEC) regardless of contact time (30 or 60s) or soil load. The two commercial products outperformed 60% ethanol regardless of contact time or soil load, providing 2·2–3·2 log₁₀ HuNoV GEC reductions by suspension assay. Product B could not be validated in the HIE model due to cytotoxicity. Following a 60s exposure, viral replication in the HIE model increased 1·9 ± 0·2 log₁₀ HuNoV GEC for the neutralization (positive) control and increased 0·9 ± 0·2 log₁₀ HuNoV GEC in challenged HIE after treatment with 60% ethanol. No HuNoV replication in HIE was observed after a 60 s exposure to Product A.

Effect of natural ageing and heat treatments on GII.4 norovirus binding to Histo-Blood Group Antigens

Human noroviruses (HuNoVs) are the leading cause of viral foodborne outbreaks worldwide. To date, no available methods can be routinely used to detect infectious HuNoVs in foodstuffs. HuNoVs recognize Histo-Blood Group Antigens (HBGAs) through the binding pocket (BP) of capsid protein VP1, which promotes infection in the host cell. In this context, the suitability of human HBGA-binding assays to evaluate the BP integrity of HuNoVs was studied on GII.4 virus-like particles (VLPs) and GII.4 HuNoVs during natural ageing at 20 °C and heat treatments. Our results demonstrate that this approach may reduce the over-estimation of potential infectious HuNoVs resulting from solely using the genome detection, even though some limitations have been identified. The specificity of HBGA-binding to the BP is clearly dependent on the HGBA type (as previously evidenced) and the ionic strength of the media without disturbing such interactions. This study also provides new arguments regarding the ability of VLPs to mimic HuNoV behavior during inactivation treatments. The BP stability of VLPs was at least 4.3 fold lower than that of HuNoVs at 20 °C, whereas capsids of both particles were disrupted at 72 °C. Thus, VLPs are relevant surrogates of HuNoVs for inactivation treatments inducing significant changes in the capsid structure.

Control of norovirus infection

PURPOSE OF REVIEW

The purpose of the review is to provide an update on control measures for norovirus (NoV), which is the most commonly implicated pathogen in acute gastroenteritis and outbreaks, causing major disruption in nurseries, schools, hospitals and care homes.

RECENT FINDINGS

Important developments include the discovery that virus particles, previously considered to be the infectious unit, also occur in clusters, which appear to be more virulent than individual virus particles; a working culture system using human stem-cell derived enteroids; promising results from early phase clinical trials of candidate NoV vaccines, which appear to be safe and immunogenic; chronic NoV affects patients with primary and secondary immune deficiencies. Although several treatments have been used none are supported by well designed clinical trials; infection control procedures are effective if properly implemented.

SUMMARY

NoV remains an important cause of morbidity and mortality. Although there are exciting developments on the vaccine front, the mainstay of control remains good hand hygiene, adherence to infection control procedures and limiting contamination of food, water and the wider environment. Once vaccines are available there will be important decisions to be made about how best to implement them.

Efficacy of Silver Dihydrogen Citrate and Steam Vapor against a Human Norovirus Surrogate, Feline Calicivirus, in Suspension, on Glass, and on Carpet

Carpets and other soft surfaces have been associated with prolonged and reoccurring human norovirus (HuNoV) outbreaks. Environmental hygiene programs are important to prevent and control HuNoV outbreaks. Despite our knowledge of HuNoV transmission via soft surfaces, no commercially available disinfectants have been evaluated on carpets. Our aim was to adapt a current standardized method for virucidal testing by assessing two disinfection technologies, silver dihydrogen citrate (SDC) and steam vapor, against one HuNoV surrogate, feline calicivirus (FCV), on wool and nylon carpets. First, we evaluated the effect of both technologies on the appearance of carpet. Next, we evaluated the efficacy of SDC in suspension and the efficacy of SDC and steam vapor against FCV on a glass surface, each with and without serum. Lastly, we tested both technologies on two types of carpet, wool and nylon. Both carpets exhibited no obvious color changes; however, SDC treatments left a residue while steam vapor left minor abrasions to fibers. SDC in suspension and on glass reduced FCV by 4.65 log10 and >4.66 log10 PFU, respectively, but demonstrated reduced efficacy in the presence of serum. However, SDC was only efficacious against FCV on nylon (3.62-log10 PFU reduction) and not wool (1.82-log10 PFU reduction). Steam vapor reduced FCV by >4.93 log10 PFU on glass in 10 s and >3.68 log10 PFU on wool and nylon carpet carriers in 90 s. There was a limited reduction of FCV RNA under both treatments compared to that of infectivity assays, but RNA reductions were higher in samples that contained serum.IMPORTANCE Human noroviruses (HuNoV) account for ca. 20% of all diarrheal cases worldwide. Disease symptoms may include diarrhea and vomit, with both known to contribute to transmission. The prevention and control of HuNoV are difficult because they are environmentally resilient and resistant to many disinfectants. Several field studies have linked both hard and soft surfaces to HuNoV outbreaks. However, many disinfectants efficacious against HuNoV surrogates are recommended for hard surfaces, but no commercially available products have demonstrated efficacy against these surrogates on soft surfaces. Our research objectives were to evaluate liquid and steam-based technologies in suspension and on hard surface carriers in addition to adapting and testing a protocol for assessing the virucidal effects of disinfection technologies on carpet carriers. These results will inform both the government and industry regarding a standard method for evaluating the virucidal effects of disinfectants on carpet while demonstrating their efficacy relative to suspension and hard-surface tests.

Alternative In Vitro Methods for the Determination of Viral Capsid Structural Integrity

Human norovirus exacts considerable public health and economic losses worldwide. Emerging in vitro cultivation advances are not yet applicable for routine detection of the virus. The current detection and quantification techniques, which rely primarily on nucleic acid amplification, do not discriminate infectious from non-infectious viral particles. The purpose of this article is to present specific details on recent advances in techniques used together in order to acquire further information on the infectivity status of viral particles. One technique involves assessing binding of a norovirus ssDNA aptamer to capsids. Aptamers have the advantage of being easily synthesized and modified, and are inexpensive and stable. Another technique, dynamic light scattering (DLS), has the advantage of observing capsid behavior in solution. Electron microscopy allows for visualization of the structural integrity of the viral capsids. Although promising, there are some drawbacks to each technique, such as non-specific aptamer binding to positively-charged molecules from sample matrices, requirement of purified capsid for DLS, and poor sensitivity for electron microscopy. Nonetheless, when these techniques are used in combination, the body of data produced provides more comprehensive information on norovirus capsid integrity that can be used to infer infectivity, information which is essential for accurate evaluation of inactivation methods or interpretation of virus detection. This article provides protocols for using these methods to discriminate infectious human norovirus particles.

Nanobodies targeting norovirus capsid reveal functional epitopes and potential mechanisms of neutralization

Norovirus is the leading cause of gastroenteritis worldwide. Despite recent developments in norovirus propagation in cell culture, these viruses are still challenging to grow routinely. Moreover, little is known on how norovirus infects the host cells, except that histo-blood group antigens (HBGAs) are important binding factors for infection and cell entry. Antibodies that bind at the HBGA pocket and block attachment to HBGAs are believed to neutralize the virus. However, additional neutralization epitopes elsewhere on the capsid likely exist and impeding the intrinsic structural dynamics of the capsid could be equally important. In the current study, we investigated a panel of Nanobodies in order to probe functional epitopes that could trigger capsid rearrangement and/ or interfere with HBGA binding interactions. The precise binding sites of six Nanobodies (Nano-4, Nano-14, Nano-26, Nano-27, Nano-32, and Nano-42) were identified using X-ray crystallography. We showed that these Nanobodies bound on the top, side, and bottom of the norovirus protruding domain. The impact of Nanobody binding on norovirus capsid morphology was analyzed using electron microscopy and dynamic light scattering. We discovered that distinct Nanobody epitopes were associated with varied changes in particle structural integrity and assembly. Interestingly, certain Nanobody-induced capsid morphological changes lead to the capsid protein degradation and viral RNA exposure. Moreover, Nanobodies employed multiple inhibition mechanisms to prevent norovirus attachment to HBGAs, which included steric obstruction (Nano-14), allosteric interference (Nano-32), and violation of normal capsid morphology (Nano-26 and Nano-85). Finally, we showed that two Nanobodies (Nano-26 and Nano-85) not only compromised capsid integrity and inhibited VLPs attachment to HBGAs, but also recognized a broad panel of norovirus genotypes with high affinities. Consequently, Nano-26 and Nano-85 have a great potential to function as novel therapeutic agents against human noroviruses.

We determined the binding sites of six novel human norovirus specific Nanobodies (Nano-4, Nano-14, Nano-26, Nano-27, Nano-32, and Nano-42) using X-ray crystallography. The unique Nanobody recognition epitopes were correlated with their potential neutralizing capacities. We showed that one Nanobody (Nano-26) bound numerous genogroup II genotypes and interacted with highly conserved capsid residues. Four Nanobodies (Nano-4, Nano-26, Nano-27, and Nano-42) bound to occluded regions on the intact particles and impaired normal capsid morphology and particle integrity. One Nanobody (Nano-14) bound contiguous to the HBGA pocket and interacted with several residues involved in binding HBGAs. We found that the Nanobodies delivered multiple inhibition mechanisms, which included steric obstruction, allosteric interference, and disruption of the capsid stability. Our data suggested that the HBGA pocket might not be an ideal target for drug development, since the surrounding region is highly variable and inherently suffers from lack of conservation among the genetically diverse genotypes. Instead, we showed that the capsid contained other highly susceptible regions that could be targeted for virus inhibition.