Mechanisms of inactivation of poliovirus by chlorine dioxide and iodine

Mechanisms of action of microbicides commonly used in infection prevention and control

SUMMARYUnderstanding how commonly used chemical microbicides affect pathogenic microorganisms is important for formulation of microbicides. This review focuses on the mechanism(s) of action of chemical microbicides commonly used in infection prevention and control. Contrary to the typical site-specific mode of action of antibiotics, microbicides often act via multiple targets, causing rapid and irreversible damage to microbes. In the case of viruses, the envelope or protein capsid is usually the primary structural target, resulting in loss of envelope integrity or denaturation of proteins in the capsid, causing loss of the receptor-binding domain for host cell receptors, and/or breakdown of other viral proteins or nucleic acids. However, for certain virucidal microbicides, the nucleic acid may be a significant site of action. The region of primary damage to the protein or nucleic acid is site-specific and may vary with the virus type. Due to their greater complexity and metabolism, bacteria and fungi offer more targets. The rapid and irreversible damage to microbes may result from solubilization of lipid components and denaturation of enzymes involved in the transport of nutrients. Formulation of microbicidal actives that attack multiple sites on microbes, or control of the pH, addition of preservatives or potentiators, and so on, can increase the spectrum of action against pathogens and reduce both the concentrations and times needed to achieve microbicidal activity against the target pathogens.

Application of chlorine dioxide and its disinfection mechanism

Chlorine dioxide (ClO2) is a strong oxidizing agent and an efficient disinfectant. Due to its broad-spectrum bactericidal properties, good inactivation effect on the vast majority of bacteria and pathogenic microorganisms, low resistance to drugs, and low generation of halogenated by-products, chlorine dioxide is widely used in fields such as water purification, food safety, medical and public health, and living environment. This review introduced the properties and application status of chlorine dioxide, compared the action mode, advantages and disadvantages of various disinfectants. The mechanism of chlorine dioxide inactivating bacteria, fungi and viruses were reviewed. The lethal target of chlorine dioxide to bacteria and fungi is to destroy the structure of cell membrane, change the permeability of cell membrane, and make intracellular substances flow out, leading to their death. The lethal targets for viruses are the destruction of viral protein capsids and the degradation of RNA fragments. The purpose of this review is to provide more scientific guidance for the application of chlorine dioxide disinfectants.

Recommendations for the Cleaning of Endocavity Ultrasound Transducers Between Patients

The COVID-19 pandemic highlighted the importance of infection prevention and control measures for all medical procedures, including ultrasound examinations. As the use of ultrasound increases across more medical modalities, including point-of-care ultrasound, so does the risk of possible transmission from equipment to patients and patients to patients. This is particularly relevant for endocavity transducers, such as trans-vaginal, trans-rectal and trans-oesophageal, which could be contaminated with organisms from blood, mucosal, genital or rectal secretions. This article proports to update the WFUMB 2017 guidelines which focussed on the cleaning and disinfection of trans-vaginal ultrasound transducers between patients.

Mitigation of viruses of concern and bacteriophage surrogates via common unit processes for water reuse: A meta-analysis

Water reuse is a growing global reality. In regulating water reuse, viruses have come to the fore as key pathogens due to high shedding rates, low infectious doses, and resilience to traditional wastewater treatments. To demonstrate the high log reductions required by emerging water reuse regulations, cost and practicality necessitate surrogates for viruses for use as challenge organisms in unit process evaluation and monitoring. Bacteriophage surrogates that are mitigated to the same or lesser extent than viruses of concern are routinely used for individual unit process testing. However, the behavior of these surrogates over a multi-barrier treatment train typical of water reuse has not been well-established. Toward this aim, we performed a meta-analysis of log reductions of common bacteriophage surrogates for five treatment processes typical of water reuse treatment trains: advanced oxidation processes, chlorination, membrane filtration, ozonation, and ultraviolet (UV) disinfection. Robust linear regression was applied to identify a range of doses consistent with a given log reduction of bacteriophages and viruses of concern for each treatment process. The results were used to determine relative conservatism of surrogates. We found that no one bacteriophage was a representative or conservative surrogate for viruses of concern across all multi-barrier treatments (encompassing multiple mechanisms of virus mitigation). Rather, a suite of bacteriophage surrogates provides both a representative range of inactivation and information about the effectiveness of individual processes within a treatment train. Based on the abundance of available data and diversity of virus treatability using these five key water reuse treatment processes, bacteriophages MS2, phiX174, and Qbeta were recommended as a core suite of surrogates for virus challenge testing.

Evaluation of chlorine dioxide in liquid state and in gaseous state as virucidal agent against avian influenza virus and infectious bronchitis virus

The antiviral activity of chlorine dioxide (ClO2) in liquid (ClO2 gas dissolved liquid) and gaseous state against avian influenza virus (AIV) and infectious bronchitis virus (IBV) was evaluated. To evaluate the effect of ClO2 in liquid state, suspension tests (10 ppm) and carrier tests in dropping / wiping techniques (100 ppm) were performed. In the suspension test, virus titers were reduced below the detection limit within 15 sec after treatment, in spite of the presence of an accompanying organic matter. In the carrier test by dropping technique, AIV and IBV were reduced to below the detection limit in 1 and 3 min, respectively. Following wiping technique, no virus was detected in the wiping sheets after 30 sec of reaction. Both viruses adhering to the carriers were also reduced by 3 logs, thereby indicating that they were effectively inactivated. In addition, the effect of ClO2 gas against IBV in aerosols was evaluated. After the exposure of sprayed IBV to ClO2 gas for a few seconds, 94.2% reduction of the virus titer was observed, as compared to the pre-treatment control. Altogether, hence, ClO2 has an evident potential to be an effective disinfectant for the prevention and control of AIV and IBV infections on poultry farms.

A review on disinfection methods for inactivation of waterborne viruses

Water contamination is a global health problem, and the need for safe water is ever-growing due to the public health implications of unsafe water. Contaminated water could contain pathogenic bacteria, protozoa, and viruses that are implicated in several debilitating human diseases. The prevalence and survival of waterborne viruses differ from bacteria and other waterborne microorganisms. In addition, viruses are responsible for more severe waterborne diseases such as gastroenteritis, myocarditis, and encephalitis among others, hence the need for dedicated attention to viral inactivation. Disinfection is vital to water treatment because it removes pathogens, including viruses. The commonly used methods and techniques of disinfection for viral inactivation in water comprise physical disinfection such as membrane filtration, ultraviolet (UV) irradiation, and conventional chemical processes such as chlorine, monochloramine, chlorine dioxide, and ozone among others. However, the production of disinfection by-products (DBPs) that accompanies chemical methods of disinfection is an issue of great concern due to the increase in the risks of harm to humans, for example, the development of cancer of the bladder and adverse reproductive outcomes. Therefore, this review examines the conventional disinfection approaches alongside emerging disinfection technologies, such as photocatalytic disinfection, cavitation, and electrochemical disinfection. Moreover, the merits, limitations, and log reduction values (LRVs) of the different disinfection methods discussed were compared concerning virus removal efficiency. Future research needs to merge single disinfection techniques into one to achieve improved viral disinfection, and the development of medicinal plant-based materials as disinfectants due to their antimicrobial and safety benefits to avoid toxicity is also highlighted.

Disinfection efficacy and mechanism of olanexidine gluconate against norovirus

BACKGROUND

The purpose of this study was to evaluate the virucidal activity of a new olanexidine-containing formulation for hand hygiene (olanexidine gluconate hand rub; OLG-HR) against non-enveloped viruses and to understand its mechanism of action.

METHODS

The virucidal activities of OLG-HR against two strains of caliciviruses and three adenovirus serotypes were evaluated through suspension tests. Also, virus-like particles were used to predict the effect of olanexidine gluconate on virus particle structure.

RESULTS

The results of suspension tests under conditions with and without interfering substances (1.5% BSA) indicated that OLG-HR had a broad-spectrum effect against non-enveloped viruses, and the virucidal effect was unaffected by organic contaminants. Furthermore, olanexidine inhibited the binding ability of virus-like particles to the binding receptor of human norovirus and increased the aggregation of virus-like particles in a dose-dependent manner. Transmission electron microscopy showed that the morphology of the virus-like particles was affected by exposure to olanexidine, indicating that the protein-denaturing effect of olanexidine gluconate caused the loss of receptor-binding capability of the viral capsid protein.

CONCLUSIONS

This study suggests that olanexidine gluconate is a potential biological and environmental disinfectant against norovirus and adenovirus.

Effectiveness of Disinfection with Chlorine Dioxide on Respiratory Transmitted, Enteric, and Bloodborne Viruses: A Narrative Synthesis

A viral spread occurrence such as the SARS-CoV-2 pandemic has prompted the evaluation of different disinfectants suitable for a wide range of environmental matrices. Chlorine dioxide (ClO₂) represents one of the most-used virucidal agents in different settings effective against both enveloped and nonenveloped viruses. This narrative synthesis is focused on the effectiveness of ClO₂ applied in healthcare and community settings in order to eliminate respiratory transmitted, enteric, and bloodborne viruses. Influenza viruses were reduced by 99.9% by 0.5–1.0 mg/L of ClO₂ in less than 5 min. Higher concentration (20 mg/L) eliminated SARS-CoV-2 from sewage. ClO₂ concentrations from 0.2 to 1.0 mg/L ensured at least a 99% viral reduction of AD40, HAV, Coxsackie B5 virus, and other enteric viruses in less than 30 min. Considering bloodborne viruses, 30 mg/L of ClO₂ can eliminate them in 5 min. Bloodborne viruses (HIV-1, HCV, and HBV) may be completely eliminated from medical devices and human fluids after a treatment with 30 mg/L of ClO₂ for 30 min. In conclusion, ClO₂ is a versatile virucidal agent suitable for different environmental matrices.

Kinetics and Mechanisms of Virus Inactivation by Chlorine Dioxide in Water Treatment: A Review

Chlorine dioxide (ClO₂), an alternative disinfectant to chlorine, has been widely applied in water and wastewater disinfection. This paper aims at presenting an overview of the inactivation kinetics and mechanisms of ClO₂ with viruses. The inactivation efficiencies vary greatly among different virus species. The inactivation rates for different serotypes within a family of viruses can differ by over 284%. Generally, to achieve a 4-log removal, the exposure doses, also being referred to as Ct values (mutiplying the concentration of ClO₂ and contact time) vary in the range of 0.06-10 mg L^-1 min. Inactivation kinetics of viruses show two phases: an initial rapid inactivation phase followed by a tailing phase. Inactivation rates of viruses increase as pH or temperature increases, but show different trends with increasing concentrations of dissolved organic matter (DOM). Both damages in viral proteins and in the 5' noncoding region within the genome contribute to virus inactivation upon ClO₂ disinfection.

Biofouling of Polyamide Membranes: Fouling Mechanisms, Current Mitigation and Cleaning Strategies, and Future Prospects

Reverse osmosis and nanofiltration systems are continuously challenged with biofouling of polyamide membranes that are used almost exclusively for these desalination techniques. Traditionally, pretreatment and reactive membrane cleanings are employed as biofouling control methods. This in-depth review paper discusses the mechanisms of membrane biofouling and effects on performance. Current industrial disinfection techniques are reviewed, including chlorine and other chemical and non-chemical alternatives to chlorine. Operational techniques such as reactive membrane cleaning are also covered. Based on this review, there are three suggested areas of additional research offering promising, polyamide membrane-targeted biofouling minimization that are discussed. One area is membrane modification. Modification using surface coatings with inclusion of various nanoparticles, and graphene oxide within the polymer or membrane matrix, are covered. This work is in the infancy stage and shows promise for minimizing the contributions of current membranes themselves in promoting biofouling, as well as creating oxidant-resistant membranes. Another area of suggested research is chemical disinfectants for possible application directly on the membrane. Likely disinfectants discussed herein include nitric oxide donor compounds, dichloroisocyanurate, and chlorine dioxide. Finally, proactive cleaning, which aims to control the extent of biofouling by cleaning before it negatively affects membrane performance, shows potential for low- to middle-risk systems.

Pretreatment with propidium monoazide/sodium lauroyl sarcosinate improves discrimination of infectious waterborne virus by RT-qPCR combined with magnetic separation

RT-qPCR allows sensitive detection of viral particles of both infectious and noninfectious viruses in water environments, but cannot discriminate non-infectious from infectious viruses. In this study, we aimed to optimize RT-qPCR-based detection of chlorine-inactivated human norovirus (NoV) and pepper mild mottle virus (PMMoV) in suspension by pretreatment with an optimal combination of a monoazide and a detergent that can efficiently penetrate damaged viral capsids. Four methods were compared to determine the efficacy of chlorine disinfection (at 1, 3, and 5 min mg/L): (A) RT-qPCR alone, (B) RT-qPCR assay preceded by magnetic bead separation for enrichment of viral particles (MBS-RT-qPCR), (C) MBS-RT-qPCR assay with pretreatment with propidium monoazide (PMA-MBS-RT-qPCR), and (D) PMA-MBS-RT-qPCR assay with pretreatment with sodium lauroyl sarcosinate (INCI-PMA-MBS-RT-qPCR). On the basis of a PMA optimization assay, 200 and 300 μM PMA were used in subsequent experiments for NoV GII.4 and PMMoV, respectively. Optimal INCI concentrations, having minimal influence on NoV GII.4 and PMMoV, were found to be 0.5% and 0.2% INCI, respectively. For NoV GII.4, there were significant differences (P < 0.05) in log₁₀ genome copies between the PMA-treated and the INCI + PMA-treated samples (log₁₀ genome copies differed by 1.11 and 0.59 log₁₀ for 3 and 5 min mg/L of chlorine, respectively). For PMMoV, INCI induced differences in log₁₀ genome copies of 0.92, 1.18, and 1.86, for 1, 3, and 5 min mg/L of chlorine, respectively. Overall, the results of this study indicate that an optimal combination of PMA and INCI could be very useful for evaluating disinfection methods in water treatment strategies.

Cross-Resistance of UV- or Chlorine Dioxide-Resistant Echovirus 11 to Other Disinfectants

The emergence of waterborne viruses with resistance to disinfection has been demonstrated in the laboratory and in the environment. Yet, the implications of such resistance for virus control remain obscure. In this study we investigate if viruses with resistance to a given disinfection method exhibit cross-resistance to other disinfectants. Chlorine dioxide (ClO₂)- or UV-resistant populations of echovirus 11 were exposed to five inactivating treatments (free chlorine, ClO₂, UV radiation, sunlight, and heat), and the extent of cross-resistance was determined. The ClO₂-resistant population exhibited cross-resistance to free chlorine, but to none of the other inactivating treatments tested. We furthermore demonstrated that ClO₂ and free chlorine act by a similar mechanism, in that they mainly inhibit the binding of echovirus 11 to its host cell. As such, viruses with host binding mechanisms that can withstand ClO₂ treatment were also better able to withstand oxidation by free chlorine. Conversely, the UV-resistant population was not significantly cross-resistant to any other disinfection treatment. Overall, our results indicate that viruses with resistance to multiple disinfectants exist, but that they can be controlled by inactivating methods that operate by a distinctly different mechanism. We therefore suggest to utilize two disinfection barriers that act by different mechanisms in order to control disinfection-resistant viruses.

Resistance of Echovirus 11 to ClO2 Is Associated with Enhanced Host Receptor Use, Altered Entry Routes, and High Fitness

Waterborne viruses can exhibit resistance to common water disinfectants, yet the mechanisms that allow them to tolerate disinfection are poorly understood. Here, we generated echovirus 11 (E11) with resistance to chlorine dioxide (ClO₂) by experimental evolution, and we assessed the associated genotypic and phenotypic traits. ClO₂ resistance emerged after E11 populations were repeatedly reduced (either by ClO₂-exposure or by dilution) and then regrown in cell culture. The resistance was linked to an improved capacity of E11 to bind to its host cells, which was further attributed to two potential causes: first, the resistant E11 populations possessed mutations that caused amino acid substitutions from ClO₂-labile to ClO₂-stable residues in the viral proteins, which likely increased the chemical stability of the capsid toward ClO₂. Second, resistant E11 mutants exhibited the capacity to utilize alternative cell receptors for host binding. Interestingly, the emergence of ClO₂ resistance resulted in an enhanced replicative fitness compared to the less resistant starting population. Overall this study contributes to a better understanding of the mechanism underlying disinfection resistance in waterborne viruses, and processes that drive resistance development.

The use of ozonized oil in the treatment of dermatophitosis caused by microsporum canis in rabbits

The ozone is effective against most microorganisms due to its high oxidant power. Low concentrations and short-term contact are sufficient to inactivate bacteria, mold, yeast, parasites, seaweeds, protozoa and fungi. Microsporum canis is an important agent of dermatophitosis in human and animal. The aim of the current study was to assess the efficacy of ozonized oil over Microsporum canis in rabbits. Eighteen male New Zealand white rabbits, weight ranging from 2 to 3.2 kg were depilated in the cranial dorso-lateral and right caudal, and cranial and left caudal regions. The regions were inoculated with Microsporum canis, excepting the right caudal region, and were denominated TM, O, OM and M, respectively. After seven days, the treatment of lesions in TM began with 0.12g of terbinaphine 1% cream; in OM and O with 0.12g of ozonized oil; all animals were treated once a day for 28 days. Region M was not treated. Material was collected from those regions for cultivation in Sabouraud agar at day 28 of treatment. In the evolution of the treatment with terbinaphine, of 14 contaminated regions with Microsporum canis ten evolved to cure. With the ozonized oil, of 15 contaminations, four were cured. Clinically, that is, the macroscopic evaluation of lesions showed improvement in the TM and OM treated regions. We can conclude that there was statistical evidence of the protection action of the oil against the dermatophyte.

Chlorine dioxide inactivation of enterovirus 71 in water and its impact on genomic targets

To control the waterborne transmission of enterovirus 71(EV71), which is associated with hand foot and mouth disease (HFMD), it is essential to know the inactivation effectiveness of disinfectants on EV71 in water. In this article, we present a comparative analysis of the effects on EV71 following exposure to chlorine dioxide (ClO2) under different doses, pH, and temperature conditions. We show that the EV71 exhibited strong resistance to ClO2 (more than the MS2 standard) and that Ct value ranges required for a 4-log reduction of EV71 in buffered, disinfectant demand-free water at pH 7.2 and 20 °C by ClO2 were 4.24-6.62 mg/L·min according to the efficiency factor Hom model. ClO2 inactivation of the virus was temperature- and pH-dependent. The virucidal efficiency was higher at pH 8.2 than at pH 5.6 and pH 7.2 and higher at 36 °C than at 4 and 20 °C. In addition, we also observed the impact of ClO2 on the entire viral genome using RT-PCR, which indicated that the 5' noncoding region (5'-NCR) within the EV71 genome, specifically the 1-118 nt region, was the most easily damaged by ClO2 and correlated with viral infectivity. Our study has not only provided guidelines for EV71 disinfection strategies of waste and drinking water, but also confirmed the importance of the 5'-NCR for EV71 infectivity and may demonstrate a general inactivation by ClO2 of enteric virus by damaging the 5'-NCR. Furthermore, 5'-NCR can be used as a target region for PCR to investigate infectious virus contamination in environmental water and evaluate the inactivation effects of ClO2.

Subtle differences in virus composition affect disinfection kinetics and mechanisms

Viral disinfection kinetics have been studied in depth, but the molecular-level inactivation mechanisms are not understood. Consequently, it is difficult to predict the disinfection behavior of nonculturable viruses, even when related, culturable viruses are available. The objective of this work was to determine how small differences in the composition of the viral genome and proteins impact disinfection. To this end, we investigated the inactivation of three related bacteriophages (MS2, fr, and GA) by UV254, singlet oxygen ((1)O2), free chlorine (FC), and chlorine dioxide (ClO2). Genome damage was quantified by PCR, and protein damage was assessed by quantitative matrix-assisted laser desorption ionization (MALDI) mass spectrometry. ClO2 caused great variability in the inactivation kinetics between viruses and was the only treatment that did not induce genome damage. The inactivation kinetics were similar for all viruses when treated with disinfectants possessing a genome-damaging component (FC, (1)O2, and UV254). On the protein level, UV254 subtly damaged MS2 and fr capsid proteins, whereas GA's capsid remained intact. (1)O2 oxidized a methionine residue in MS2 but did not affect the other two viruses. In contrast, FC and ClO2 rapidly degraded the capsid proteins of all three viruses. Protein composition alone could not explain the observed degradation trends; instead, molecular dynamics simulations indicated that degradation is dictated by the solvent-accessible surface area of individual amino acids. Finally, despite the similarities of the three viruses investigated, their mode of inactivation by a single disinfectant varied. This explains why closely related viruses can exhibit drastically different inactivation kinetics.

Chemometric analysis of the consumption of oral rinse chlorite (ClO2-) by human salivary biomolecules

OBJECTIVES

Oral rinse formulations containing chlorite anion (ClO(2)(-)) as an active agent exert a range of valuable oral healthcare activities. However, salivary biomolecules which chemically react with this oxidant can, at least in principle, serve as potentially significant barriers to these therapeutic properties in the oral environment. Therefore, in this investigation, we have explored the extent of ClO(2)(-) consumption by biomolecules which scavenge this agent in human salivary supernatants (HSSs) in vitro.

MATERIALS AND METHODS

HSS samples were equilibrated with oral rinse formulations containing this active agent (30 s at 35 °C in order to mimic oral rinsing episodes). Differential spectrophotometric and ion-pair reversed-phase high-performance liquid chromatographic analyses were employed to determine residual ClO(2)(-) in these admixtures.

RESULTS

Bioanalytical data acquired revealed the rapid consumption of ClO(2)(-) by biomolecular electron donors and/or antioxidants present in HSS samples. Mean ± 95 % confidence interval (CI) consumption levels of 7.14 ± 0.69 and 5.34 ± 0.69 % of the total ClO(2)(-) available were found for oral rinse products containing 0.10 and 0.40 % (w/v) ClO(2)(-), respectively. A mixed model analysis-of-variance performed on experimental data acquired demonstrated highly-significant differences between oral rinse ClO(2)(-) contents (p < 0.0001), trial participants (p < 0.001) and sampling days-within-participants (p < 0.001), and also revealed non-additive ClO(2)(-)-scavenging responses of participants' HSSs to increases in the oral rinse content of this oxidant (p < 0.0001). A slower, second phase of the reaction process (t (1/2) = 1.7-2.8 h) involved the oxidative consumption of salivary urate.

CONCLUSIONS

These data clearly demonstrate that for recommended 30 s oral rinsing episodes performed at physiological temperature, <10 % of the total oral rinse ClO(2)(-) available is chemically and/or reductively consumed by HSS biomolecules for both oral rinse formulations investigated.

CLINICAL RELEVANCE

These observations are of much clinical significance in view of the retention of these products' active agent, i.e. <10 % of ClO(2)(-) is consumed by HSS biomolecules within recommended 30 s oral rinsing episodes, and hence, the bulk of this oxyhalogen oxidant (>90 %) may effectively exert its essential microbicidal, anti-periodontal and oral malodour-neutralising actions.

The 40-80 nt region in the 5'-NCR of genome is a critical target for inactivating poliovirus by chlorine dioxide

Chemical disinfection is the most common method used to inactivate viruses from drinking water throughout the world. In this study, cell culture, ELISA, RT-PCR, and spot hybridization were employed to investigate the mechanism underlying chlorine dioxide (ClO(2) )-induced inactivation of Poliovirus type 1 (PV1), which was also confirmed by recombinant viral genome RNA infection models. The results suggested that ClO(2) inactivated PV1 primarily by disrupting the 5'-non-coding region (5'-NCR) of the PV1 genome. Further study revealed that ClO(2) degraded specifically the 40-80 nucleotides (nt) region in the 5'-NCR. Recombinant viral genome RNA infection models confirmed that PV1 RNA lacking this 40-80 nt region was not infectious. This study not only elucidated the mechanism of PV1 inactivation by ClO(2), but also defined the critical genetic target for the disinfectant to inactivate Poliovirus. This study also provides a strategy by which rapid, accurate, and molecular methods based on sensitive genetic targets may be established for evaluating the effects of disinfectants on viruses.

Virus disinfection mechanisms: the role of virus composition, structure, and function

Drinking waters are treated for enteric virus via a number of disinfection techniques including chemical oxidants, irradiation, and heat, however the inactivation mechanisms during disinfection remain elusive. Owing to the fact that a number of significant waterborne virus strains are not readily culturable in vitro at this time (e.g. norovirus, hepatitis A), the susceptibility of these viruses to disinfection is largely unknown. An in-depth understanding of the mechanisms involved in virus inactivation would aid in predicting the susceptibility of non-culturable virus strains to disinfection and would foster the development of improved disinfection methods. Recent technological advances in virology research have provided a wealth of information on enteric virus compositions, structures, and biological functions. This knowledge will allow for physical/chemical descriptions of virus inactivation and thus further our understanding of virus disinfection to the most basic mechanistic level.

Inactivation of bacteriophage MS2 upon exposure to very low concentrations of chlorine dioxide

This study investigates the effects of very low concentrations of ClO(2) applied in drinking water practice on the inactivation of bacteriophage MS2. Concentrations of 0.5 mg/L, 0.1 mg/L and 0.02 mg/L ClO(2) inactivated at least 5 log units of MS2 after an exposure time of approximately 20, 50 and 300 min respectively. When the ClO(2) concentration was as low as 0.005 mg/L, inactivation of 1 log unit MS2 was observed after 300 min exposure. Increasing the contact time to 24 h did not increase the inactivation any further. Non-linear inactivation kinetics (tailing) were observed for all conditions tested. Repeated addition of MS2 to the reactor showed that tailing was not caused by a reduction of the biocidal effect of ClO(2) during disinfection. The Modified Chick-Watson, the Efficiency Factor Hom (EFH) model and the Modified Cerf model, a modification of the two-fraction Cerf model, were fitted to the non-linear inactivation curves. Both the EFH and the modified Cerf model did fit accurately to the inactivation data of all experiments. The good fit of the Modified Cerf model supports the hypothesis of the presence of two subpopulations. Our study showed that ClO(2) is an effective disinfectant against model organism MS2, also at the low concentrations applied in water treatment practice. The inactivation kinetics followed a biphasic pattern due to the presence of a more ClO(2)-resistant subpopulation of MS2 phages, either caused by population heterogeneity or aggregation/adhesion of MS2.

Virucidal properties of metal oxide nanoparticles and their halogen adducts

Selected metal oxide nanoparticles are capable of strongly adsorbing large amounts of halogens (Cl(2), Br, I(2)) and mixed halogens. These solid adducts are relatively stable thermally, and they can be stored for long periods. However, in the open environment, they are potent biocides. Herein are described studies with a number of bacteriophage MS2, phiX174, and PRD-1 (virus examples). PRD-1 is generally more resistant to chemical disinfection, but in this paper it is shown to be very susceptible to selected interhalogen and iodine adducts of CeO(2), Al(2)O(3), and TiO(2) nanoparticles. Overall, the halogen adducts of TiO(2) and Al(2)O(3) were most effective. The mechanism of disinfection by these nanoparticles is not completely clear, but could include abrasive properties, as well as oxidative powers. A hypothesis that nanoparticles damage virons or stick to them and prevent binding to the host cell is a consideration that needs to be explored. Herein are reported comparative biocidal activities of a series of adducts and electron microscope images of before and after treatment.

Evaluation of the survivability of MS2 viral aerosols deposited on filtering face piece respirator samples incorporating antimicrobial technologies

Background

Respiratory protective devices exposed to pathogenic microorganisms present a potential source of transmission of infection during handling. In this study, the efficacy of 4 antimicrobial respirators to decontaminate MS2, a surrogate for pathogenic viruses, was evaluated and compared with control N95 filtering face piece respirators, which did not contain any known antimicrobial components.

Methods

MS2 containing droplet nuclei were generated using a Collison nebulizer and loaded onto respirator coupons at a face velocity of 13.2 cm/seconds for 30 minutes. The coupons were incubated at 2 different temperature and relative humidity (RH) conditions and analyzed for viable MS2 at different time intervals.

Results

Results showed that log₁₀ reduction of MS2 was not statistically significant (P > .05) between the control and antimicrobial respirator coupons, when stored at 22°C and 30% RH up to 20 hours. Coupons from 1 of the 4 antimicrobial respirators showed an average MS2 log₁₀ reduction of 3.7 at 37°C and 80% RH for 4 hours, which was statistically significant (P ≤ .05) compared with coupons from the control respirators.

Conclusion

Results from this study suggest that MS2 virus decontamination efficacy of antimicrobial respirators is dependent on the antimicrobial agent and storage conditions.

Viral Inactivation in Foods: A Review of Traditional and Novel Food-Processing Technologies

  Over one-half of foodborne illnesses are believed to be viral in origin. The ability of viruses to persist in the environment and foods, coupled with low infectious doses, allows even a small amount of contamination to cause serious problems. An increased incidence of foodborne illnesses and consumer demand for fresh, convenient, and safe foods have prompted research into alternative food-processing technologies. This review focuses on viral inactivation by both traditional processing technologies such as use of antimicrobial agents and the application of heat, and also novel processing technologies including high-pressure processing, ultraviolet- and gamma-irradiation, and pulsed electric fields. These industrially applicable control measures will be discussed in relation to the 2 most common causes of foodborne viral illnesses, hepatitis A virus and human noroviruses. Other enteric viruses, including adenoviruses, rotaviruses, aichi virus, and laboratory and industrial viral surrogates such as feline caliciviruses, murine noroviruses, bacteriophage MS2 and ΦX174, and virus-like particles are also discussed. The basis of each technology, inactivation efficacy, proposed mechanisms of viral inactivation, factors affecting viral inactivation, and applicability to the food industry with a focus on ready-to-eat foods, produce, and shellfish, are all featured in this review.

Plasma membrane damage to Candida albicans caused by chlorine dioxide (ClO2)

AIM

To investigate the plasma membrane damage of chlorine dioxide (ClO(2)) to Candida albicans ATCC10231 at or below the minimal fungicidal concentration (MFC).

METHODS AND RESULTS

ClO(2) at MFC or below was adopted to treat the cell suspensions of C. albicans ATCC10231. Using transmission electron microscopy, no visible physiological alteration of cell shape and plasma membrane occurred. Potassium (K(+)) leakages were significant; likewise, it showed time- and dose-dependent increases. However, adenosine triphosphate (ATP) leakages were very slight. Research shows that when 99% of the cells were inactivated, the leakage was measured at 0.04% of total ATP. Compared with the mortality-specific fluorescent dye of DiBAC(4)(3), majority of the inactivated cells were poorly stained by propidium iodide, another mortality-specific fluorescent dye which can be traced by flow cytometry.

CONCLUSION

At or below MFC, ClO(2) damages the plasma membranes of C. albicans mainly by permeabilization, rather than by the disruption of their integrity. K(+) leakage and the concomitant depolarization of the cell membrane are some of the critical events.

SIGNIFICANCE AND IMPACT OF THE STUDY

These insights into membrane damages are helpful in understanding the action mode of ClO(2).

Degradation of the Poliovirus 1 genome by chlorine dioxide

AIMS

This study was undertaken to gain an understanding of the factors that influence viral RNA degradation in the presence of chlorine dioxide (ClO(2)), which will be very useful in helping to define the significance of the presence of the viral genome in disinfected water.

METHODS AND RESULTS

We focused our investigation on the influence of ClO(2) on extracted RNA on the one hand, and on the infectious virus on the other. Our first results show that RNA degradation, like viral inactivation, is dose dependent. The influence of the spatial organization of the targeted genomic sequence, as well as that of its size and location (and/or sequence) on degradation of the Poliovirus 1 genome by ClO(2), was studied using real-time reverse transcriptase-polymerase chain reaction (RT-PCR). The results show that the preferential sites of action of ClO(2) appear to be located in the untranslated regions, 5'- and 3'-UTR, a phenomenon influenced by both the presence of secondary structures and the genomic sequence in these regions. Our results also reveal a rapid decrease of infectious particles quantified by the cell culture for the applied dose. Comparison between cell culture and real-time PCR for viral detection reveals disagreement following disinfection treatment, even for the largest targeted fragment (a 6,989-base fragment representing the quasi-whole viral genome).

CONCLUSIONS

The detection of genome fragments is insufficient to confirm the presence of the infectious virus, as each targeted fragment shows a different sensitivity. Hence, the smallest targeted fragment (76 bp) persisted throughout the analysis period, while the longest targeted fragment (6,989 bp) disappeared very rapidly. Highly sensitive regions (i.e. 5'- and 3'-UTR) should be targeted to avoid an overestimation of the risk of viral infection using molecular biology methods in water following disinfection. Further studies in this area are needed.

SIGNIFICANCE AND IMPACT OF THE STUDY

To date, it has not been possible to routinely apply virological controls to drinking water because of the time-consuming nature of the gold standard technique (cell culture) and its inability to detect all serotypes (e.g. Norovirus). Molecular techniques (e.g. real-time RT-PCR) constitute a solution to the rapid and specific detection of all the serotypes. However, ignorance of the mechanisms of viral degradation prevents the validation of PCR for the measurement of the risk of infection to humans following disinfection treatment.

Inactivation of enteric adenovirus and feline calicivirus by chlorine dioxide

Chlorine dioxide (ClO2) inactivation experiments were conducted with adenovirus type 40 (AD40) and feline calicivirus (FCV). Experiments were carried out in buffered, disinfectant demand-free water under high- and low-pH and -temperature conditions. Ct values (the concentration of ClO2 multiplied by contact time with the virus) were calculated directly from bench-scale experiments and from application of the efficiency factor Hom (EFH) model. AD40 Ct ranges for 4-log inactivation (Ct99.99%) at 5 degrees C were >0.77 to <1.53 mg/liter x min and >0.80 to <1.59 mg/liter x min for pH 6 and 8, respectively. For 15 degrees C AD40 experiments, >0.49 to <0.74 mg/liter x min and <0.12 mg/liter x min Ct99.99% ranges were observed for pH 6 and 8, respectively. FCV Ct99.99% ranges for 5 degrees C experiments were >20.20 to <30.30 mg/liter x min and >0.68 mg/liter x min for pH 6 and 8, respectively. For 15 degrees C FCV experiments, Ct99.99% ranges were >4.20 to <6.72 and <0.18 mg/liter x min for pH 6 and 8, respectively. Viral inactivation was higher at pH 8 than at pH 6 and at 15 degrees C than at 5 degrees C. Comparison of Ct values and inactivation curves demonstrated that the EFH model described bench-scale experiment data very well. Observed bench-scale Ct99.99% ranges and EFH model Ct99.99% values demonstrated that FCV is more resistant to ClO2 than AD40 for the conditions studied. U.S. Environmental Protection Agency guidance manual Ct99.99% values are higher than Ct99.99% values calculated from bench-scale experiments and from EFH model application.

Inactivation of enteric adenovirus and feline calicivirus by chlorine dioxide

Chlorine dioxide (ClO2) inactivation experiments were conducted with adenovirus type 40 (AD40) and feline calicivirus (FCV). Experiments were carried out in buffered, disinfectant demand-free water under high- and low-pH and -temperature conditions. Ct values (the concentration of ClO2 multiplied by contact time with the virus) were calculated directly from bench-scale experiments and from application of the efficiency factor Hom (EFH) model. AD40 Ct ranges for 4-log inactivation (Ct99.99%) at 5 degrees C were >0.77 to <1.53 mg/liter x min and >0.80 to <1.59 mg/liter x min for pH 6 and 8, respectively. For 15 degrees C AD40 experiments, >0.49 to <0.74 mg/liter x min and <0.12 mg/liter x min Ct99.99% ranges were observed for pH 6 and 8, respectively. FCV Ct99.99% ranges for 5 degrees C experiments were >20.20 to <30.30 mg/liter x min and >0.68 mg/liter x min for pH 6 and 8, respectively. For 15 degrees C FCV experiments, Ct99.99% ranges were >4.20 to <6.72 and <0.18 mg/liter x min for pH 6 and 8, respectively. Viral inactivation was higher at pH 8 than at pH 6 and at 15 degrees C than at 5 degrees C. Comparison of Ct values and inactivation curves demonstrated that the EFH model described bench-scale experiment data very well. Observed bench-scale Ct99.99% ranges and EFH model Ct99.99% values demonstrated that FCV is more resistant to ClO2 than AD40 for the conditions studied. U.S. Environmental Protection Agency guidance manual Ct99.99% values are higher than Ct99.99% values calculated from bench-scale experiments and from EFH model application.

Efficacy and Tolerability of ClO2‐Generating Gloves

The transmission of pathogenic microorganisms by the hands of workers continues to be a problem in the medical field and the food industry. Compliance with hand hygiene is often poor, and gloves may be contaminated after being donned and may transmit microorganisms. A novel, patented technology allows materials to be impregnated with microspheres that, when activated by light or moisture, generate ClO2 at sustained rates to produce a disinfecting microatmosphere. Gloves that were seeded with bacteria and then exposed to light were able to reduce the numbers of Staphylococcus aureus, Escherichia coli, Salmonella serotype Typhimurium, and Listeria monocytogenes by 1-3 logs within 20 min, both on the gloves and on the hands of wearers. The gloves look and feel like their standard counterparts and were well tolerated in the Draize test. This technology holds promise for reducing cross-contamination and the transmission of pathogens in the medical and food handling environments.

Mechanisms of inactivation of hepatitis A virus in water by chlorine dioxide

In this study, to elucidate the mechanisms of inactivation of hepatitis A virus (HAV) by chlorine dioxide, cell culture, enzyme-linked immunosorbent assay (ELISA), and long-overlapping RT-PCR were used to detect the infectivity, antigenicity, and entire genome of HAV before and after disinfection. The results revealed the complete inactivation of infectivity after a 10-min exposure to 7.5mg of chlorine dioxide per liter; and the highest level of sensitivity in the 5'non-translated regions (5'NTR) (the sequence from bp 1 to 671), inactivation of which took as much time as the inactivation of infectivity of HAV by chlorine dioxide; the complete destruction of antigenicity after a 10-min exposure to 7.5mg of chlorine dioxide per liter. It is suggested that the inactivation mechanism of HAV by chlorine dioxide was due to the loss of the 5'NTR and/or destruction of the antigenicity, which is not similar to that of chlorine (Appl Environ Microbiol 68: 4951).

Evaluation of ultrasonic scaling unit waterline contamination after use of chlorine dioxide mouthrinse lavage

BACKGROUND

An infection control problem in dental operatories which is not fully controlled is waterline contamination by heterotrophic mesophilic bacteria. These bacteria are present in water supplies as a planktonic phase and adhere to the lumen of tubings as a biofilm comprised of their external cell surface glycocalyx and by production of extracellular carbohydrate polymers. The adherent film is most difficult to remove. The accumulated planktonic phase can be reduced significantly by flushing water from the lines before use in patient treatment, but will return when the equipment is idle through the accumulation of more planktonic phase and by slough of the biofilm surface-adsorbed phase not yet enmeshed in the carbohydrate matrix. Chlorine dioxide has antimicrobial activity against many bacteria, spores, and viruses. It is used in water supply treatment as a disinfectant and slime preventive and has an advantage over chlorine in that carcinogenic trihalomethanes are not generated.

METHODS

This study compared use of phosphate buffer-stabilized chlorine dioxide (0.1%) mouthrinse as a lavage in ultrasonic dental scaler units with the use of tap water as a control. Sterile water flushed through the units onto heterotrophic plate count (HPC) sampler plates was cultured 7 days at room temperature and colonies were counted at 12x. One test and one control unit were used for biopsy of internal tubing and scanning electron microscopy imaging.

RESULTS

The HPC counts, in colony forming units (CFU)/ml, were reduced 3- to 5-fold by flushing tap water through the units, but they returned after units were idle overnight. When phosphate-buffered chlorine dioxide mouthrinse was used as a lavage, CFU/ml were reduced 12- to 20-fold. Holding chlorine dioxide in waterlines overnight reduced recurrent buildup compared to water (P <0.05). Scanning electron microscopy images indicated a significant reduction of biofilm coverage by chlorine dioxide as compared to water (P<0.001).

CONCLUSIONS

Phosphate-buffered chlorine dioxide mouthrinse was effective in these short-term trials for control of waterline contamination in ultrasonic dental scaling units. It should prove as useful in dental professional waterline applications as it has in industrial uses for biofilm control.

Antibacterial activity of ozonized sunflower oil (Oleozon)

AIMS

To evaluate the antimicrobial effect of the ozonized sunflower oil (Oleozon) on different bacterial species isolated from different sites.

METHODS AND RESULTS

The effect of Oleozon on Mycobacteria, staphylococci, streptococci, enterococci, Pseudomonas and Escherichia coli was tested. The sunflower oil was ozonized at the Centro de Investigaciones del Ozone (CENIC, Havana, Cuba) by an ozone generator. MICs were determined by the agar dilution method. For Mycobacteria, the MIC of Oleozon was determined on solid medium by a microdrop agar proportion test. Oleozon showed antimicrobial activity against all strains analysed, with an MIC ranging from 1.18 to 9.5 mg ml-1.

CONCLUSION

Oleozon showed a valuable antimicrobial activity against all micro-organisms tested. Results suggest that Mycobacteria are more susceptible to Oleozon than the other bacteria tested.

SIGNIFICANCE AND IMPACT OF THE STUDY

The wide availability of sunflower oil makes Oleozon a competitive antimicrobial agent. These results should prompt the setting up of some clinical trials to compare Oleozon with other antimicrobial agents.

Inactivation of MS-2 phage and poliovirus in groundwater

Since temperature affects the inactivation rate of viruses in natural water systems, the aim of this study was to determine if a temperature shift could influence the structural integrity of model viruses. When crude lysates of MS-2 phage were seeded into groundwater microcosms and incubated at 27 degrees C, complete virus inactivation took place in eight days. The temperature was then shifted to 4 degrees C. Three days after the temperature shift, a two-log increase in virus titer (reactivation) occurred. However, when purified MS-2 lysates were added to groundwater microcosms, no reactivation was obtained. No reactivation of poliovirus took place when similar microcosm experiments were done. The sedimentation coefficients of MS-2 shifted from 80S to 58S, 48S, 37S, 32S, and 18S as inactivation proceeded in groundwater and distilled water controls. Similarly, the sedimentation coefficients of polioviruses changed from 156S to 142S, 135S, 117S, 105S, 95S, and 80 S as inactivation took place. There was no correlation between % virus inactivation and % decrease in virions with intact sedimentation coefficients, as reported earlier for poliovirus inactivated by chlorine. The results presented support our hypothesis that virus inactivation proceeds gradually, involving the rearrangement and (or) loss of capsomere components that may eventually lead to the ejection of nucleic acids. The intermediate particles generated as inactivation proceeds may be in a reversibly inactivated state, and may revert back to a fully infectious state when chemical components stabilize the virus particle.

Disinfection of hospital waste sludge using hypochlorite and chlorine dioxide

Hypochlorite and chlorine dioxide were used to disinfect hospital waste-water sludge. Their abilities to inactivate pathogenic micro-organisms were compared. Reductions in indigenous coliform organisms and Pseudomonas aeruginosa were estimated. The results indicate that hypochlorite is a better disinfectant than chlorine dioxide for coliforms. Higher disinfection efficiency was obtained by treating a lower concentration of sludge. In addition, a higher agitation speed gave a higher disinfection efficiency with hypochlorite. The disinfection efficiencies of both disinfectants were higher against settled sludge than against thickened sludge. Therefore, it is recommended that disinfection should be performed on settled sludge rather than in a thickening tank.

Multicomponent spectroscopic investigations of salivary antioxidant consumption by an oral rinse preparation containing the stable free radical species chlorine dioxide (ClO2.)

A multicomponent evaluation of the oxidative consumption of salivary biomolecules by a commercially-available oral rinse preparation containing an admixture of the stable free radical species chlorine dioxide (ClO2.) with chlorite anion (ClO2-) has been investigated using high resolution 1H NMR spectroscopy. The results obtained demonstrated that ClO2. and/or ClO2- present in this preparation effected the oxidative decarboxylation of salivary pyruvate (to acetate and CO2). Experiments conducted on chemical model systems confirmed the oxidative decarboxylation of pyruvate by this oral rinse, and also demonstrated that urate, thiocyanate anion, and the amino acids cysteine and methionine (precursors to volatile sulphur compounds responsible for oral malodour), were oxidatively consumed. The biochemical, periodontal and therapeutic significance of the results are discussed.

Ozone disinfection dynamics of enteric viruses provide evidence that infectious titer reduction is triggered by alterations to viral colloidal properties

The inactivation dynamics of three enteric virus species (polio-, rota- and parvovirus) were analysed in different aqueous suspensions by using O3 under continuous flow conditions. A mathematical model for the reaction rate of infectious titer reduction was proposed, based on the thermodynamic principles of phase behaviour of colloids suspended in aqueous environments. Up to a certain threshold dosage of residual ozone (RO), and depending on the type of test virus and the ionic or organic load in the stock suspension, the logarithm of the reaction rate constant of viral inactivation rate was observed to vary in a rather sigmoidal manner with log RO concentration. Data from photon correlation spectroscopy, electron microscopy and tensiometric analysis suggested that below the threshold RO, the pattern of virus inactivation dynamics reflects the varying potential of different-sized viral particles (VPs) to adsorb to the cellular monolayer. There is strong evidence that oxidant-induced surface activity of organic matter causes redistribution of VP infectivity. This hypothesis was statistically corroborated inasmuch as experimental inactivation data proved to be satisfactorily fitted by a logistic equation. It was concluded that viral infection, and thus viral inactivation, is a complex process which is governed largely by the classical laws of colloidal behaviour. The latter is suggested to appreciably determine the capability of inoculated VPs to infect host cultures. This notion may especially be cause for concern when regulatory requirements for virus disinfection are being based on titration results from in vitro testing procedures.

Efficacy of Nucleic Acid Probes for Detection of Poliovirus in Water Disinfected by Chlorine, Chlorine Dioxide, Ozone, and UV Radiation

MilliQ water was inoculated with poliovirus type 1 strain LSc-1 and was treated with disinfectants, including chlorine, chlorine dioxide, ozone, and UV light. No relationship between probes and plaque assays were seen, demonstrating that viral nucleic acids were not destroyed. These findings suggest that nucleic acid probes cannot distinguish between infectious and noninfectious viruses and cannot be used in the evaluation of treated waters.