Stability of Weakly Acidic Hypochlorous Acid Solution with Microbicidal Activity

C, Balcom P, Omole DO, Álvarez-Mejía C, López-Ramrez V, Gadgil A. Low-cost, local production of a safe and effective disinfectant for resource-constrained communities

Improved hygiene depends on the accessibility and availability of effective disinfectant solutions. These disinfectant solutions are unavailable to many communities worldwide due to resource limitations, among other constraints. Safe and effective chlorine-based disinfectants can be produced via simple electrolysis of salt water, providing a low-cost and reliable option for on-site, local production of disinfectant solutions to improve sanitation and hygiene. This study reports on a system (herein called "Electro-Clean") that can produce concentrated solutions of hypochlorous acid (HOCl) using readily available, low-cost materials. With just table salt, water, graphite welding rods, and a DC power supply, the Electro-Clean system can safely produce HOCl solutions (~1.5 liters) of up to 0.1% free chlorine (i.e.,1000 ppm) in less than two hours at low potential (5 V DC) and modest current (~5 A). Rigorous testing of free chlorine production and durability of the Electro-Clean system components, described here, has been verified to work in multiple locations around the world, including microbiological tests conducted in India and Mexico to confirm the biocidal efficacy of the Electro-Clean solution as a surface disinfectant. Cost estimates are provided for making HOCl locally with this method in the USA, India, and Mexico. Findings indicate that Electro-Clean is an affordable alternative to off-the-shelf commercial chlorinator systems in terms of first costs (or capital costs), and cost-competitive relative to the unit cost of the disinfectant produced. By minimizing dependence on supply chains and allowing for local production, the Electro-Clean system has the potential to improve public health by addressing the need for disinfectant solutions in resource-constrained communities.

Wastewater reuse in agriculture: Prospects and challenges

Sustainable water recycling and wastewater reuse are urgent nowadays considering water scarcity and increased water consumption through human activities. In 2015, United Nations Sustainable Development Goal 6 (UN SDG6) highlighted the necessity of recycling wastewater to guarantee water availability for individuals. Currently, wastewater irrigation (WWI) of crops and agricultural land appears essential. The present work overviews the quality of treated wastewater in terms of soil microbial activities, and discusses challenges and benefits of WWI in line with wastewater reuse in agriculture and aquaculture irrigation. Combined conventional-advanced wastewater treatment processes are specifically deliberated, considering the harmful impacts on human health arising from WWI originating from reuse of contaminated water (salts, organic pollutants, toxic metals, and microbial pathogens i.e., viruses and bacteria). The comprehensive literature survey revealed that, in addition to the increased levels of pathogen and microbial threats to human wellbeing, poorly-treated wastewater results in plant and soil contamination with toxic organic/inorganic chemicals, and microbial pathogens. The impact of long-term emerging pollutants like plastic nanoparticles should also be established in further studies, with the development of standardized analytical techniques for such hazardous chemicals. Likewise, the reliable, long-term and extensive judgment on heavy metals threat to human beings's health should be explored in future investigations.

Scalability of advanced oxidation processes (AOPs) in industrial applications: A review

Disinfection and decontamination of water by application of oxidisers is an essential treatment step across numerous industrial sectors including potable supply and industry waste management, however, could be greatly enhanced if operated as advanced oxidation processes (AOPs). AOPs destroy contaminants including pathogens by uniquely harnessing radical chemistry. Despite AOPs offer great practical opportunities, no reviews to date have highlighted the critical AOP virtues that facilitate AOPs' scale up under growing industrial demand. Hence, this review analyses the critical AOP parameters such as oxidant conversion efficiency, batch mode vs continuous-flow systems, location of radical production, radical delivery by advanced micro-/mesoporous structures and AOP process costs to assist the translation of progressing developments of AOPs into their large-scale applications. Additionally, the state of the art is analysed for various AOP inducing radical/oxidiser measurement techniques and their half-lives with a view to identify radicals/oxidisers that are suitable for in-situ production. It is concluded that radicals with short half-lives such as hydroxyl (10-4 μsec) and sulfate (30-40 μsec) need to be produced in-situ via continuous-flow reactors for their effective transport and dosing. Meanwhile, radicals/oxidisers with longer half-lives such as ozone (7-10 min), hydrogen peroxide (stable for several hours), and hypochlorous acid (10 min -17 h) need to be applied through batch reactor systems due to their relatively longer stability during transportation and dosing. Complex and costly synthesis as well as cytotoxicity of many micro-/mesoporous structures limit their use in scaling up AOPs, particularly to immobilising and delivering the short-lived hydroxyl and sulfate radicals to their point of applications. Overall, radical delivery using safe and advanced biocompatible micro-/mesoporous structures, radical conversion efficiency using advanced reactor design and portability of AOPs are priority areas of development for scaling up to industry.

Electrolyzed hypochlorous acid water exhibits potent disinfectant activity against various viruses through irreversible protein aggregation

It is essential to employ efficient measures to prevent the transmission of pathogenic agents during a pandemic. One such method involves using hypochlorous acid (HClO) solution. The oxidative properties of HClO water (HAW) can contribute to its ability to eliminate viral particles. Here, we examined a highly purified slightly acidic hypochlorous acid water (Hp-SA-HAW) obtained from the reverse osmosis membrane treatment of an electrolytically-generated SA-HAW for its anti-viral activity and mode of action on viral proteins. Hp-SA-HAW exhibited broad-spectrum antiviral effects against various viruses, including adenovirus, hepatitis B virus, Japanese encephalitis virus (JEV), and rotavirus. Additionally, Hp-SA-HAW treatment dose-dependently resulted in irreversibly aggregated multimers of the JEV envelope and capsid proteins. However, Hp-SA-HAW treatment had no discernible effect on viral RNA, indicating that Hp-SA-HAW acts against amino acids rather than nucleic acids. Furthermore, Hp-SA-HAW substantially reduced the infectivity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), including the ancestral variant and other multiple variants. Hp-SA-HAW treatment induced the aggregation of the SARS-CoV-2 spike and nuclear proteins and disrupted the binding of the purified spike protein of SARS-CoV-2 to human ACE2. This study demonstrates that the broad-spectrum virucidal activity of highly purified HClO is attributed to viral protein aggregation of virion via protein oxidation.

New Advances in Viral and Microorganism Disinfectants

Nanomaterials are used to develop simpler, cheaper, and faster methods for disease diagnosis [...].

In vitro activity of hypochlorous acid generating electrochemical bandage against monospecies and dual-species bacterial biofilms

AIMS

As antimicrobial resistance is on the rise, treating chronic wound infections is becoming more complex. The presence of biofilms in wound beds contributes to this challenge. Here, the activity of a novel hypochlorous acid (HOCl) producing electrochemical bandage (e-bandage) against monospecies and dual-species bacterial biofilms formed by bacteria commonly found in wound infections was assessed.

METHODS AND RESULTS

The system was controlled by a wearable potentiostat powered by a 3V lithium-ion battery and maintaining a constant voltage of + 1.5V Ag/AgCl, allowing continuous generation of HOCl. A total of 19 monospecies and 10 dual-species bacterial biofilms grown on polycarbonate membranes placed on tryptic soy agar (TSA) plates were used as wound biofilm models, with HOCl producing e-bandages placed over the biofilms. Viable cell counts were quantified after e-bandages were continuously polarized for 2, 4, 6, and 12 hours. Time-dependent reductions in colony forming units (CFUs) were observed for all studied isolates. After 12 hours, average CFU reductions of 7.75 ± 1.37 and 7.74 ± 0.60 log10 CFU/cm2 were observed for monospecies and dual-species biofilms, respectively.

CONCLUSIONS

HOCl producing e-bandages reduce viable cell counts of in vitro monospecies and dual-species bacterial biofilms in a time-dependent manner in vitro. After 12 hours, >99.999% reduction in cell viability was observed for both monospecies and dual-species biofilms.

Antiviral agents and disinfectants for foot‑and‑mouth disease (Review)

Fluorouracil, 5-azacytidine, 6-azauridine, ribavirin, favipiravir (T-705) and its derivative (T-1105) exhibit anti-foot-and-mouth disease virus (FMDV) effects. In particular, T-1105 exhibits promising results when administered to guinea pigs orally, and pigs in their feed. FMDV is excreted in the early stages of infection in aerosols and oral or nasal droplets from animals. T-1105 along with the FMDV vaccine can be used to combat foot-and-mouth disease (FMD) epidemics. Several studies have shown that sodium hypochlorous solutions are widely used to inactivate viruses, including FMDV. However, these solutions must be stored under cool and dark conditions to maintain their virucidal effects. Interestingly, a study indicated that the virucidal activity of a calcium bicarbonate solution with a mesoscopic structure (CAC-717) did not decrease after storage at room temperature for at least four years outside direct sunlight. Numerous lessons acquired from the 2010 FMD outbreak in Japan are relevant for the control of COVID-19. However, the widespread use of chlorite can cause environmental issues. Chlorite can be combined with nitrogen to produce chloramine or N-nitrosodimethylamine, which plays a role in carcinogenesis. Therefore, risk assessments should be conducted in aquatic environments. Moreover, there is a need to develop nonchlorine disinfectants that can be used during epidemics, including FMD. The approach of 'One Health' should be shared between the public health and veterinary fields to improve the management of viral outbreaks, including those due to FMD.

Hypochlorous acid inactivates oral pathogens and a SARS-CoV-2-surrogate

BACKGROUND

Droplets and aerosols produced during dental procedures are a risk factor for microbial and viral transmission. Unlike sodium hypochlorite, hypochlorous acid (HOCl) is nontoxic to tissues but still exhibits broad microbicidal effect. HOCl solution may be applicable as a supplement to water and/or mouthwash. This study aims to evaluate the effectiveness of HOCl solution on common human oral pathogens and a SARS-CoV-2 surrogate MHV A59 virus, considering the dental practice environment.

METHODS

HOCl was generated by electrolysis of 3% hydrochloric acid. The effect of HOCl on human oral pathogens, Fusobacterium nucleatum, Prevotella intermedia, Streptococcus intermedius, Parvimonas micra, and MHV A59 virus was studied from four perspectives: concentration; volume; presence of saliva; and storage. HOCl solution in different conditions was utilized in bactericidal and virucidal assays, and the minimum inhibitory volume ratio that is required to completely inhibit the pathogens was determined.

RESULTS

In the absence of saliva, the minimum inhibitory volume ratio of freshly prepared HOCl solution (45-60 ppm) was 4:1 for bacterial suspensions and 6:1 for viral suspensions. The presence of saliva increased the minimum inhibitory volume ratio to 8:1 and 7:1 for bacteria and viruses, respectively. Applying a higher concentration of HOCl solution (220 or 330 ppm) did not lead to a significant decrease in the minimum inhibitory volume ratio against S. intermedius and P. micra. The minimum inhibitory volume ratio increases in applications of HOCl solution via the dental unit water line. One week of storage of HOCl solution degraded HOCl and increased the minimum growth inhibition volume ratio.

CONCLUSIONS

HOCl solution (45-60 ppm) is still effective against oral pathogens and SAR-CoV-2 surrogate viruses even in the presence of saliva and after passing through the dental unit water line. This study indicates that the HOCl solution can be used as therapeutic water or mouthwash and may ultimately reduce the risk of airborne infection in dental practice.

In Vitro Activity of a Hypochlorous Acid-Generating Electrochemical Bandage against Yeast Biofilms

The antibiofilm activity of a hypochlorous acid (HOCl)-producing electrochemical bandage (e-bandage) was assessed against 14 yeast isolates in vitro. The evaluated e-bandage was polarized at +1.5 VAg/AgCl to allow continuous production of HOCl. Time-dependent decreases in the biofilm CFU counts were observed for all isolates with e-bandage treatment. The results suggest that the described HOCl-producing e-bandage could serve as a potential alternative to traditional antifungal wound biofilm treatments.

Hypochlorous acid produced at the counter electrode inhibits catalase and increases bactericidal activity of a hydrogen peroxide generating electrochemical bandage

Previously, an electrochemical bandage (e-bandage) that uses a three-electrode system to produce hydrogen peroxide (H2O2) electrochemically on its working electrode was developed as a potential strategy for treating biofilms; it showed activity in reducing biofilms in an agar biofilm model. Xanthan gum-based hydrogel, including NaCl, was used as the electrolyte. While H2O2 generated at the working electrode in the vicinity of a biofilm is a main mechanism of activity, the role of the counter electrode was not explored. The goal of this research was to characterize electrochemical reactions occurring on the counter electrode of the e-bandage. Counter electrode potential varied between 1.2 and 1.5 VAg/AgCl; ∼125 µM hypochlorous acid (HOCl) was generated within 24 h in the e-bandage system. When HOCl was not produced on the counter electrode (achieved by removing NaCl from the hydrogel), reduction of Acinetobacter baumannii BAA-1605 biofilm was 1.08 ± 0.38 log10 CFU/cm2 after 24 h treatment, whereas when HOCl was produced, reduction was 3.87 ± 1.44 log10 CFU/cm2. HOCl inhibited catalase activity, abrogating H2O2 decomposition. In addition to H2O2 generation, the previously described H2O2-generating e-bandage generates HOCl on the counter electrode, enhancing its biocidal activity.

The antibacterial and antibiofilm activity of Granudacyn in vitro in a 3D collagen wound infection model

Objective:

It is widely agreed that infection and the formation of biofilms play a major role in increasing inflammation and delaying wound healing. The aim of this study was to evaluate, in vitro, the antimicrobial activity of the wound irrigation solution, Granudacyn (Mölnlycke Health Care AB, Sweden) against planktonic bacteria and mature biofilms of clinically relevant bacterial species.

Method:

Quantitative evaluation of bacterial numbers and confocal and/or scanning electron microscopy were used to evaluate the wound irrigation solution's antimicrobial/antibiofilm activity in standard laboratory conditions as well as in a three-dimensional (3D) collagen wound infection model.

Results:

The wound irrigation solution exhibited a rapid and strong antibacterial activity against both Gram-positive and Gram-negative strains isolated from infected wounds in planktonic form, with a reduction in bacterial number of >4 Logs after as little as one minute of treatment. The wound irrigation solution also exerted an evident activity against preformed biofilms of Pseudomonas aeruginosa and Staphylococcus aureus (>3 Log and >1 Log reduction in colony forming unit number, respectively, after 15 minutes of incubation). Although the wound irrigation solution was partially inhibited in the presence of simulated wound fluid, it maintained a marked antibiofilm activity in in vivo-like conditions (ie. in a 3D collagen wound infection model) with a strong killing and a mild debridement effect, which was superior to standard saline.

Conclusion:

The results obtained in this study suggest that although the wound irrigation solution used might be partially inhibited by wound exudate, it has the potential to effectively kill wound infecting planktonic as well as biofilm bacteria.

Effects of stabilized hypochlorous acid on oral biofilm bacteria

Background

Caries and periodontitis are amongst the most prevalent diseases worldwide, leading to pain and loss of oral function for those affected. Prevention relies heavily on mechanical removal of dental plaque biofilms but for populations where this is not achievable, alternative plaque control methods are required. With concerns over undesirable side-effects and potential bacterial resistance due to the use of chlorhexidine gluconate (CHX), new antimicrobial substances for oral use are greatly needed. Here we have investigated the antimicrobial effect of hypochlorous acid (HOCl), stabilized with acetic acid (HAc), on oral biofilms and compared it to that of CHX. Possible adverse effects of stabilized HOCl on hydroxyapatite surfaces were also examined.

Methods

Single- and mixed-species biofilms of six common oral bacteria (Streptococcus mutans, Streptococcus gordonii, Actinomyces odontolyticus, Veillonella parvula, Parvimonas micra and Porphyromonas gingivalis) within a flow-cell model were exposed to HOCl stabilized with 0.14% or 2% HAc, pH 4.6, as well as HOCl or HAc alone. Biofilm viability was assessed in situ using confocal laser scanning microscopy following LIVE/DEAD® BacLight™ staining. In-situ quartz crystal microbalance with dissipation (QCM-D) was used to study erosion of hydroxyapatite (HA) surfaces by stabilized HOCl.

Results

Low concentrations of HOCl (5 ppm), stabilized with 0.14% or 2% HAc, significantly reduced viability in multi-species biofilms representing supra- and sub-gingival oral communities, after 5 min, without causing erosion of HA surfaces. No equivalent antimicrobial effect was seen for CHX. Gram-positive and Gram-negative bacteria showed no significant differential suceptibility to stabilized HOCl.

Conclusions

At low concentrations and with exposure times which could be achieved through oral rinsing, HOCl stabilized with HAc had a robust antimicrobial activity on oral biofilms, without causing erosion of HA surfaces or affecting viability of oral keratinocytes. This substance thus appears to offer potential for prevention and/or treatment of oral biofilm-mediated diseases.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-022-02453-2.

Virucidal properties of new multifunctional fibrous N-halamine-immobilized styrene-divinylbenzene copolymers

Virucidal properties of N-chlorosulfonamides immobilized on fibrous styrene-divinylbenzene copolymers have been studied. Corresponding materials with different functional group structures and chlorine content have been synthesized on FIBAN polymer carriers in the form of staple fibers and non-woven fabrics. The study has been conducted in general accordance with EN 14476 standard on poliovirus type-1 and adenovirus type-5. It has been found that all tested samples exhibit pronounced virucidal activity: regardless of the carrier polymer form, sodium N-chlorosulfonamides inactivated both viruses in less than 30 s, and N,N-dichlorosulfonamides—in 30–60 s. The main mechanism of action of these materials, obviously, consists in the emission of active chlorine from the functional group into the treated medium under the action of the amino groups of virus fragments and cell culture. Considering the previously described antimicrobial and reparative properties of such materials, as well as their satisfactory physical and mechanical properties, the synthesized polymers are promising for the creation of medical devices with increased resistance to microbial contamination, such as protective masks, filter elements, long-acting wound dressings, and others.

The Effect of Hypochlorous Acid on the Filtration Performance and Bacterial Decontamination of N95 Filtering Facemask Respirators

BACKGROUND

Stabilized Hypochlorous acid (HOCl) is increasingly used as a hospital disinfectant and antiseptic, yet its effect on N95 filtration facemask respirators (FFR) is unknown. These FFRs could also contribute to fomite-based transmission of nosocomial infections if worn for extended use between patient rooms.

METHODS

Filtration performance of N95 FFR fabric swatches was assessed after various levels of HOCl exposure. N95 swatches were then contaminated with 10⁸ E. coli or 10⁸ Staph aureus and treated with HOCl solution, 70% ethyl alcohol, or normal saline. Surviving bacterial numbers were assessed by plate counts.

RESULTS

The size-dependent filtration efficiency of HOCl-sprayed N95 FFR fabric ranged from 96 to 100%, showing no significant change. Flow resistance testing revealed almost no change compared to control. Submersion in HOCl, but not spraying, had an excellent bactericidal effect on contaminated swatches.

DISCUSSION

The role of the outer hydrophobic layer of N95 FFRs is discussed regarding the effects of HOCl on filtration and bacterial decontamination.

CONCLUSION

N95 material, sprayed with or briefly submerged in HOCl, maintained its filtration function. HOCl delivery by spray pump, however, would not accomplish decontamination of extended use FFRs between patient encounters. HOCl submersion of intact FFRs, contaminated with various hospital pathogens, is worth further study.

Addition of metal chlorides to a HOCl conditioner can enhance bond strength to smear layer deproteinized dentin

OBJECTIVES

To evaluate the effect of smear layer deproteinization using hypochlorous acid (HOCl) with/without metal chlorides (SrCl₂ and ZnCl₂) on the microtensile bond strength (µTBS) of two simplified adhesives to dentin.

METHODS

Human dentin surfaces with a standardized smear layer were pretreated using a 105 ppm HOCl solution with/without SrCl₂ (0.05 M, 0.1 M, 0.2 M, 0.4 M) or ZnCl₂ (0.05 M, 0.1 M, 0.2 M) for 5 s, 15 s, or 30 s. After the deproteinizing solution was washed out with water for 5 s, 15 s, or 30 s, pretreated surfaces were bonded with one-step self-etch adhesive Bond Force II or universal adhesive Clearfil Universal Bond Quick, and µTBS was measured after 24 h. Additionally, the deproteinizing effects of HOCl solutions with/without the metal chlorides were compared by measuring changes in the amide:phosphate ratio using attenuated total reflection Fourier transform infrared spectroscopy. Statistical analysis was performed using multifactor ANOVA, Tukey's post hoc tests and t-tests (p < 0.05).

RESULTS

Pretreatment with pure HOCl for 15 s and 30 s significantly decreased the amide:phosphate ratio (p < 0.05), indicating effective deproteinization, but the µTBS of both adhesives increased significantly only if HOCl was washed out for 30 s (p < 0.05). Increasing the concentrations of metal chlorides enabled shortening of the wash-out time down to 5 s while maintaining the improved µTBS (p < 0.05). The deproteinizing effect of HOCl was not significantly altered by the addition of metal chlorides (p > 0.05).

SIGNIFICANCE

The effectiveness of smear layer deproteinization using HOCl can be improved by the addition of metal chlorides, as their increasing concentration allowed to shorten the wash-out time from 30 s down to 5 s.

Calcium bicarbonate as an antimicrobial, antiviral, and prion‑inhibiting agent (Review)

Calcium bicarbonate does not act as a disinfectant at neutral pH; however, it exerts strong antimicrobial activity after it is placed in a high-voltage electric field, whereby it assumes an alkaline pH (12.4). Moreover, the microbicidal activity of the resulting solution (named CAC-717) is not influenced by the presence of organic material or resistance of the agent to inactivation. When sprayed on the skin surface, the pH of CAC-717 decreases rapidly to 8.84. CAC-717 comprises fine particles of 50-500 nm. When these mesoscopic crystals are dissolved in water, they destroy the genomes of bacteria or viruses and neutralize the infectious properties of abnormal prion proteins produced in ScN2a cells. The severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) pandemic has resulted in unprecedented international demand for disinfectants. A small titer of SARS-CoV-2 remains infectious even after 30 sec in growth medium at pH 12.4. CAC-717 has exhibited a strong virucidal effect (3.6 to 4.4 log₁₀ decrease) against all examined SARS-CoV-2 isolates, including mutant forms. Similarly, human noroviruses also remain intact at pH 12.4; however, CAC-717 has been shown to cause a 3.25 log₁₀ reduction in norovirus genomic RNA compared to untreated samples. Existing evidence suggests that an unidentified mechanism controls the virucidal activity of CAC-717.

Stability of Free Available Chlorine Levels in Dilute Sodium Hypochlorite Solutions over a 6-Week Period

Animal care and use programs commonly use chlorine and chlorine-based disinfectants to help prevent facility acquired infections in animals. The Department of Comparative Medicine (DCM) at Oregon Health and Science University (OHSU) follows the Centers for Disease Control and Prevention (CDC) disinfection guidelines for preparing and storing these disinfectants. DCM prepares bottles of dilute solutions of sodium hypochlorite (that is, commercial bleach) daily. In this study, we tested whether dilute bleach solutions, as prepared following the DCM protocol, remained stable under real-world practice conditions for up to 6 wk. We tested 4 groups of spray bottles filled with 0.5% bleach solutions in these experiments. Specifically, we sprayed 2 groups of bottles daily to mimic use while 2 other groups of bottles were not sprayed. We then measured free available chlorine (FAC) using 2 methods, spectrophotometry and colorimetric strips. All 4 test groups showed stable maintenance of FAC concentration for the length of the experiment. Mean FAC loss from baseline levels was not significantly different in the group of bottles not sprayed daily (6% for group 2 at week 5 compared with 7% for Group 4 at week 6). All bottles in Groups 1 and 3 measured by colorimetric strips showed concentrations at or near 5000 mg/L at all weekly time points throughout the experiment. This study shows that 0.5% sodium hypochlorite solutions stored and used in a standard rodent housing room and sprayed daily will maintain acceptable FAC concentrations for at least 5 to 6 wk, perhaps longer. In addition, we report that colorimetric strips may be a useful and accessible quality control tool for testing freshly prepared solutions at regular intervals. We conclude that sodium hypochlorite solutions can be prepared on a weekly, biweekly, or monthly basis with no loss in disinfection effectiveness.

Universal Virucidal Activity of Calcium Bicarbonate Mesoscopic Crystals That Provides an Effective and Biosafe Disinfectant

We investigated the virucidal effects in solution of a new type of disinfectant, calcium bicarbonate mesoscopic crystals, designated CAC-717, against various types of virus. CAC-717 in solution is alkaline (pH 12.4) and has a self-electromotive force that generates pulsed electrical fields. Upon application to human skin, the pH of the solution becomes 8.4. CAC-717 contains no harmful chemicals and is thus non-irritating and harmless to humans and animals. Its virucidal effects were tested against six types of animal virus: enveloped double-strand (ds)-DNA viruses, non-enveloped ds-DNA viruses, non-enveloped single strand (ss)-DNA viruses, enveloped ss-RNA viruses, non-enveloped ss-RNA viruses, and non-enveloped ds-RNA viruses. The treatment resulted in a reduction in viral titer of at least 3.00 log₁₀ to 6.38 log₁₀. Fetal bovine serum was added as a representative organic substance. When its concentration was ≥20%, the virucidal effect of CAC-717 was reduced. Real-time PCR revealed that CAC-717 did not reduce the quantity of genomic DNA of most of the DNA viruses, but it greatly reduced that of the genomic RNA of most of the RNA viruses. CAC-717 may therefore be a useful biosafe disinfectant for use against a broad range of viruses.

Investigation and disinfection of bacteria and fungi in sports fitness center

This study investigated the air quality improvement in terms of bacterial and fungal contamination in an exercise room of a fitness center under normal operating conditions. Environmental conditions including air conditioning, ventilation, moisture, CO₂, particulate matters, and total number of users were also recorded. In addition, fungal and bacterial load were assessed and disinfection on sports equipment surface was also examined. Background bacteria and fungi densities in bioaerosols were in the range of 249 ± 65 to 812 ± 111 CFU/m³ and 226 ± 39 to 837 ± 838 CFU/m³ in the exercise room of the fitness center and 370 ± 86 to 953 ± 136 CFU/m³ and 465 ± 108 to 1734 ± 580 CFU/m³ in the outdoor air, respectively. Chlorine dioxide and weak acid hypochlorous water aerosols could remove both bacteria and fungi much better than water scrubbing. Contact time of 15 min was sufficient to control both bacteria and fungi to comply with the official air quality standards. User density and carbon dioxide deteriorated both bacteria and fungi disinfection performance whereas temperature was only statistically significant on fungi disinfection. Other factors including relative humidity, airflow velocity, and particulate matters did not have any statistically significant effect on microbial inactivation. Apart from bioaerosol disinfection, inactivation of microorganisms on surfaces of sports equipment was also conducted using chlorine dioxide, zinc oxide, weak acid hypochlorous water, and commercial disinfectant. The surfaces of bicycle handle, dumbbell, and sit-up bench were found to be contaminated with bacteria. Overall bacterial load was 390 to 3720 CFU/cm² with Escherichia coli specifically 550 to 1080 CFU/cm². Chlorine dioxide and zinc oxide were noticeably better than weak acid hypochlorous water and commercial disinfectant in terms of bacteria inactivation whereas all tested disinfectants had comparable effectiveness on E. coli disinfection. Targeted microorganisms on the sports equipment surface were sufficiently inactivated within 2 min after the application of disinfectant.

Recent Progress in the Development of Disinfectants from Scallop Shell-Derived Calcium Oxide for Clinical and Daily Use

The current pandemic of novel coronavirus disease (COVID-19) has highlighted the importance of disinfectants. As a raw material for next-generation disinfectants, scallop shell-derived calcium oxide (CaO) has been revealed to exhibit significant virucidal and microbicidal activities and is compatible with living tissues and the environment. This minireview summarizes recent progress in the development of disinfectants from scallop shell-CaO, focusing especially on studies of clinical and daily use applications. We describe the preparation, basic characteristics, and virucidal and microbicidal activities of scallop shell-CaO disinfectants. Furthermore, their applications in the disinfection of contaminated masks and the treatment of infected wounds are briefly introduced.

Bioshell calcium oxide (BiSCaO) for cleansing and healing Pseudomonas aeruginosa-infected wounds in hairless rats

BACKGROUND

Scallop shell powder is called bioshell calcium oxide (BiSCaO), which is known to possess deodorizing properties and broad antimicrobial activity against various pathogenic microbes, including viruses, bacteria, spores, and fungi.

OBJECTIVE

This study aims to investigate the applications of BiSCaO suspension cleansing in clinical situations, for instance for the prevention and treatment of infections in chronic wounds in healing-impaired patients, without delaying wound healing.

METHODS

The bactericidal activities of 1000 ppm BiSCaO suspension; 500 ppm hypochlorous acid; 1000 ppm povidone iodine; and saline were compared to evaluate in vivo disinfection and healing of Pseudomonas aeruginosa-infected wounds in hairless rats.

RESULTS

Cleansing of the infected wounds with BiSCaO suspension daily for 3 days significantly enhanced wound healing and reduced the in vivo bacterial counts, in comparison to hypochlorous acid, povidone iodine, and saline. Furthermore, histological examinations showed significantly advanced granulation tissue and capillary formation in the wounds cleansed with BiSCaO suspension than in those cleansed with the other solutions.

CONCLUSIONS

This study suggested that the possibility of using BiSCaO suspension as a disinfectant for infected wounds and limiting disinfection to 3 days may be sufficient to avoid the negative effects on wound repair.

The Safety and Antimicrobial Properties of Stabilized Hypochlorous Acid in Acetic Acid Buffer for the Treatment of Acute Wounds-a Human Pilot Study and In Vitro Data

Acute wounds may require cleansing to reduce the risk of infection. Stabilized hypochlorous acid in acetic buffer (HOCl + buffer) is a novel wound irrigation solution with antimicrobial properties. We performed a first-in-man, prospective, open-label pilot study to document preliminary safety and performance in the treatment of acute wounds. The study enrolled 12 subjects scheduled for a split-skin graft transplantation, where the donor site was used as a model of an acute wound. The treatment time was 75 s, given on 6 occasions. A total of 7 adverse events were regarded as related to the treatment; all registered as pain during the procedure for 2 subjects. One subject had a wound infection at the donor site. The mean colony-forming unit (CFU) decreased by 41% after the treatment, and the mean epithelialization was 96% on both days 14 (standard deviation [SD] 8%) and 21 (SD 10%). The study provides preliminary support for the safety, well-tolerance, and efficacy of HOCl + buffer for acute wounds. The pain was frequent although resolved quickly. Excellent wound healing and satisfying antimicrobial properties were observed. A subsequent in vitro biofilm study also indicated good antimicrobial activity against Pseudomonas aeruginosa with a 96% mean reduction of CFU, when used for a treatment duration of 15 min (P < .0001), and a 50% decrease for Staphylococcus aureus (P = .1010). Future larger studies are needed to evaluate the safety and performance of HOCl + buffer in acute wounds, including the promising antimicrobial effect by prolonged treatment on bacterial biofilms.

An Integrated HOCl-Producing E-Scaffold Is Active against Monomicrobial and Polymicrobial Biofilms

Oxidizing agents like hypochlorous acid (HOCl) have antimicrobial activity. We developed an integrated electrochemical scaffold, or e-scaffold, that delivers a continuous low dose of HOCl aimed at targeting microbial biofilms without exceeding concentrations toxic to humans as a prototype of a device being developed to treat wound infections in humans. In this work, we tested the device against 33 isolates of bacteria (including isolates with acquired antibiotic resistance) grown as in vitro biofilms alongside 12 combinations of dual-species in vitro biofilms. Biofilms were grown on the bottoms of 12-well plates for 24 h. An integrated e-scaffold was placed atop each biofilm and polarized at 1.5 V for 1, 2, or 4 h. HOCl was produced electrochemically by oxidizing chloride ions (Cl^-) in solution to chlorine (Cl₂); dissolved Cl₂ spontaneously dissociates in water to produce HOCl. The cumulative concentration of HOCl produced at the working electrode in each well was estimated to be 7.89, 13.46, and 29.50 mM after 1, 2, and 4 h of polarization, respectively. Four hours of polarization caused an average reduction of 6.13 log₁₀ CFU/cm² (±1.99 log₁₀ CFU/cm²) of viable cell counts of monospecies biofilms and 5.53 log₁₀ CFU/cm² (±2.31 log₁₀ CFU/cm²) for the 12 dual-species biofilms studied. The described integrated e-scaffold reduces viable bacterial cell counts in biofilms formed by an array of antibiotic-susceptible and -resistant bacteria alone and in combination.

Efficacy of Bioshell Calcium Oxide Water as Disinfectants to Enable Face Mask Reuse

Bioshell calcium oxide (BiSCaO) is derived from scallop shells and after heat treatment exhibits broad microbicidal activity. BiSCaO Water is a disinfectant prepared by collecting the aqueous layer after adding BiSCaO powder to water, is colorless and transparent, and has a pH of 12.8. We compared the utility of commercially available BiSCaO Water, ethanol, sodium hypochlorite, hypochlorous acid and hydrogen peroxide solutions as sterilization agents to enable the reuse of surgical and N95 face masks. The microbicidal efficacy of each disinfectant was evaluated using pieces of surgical and N95 face masks contaminated with normal bacterial flora. The results suggest that BiSCaO Water has excellent disinfection activity toward contaminated polypropylene masks and has minimal adverse effect on the structure of non-woven masks.

Skin Cleansing Technique with Disinfectant using Improved High-Velocity Steam-Air Micromist Jet Spray

Application of a high-velocity steam-air micromist jet spray (HVS-AMJS) with disinfectants for cleansing the skin is proposed. Low-pressure steam is mixed with compressed air in a nozzle and then sprayed onto a surface of skin or material located approximately 22 cm from the nozzle. The temperature on the sprayed surface was controlled between 40ºC and 45 ºC. The improved HVS-AMJS installed scattering prevention cover with tap water effectively removed normal bacterial flora (total viable count and coliform bacteria) from contaminated skin pieces and pig skin wounds. Furthermore, the cleansing efficacy increased by advanced-treating with bio-shell calcium oxide (BiSCaO), hypochlorous acid (HClO), sodium hypochlorite (NaClO), povidone iodine, or chlorhexidine gluconate. Especially, the improved HVS-AMJS combined with BiSCaO had higher bactericidal activity than when combined with other disinfectants. This study suggests that application of the HVS-AMJS with disinfectants, especially BiSCaO, may be useful for skin cleansing to prevent infection.

Safety of Concentrated Bioshell Calcium Oxide Water Application for Surface and Skin Disinfections against Pathogenic Microbes

Immediately post-production, commercially available bioshell calcium oxide (BiSCaO) water is colorless, transparent, and strongly alkaline (pH 12.8), and is known to possess deodorizing properties and broad microbicidal activity. However, BiSCaO Water may represent a serious safety risk to the living body, given the strong alkalinity. This study aimed to investigate the safety of BiSCaO Water for use as an antiseptic/disinfectant despite concerns regarding its high alkalinity. The change over time in pH of BiSCaO Water was measured during air contact (stirring BiSCaO Water in ambient air). When sprayed on metal, plastic, wood piece, paper, and skin surfaces, the pH of BiSCaO Water decreased rapidly, providing a white powder coating upon drying. Scanning electron microscopy images, energy dispersive X-ray elemental mapping, and X-ray diffractograms showed that the dried powder residues of BiSCaO Water were composed primarily of calcium carbonate. These results suggested that BiSCaO Water is a potent reagent that may overcome the obstacles of being strongly alkaline, making this material appropriate for use in disinfection against pathogenic microbes.

Bioshell Calcium Oxide-Containing Liquids as a Sanitizer for the Reduction of Histamine Production in Raw Japanese Pilchard, Japanese Horse Mackerel, and Chub Mackerel

Recently, there has been an increase in the number of food poisoning cases associated with histamine in food, mainly in relation to histamine in fish. Here, we investigated methods to decrease histamine levels in Japanese pilchard, Japanese horse mackerel, and chub Mackerel, stored at 10 °C using various concentrations of heated scallop bioshell calcium oxide (BiSCaO) suspension, dispersion (BiSCaO + Na₂HPO₄), colloidal dispersion (BiSCaO + NapolyPO₄), scallop shell powder (SSP) Ca(OH)₂ in pure water (PW) or saline, and BiSCaO water. BiSCaO in a high alkaline pH solution chemically decomposes histamine poorly, but the partial flocculation/precipitation of histamine was observed with 1 and 0.2 wt.% BiSCaO dispersion and BiSCaO colloidal dispersion, respectively. Cleaning fish samples with BiSCaO suspension, dispersion, colloidal dispersion, or BiSCaO water remarkably reduced histamine levels and normal bacterial flora (coliform bacteria (CF) and total viable bacterial cells (TC)) after storage for four days at 10 °C, while much higher histamine levels were observed after cleaning with saline. These results suggest that cleaning fish with BiSCaO dispersion, colloidal dispersion, or BiSCaO water can significantly reduce histamine levels through their bactericidal activity against histamine-producing bacteria.

Concentrated Bioshell Calcium Oxide (BiSCaO) Water Kills Pathogenic Microbes: Characterization and Activity

Bioshell calcium oxide (BiSCaO) exhibits deodorizing properties and broad microbicidal activity. In this study, we examined possible utility of BiSCaO Water for that purpose. BiSCaO Water was prepared by adding 10 wt% BiSCaO to clean water and gently collecting the supernatant in a bottle. The same volume of clean water was gently poured onto the BiSCaO precipitate and the supernatant was gently collected in a bottle; this process was repeated fifty times. The produced BiSCaO Water contained nanoparticles (about 400-800 nm) composed of smaller nanoparticles (100-200 nm), and was colorless and transparent, with a pH > 12.7. In vitro assays demonstrated that BiSCaO Water eliminated more than 99.9% of influenza A (H1N1) and Feline calicivirus, Escherichia coli such as NBRC 3972 and O-157:H7, Pseudomonas aeruginosa, Salmonella, and Staphylococcus aureus within 15 min. We compared BiSCaO Water with the other microbicidal reagents such as ethanol, BiSCaO, BiSCa(OH)₂ suspensions, povidone iodine, NaClO, BiSCaO dispersion and colloidal dispersion with respect to deodorization activity and microbicidal efficacy. The results showed that BiSCaO Water was a potent reagent with excellent deodorization and disinfection activities against pathogenic bacteria and viruses (including both enveloped and nonenveloped viruses).

Hypochlorous Acid: A Review

The surgeon needs to have an inexpensive, available, nontoxic, and practical disinfectant that is effective in sanitizing against the COVID-19 (Coronavirus Disease 2019) virus. The purpose of this article was to review the evidence for using hypochlorous acid in the office setting on a daily basis. The method used to assemble recommendations was a review of the literature including evidence for this solution when used in different locations and industries other than the oral-maxillofacial clinic facility. The results indicate that this material can be used with a high predictability for disinfecting against the COVID-19 (Coronavirus Disease 2019) virus.

Bioshell Calcium Oxide (BiSCaO) Ointment for the Disinfection and Healing of Pseudomonas aeruginosa-Infected Wounds in Hairless Rats

Bioshell calcium oxide (BiSCaO) possesses deodorizing properties and broad microbicidal activity. This study aimed to investigate the application of BiSCaO ointment for the prevention and treatment of infection in chronic wounds in healing-impaired patients, without delaying wound healing. The bactericidal activities of 0.04, 0.2, 1, and 5 wt% BiSCaO ointment, 3 wt% povidone iodine ointment, and control (ointment only) were compared to evaluate the in vivo disinfection and healing of Pseudomonas aeruginosa-infected wounds in hairless rats. Treatment of the infected wounds with 0.2 wt% BiSCaO ointment daily for 3 days significantly enhanced wound healing and reduced the in vivo bacterial counts compared with povidone iodine ointment and control (no wound cleaning). Although 5 wt% BiSCaO ointment provided the lowest bacterial counts during 3 days' treatment, it delayed wound healing. Histological examinations showed significantly advanced granulation tissue and capillary formation in wounds treated with 0.2 wt% BiSCaO ointment for 3 days compared to wounds treated with the other ointments. This study suggested that using 0.2 wt% BiSCaO ointment as a disinfectant for infected wounds and limiting disinfection to 3 days may be sufficient to avoid the negative effects of BiSCaO on wound repair.

Sanitizing agents for virus inactivation and disinfection

Viral epidemics develop from the emergence of new variants of infectious viruses. The lack of effective antiviral treatments for the new viral infections coupled with rapid community spread of the infection often result in major human and financial loss. Viral transmissions can occur via close human-to-human contact or via contacting a contaminated surface. Thus, careful disinfection or sanitization is essential to curtail viral spread. A myriad of disinfectants/sanitizing agents/biocidal agents are available that can inactivate viruses, but their effectiveness is dependent upon many factors such as concentration of agent, reaction time, temperature, and organic load. In this work, we review common commercially available disinfectants agents available on the market and evaluate their effectiveness under various application conditions. In addition, this work also seeks to debunk common myths about viral inactivation and highlight new exciting advances in the development of potential sanitizing agents.

Application of Colloidal Dispersions of Bioshell Calcium Oxide (BiSCaO) for Disinfection

Bioshell calcium oxide (BiSCaO) is a scallop-shell powder heated at a high temperature. BiSCaO is composed mainly of calcium oxide and exhibits broad microbicidal properties. The aim of this study is to evaluate the disinfection and decontamination abilities of BiSCaO colloidal dispersions with that of commercially available bioshell calcium hydroxide (BiSCa(OH)2) following the formation of flocculants/precipitates under strongly alkaline conditions (pH 11.5-12.2). Various concentrations of BiSCaO and BiSCa(OH)2 colloidal dispersions were prepared by mixing with Na-polyPO4 (PP) and Na-triPO4 (TP) as flocculating agents. The microbicidal activities, and the degree of flocculation/precipitation of trypan blue, albumin, chondroitin sulfate, heparin, non-anticoagulant heparin carrying polystyrene (NAC-HCPS), and low-molecular-weight heparin/protamine nanoparticles (LMWH/P NPs) were dependent on the pH, the average particle diameter, and the concentration of BiSCaO or BiSCa(OH)2 and of the phosphate compound. BiSCaO (average particle diameter: 6 μm) colloidal dispersions (0.2 wt.%) containing 0.15 wt.% PP or TP exhibited substantially stronger microbicidal activity and flocculation/precipitation under strongly alkaline conditions. These results suggest that BiSCaO colloidal dispersions together with phosphate compounds have practical applicability for disinfection.

Comparison of Various Disinfectants on Bactericidal Activity Under Organic Matter Contaminated Environments

The bactericidal activity of heated bio-shell calcium oxide (BiSCaO) powder suspension (pH 12.4) , hypochlorous acid (HClO; pH 6), sodium hypochlorite (NaClO; pH 8) , povidone-iodine (Isodine solution^®) , and chlorhexidine gluconate (Hibiscrub^®) under organic matter contaminated environments were compared for tests conducted on wood scraps and pig skin pieces that were incubated with normal bacterial flora (total viable counts and coliform bacteria) . The test results showed that BiSCaO suspension had higher bactericidal activity than HClO and NaClO. Furthermore, more than 10-fold higher concentrations of antiseptics such as povidone-iodine and chlorhexidine gluconate were required to achieve bactericidal activity comparable to that of BiSCaO suspension. Our results demonstrate the possibility of using BiSCaO suspension under organic matter contaminated environments as a disinfectant for environmental and food hygiene applications.

Preparation and Application of Bioshell Calcium Oxide (BiSCaO) Nanoparticle-Dispersions with Bactericidal Activity

Scallop-shell powder (SSP) heated at high temperature exhibits high pH and broad antimicrobial activity. Bioshell calcium oxide (BiSCaO) is an SSP composed mainly of calcium oxide. It is poorly water-soluble under alkaline conditions and the generated precipitate can plug spray nozzles. The aim of this study was to establish that BiSCaO dispersion caused no significant CaO loss and plugging of spray nozzles, and to evaluate its deodorization and microbicidal abilities and its ability to reduce the concentrations of NO₂^- and NO₃^-. BiSCaO dispersions were prepared by mixing various concentrations of BiSCaO suspension, while phosphate compounds such as Na₃PO₄, Na₂HPO₄ or NaH₂PO₄ and the pH, average diameter, zeta potential, and form of the compounds with cryo-SEM were evaluated. We evaluated deodorization using tainted pork meat and microbicidal efficacy using contaminated suspension with normal bacterial flora. The concentration of NO₂^- and NO₃^- after mixing BiSCaO dispersion and pure water containing a high proportion of NO₂^- and NO₃^- were measured. BiSCaO dispersion formed with Na₂HPO₄, whose ratio to BiSCaO was 60%, showed a high pH (>12), a small particle diameter (>181 nm) and was stable for seven days. The BiSCaO dispersion showed higher deodorization and microbicidal activities than SSP-Ca(OH)₂, which was mainly composed of Ca(OH)₂. BiSCaO, but not SSP-Ca(OH)₂, could reduce the concentration of NO₂^- and NO₃^- by more than 90% within 15 min. We developed a stable BiSCaO dispersion, and it had high deodorization and microbicidal efficacy. These activities of BiSCaO might result from the high pH caused by CaO hydration and a reduction activity causing active radical species.

The molecular chaperone Hsp33 is activated by atmospheric-pressure plasma protecting proteins from aggregation

Non-equilibrium atmospheric-pressure plasmas are an alternative means to sterilize and disinfect. Plasma-mediated protein aggregation has been identified as one of the mechanisms responsible for the antibacterial features of plasma. Heat shock protein 33 (Hsp33) is a chaperone with holdase function that is activated when oxidative stress and unfolding conditions coincide. In its active form, it binds unfolded proteins and prevents their aggregation. Here we analyse the influence of plasma on the structure and function of Hsp33 of Escherichia coli using a dielectric barrier discharge plasma. While most other proteins studied so far were rapidly inactivated by atmospheric-pressure plasma, exposure to plasma activated Hsp33. Both, oxidation of cysteine residues and partial unfolding of Hsp33 were observed after plasma treatment. Plasma-mediated activation of Hsp33 was reversible by reducing agents, indicating that cysteine residues critical for regulation of Hsp33 activity were not irreversibly oxidized. However, the reduction yielded a protein that did not regain its original fold. Nevertheless, a second round of plasma treatment resulted again in a fully active protein that was unfolded to an even higher degree. These conformational states were not previously observed after chemical activation with HOCl. Thus, although we could detect the formation of HOCl in the liquid phase during plasma treatment, we conclude that other species must be involved in plasma activation of Hsp33. E. coli cells over-expressing the Hsp33-encoding gene hslO from a plasmid showed increased survival rates when treated with plasma while an hslO deletion mutant was hypersensitive emphasizing the importance of protein aggregation as an inactivation mechanism of plasma.

Behavior of Nitrate-Nitrogen and Nitrite-Nitrogen in Drinking Water

Nitrate-nitrogen (NO₃-N) and nitrite-nitrogen (NO₂-N) are constituents of the nitrogen cycle. NO₃-N is toxic to humans, primarily due to its reduction to NO₂-N. In Japan, NO₃-N and NO₂-N levels in tap water must not exceed 10 mg/L and only NO₂-N alone not 0.04 mg/L, respectively. In this study, we verified the effect of microorganisms and ultraviolet (UV) to increase of NO₂-N in water. First, all tested drinking-waters including tap water and commercial mineral water in PET bottles had < 2 mg/L NO₃-N and undetectable levels (< 0.01 mg/L) of NO₂-N. However, we found that NO₂-N was generated in tap water left to stand at room temperature for several days, leading to increases in CF and TC counts and reduction of NO₃-N. We also demonstrated that direct UV and sunlight irradiation of NO₃-N-containing drinking water generated NO₂-N in 1-2 h, with NO₂-N reaching > 0.04 mg/mL by 4-6 h. On the other hand, NO₃-N and NO₂-N were undetectable in commercially purified water.