Comparative evaluation of chlorous acid and sodium hypochlorite activity against SARS-CoV-2.

A novel coronavirus, named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), suddenly emerged in China in 2019, spread globally and caused the present COVID-19 pandemic. Therefore, to mitigate SARS-CoV-2 infection effective measures are essential. Chlorous acid (HClO2) has been shown to be an effective antimicrobial agent. However, at present there is no experimental evidence showing that HClO2 can inactivate SARS-CoV-2. Therefore, in this study, we examined the potential of HClO2 to inactivate SARS-CoV-2 in presence or absence of organic matter and the results were compared with that of sodium hypochlorite (NaClO), another potent antimicrobial agent. When concentrated SARS-CoV-2 was incubated with 10 ppm HClO2 for 10 s, viral titre was decreased by 5 log of 50% tissue culture infective dose per mL (TCID50 ml-1). However, the same concentration of NaClO could not inactivate SARS-CoV-2 as effectively as HClO2 did even after incubation for 3 min. Furthermore, 10 ppm HClO2 also inactivated more than 4.0 log of TCID50 within 10 s in the presence of 5 % fetal bovine serum used as mixed organic matters. Our results obtained with HClO2 are more effective against SARS-CoV-2 as compared to NaClO that can be used for disinfectant against SARS-CoV-2 .

Inactivation of human norovirus by chlorous acid water, a novel chlorine-based disinfectant.

INTRODUCTION: Human norovirus (HuNoV) is a leading cause of infectious gastroenteritis. Since HuNoV shows resistance to alcohol, chlorine-based sanitizers are applied to decontaminate the virus on environmental surfaces. Chlorous acid water (CA) has been recently approved as a novel chlorine-based disinfectant categorized as a Type 2 OTC medicine in Japan. In this study, we aimed to evaluate the capability of CA to inactivate HuNoV. METHODS: HuNoV (genogroups GII.2 and GII.4) was exposed to the test disinfectants including CA and sodium hypochlorite (NaClO), and the residual RNA copy was measured by reverse transcription quantitative PCR (RT-qPCR) after pretreatment with RNase. In addition, the log10 reduction of HuNoV RNA copy number by CA and NaClO was compared in the presence of bovine serum albumin (BSA), sheep red blood cells (SRBC), polypeptone, meat extract or amino acids to evaluate the stability of these disinfectants under organic-matter-rich conditions. RESULTS: In the absence of organic substances, CA with 200 ppm free available chlorine provided >3.0 log10 reduction in the HuNoV RNA copy number within 5 min. Even under high organic matter load (0.3% each of BSA and SRBC or 0.5% polypeptone), 200 ppm CA achieved >3.0 log10 reduction in HuNoV RNA copy number while less than 1.0 log10 reduction was observed with 1,000 ppm sodium hypochlorite (NaClO) in the presence of 0.5% polypeptone. CA reacted with only cysteine, histidine and glutathione while NaClO reacted with all of the amino acids tested. CONCLUSIONS: CA is an effective disinfectant to inactivate HuNoV under organic-matter-rich conditions.

Acidified sodium chlorite solution: A potential prophylaxis to mitigate impact of multiple exposures to COVID-19 in frontline health-care providers.

Limited availability of personal protective equipment is endangering first-line health-care providers treating patients with presumed or confirmed COVID-19 infections. This editorial has multiple objectives in regard to this reality: First, to raise awareness of the need for safe and effective prophylaxis to protect health-care providers with insufficient personal protective equipment from repeated exposures to COVID-19. Second, to summarize the scientific evidence in support of solutions of acidified sodium chlorite (ASC) and its daughter compounds, chlorous acid and chlorine dioxide, as potential targets for said prophylactic use. Third, to propose a regimented protocol using commercially available solutions of ASC having sufficient concentrations of chlorine dioxide for virucidal activity to support safe and effective prophylactic use. And fourth, to raise awareness of and compare other potential prophylactic options currently under investigation.

Microbicidal effects of slightly acidic hypochlorous acid water and weakly acidified chlorous acid water on foulbrood pathogens.

Paenibacillus larvae and Melissococcus plutonius are bacterial pathogens of honey bee brood. As decontamination of beekeeping equipment, including combs, is essential to control these pathogens, we evaluated the disinfecting effects of slightly acidic hypochlorous acid water (SAHAW) and weakly acidified chlorous acid water (WACAW) on the pathogens. Both disinfectants exhibited strong disinfecting effects in suspension tests under no organic matter conditions and reduced both pathogens by >5 log10 CFU/ml. Although the microbicidal activity of SAHAW with an available chlorine concentration (ACC) of 10-30 ppm was decreased by organic matter, it reduced viable P. larvae spores in combs more efficiently than H2O when the comb was not as dirty. However, its efficacy on combs decreased at 4°C and when overused or highly contaminated combs were tested. WACAW with an ACC of ≥600 ppm had a higher disinfecting capacity than SAHAW, and efficiently removed P. larvae spores from combs even under organic matter-rich and low-temperature conditions. However, even by WACAW, the amount of viable spores in combs was not markedly reduced depending on contamination levels and P. larvae genotypes. These results suggest the usefulness of both disinfectants for decontaminating beekeeping equipment depending on the situations expected.

Characterization of Virucidal Activities of Chlorous Acid.

Virucidal effects of chlorous acid on enveloped and non-enveloped viruses were characterized. The virucidal activity was prominent in enveloped viruses. However, among non-enveloped viruses, viruses such as human rhinovirus and feline calicivirus showed a significant sensitivity to the reagent, whereas others such as poliovirus and coxsackievirus showed a weak sensitivity to the reagent, suggesting the presence of 2 classes of sensitivity to the reagent, among non-enveloped viruses. In addition, characterization of the mode of inactivation by the reagent revealed that virus inactivation is strongly dependent on virus species, contaminated proteins, and solvent system composition. Comparison of the cytotoxic effects of chlorous acid with those of sodium hypochlorite or sodium dodecyl sulfate (SDS) revealed that chlorous acid was similar to SDS and remarkably weaker than sodium hypochlorite. These results indicate the unique nature of chlorous acid as a potent virucidal agent with tolerable tissue damage, and reveal the merits and limitations of chlorous acid as a disinfectant in food hygiene and sanitizer in healthcare.

Tetramethylbenzidine method for monitoring the free available chlorine and microbicidal activity of chlorite-based sanitizers under organic-matter-rich environments.

UNLABELLED: Chlorine is a principal disinfectant for food and environmental sanitation. Monitoring of free available chlorine (FAC) is essential for ensuring the efficacy of food disinfection processes that rely on chlorine. N,N-diethyl-p-phenylenediamine (DPD) is commonly used for FAC monitoring. However, here, we show that upon contact with bovine serum albumin (BSA) or broiler carcasses, chlorite (HClO2 )-based sanitizers acquire a pink colour, which can interfere with measurement of oxidized DPD absorbance at 513-550 nm. Alternatively, the pink colour did not interfere with 3,3',5,5'-tetramethylbenzidine (TMB)-based FAC monitoring. The FAC levels of NaClO and weakly acidified chlorous acid water (WACAW) were first adjusted by the TMB method and the killing activity of these sanitizers towards methicillin-resistant Staphylococcus aureus (MRSA) and feline calicivirus (FCV) was compared in the presence or absence of 0·5% BSA. At 200 ppm FAC, NaClO lost its bactericidal activity against MRSA after 10-min incubation with 0·5% BSA. Meanwhile, under the same conditions WACAW reduced the number of bacteria to below the detection limit. Similar results were obtained with FCV, indicating that the chlorite-based WACAW sanitizer is relatively stable under organic-matter-rich conditions. Moreover, TMB is suitable for in situ FAC monitoring of chlorite-based sanitizers in food and environmental disinfection processes. SIGNIFICANCE AND IMPACT OF THE STUDY: For practical applications of chlorine in food processing, monitoring of FAC is critical to validate disinfection efficacy. In this study we found that chlorite-based sanitizers acquired a pink colour upon contact with BSA or broiler carcasses. This pink colour interfered with FAC monitoring by methods that measure oxidized N,N-diethyl-p-phenylenediamine absorbance between 513-550 nm. Alternatively, FAC levels of chlorite-based sanitizers could be monitored using the absorbance of 3,3',5,5'-tetramethylbenzidine at 650 nm, which does not overlap with the acquired pink colour. These data provide valuable information for safety management of disinfection processes that use chlorite-based sanitizers.