Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a threat to human health. Acidic electrolyzed water (AEW) has recently been suggested to demonstrate virucidal activity. Many types of AEW with different pH values, generated by the electrolysis of different chemicals, such as sodium chloride, potassium chloride, and hydrochloric acid, are commercially available. In this study, we compared the virucidal activities of these types of AEW against SARS-CoV-2, including the ancestral strain and variant Alpha, Beta, Gamma, Delta, and Omicron strains. Virus solution (viral titer, 6.9 log10 50% tissue culture infective dose [TCID50]/mL) was mixed with AEW (free available chlorine concentration, 34.5 ppm) at mixing ratios of 1:9, 1:19, and 1:49. At mixing ratios of 1:9 and 1:19, AEW with a pH of 2.8 showed stronger virucidal activities than AEW with a pH of 4.1 to 6.5 against the SARS-CoV-2 ancestral strain in 20 s. From the strongest to the weakest virucidal activity, the AEW pH levels were as follows: pH 2.8, pH 4.1 to 5.4, pH 6.4 to 6.5. At a ratio of 1:49, the viral titers of viruses treated with all AEW solutions at pH 2.8 to 6.5 were almost below the detection limit, which was 1.25 log10 TCID50/mL. The virus inactivation efficiency of AEW was reduced in the presence of fetal bovine serum and other substances contained in the virus solution used in this study. AEW with pH values of 2.8 to 6.5 showed virucidal activity against all of the tested SARS-CoV-2 strains, including the ancestral and variant strains. These results provide useful knowledge for the effective application of AEW as a SARS-CoV-2 disinfectant. IMPORTANCE Acidic electrolyzed water (AEW) demonstrates virucidal activity against multiple viruses. Since AEW exhibits low toxicity, is inexpensive, and is environmentally friendly, it can be a useful disinfectant against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Although the pH values of currently available AEW products vary, the impact of different pH values on SARS-CoV-2 inactivation has not previously been evaluated in detail. In this study, we compared the virucidal activities of multiple AEW solutions with different pH values, under the same experimental conditions. We found that AEW solutions with lower pH values demonstrated more potent virucidal activity. Also, we showed that the extent of virus inactivation by the AEW was based on the balance of the abundance of free available chlorine, virus, and other organic substances in the mixture. AEW exhibited rapid virucidal activity against multiple SARS-CoV-2 strains. This study demonstrated the usefulness of AEW as a disinfectant which can be applied to the inactivation of SARS-CoV-2.
Keywords: SARS-CoV-2; acidic electrolyzed water; disinfectant; pH; variant strain.