Fig 1.
Inactivation of SARS-CoV-2 by chlorous acid water.
The virus was incubated with chlorous acid water with different concentrations for 10 min and the infectivity was measured by the TCID50 method after quenching chloride ions with sodium thiosulphate. The final concentrations in the reaction solution are shown in the graph. The dotted lines indicate the detection limits of the infectivity assay due to the cytotoxicity of chlorous acid water. Experiments were performed in triplicate, and error bars indicate standard error. *: P < 0.05, Mann-Whitney U test, compared with 0 ppm (water).
Fig 2.
Inactivation of SARS-CoV-2 by chlorous acid water.
(A) D614G, Lineage B.1.1, (B) a Delta variant, Lineage AY.29, and (C) an Omicron variant, Lineage BA.1.1. The virus was incubated with chlorous acid water with different concentrations for 10 min and the infectivity was measured by the TCID50 method after quenching chloride ions with sodium thiosulphate. Measurements were made and fitted to an approximate equation based on the Chick-Watson model. Approximation equations and R2 values are shown in the graphs. R2: coefficient of determination, Log10(N/N0): log reduction in survival ratio.
Table 1.
Inactivation concentrations of SARS-CoV-2 variants with chlorous acid water.
Fig 3.
Analysis of PEG-purified and ultracentrifuged viruses.
(A) SDS-PAGE analysis. Equivalent amounts of the virus after concentration (concentrated by an Amicon Ultra-15 filter unit, MWCO 100kDa) (lane “control”), the virus precipitated by polyethylene glycol (PEG) precipitation, and the virus sedimented by ultracentrifugation were analyzed by SDS-PAGE and Coomassie brilliant blue staining. The possible major cellular protein band is marked by stars. The position of the SARS-CoV-2 N protein is shown. (B) Electron microscopy. SARS-CoV-2 was purified and concentrated by PEG precipitation or ultracentrifugation, negative stained, and observed by transmission electron microscopy. Red arrows indicate relatively intact viral particles, and yellow arrows indicate viral particles that have been destroyed. (C) Graph showing the ratio of apparent intact and destroyed viruses in B.
Table 2.
Infectivity of PEG-precipitated and ultracentrifuged viruses.
Fig 4.
Inactivation of PEG-purified and ultracentrifuged SARS-CoV-2 by chlorine reagents.
The 1/10-diluted PEG-purified virus (A) and the ultracentrifuged virus (B) were incubated with chlorous acid water with different concentrations. (C) The 1/10-diluted PEG-precipitated SARS-CoV-2 was incubated with sodium hypochlorite solution. The incubation time of the virus and chlorine reagents was 1 min, and the infectivity was measured by the TCID50 method. Measurements were made and fitted to an approximate equation based on the Chick-Watson model. Approximation equations and R2 values are shown in the graphs. R2: coefficient of determination, Log10(N/N0): log reduction in survival ratio.
Table 3.
Inactivation concentrations of PEG-purified SARS-CoV-2 with chlorous acid water under protein loading.
Fig 5.
Inactivation of PEG-purified SARS-CoV-2 by chlorous acid water under various protein loads.
The 1/10-diluted, PEG-precipitated SARS-CoV-2 was incubated with chlorous acid water along with 0.03% bovine serum albumin (BSA) (A), 0.3% sheep red blood cells (SRBCs) + 0.3% BSA (B), 0.5% polypeptone (PP) (C), and 5% fetal bovine serum (FBS). The incubation time for the virus and the chlorous acid water was 10 minutes, and the infectivity was assessed using the TCID50 method. Measurements were made and then fitted to an approximate equation based on the Chick-Watson model. The approximation equations and R2 values are displayed in the graphs. R2: coefficient of determination, Log10(N/N0): log reduction in the survival ratio.