## 4 Discussion  
\"Antibacterial/antiviral products\" are attracting considerable social attention. Safe and secure active substances that do not induce resistant strains are needed. Among conventional PM compounds, those with specific transition metal elements and certain three-dimensional structures have been found to have antiviral activity [5]. Of these, VB1(VOSO4), VB 2, and VB 3 were combined with antibiotic oxacillin and antibacterial agent Irgasan to develop antibacterial/antiviral mixtures as broad-spectrum antiviral and antibacterial agents [10]. As in the United States, the use of oxacillin and Irgasan has been prohibited in European countries because of their adverse effects on the bacterial purification of sewage. In the present study, a new version VB was prepared by adding PHMB in addition to a PM compound (patent number 6739772). The antiviral effects of VB were demonstrated in cultured cells (Figure 1a-c). As the maximum effect, TCID50 changed by four orders of magnitude (99.99% inhibition). The effects were observed in a concentration-dependent manner (Figure 1b,c). Additionally, the direct inactivating effects occurred in a concentration-dependent manner (Figure 2a,b). In the cultured cells, virus molecules decreased and TCID50 changed by four orders of magnitude each, suggesting the usefulness of quantitative RT-PCR in evaluation. However, as direct inactivating effects, TCID50 decreased by only one order of magnitude, although the number of virus molecules decreased by four orders of magnitude. Thus, about 1000 viral RNA molecules correspond to one infectious titer. In addition to the direct inactivation, VB inhibits virus adsorption and invasion by binding to the surfaces of living cells. Furthermore, VB significantly influences TCID50 because of its inhibitory effects on cell surfaces upon the secondary infection of virus particles released during the primary infection. A high affinity for the Matrix 2 protein, i.e., the surface protein of the influenza virus, was demonstrated (Table 2). Indeed, the high affinities of PM compounds for virus receptors on cell surfaces have also been demonstrated in HSV infection, suggesting that these compounds act in a similar way on the influenza virus. High affinities were also demonstrated for the SARS-CoV-2 S1 protein of the same coronavirus species as the influenza virus and GII.4 VP1 VLPs of a nonenveloped norovirus. Therefore, VB may act as a broad-spectrum antiviral agent. This may be explained by the fact that VB mainly acts on the cell surface. We examined whether the effects of the hygienic products containing VB, which showed high antiviral activity in cultured cells, were maintained. For this purpose, a quantitative RT-qPCR was established for viral and bacterial component RNAs because of the difficulties of handling infectious viruses in terms of equipment and throughput. Representative viruses and bacteria, with a significant impact on the human body in the living environment, were selected (six viral and five bacterial species in Figure 3). In addition, general bacteria and fungi were simultaneously examined by the plate culture method according to the manufacturing standards for hygiene products. Commercially available products were randomly collected for examination in cooperation with 22 manufacturers of VB-containing products. As shown in Figure S1, >300 colonies of general bacteria, detected in a petri dish, corresponded to the reference value (30,000/sample). All the samples met the reference value, with no fungi detected, and were negative for viral and bacterial RNA molecules. Safety can be examined to some extent because infectivity can be negated if no gene molecule is detected. In the evaluation of antiviral effects, the results of quantitative RT-PCR were correlated with the TCID50 assay. VB has only been used in solutions. In the present study, its application to solids was examined. In the conventional use of VB in solutions, the crystals of VB are ground for dissolution in water.