Enhancing cationic surfactants’ inactivation of non-enveloped viruses by sulfate ions

Abstract Quaternary cationic surfactants with bactericidal activity such as didecyldimethylammonium chloride (DDAC) show an inactivation effect on enveloped viruses, but they have little effect on non-enveloped viruses such as noroviruses. Therefore, we examined additives that enhance the inactivation effect of cationic surfactants by using feline calicivirus (FCV) as a representative of a non-enveloped virus. The result was that SO42- ions, which are a general-purpose salt, had a strong salting-out effect that reduced the solubility of proteins, greatly enhancing the inactivation ability of DDAC. The SO42- ions also enhanced FCV inactivation by other cationic surfactants such as cetylpyridinium chloride (CPC) and benzalkonium chloride (ADBAC). To clarify the mechanism, we evaluated the denaturation and binding process of DDAC to bovine serum albumin (BSA) as a model protein by means of circular dichroism (CD) spectrum and isothermal titration calorimeter (ITC), respectively. The SO42- ions disturbed the protein structure by their salting-out effect and promoted cooperative binding from lower DDAC concentrations by reducing the critical micelle concentration (cmc), indicating that these synergistic effects caused a large structural change in the protein. These results suggested that increasing the protein denaturation of the cationic surfactants by adding SO42- ions enhanced the inactivation effect on the non-enveloped virus.