Rosin Soap Exhibits Virucidal Activity

Abstract

Chemical methods of virus inactivation are used routinely to prevent viral transmission in both a personal hygiene capacity but also in at-risk environments like hospitals. Several virucidal products exist, including hand soaps, gels, and surface disinfectants. Resin acids, which can be derived from tall oil, produced from trees, have been shown to exhibit antibacterial activity. However, whether these products or their derivatives have virucidal activity is unknown. Here, we assessed the capacity of rosin soap to inactivate a panel of pathogenic mammalian viruses in vitro. We show that rosin soap can inactivate human enveloped viruses: influenza A virus (IAV), respiratory syncytial virus, and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). For IAV, rosin soap could provide a 100,000-fold reduction in infectivity. However, rosin soap failed to affect the nonenveloped encephalomyocarditis virus (EMCV). The inhibitory effect of rosin soap against IAV infectivity was dependent on its concentration but not on the incubation time or temperature. In all, we demonstrate a novel chemical inactivation method against enveloped viruses, which could be of use for preventing virus infections in certain settings. IMPORTANCE Viruses remain a significant cause of human disease and death, most notably illustrated through the current coronavirus disease 2019 (COVID-19) pandemic. Control of virus infection continues to pose a significant global health challenge to the human population. Viruses can spread through multiple routes, including via environmental and surface contamination, where viruses can remain infectious for days. Methods for inactivating viruses on such surfaces may help mitigate infection. Here, we present evidence identifying a novel virucidal product, rosin soap, which is produced from tall oil from coniferous trees. Rosin soap was able to rapidly and potently inactivate influenza virus and other enveloped viruses.

Keywords: antimicrobial; antiviral; fomite; inactivation; soap; virucidal; virus.

FIG 1

Effect of rosin soap treatment on IAV (strain WSN) infectivity in solution compared to mock DMEM without (A) and with (B) the removal of residual rosin acid by filtration. IAV suspension was incubated with rosin soap solution at 37°C for 5 min before the residual infectivity was determined via dilution on susceptible cells (MDCK cells). The infectious virus titer corresponds to the reciprocal of the final dilution showing a virus-induced cytopathic effect. The dashed line delineates the dilution at which the rosin soap treatment was toxic to the MDCK cells.

FIG 2

Effect of rosin soap treatment on a panel of virus infectivity in solution compared to mock DMEM. Three enveloped (IAV strain Udorn, RSV, and SARS-CoV-2 [SARS2]) and one nonenveloped EMCV virus were used. Virus suspensions were incubated with rosin acid solution at 37°C for 5 min before the residual infectivity was determined via dilution on susceptible cells (MDCK cells for IAV; Vero cells for RSV, SARS2, and EMCV). The infectious virus titer corresponds to the reciprocal of the final dilution giving a virus-induced cytopathic effect. The dashed line delineates the dilution at which the rosin soap treatment was toxic to the susceptible cells.

FIG 3

Effect of rosin soap treatment on IAV infectivity in solution compared to mock DMEM at different concentrations, treatment times, and temperatures. IAV suspensions were incubated with rosin soap solution (final concentration: 2.5, 0.25, or 0.025% [wt/vol]) under distinct conditions before the residual infectivity was determined via dilution on susceptible cells (MDCK). The effect of temperature—37°C (A), room temperature (B), or 4°C (C)—is shown alongside the incubation time—5 (blue), 15 (red), or 30 min (green). The infectious virus titer corresponds to the reciprocal of the final dilution showing a virus-induced cytopathic effect. These experiments were carried out in three replicates in two independent experiments.