Mechanism of inactivation of enveloped viruses by the biosurfactant surfactin from Bacillus subtilis

Abstract

The antiviral activity of surfactin, a cyclic lipopeptide antibiotic and biosurfactant produced by Bacillus subtilis, was determined for a broad spectrum of different viruses, Semliki Forest virus (SFV), herpes simplex virus (HSV-1, HSV-2), suid herpes virus (SHV-1), vesicular stomatitis virus (VSV), simian immunodeficiency virus (SIV), feline calicivirus (FCV), murine encephalomyocarditis virus (EMCV). In vitro experiments showed biphasic virus inactivation kinetics for enveloped viruses during treatment. Inactivation of enveloped viruses, especially herpes- and retroviruses, was much more efficient than that of non-enveloped viruses. For those viruses susceptible to its action, surfactin was active at 25 microM in medium containing 5% fetal calf serum (FCS). Concentrations up to 80 microM of surfactin led to a titre reduction of >4.4 log10 CCID50/ml for HSV-1 in 15 min and for SIV and VSV in 60 min. The inactivation rate increased linearly with the incubation temperature by a factor 2.4/10 degrees C and logarithmically with the concentration. Serum components, probably proteins and/or lipids, influence the effective surfactin concentration. A disruption of the viral lipid membrane and partially of the capsid was observed by electron microscopy. These findings suggest that the antiviral action, postulated also in other investigations, seems to be due to a physicochemical interaction of the membrane-active surfactant with the virus lipid membrane. Surfactin may be useful for application in virus safety enhancement of biotechnological and pharmaceutical products.