Evaluation of Potential Antiviral Activity of the Hydroalcoholic Extract of Lemon Balm L. against Herpes Simplex Virus Type 1

Background and Aims: Lemon Balm L (Lamiaceae) has been used in a variety of practical applications in medical sciences. Its antiviral activity against herpes simplex virus type-1 (HSV-1) was investigated in cell culture. Lemon Balm hydroalcoholic extract was found to be non-toxic to Vero cells up to concentration 800 ug/ml and inhibited the growth and development of HSV-1 in dose-dependent manner in Vero cells. Methods: In order to study the possible mechanisms of the antiviral activity of Lemon Balm extract, cells were treated with extract before, during and after infection, and the viral titers were tested by TCID50 assay. Results: The antiviral effects in treatment of post and during virus infection were more remarkable than the treatment of preinfection. For further investigation indirect immunofluorescence technique was used to elucidate the antiviral mechanism of the extract by infecting Vero cells at different times and monitoring the synthesis of viral proteins. Conclusion: Although the precise mechanism has not yet to be defined, our work indicated that lemon Balm L. extract could inhibit growth and development of HSV-1 in cells in vitro.