Abstract: This paper studied the effect of the total extract of Hypericum perforatum L. on three strains of Staphylococcus aureus in the course of 24 hour's incubation with and without illumination, during which the Optical Density value (640 nm), Colony Forming Unit, Total Cell Count, Minimum Bactericidal Concentration and superoxcide dismutase (SOD)were tested. The results showed that the extract had antibacterial effect on the three strains of S.aureus, its effect depended on its concentrations but was independent of illumination and it induced the increase of SOD activity in bacterial cells.

Key words: Hypericum perforatum