Antibacterial and free-radical-scavenging properties of Stachys schtschegleevii (Lamiaceae)

Stachys schtschegleevii Sosn. (Lamiaceae alt. Labiatae) is one of 34 Stachys species found in Iran, and is morphologically similar to Stachys inflata. This plant has been used in the Iranian traditional medicine as a remedy for bacterial infections, rheumatic fever and other inflammatory conditions. The n-hexane, dichloromethane (DCM) and methanol (MeOH) extracts of the non-flowering aerial parts of this plant were assessed for their antibacterial and free- radical-scavenging activities using the micro-titer-based antimicrobial assay incorporating resazurin as an indicator of cell growth and the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, respectively. While the n-hexane extract did not show any free-radical-scavenging activity, the MeOH extract showed the highest level of activity with a RC50 value of 2.94 x 10 -2 mg/mL, which was about ten-fold less active than the positive control Trolox® (RC50 = 2.60 x 10 -3 mg/mL). None of the extracts showed any antibacterial property against Bacillus cereus and B. subtilis at test concentrations. However, all extracts were active against ampicillin-resistant Escherichia coli and Staphylococcus aureus. The MeOH extract was the most potent (MIC range 1.56-6.25 mg/mL) among the extracts and was most active against ampicillin-resistant E. coli (MIC = 1.56 mg/mL).