Chemical composition and antimicrobial activity of Sideritis raeseri subsp. raeseri Hekdri. et Boiss. polar extracts

Aerial parts of plants from the Sideritis genus, known as „mountain tea“, are widely used in Mediterranean folk medicine as a very popular tea. Antiinflammatory, anti-ulcer, antioxidant, antispasmodic, stomachic, and antimicrobial properties were reported for some of these species [1]. Biological activities are mainly attributed to the flavonoid content of those plants. Aerial parts of Sideritis raeseri subsp. raeseri were collected on mountain Galičica, Former Yugoslav Republic of Macedonia (FYRM) in the phase of full flowering (July, 2008). Three different dry extracts were obtained: dry ethanolic extract (DEE), dry water extract (DWE) and dry ethyl acetate extract (DEAE). Six flavonoid compounds were isolated using preparative HPLC. LC/MS analysis was performed on an Agilent MSD TOF coupled to an Agilent 1200 series HPLC, using RR Zorbax Eclipse Plus C18 column (1.8 µm, 150×4.6mm). Antimicrobial activity of the extracts as well as of some isolated compounds were tested.The MIC values were determined using the broth microdilution method in 96-hole plates according to NCCLS [2]. Combination of the UV and ESI data allowed the characterization of 16 phenolic compounds, which could be classified into flavonoid glycosides or hydroxycynnamic acid derivatives. Among flavonoid glycosides the most numerous were derivatives of isoscutellarein and hypolaetin. Chlorogenic acid, verbascoside, leucosceptoside A and apigenin 7-O-glucoside were also detected and their amounts varied beetween samples. All tested substances were active against C. albicans, whereas only DEE extract showed antibacterial activity.

References:

[1] Gabrieli, C. N. et al. (2005) Journal of Ethnopharmacology 96: 423–428.

[2] NCCLS (2000) Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria That Grow Aerobically; Approved Standard – Fifth Edition. NCCLSocument M7-A5. NCCLS: Wayne, PA, USA