In vitro anti-Helicobacter pylori activity of extracts and essential oil of Thymus pannonicus All. (Lamiaceae)

Thymus pannonicus All. is an aromatic herbaceous plant distributed in Central and Eastern Europe (Jalas, 1972). The aerial parts of the lemon-scented chemotype from Serbia are considered a traditional remedy for various gastrointestinal complaints (Maksimović et al., 2008). In this work, we tested its antibacterial activity against Helicobacter pylori, a bacterium associated with the risk of developing complicated chronic diseases of the gastrointestinal tract. T. pannonicus hexane (HE), dichloromethane (DE), and methanol extracts (ME), the fraction of diethyl ether extract soluble in 80% aqueous methanol (FDM), and essential oil (EO), were tested by broth microdilution method against H. pylori ATCC 43504 (reference strain) and 10 clinical isolates, including strains resistant to metronidazole and/or clarithromycin. ME showed the best activity, with MIC50 (minimum concentration that inhibits the growth of 50% of the tested strains) and MIC90 of 4 and 16 μg/mL, respectively. FDM exhibited MIC50 16 μg/mL and MIC90 32 μg/ mL, while EO showed MIC50 2 μg/mL and MIC90 64 μg/mL. HE and DE were less active (MIC50 and MIC90 were 32 and 128 μg/mL, respectively). Liquid chromatography with ultraviolet and mass spectrometric detection revealed that ME was characterized by a high content of rosmarinic acid (64 mg/g) and salvianolic acid H, while FDM was rich in methylated flavonoid aglycons. The dominant compounds in EO, analyzed by gas chromatography with mass spectrometry and flame-ionization detectors, were geranial and neral (36.7% and 27.2%, respectively). The results indicate that preparations of T. pannonicus may be potential therapeutic agents against H. pylori infections.