In vitro anti-Helicobacter pylori activity of usnic acid.

Eradication of Helicobacter pylori is an important objective in overcoming gastric diseases. Many regimens are currently available but none of them could achieve 100% success in eradication. Medicinal lichen is used in the treatment of gastric ulcer in local folk medicine in Anatolia (Turkey). The present study was performed to assess the in vitro effects of usnic acid from Usnea dasypoga against clinical isolates and standard H. pylori strains and their minimum inhibitory concentrations (MICs). A total of 38 strains was assayed for anti-H. pylori activity. The agar dilution method was used for the determination of usnic acid and clarithromycin resistance.Six (16.2%) clinical isolates were resistant to usnic acid and five (13.5%) were resistant to clarithromycin. Dual susceptibility to usnic acid and clarithromycin rate was detected as very high (97.3%). Usnic acid has a strong and dose-dependent activity against H. pylori strains. The synergism between usnic acid and clarithromycin may be effective in the treatment of H. pylori infection.