In vitro anti-Helicobacter pylori activity of diallyl sulphides and protocatechuic acid

The in vitro inhibitory effects of diallyl disulphide (DADS), diallyl trisulphide (DAT), roselle calyx extract and protocatechuic acid (PA) on the growth of Helicobacter pylori (15 susceptible, 11 clarithromycin-resistant and 9 metronidazole-resistant strains) were studied. The inhibition zone was determined after each agent had been heated at 25, 60, 100 degrees C for 60 min. The minimal inhibitory concentration (MIC) of each agent was determined by the tube dilution assay. The results showed that heat treatment did not affect the anti-H. pylori activity of DADS, DAT, roselle calyx extract and PA, and the MIC values of these agents against test H. pylori strains were in the range 8-64 mg/L. The time-kill study assay for DAT and PA at 1x MIC was monitored in Muller Hinton broth supplemented with 10% horse blood or mice stomach homogenate. Both DAT and PA inhibited the growth of all test H. pylori in broth and mice stomach homogenate (p < 0.05); however, the inhibitory effects of these two agents were less in mice stomach homogenate than in broth (p < 0.05). DAT at 4, 6, 8, 10, 12, 14 mg/L and PA at 8, 16, 24, 32, 40, 48 mg/L were used for urease activity assay. These two agents significantly reduced urease activity of test H. pylori strains (p < 0.05), in which DAT and PA at 1x MIC reduced the urease activity of H. pylori to 70% and 40%, respectively. These agents, based on their lower MIC values and heat tolerance, might be useful in the prevention or therapy of H. pylori.