Antimicrobial effects of antioxidants with and without clarithromycin on Helicobacter pylori

Increasing resistance to currently used antimicrobials has resulted in the evaluation of other agents that have antimicrobial activity against Helicobacter pylori. H. pylori American Type Culture Collection (ATCC) strain 49503 (a toxin-producing strain known to be associated with gastric cancer) was grown, a cell suspension prepared in 2 mL PBS and diluted 10-fold. One hundred microL of this cell suspension was added to vitamin C 0.5%, vitamin E 0.5%, garcinol 100 microg/mL, Protykin (containing 50% trans-resveratrol) 100 microg/mL and garcinol + Protykin 100 microg/mL in Lennox broth, and incubated for 16 h under microaerophilic conditions. Three replicates of 10 microL from each 10(-7) dilution tube were plated, colonies were counted after 16 h, and growth of H. pylori was confirmed by the CLO test. These colony counts were compared to control cultures without the addition of any antioxidants. The experiments were then repeated with the addition of 15 microg/mL of clarithromycin to experimental and control samples. Enhanced killing of H. pylori by 37.6% was noted when vitamin C was added, which increased to 66% when clarithromycin was added, compared to controls (p < 0.05). With garcinol and Protykin alone there was 91.4 and 87% killing of H. pylori, respectively, while a combination of garcinol + Protykin resulted in 90.8% killing compared to controls (p < 0.05). When clarithromycin was added, there was 76.3% increased killing with garcinol alone, 55.3% with Protykin alone, and 73.7% with garcinol + Protykin compared to controls (containing clarithromycin) (p < 0.05). Vitamin E had no effect on H. pylori growth compared to controls. We conclude from this study that some antioxidants such as vitamin C, garcinol and Protykin, but not vitamin E, may have potential as antimicrobial agents against H. pylori.