Acidic Conditions Enhance Bactericidal Effects of Sodium Bisulfite on Helicobacter pylori

BACKGROUND: The Brucella broth medium, which is often used for the cultivation of microaerobic bacteria including Helicobacter pylori. It contains sodium bisulfite to decrease oxygen content in the medium. The growth of H. pylori, however, is inhibited by sodium bisulfite. In this study, the effect of sodium bisulfite was compared with several antioxidants and quantified under acidic conditions, mimicking the gastric environment. METHODS: Growth of H. pylori in the presence of several antioxidants was evaluated at OD655 nm. Effect of sodium bisulfite on H. pylori under acidic conditions was evaluated by measuring colony forming units (cfu). RESULTS: Under neutral conditions, sodium bisulfite was a more potent suppressor of H. pylori. Resveratrol, a polyphenol found in wine, exhibited the most potent inhibitory activity. To quantify the effect of sodium bisulfite on H. pylori under acidic conditions, the bacteria were grown at 37 degrees C for 30 minutes in 0.15 mol/l HCl/KCl (pH 2.0) with or without urea and sodium bisulfite. Sodium bisulfite (0.5 mmol/l) did not affect the viability at neutral pH 7.0, however, it killed H. pylori under acidic conditions, even if urea, the key substance enabling H. pylori to survive under acidic conditions, was present. The bacteria, which had been incubated under acidic conditions in the presence of urea, could survive a subsequent 30 minute-incubation at pH 2.0 without urea. Presence of sodium bisulfite, however, in the subsequent 30 minute-incubation, killed the bacteria. CONCLUSIONS: The bactericidal effect of sodium bisulfite on H. pylori was greater under acidic conditions and independent of urease activity.