The inhibition of physiological gastric acid secretion induced by proton pump inhibitors (PPIs), the most widely used drugs in the world, may cause a significant bacterial overgrowth in the gastrointestinal tract as a side effect. This study was undertaken firstly to correlate PPI intake with concentration of specific bacterial groups in the stomach as well as possible Helicobacter pyloriinfection, and secondly to assess the efficacy of the 4 lactobacilli L. rhamnosusLR06 (DSM 21981), L. pentosusLPS01 (DSM 21980), L. plantarumLP01 (LMG P-21021), and L. delbrueckiisubsp. delbrueckiiLDD01 (DSM 22106) in the restoration of a physiological gastric barrier.