Background: Several studies have reported inhibitory effects of lactic acid bacteria on bacterial pathogens.
Aim: To test whether a drink containing Lactobacillus casei strain Shirota inhibits Helicobacter pylori growth.
Methods: The in vitro growth inhibition of H. pylori was studied when L. casei was added to plates previously inoculated with H. pylori reference strain NCTC 11637. In an intervention study, 14 H. pylori-positive subjects were given Yakult drink (10(8) colony-forming units/mL L. casei) thrice daily during meals for 3 weeks. Six untreated H. pylori-positive subjects served as controls. H. pylori bacterial loads were determined using the 13C-urea breath test, which was performed before and 3 weeks after the start of L. casei supplementation.
Results: In vitro, L. casei inhibits H. pylori growth. This effect was stronger with L. casei grown in milk solution than in DeMan-Rogosa-Sharpe medium. No growth inhibition was shown with medium inoculated with lactic acid, Escherichia coli strain DH5alpha or uninoculated medium. Filtration of L. casei culture before incubation with H. pylori completely abolished the inhibitory effect. Urease activity decreased in nine of the 14 (64%) subjects with L. casei supplementation and in two of the six (33%) controls (P = 0.22).
Conclusions: Viable L. casei are required for H. pylori growth inhibition. This does not result from changes in lactic acid concentration. In addition, a slight, but non-significant, trend towards a suppressive effect of L. casei on H. pylori in vivo may exist.