Omeprazole inhibits growth of gram-positive and gram-negative bacteria including Helicobacter pylori in vitro.

The antibacterial effects of omeprazole (100, 200 and 300 mg/L) were assessed using bacterial growth curves. A dose-related permanent inhibition was seen with actively growing Gram-positive cocci. A reduced and only temporary effect was observed with Gram-negative bacilli. After 1 day the bacterial count of Helicobacter pylori in the presence of omeprazole 200 mg/L was reduced from 10(4) cfu/mL for the control to zero. No synergic or antagonistic interaction of omeprazole with amoxycillin or doxycycline was observed for Escherichia coli and Enterococcus faecalis.