['Triple therapy with amoxicillin, clarithromycin, and a proton-pump inhibitor is a common therapeutic strategy for the eradication of Helicobacter pylori (H. pylori). However, frequent appearance of clarithromycin-resistant strains is a therapeutic challenge. While various quinones are known to specifically inhibit the growth of H. pylori, the quinone 1,4-dihydroxy-2-naphthoic acid (DHNA) produced by Propionibacterium has strong stimulating effect on Bifidobacterium. We were interested to see whether DHNA could inhibit the growth of H. pylori in in vitro or in vivo experimental setting.', 'The minimum inhibitory concentration (MIC) of DHNA was determined by the agar dilution method. The inhibitory action of DHNA on the respiratory activity was measured by using an oxygen electrode. Germ-free mice infected with H. pylori were given DHNA in free drinking water containing 100 μg/mL for 7\u2003days.', "DHNA inhibited H. pylori growth at low MIC values, 1.6-3.2 μg/mL. Likewise, DHNA inhibited clinical isolates of H. pylori, resistant to clarithromycin. However, DHNA did not inhibit other Gram negative or anaerobic bacteria in the normal flora of the human intestine. Both H. pylori cellular respiration and adenosine 5'-triphosphate (ATP) generation were dose-dependently inhibited by DHNA. Similarly, the culture filtrates of propionibacterial strains inhibited the growth of H. pylori, and oral administration of DHNA could eradicate H. pylori in the infected germ-free mice."] Does the bifidogenic growth stimulator inhibit the growth and respiration of Helicobacter pylori?