The aim of the present study was to assess antimicrobial effects of naringenin (NRG), luteolin (LUT), myricetin (MCT), and protocatechuic acid (PCA) identified in a Hibiscus rosa sinensis flower against two reference strains and five clinical isolates of Helicobacter pylori . NRG displayed the most growth inhibitory and bactericidal activities to seven bacterial strains including six strains resistant to one or several antibiotics, azithromycin (MIC, 16–32 mg/L), erythromycin (MIC, 32 mg/L), levofloxacin (MIC, 32 mg/L), and/or metronidazole (24–64 mg/L), followed by LUT and MCT, while PCA showed weak activities toward the strains. These constituents had similar antibacterial activities toward the seven tested strains suggesting that these constituents and the antibiotics do not have a common mechanism of anti- H. pylori activity. NRG, LUT, and MCT resulted in a high percentage of coccoid forms of H. pylori . NRG exhibited the highest anti-biofilm formation activity. MCT produced the strongest inhibition of urease activity followed by LUT and PCA, whereas the activity of NRG was similar to standard inhibitor thiourea. The four constituents had no significant toxicity to human cell lines. A global attempt to decrease utilization of antibiotics justifies the need for further research on H. rosa sinensis derived materials containing NRG, LUT, MCT, and PCA as potential products or lead compounds for the prevention or treatment of diseases caused by H. pylori infection.

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