Utilization of plant resources for treatment of Helicobacter pylori infections is one of the appealing approaches as rapid emergence of antibiotic-resistant strains is occurring throughout the world. Ethanol extract and its fractions from Hibiscus rosa-sinensis red flower were assessed for antibacterial and urease inhibitory activities towards forty-three clinical strains and two reference strains of H. pylori. The ethyl acetate fraction exhibited the most potent bacteriostatic activity with minimum inhibitory concentrations (MICs) of 0.2-0.25 mg/mL and minimum bactericidal concentrations (MBCs) of 1.25-1.5 mg/mL against all test strains, including forty-three strains resistant to one to four antibiotics, azithromycin (MICs, 8-256 µg/mL), erythromycin (MICs, 8-128 µg/mL), levofloxacin (MICs, 8-256 µg/mL), and/or metronidazole (MICs, 8-256 µg/mL). The fraction had similar antibacterial activities toward these test strains suggesting the preparation and the antibiotics do not have a common mechanism of anti-H. pylori activity. The fraction also had stronger effects on biofilm formation, morphological conversion, and urease activity of H. pylori than the other fractions and the ethanol extract. These flower preparations were non-toxic to three human cell lines, and nine compounds were also isolated and identified from the ethyl acetate fraction. In vivo research needs to be conducted to confirm the potential usefulness of H. rosa-sinensis flower and its constituents for effective prevention and treatment of H. pylori disease.

Six solvent fractions isolated from flower bud and leaf ethanolic extracts of Cleistocalyx operculatus were analyzed for their phytochemical contents, including phenolics, flavonoids, saponins, tannins, and alkaloids. Antioxidant activities were measured using the ABTS, DPPH, and FRAP assays. The results showed that the flower bud aqueous fraction (BAF) and the leaf aqueous fraction (LAF) rich in phenolic content (768.18 and 490.74 mg GAE/g dry extract, respectively) exhibited significantly higher antioxidant activities than the other fractions. The flower bud hexane fraction (BHF) had remarkably high flavonoid and saponin contents (134.77 mg QE/g and 153.33 mg OA/g dry extract, respectively), followed by that of the leaf hexane fraction (LHF) (76.54 mg QE/g and 88.25 mg OA/g dry extract, respectively). The BHF and LHF were found to have extremely high antibacterial activity against two H. pylori strains, ATCC 51932 and 43504 (MICs of 125 µg/mL). Interestingly, DMC (2′,4′-Dihydroxy-6′-methoxy-3′,5′-dimethylchalcone) isolated from the BHF displayed greater antibacterial activity against the bacterial strains (MICs of 25–50 µg/mL) than those of the fractions. In addition, DMC presented potent inhibitory effects on H. pylori urease (IC₅₀ of 3.2 µg/mL) and α-amylase (IC₅₀ of 83.80 µg/mL), but no inhibition against α-glucosidase. It was also demonstrated that DMC showed pronounced inhibitory effects on the urease activity and biofilm formation of H. pylori, and could increase the membrane permeability of the bacterial cells. Scanning electron micrographs depicted that the BHF and DMC had strong effects on the cell shape and significantly induced the distortion and damage of the cell membrane. The fractions and DMC showed no significant toxicity to four tested human cell lines. Efforts to reduce antibiotic use indicate the need for further studies of the flower buds and DMC as potential products to prevent or treat gastric H. pylori infections.

Six solvent fractions isolated from flower bud and leaf ethanolic extracts of Cleistocalyx operculatus were analyzed for their phytochemical contents including phenolics, flavonoids, saponins, tannins, and alkaloids. Antioxidant activities were measured using the ABTS, DPPH, and FRAP assays. The results showed that flower bud aqueous fraction (BAF) and leaf aqueous fraction (LAF) rich in phenolic content (768.18 and 490.74 mg GAE/g dry extract, respectively) exhibited significantly higher antioxidant activities than other fractions. Flower bud hexane fraction (BHF) had remarkably high flavonoid and saponin contents (134.77 mg QE/g and 153.33 mg OA/g dry extract, respectively), followed by that of leaf hexane fraction (LHF) (76.54 mg QE/g and 88.25 mg OA/g dry extract, respectively). BHF and LHF were found to have extremely high antibacterial activity against two H. pylori strains ATCC 51932 and 43504 (MICs of 125 µg/ml). Interestingly, DMC (2’,4’-Dihydroxy-6’-methoxy-3’,5’-dimethylchalcone) isolated from BHF displayed greater antibacterial activity against the bacterial strains (MICs of 25–50 µg/ml) than those of the fractions. In addition, DMC presented potent inhibitory effects on H. pylori-urease (IC50 of 3.2 µg/ml) and α-amylase (IC50 of 83.80 µg/ml), but no inhibition against α-glucosidase. It was also demonstrated that DMC showed its pronounced inhibitory effects on urease activity and biofilm formation of H. pylori, and could increase the membrane permeability of the bacterial cells. Scanning electron micrographs depict that BHF and DMC had strong effects on the cell shape and significantly induced distortion and damage of the cell membrane. The fractions and DMC showed no significant toxicity to four tested human cell lines. Efforts to reduce antibiotic use indicate the need for further researches of the flower buds and DMC as potential products to prevent or treat gastric H. pylori infections.

Boesenbergia rotunda (Zingiberaceae) is a well-known traditional medicinal and culinary plant found in Southeast Asia and China. The extracts of this plant have been shown to have antibacterial potential against several pathogenic bacteria, including Helicobacter pylori. However, the antibacterial activity of the essential oils (EOs) from B. rotunda toward H. pylori has not been reported. Hence, the present study investigated the chemical compositions and antibacterial properties of the EOs extracted from the rhizomes and tuberous roots of B. rotunda against H. pylori. GC–MS analysis revealed that the rhizome EO was rich in camphor (28.6 %), 1,8-cineole (16.0 %), geraniol (15.5 %) and E-β-ocimene (12.8 %), while the tuberous root EO predominantly contained E-β-ocimene (31.9 %), camphor (19.9 %), geraniol (16.3 %), limonene (7.5 %) and 1,8-cineole (4.3 %). Both of the EOs exhibited strong anti-H. pylori activity, with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of 0.31 and 2.50 mg/mL for the rhizome EO and 0.16 and 1.25 mg/mL for the tuberous root EO, respectively. In vitro urease inhibition assay revealed that these EOs exhibited comparable and significant inhibitory action on the urease activity of H. pylori. Mechanism of action showed that the tuberous root EO had a stronger antibiofilm effect than the rhizome EO and both of the EOs demonstrated potent membrane-permeabilising properties resulting in the leakage of intracellular proteins from H. pylori cells. These findings support the potential application of B. rotunda EOs as effective natural agents for the prevention and control of H. pylori infections.