An assessment was made of the growth-inhibiting, bactericidal, and urease inhibitory activities of paeonol (PA), benzoic acid (BA), methyl gallate (MG), and 1,2,3,4,6-penta-O-galloyl-β-d-glucopyranose (PGG) identified in Paeonia lactiflora root, structurally related compounds, and four antibiotics toward three reference strains and four clinical isolates of Helicobacter pylori using broth dilution bioassay and Western blot. BA and PA showed strong bactericidal effect at pH 4, while MG and PGG were effective at pH 7. These constituents exhibited strong growth-inhibiting and bactericidal activity toward the five strains resistant to amoxicillin (minimal inhibitory concentration (MIC) 12.5 mg/L), clarithromycin (64 mg/L), metronidazole (64 mg/L), or tetracycline (15 mg/L), indicating that these constituents and the antibiotics do not share a common mode of action. Structural characteristics, such as types of functional groups and carbon skeleton, and hydrophobicity appear to play a role in determining the anti- H. pylori activity. H. pylori urease inhibitory activity of PGG was comparable to that of acetohydroxamic acid, while MG was less potent at inhibiting urease than thiourea. The UreB band disappeared at 250 mg/L PGG on Western blot, while the UreA bands were faintly visible at 1000 mg/L PGG. These constituents showed no significant cytotoxicity. Global efforts to reduce the level of antibiotics justify further studies on P. lactiflora root-derived materials containing MG, PA, and PGG as potential antibacterial products or lead molecules for the prevention or eradication from humans from diseases caused by H. pylori .

The growth-inhibiting activities of Paeonia lactiflora (Paeoniaceae) root steam distillate constituents and structurally related compounds against nine harmful intestinal bacteria and eight lactic acid-producing bacteria were compared with those of two antibiotics, amoxicillin and tetracycline. Thymol, α-terpinolene, (-)-perilla alcohol and (1R)-(-)-myrtenol exhibited high to extremely high levels of growth inhibition of all the harmful bacteria, whereas thymol and α-terpinolene (except for Lactobacillus casei ATCC 393) inhibited the growth of all the beneficial bacteria (MIC, both 0.08-0.62 mg mL(-1)). Tetracycline and amoxicillin exhibited extremely high level of growth inhibition of all the test bacteria (MIC, <0.00002-0.001 mg mL(-1)). 1,8-Cineole, geraniol, (-)-borneol, (1S,2S,5S)-(-)-myrtanol, nerol, (S)-(-)-β-citronellol and (±)-lavandulol also exhibited inhibitory activity but with differing specificity and levels of activity. Structure-activity relationship indicates that structural characteristics, such as geometric isomerism, degrees of saturation, types of functional groups and types of carbon skeleton, appear to play a role in determining the growth-inhibiting activity of monoterpenoids. Global efforts to reduce the level of antibiotics justify further studies on naturally occurring P. lactiflora root-derived materials as potential preventive agents against various diseases caused by harmful intestinal bacteria such as clostridia.

Helicobacter pylori is associated with various diseases of the upper gastrointestinal tract, such as gastric inflammation and duodenal and gastric ulcers. The aim of the study was to assess anti-H. pylori effects of the sesquiterpene lactone dehydrocostus lactone (DCL) from Magnolia sieboldii leaves, compared to commercial pure DCL, two previously known sesquiterpene lactones (costunolide and parthenolide), (–)-epigallocatechin gallate, and four antibiotics. The antibacterial activity of natural DCL toward antibiotic-susceptible H. pylori ATCC 700392 and H. pylori ATCC 700824 strains (MIC, 4.9 and 4.4 mg/L) was similar to that of commercial DCL and was more effective than costunolide, parthenolide, and EGCG. The activity of DCL was slightly lower than that of metronidazole (MIC, 1.10 and 1.07 mg/L). The antibacterial activity of DCL was virtually identical toward susceptible and resistant strains, even though resistance to amoxicillin (MIC, 11.1 mg/L for PED 503G strain), clarithromycin (49.8 mg/L for PED 3582GA strain), metronidazole (21.6 mg/L for H. pylori ATCC 43504 strain; 71.1 mg/L for 221 strain), or tetracycline (14.2 mg/L for B strain) was observed. This finding indicates that DCL and the antibiotics do not share a common mode of action. The bactericidal activity of DCL toward H. pylori ATCC 43504 was not affected by pH values examined (4.0–7.0). DCL caused considerable conversion to coccoid form (94 versus 49% at 8 and 4 mg/L of DCL for 48 h). The Western blot analysis revealed that urease subunits (UreA and UreB) of H. pylori ATCC 43504 were not affected by 10 mM of DCL, whereas UreA monomer band completely disappeared at 0.1 mM of (–)-epigallocatechin gallate. Global efforts to reduce the level of antibiotics justify further studies on M. sieboldii leaf-derived materials containing DCL as potential antibacterial products or a lead molecule for the prevention or eradication of drug-resistant H. pylori.

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.