Reversing β-lactam antibiotic resistance of Staphylococcus aureus with galangin from Alpinia officinarum Hance and synergism with ceftazidime

Quercitrin and taxifolin stimulate osteoblast differentiation in MC3T3-E1 cells and inhibit osteoclastogenesis in RAW 264.7 cells

Flavonoids are natural antioxidants that positively influence bone metabolism. The present study screened among different flavonoids to identify biomolecules for potential use in bone regeneration. For this purpose, we used MC3T3-E1 and RAW264.7 cells to evaluate their effect on cell viability and cell differentiation. First, different doses of chrysin, diosmetin, galangin, quercitrin and taxifolin were analyzed to determine the optimum concentration to induce osteoblast differentiation. After 48h of treatment, doses ≥100μM of diosmetin and galangin and also 500μM taxifolin revealed a toxic effect on cells. The same effect was observed in cells treated with doses ≥100μM of chrysin after 14 days of treatment. However, the safe doses of quercitrin (200 and 500μM) and taxifolin (100 and 200μM) induced bone sialoprotein and osteocalcin mRNA expression. Also higher osteocalcin secreted levels were determined in 100μM taxifolin osteoblast treated samples when compared with the control ones. On the other hand, quercitrin and taxifolin decreased Rankl gene expression in osteoblasts, suggesting an inhibition of osteoclast formation. Indeed, osteoclastogenesis suppression by quercitrin and taxifolin treatment was observed in RAW264.7 cells. Based on these findings, the present study demonstrates that quercitrin and taxifolin promote osteoblast differentiation in MC3T3-E1 cells and also inhibit osteoclastogenesis in RAW264.7 cells, showing a positive effect of these flavonoids on bone metabolism.

Antifibrotic activity of galangin, a novel function evaluated in animal liver fibrosis model

This study aimed to investigate the effects of galangin on liver fibrosis in rats induced by subcutaneous injection of carbon tetrachloride (CCl4). The administration of CCl4 to rats for 12 weeks caused significant increase of hyaluronic acid, laminin, alanine transaminase, aspartate transaminase and decrease of total protein, albumin in serum, while the influences could be reversed by galangin. Galangin markedly reduced hepatic malondialdehyde, hydroxyproline concentration, increased activities of liver superoxide dismutase, glutathione peroxidase compared with CCl4-treated rats. Histological results indicated that galangin alleviated liver damage. In addition, treatment with galangin significantly down-regulated expressions of α-smooth muscle actin and transforming growth factor β1. These results suggest galangin can inhibit liver fibrosis induced by CCl4 in rats, which was probably associated with its effect on removing oxygen free radicals, decreasing lipid peroxidation, as well as inhibiting hepatic stellate cells activation and proliferation.

Synergistic activity and mechanism of action of ceftazidime and apigenin combination against ceftazidime-resistant Enterobacter cloacae

The purpose of this investigation was to examine the antibacterial and synergistic effect of naturally occurring flavonoids, apigenin, quercetin, naringenin and ceftazidime when use singly and in combination against ceftazidime-resistant Enterobacter cloacae strains by minimum inhibitory concentration (MIC), checkerboard and viable count methods. The mode of actions were also studied by electronmicoscopy, enzyme assay, outer and inner membrane permeabilisation. The results showed that these strains were positive in the ESBL-ampC genes combination by multiplex PCR. These findings were confirmed by MICs that these strains were resistant to ceftazidime, cefepime and flomoxef at >1024, 16-24, >256 μg/ml respectively, while susceptible to imipenem at 1-2 μg/ml. The synergistic activity was observed at ceftazidime plus either apigenin or naringenin combinations with FIC indixes between <0.01 and <0.27 against these strains, whereas ceftazidime plus clavulanic acid or quercetin did not exhibit synergy. The modulation of ceftazidime-resistance by apigenin or narigenin significantly enhanced the activities of ceftazidime. The 5,7-OH group of A ring and one 4'-OH group of the B ring in apigenin and naringenin are important for synergistic activity. Viable counts showed that the killing of ceftazidime-resistant E. cloacae DMST 21394 (CREC) cells by 3 μg/ml ceftazidime was potentiated by 3 μg/ml apigenin to low levels (10(3) cfu/ml) over 6h. Electronmicroscopy clearly showed that ceftazidime 3 μg/ml in combination with 3 μg/ml of apigenin also caused marked morphological damage of cell wall, cell shape and plasma membrane of this strain. Enzymes assays indicated that apigenin showed marked inhibitory activity against penicillinase type IV from E. cloacae. The results for outer membrane (OM) permeabilization in both nitrocefin (NCF) assay and crystal violet uptake showed that the combination of ceftazidime plus apigenin significantly altered OM permeabilisation of CREC compared to control or single treatment of these agents. Both o-nitrophenyl-β-D-galactoside (ONPG) uptake and release of UV-absorbing material concentrations results exhibited that ceftazidime and apigenin combination damaged CREC cytoplasmic membrane (CM) and caused subsequent leakage of intracellular constituents. From the results, it can be concluded that apigenin and naringenin have the synergistic effect with ceftazidime to reverse bacterial resistance to this cephalosporin against CREC. This activity may be involved three mechanisms of action by apigenin. The first is on the peptidoglycan synthesis inhibition. The second mechanism is inhibition the activity of certain β-lactamase enzymes. The third mode of action is alteration of OM and CM permeabilization. Apigenin and naringenin have a sufficient margin of safety for therapeutic use. For this reason, apigenin and naringenin offer for the development of a valuable adjunct to ceftazidime against CREC, which currently almost cephalosporins resistance.

In vitro antimicrobial activity of pistachio (Pistacia vera L.) polyphenols

We investigated the antimicrobial properties of polyphenol-rich fractions derived from raw shelled and roasted salted pistachios. American Type Culture Collection (ATCC), food and clinical isolates, of Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa, Pseudomonas mirabilis), Gram-positive bacteria (Listeria monocytogenes, Enterococcus hirae, Enterococcus faecium, Bacillus subtilis, Staphylococcus epidermidis, Staphylococcus aureus), the yeasts Candida albicans and Candida parapsilosis and the fungus Aspergillus niger were used. Pistachio extracts were active against Gram-positive bacteria with a bactericidal effect observed against L. monocytogenes (ATCC strains and food isolates), S. aureus and MRSA clinical isolates. Extracts from raw shelled pistachios were more active than those from roasted salted pistachios. The bactericidal activity of pistachio extracts could be used to help control the growth of some microorganisms in foods to improve safety and may find application as a topical treatment for S. aureus.

Synergistic activity of luteolin and amoxicillin combination against amoxicillin-resistant Escherichia coli and mode of action

The purpose of this research was to investigate whether luteolin has antibacterial and synergistic activity against amoxicillin-resistant Escherichia coli (AREC) when use singly and in combination with amoxicillin. The primarily mode of action is also investigated. The susceptibility assay (minimum inhibitory concentration and checkerboard determination) was carried out by the broth macrodilution method's in Müeller-Hinton medium. MIC and checkerboard determination were carried out after 20 h of incubation at 35°C by observing turbidity. The MICs of amoxicillin and luteolin against all AREC strains were >1000 and ≥ 200 μg/ml respectively. Synergistic activity were observed on amoxicillin plus luteolin against these strains. Viable count of this combination showed synergistic effect by reducing AREC cell numbers. The results indicated that this combination altered both outer and inner membrane permeabilisation. Enzyme assay showed that luteolin had an inhibitory activity against penicillinase. Fourier Transform-Infrared (FT-IR) spectroscopy exhibited that luteolin alone and when combined with amoxicillin caused increase in fatty acid and nucleic acid, but decrease in amide I of proteins in bacterial envelops compared with control. These results indicated that luteolin has the potential to reverse bacterial resistance to amoxicillin in AREC and may operate via three mechanisms: inhibition of proteins and peptidoglycan synthesis, inhibition of the activity of certain extended-spectrum β-lactamases and alteration of outer and inner membrane permeability. These findings offer the potential to develop a new generation of phytopharmaceuticals to treat AREC.

Propolis can potentialise the anti-adhesion activity of proanthocyanidins on uropathogenic Escherichia coli in the prevention of recurrent urinary tract infections

Background

Escherichia coli, the main bacteria found in recurrent urinary tract infections (UTI), is now frequently resistant to several currently used antibiotic treatments making new solutions essential. In this study, we evaluated the association propolis and proanthocyanidins type A to reduce bacterial anti-adhesion activity of E. coli on urothelial cells.

Results

This first double-blind, randomized, cross-over human trial included 5 volunteers that followed 6 different regimens with or without variable doses of cranberry and propolis with a washout period of at least 1 week between each regimen. Urine samples were collected at 0 h, 4-6 h, 12 h and 24 h after cranberry plus propolis or placebo capsule consumption. In vivo urinary bacterial anti-adhesion activity was assessed with a bioassay (a human T24 epithelial cell-line assay) and an in vivo Caenorhabditis elegans model. HPLC-PDA-MS was used to detect propolis and cranberry compounds in urine. Bioassays indicated significant bacterial anti-adhesion activity in urine collected from volunteers who had consumed cranberry plus propolis powder compared to placebo (p < 0.001). This inhibition was clearly dose-dependent, increasing with the amount of PACs and propolis equivalents consumed in each regimen. Results suggested that propolis had an additional effect with PACs and prevent a bacterial anti-adhesion effect over 1 day. An in vivo model showed that the E. coli strain presented a reduced ability to kill C. elegans after their growth in urine samples of patients who took cranberry plus propolis capsules. HPLC confirmed that propolis is excreted in urine.

Conclusions

This study presents an alternative to prevent recurrent UTI. Administration of PACs plus propolis once daily offers some protection against bacterial adhesion, bacterial multiplication and virulence in the urinary tract, representing an interesting new strategy to prevent recurrent UTI.

Synergistic activity and mode of action of flavonoids isolated from smaller galangal and amoxicillin combinations against amoxicillin-resistant Escherichia coli

AIM

The smaller galangal is extracted, purified and identified the bioactive compounds. The purpose of this research was to investigate whether these isolated compounds have antibacterial and synergistic activity against amoxicillin-resistant Escherichia coli (AREC) when used singly and in combination with amoxicillin. The primarily mode of action is also studied.

METHOD AND RESULTS

The galangin, kaempferide and kaempferide-3-O-β-d-glucoside were isolated. The minimum inhibitory concentrations(MIC) of amoxicillin and these flavonoids against AREC were between 500 and >1000 μg ml(-1). Synergistic activity was observed on combining amoxicillin with these flavonoids. The combinations of amoxicillin and these flavonoids exhibited a synergistic effect, reducing AREC cell numbers. Electron microscopy showed that these combinations damaged the ultrastructure of AREC cells. The results indicated that these combinations altered outer membrane permeability but not affecting cytoplasmic membrane. Enzyme assays showed that these flavonoids had an inhibitory activity against penicillinase.

CONCLUSION

These results indicated that these flavonoids have the potential to reverse bacterial resistance to amoxicillin in AREC and may operate via three mechanisms: inhibition of peptidoglycan and ribosome synthesis, alteration of outer membrane permeability, and interaction with β-lactamases.

SIGNIFICANCE AND IMPACT OF THE STUDY

These findings offer the potential to develop a new generation of phytopharmaceuticals to treat AREC.

Polyphenols as antimicrobial agents

Polyphenols are secondary metabolites produced by higher plants, which play multiple essential roles in plant physiology and have potential healthy properties on human organism, mainly as antioxidants, anti-allergic, anti-inflammatory, anticancer, antihypertensive, and antimicrobial agents. In the present review the antibacterial, antiviral, and antifungal activities of the most active polyphenol classes are reported, highlighting, where investigated, the mechanisms of action and the structure-activity relationship. Moreover, considering that the microbial resistance has become an increasing global problem, and there is a compulsory need to find out new potent antimicrobial agents as accessories to antibiotic therapy, the synergistic effect of polyphenols in combination with conventional antimicrobial agents against clinical multidrug-resistant microorganisms is discussed.

Recent advances in understanding the antibacterial properties of flavonoids

Antibiotic resistance is a major global problem and there is a pressing need to develop new therapeutic agents. Flavonoids are a family of plant-derived compounds with potentially exploitable activities, including direct antibacterial activity, synergism with antibiotics, and suppression of bacterial virulence. In this review, recent advances towards understanding these properties are described. Information is presented on the ten most potently antibacterial flavonoids as well as the five most synergistic flavonoid-antibiotic combinations tested in the last 6 years (identified from PubMed and ScienceDirect). Top of these respective lists are panduratin A, with minimum inhibitory concentrations (MICs) of 0.06-2.0 μg/mL against Staphylococcus aureus, and epicatechin gallate, which reduces oxacillin MICs as much as 512-fold. Research seeking to improve such activity and understand structure-activity relationships is discussed. Proposed mechanisms of action are also discussed. In addition to direct and synergistic activities, flavonoids inhibit a number of bacterial virulence factors, including quorum-sensing signal receptors, enzymes and toxins. Evidence of these molecular effects at the cellular level include in vitro inhibition of biofilm formation, inhibition of bacterial attachment to host ligands, and neutralisation of toxicity towards cultured human cells. In vivo evidence of disruption of bacterial pathogenesis includes demonstrated efficacy against Helicobacter pylori infection and S. aureus α-toxin intoxication.