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

Flavonoids: A treasure house of prospective pharmacological potentials

Flavonoids are organic compounds characterized by a range of phenolic structures, which are abundantly present in various natural sources such as fruits, vegetables, cereals, bark, roots, stems, flowers, tea, and wine. The health advantages of these natural substances are renowned, and initiatives are being taken to extract the flavonoids. Apigenin, galangin, hesperetin, kaempferol, myricetin, naringenin, and quercetin are the seven most common compounds belonging to this class. A thorough analysis of bibliographic records from reliable sources including Google Scholar, Web of Science, PubMed, ScienceDirect, MEDLINE, and others was done to learn more about the biological activities of these flavonoids. These flavonoids appear to have promising anti-diabetic, anti-inflammatory, antibacterial, antioxidant, antiviral, cytotoxic, and lipid-lowering activities, according to evidence from in vitro, in vivo, and clinical research. The review contains recent trends, therapeutical interventions, and futuristic aspects of flavonoids to treat several diseases like diabetes, inflammation, bacterial and viral infections, cancers, and cardiovascular diseases. However, this manuscript should be handy in future drug discovery. Despite these encouraging findings, a notable gap exists in clinical research, hindering a comprehensive understanding of the effects of flavonoids at both high and low concentrations on human health. Future investigations should prioritize exploring bioavailability, given the potential for high inter-individual variation. As a starting point for further study on these flavonoids, this review paper may promote identifying and creating innovative therapeutic uses.

Pharmacological activities and therapeutic potential of galangin, a promising natural flavone, in age-related diseases

BACKGROUND

The extension of average life expectancy and the aggravation of population aging have become the inevitable trend of human development. In an aging society, various problems related to medical care for the elderly have become increasingly prominent. However, most of the age-related diseases have the characteristics of multiple diseases at the same time, prone to complications, and atypical clinical manifestations, which bring great difficulties to its treatment. Galangin (3,5,7-trihydroxyflavone) is a natural active compound extracted from the root of Alpinia officinarum Hance (Zingiberaceae). Recently, many studies have shown that galangin has potential advantages in the treatment of neurodegenerative diseases and cardiovascular and cerebrovascular diseases, which are common in the elderly. In addition, it also showed that galangin had prospective activities in the treatment of tumor, diabetes, liver injury, asthma and arthritis.

PURPOSE

This review aims to systematically summarize and discuss the effects and the underlying mechanism of galangin in the treatment of age-related diseases.

METHODS

We searched PubMed, SciFinder, Web of Science and CNKI literature database resources, combined with the keywords "galangin", "neurodegenerative disease", "tumor", "diabetes", "pharmacological activity", "drug combination", "pharmacokinetics", "drug delivery system" and "safety", and comprehensively reviewed the pharmacological activities and mechanism of galangin in treating age-related diseases.

RESULTS

According to the previous studies on galangin, the anti-neurodegenerative activity, cardiovascular and cerebrovascular protective activity, anti-tumor activity, anti-diabetes activity, anti-arthritis activity, hepatoprotective activity and antiasthmatic activity of galangin were discussed, and the related mechanisms were classified and summarized in detail. In addition, the drug combination, pharmacokinetics, drug delivery system and safety of galangin were furtherly discussed.

CONCLUSIONS

This review will provide reference for galangin in the treatment of age-related diseases. Meanwhile, further experimental research and long-term clinical trials are needed to determine the therapeutic safety and efficacy of galangin.

Vancomycin Resistance in Enterococcus and Staphylococcus aureus

Enterococcus faecalis, Enterococcus faecium and Staphylococcus aureus are both common commensals and major opportunistic human pathogens. In recent decades, these bacteria have acquired broad resistance to several major classes of antibiotics, including commonly employed glycopeptides. Exemplified by resistance to vancomycin, glycopeptide resistance is mediated through intrinsic gene mutations, and/or transferrable van resistance gene cassette-carrying mobile genetic elements. Here, this review will discuss the epidemiology of vancomycin-resistant Enterococcus and S. aureus in healthcare, community, and agricultural settings, explore vancomycin resistance in the context of van and non-van mediated resistance development and provide insights into alternative therapeutic approaches aimed at treating drug-resistant Enterococcus and S. aureus infections.

Characterization and Potentiating Effects of the Ethanolic Extracts of the Red Seaweed Gracillaria sp. on the Activity of Carbenicillin against Vibrios

β-lactam-resistant Vibrio strains are a significant clinical problem, and β-lactamase inhibitors are generally coadministered with β-lactam drugs to control drug-resistant bacteria. Seaweed is a rich source of natural bioactive compounds; however, their potential as β-lactamase inhibitors against bacterial pathogens remains unknown. Herein, we evaluated the potential β-lactamase inhibitory effect of the ethanolic extracts of the red seaweed Gracilaria sp. (GE) against four Vibrio strains. The minimum inhibitory concentration, half-maximal inhibitory concentration, checkerboard assay results, and time-kill study results indicate that GE has limited antibacterial activity but can potentiate the activity of the β-lactam antibiotic carbenicillin against Vibrio parahemolyticus and V. cholerae. We overexpressed and purified recombinant metallo-β-lactamase, VarG, from V. cholerae for in vitro studies and observed that adding GE reduced the carbenicillin and nitrocefin degradation by VarG by 20% and 60%, respectively. Angiotensin I-converting enzyme inhibition studies demonstrated that GE did not inhibit VarG via metal chelation. Toxicity assays indicated that GE exhibited mild toxicity against human cells. Through gas chromatography and mass spectrometry, we showed that GE comprises alkaloids, phenolic compounds, terpenoids, terpenes, and halogenated aromatic compounds. This study revealed that extracts of the red seaweed Gracillaria sp. can potentially inhibit β-lactamase activity.

Antimicrobial activities and mechanisms of extract and components of herbs in East Asia

Antibacterial drugs face increasing challenges due to drug resistance and adverse reactions, which has created a pressing need for the discovery and development of novel antibacterial drugs. Herbs have played an important role in the treatment of infectious diseases. This review aims to summarize, analyze and evaluate the antibacterial activities and mechanisms of components from popular herbs in East Asia. In this review, we have searched and summarized the scientific papers published during the past twenty-year period from electronic databases such as PubMed, ScienceDirect, and Web of Science. These herbs and their components, including alkaloids, flavonoids, essential oils, terpenes, organic acids, coumarins and lignans, display potential antimicrobial effects. Herbal medicine formulas (HMFs) usually show stronger antibacterial activity than single herbs. Herbs and HMFs bring forth antibacterial activities by damaging cell membranes and walls, inhibiting nucleic acid and protein synthesis, and increasing intracellular osmotic pressure. These herbs and their components can be developed as potential and promising novel antibacterial herbal products.

Identification of Allosteric Hotspots regulating the ribosomal RNA-binding by Antibiotic Resistance-Conferring Erm Methyltransferases

Antibiotic resistance via epigenetic methylation of ribosomal RNA is one of the most prevalent strategies adopted by multidrug resistant pathogens. The erythromycin-resistance methyltransferase (Erm) methylates rRNA at the conserved A2058 position and imparts resistance to macrolides such as erythromycin. However, the precise mechanism adopted by Erm methyltransferases for locating the target base within a complicated rRNA scaffold remains unclear. Here, we show that a conserved RNA architecture, including specific bulge sites, present more than 15 Å from the reaction center, is key to methylation at the pathogenic site. Using a set of RNA sequences site-specifically labeled by fluorescent nucleotide surrogates, we show that base flipping is a prerequisite for effective methylation and that distal bases assist in the recognition and flipping at the reaction center. The Erm–RNA complex model revealed that intrinsically flipped-out bases in the RNA serve as a putative anchor point for the Erm. Molecular dynamic simulation studies demonstrated the RNA undergoes a substantial change in conformation to facilitate an effective protein–rRNA handshake. This study highlights the importance of unique architectural features exploited by RNA to impart fidelity to RNA methyltransferases via enabling allosteric crosstalk. Moreover, the distal trigger sites identified here serve as attractive hotspots for the development of combination drug therapy aimed at reversing resistance.

Comparison for quantification of eight components in Alpinia officinarum Hance by using high-performance liquid chromatography coupled with diode array detector and charged aerosol detector with individual and substitute reference compound

An efficient HPLC-DAD-CAD method was developed and compared for simultaneous quantification of four flavonoids and four diarylheptanoids in Alpinia officinarum Hance (A. officinarum) using individual and substitute reference compound. All calibration curves for investigated analytes showed good linear regression (R²> 0.9991). The LODs of investigated compounds for DAD and CAD were 0.15-7.92 ng (0.03-1.58 μg/mL) and 2.91-3.95 ng (0.58-0.79 μg/mL), respectively, whereas the LOQs were 0.52-26.39 ng (0.10-5.28 μg/mL) for DAD, and 9.70-13.18 ng (1.94-2.64 μg/mL) for CAD. Recoveries of all analytes, which ranged from 96.58% to 100.06% for DAD, and from 96.29% to 99.61% for CAD, were acceptable. According to the quantitative results, the eight compounds in A. officinarum can be accurately quantified with individual calibration curves by two detectors. In addition, to overcome the bottleneck of shortage of reference standards, diphenylheptane A and galangin, respectively, were selected for direct or calibrated quantitative determination of other diarylheptanoids and flavonoids in A. officinarum. The results showed the contents of eight components in A. officinarum determined by these methods were similar, which suggested that substitute reference compound was suitable for quantification of its analogues.

An overview of the chemical composition and biological activities of essential oils from Alpinia genus (Zingiberaceae)

Alpinia Roxb. is the largest genus of the Zingiberaceae family. A large number of Alpinia species has been used as food and traditional medicines. Alpinia essential oils have been studied for their chemical profiles, in which 1,8-cineole, β-pinene, α-pinene, β-myrcene, camphor, γ-terpinene, p-cymene, geraniol, α-fenchyl acetate, ocimene, methyl cinnamate, and β-caryophyllene have been found to be the major compounds. Essential oils isolated from Alpinia plants have been reported to have antimicrobial, cytotoxic, antioxidant, anti-inflammatory, anti-asthmatic, tyrosinase inhibitory, insecticidal, and larvicidal activities and slimming aromatherapy. In this review, the comprehensive information regarding the volatile components of various Alpinia plants, the bioactivities of Alpinia essential oils and their major compounds are provided.

Lippia graveolens HBK oleoresins, extracted by supercritical fluids, showed bactericidal activity against multidrug resistance Enterococcus faecalis and Staphylococcus aureus strains

OBJECTIVE

The aim of this work was to characterize Lippia graveolens oleoresins, obtained by Supercritical Fluid Extraction (SFE), from crops collected at different locations in Mexico. The antimicrobial effect of oleoresins was tested in reference strains and clinical isolates of susceptible and multidrug resistant (MDR) strains of Enterococcus faecalis and Staphylococcus aureus.

SIGNIFICANCE

The increasing of MDR strains is becoming a global public health problem that has led to the search for new treatments, and essential oils have resurged as a source of compounds with bactericidal functions. Oregano essential oil has attracted attention recently, however, this oil is mainly obtained by hydro-distillation (uses large amounts of water) or solvents extraction (potential contaminant). SFE has gained popularity as it represents an environmentally friendly technology.

METHODS

L. graveolens oleoresins were obtained by SFE, total phenol contents were quantified by Folin-Ciocalteu method, the identification of compounds and thymol and carvacrol quantification was carried out by GC-MS. The antimicrobial activity was tested by minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC).

RESULTS

SFE showed higher yields compared with the hydro-distillation process. L. graveolens grown in different Mexican locations showed differences in oleoresin composition and a slightly different antimicrobial capacity against clinical isolates.

CONCLUSIONS

It was demonstrated that SFE is an efficient technology for extracting L. graveolens oleoresins. Additionally, the solvent-free extraction method and the observed antimicrobial effect, increases the applications of these oleoresins in fields such as cosmetics, food industry, medicine, amongst others.

Phytochemicals: A Promising Weapon in the Arsenal against Antibiotic-Resistant Bacteria

The extensive usage of antibiotics and the rapid emergence of antimicrobial-resistant microbes (AMR) are becoming important global public health issues. Many solutions to these problems have been proposed, including developing alternative compounds with antimicrobial activities, managing existing antimicrobials, and rapidly detecting AMR pathogens. Among all of them, employing alternative compounds such as phytochemicals alone or in combination with other antibacterial agents appears to be both an effective and safe strategy for battling against these pathogens. The present review summarizes the scientific evidence on the biochemical, pharmacological, and clinical aspects of phytochemicals used to treat microbial pathogenesis. A wide range of commercial products are currently available on the market. Their well-documented clinical efficacy suggests that phytomedicines are valuable sources of new types of antimicrobial agents for future use. Innovative approaches and methodologies for identifying plant-derived products effective against AMR are also proposed in this review.

Antioxidant and Antibacterial Effects of Pollen Extracts on Human Multidrug-Resistant Pathogenic Bacteria

The present work was designed to search the possible antibacterial effect of the ethanolic extract of pollens from six botanical origins, Punica granatum, Quercus ilex, Centaurium erythraea, Coriandrum sativum, Ruta graveolens, and Citrus aurantium, against multidrug pathogenic bacteria, Escherichia coli, Pseudomonas aeruginosa, Enterobacter cloacae, Acinetobacter baumannii, Klebsiella pneumoniae, and Staphylococcus aureus. The content of phenolic compounds, flavones, and flavonols was measured. The antioxidant activities were evaluated using four assays: total antioxidant capacity, DPPH, ABTS, and reducing power. Antibacterial activity was studied using the agar disk diffusion method, and the MIC and MBC were determined. Results obtained showed a positive correlation between the antioxidant content of pollen extracts and the antibacterial capacity, Punica granatum and Quercus ilex pollen extracts were the most efficient against Gram-positive and Gram-negative bacteria, and Centaurium erythraea, Coriandrum sativum, and Ruta graveolens had a moderate effect, while Citrus aurantium had no antibacterial effect. It is concluded that pollens can be a good source of bioactive molecules that exhibit potent antioxidant effects and strong antibacterial activities.

Effect of Alpinia officinarum extract on reproductive damages in streptozotocin induced diabetic male rats

PURPOSE

Infertility is one of the systemic problems in diabetic men. The purpose of the present study is investigation of the effects of the Alpinia officinarum (AO) hydro-alcoholic extract on the reproductive system damages in diabetic male rats.

METHODS

Twenty four male rats were randomly assigned into 4 groups (n = 6); i.e., control, diabetic control, and diabetic rats treated orally with AO extract (200 and 500 mg kg-1). A single dose (60 mg kg-1) of streptozotocin (STZ) was injected intraperitoneally (IP) to induce diabetes. After 8 weeks of treatment, blood samples, testis, and cauda epididymis were excised to evaluate specific hormonal changes, sperm parameters, and testis morphology.

RESULTS

Diabetic control rats showed remarkably lower body and testicular weights, testicular volumes, and sperm parameters compared with the control group (p <0.05). Diabetic control rats also exhibited significantly decreased serum testosterone and follicle stimulating hormone (FSH). Sperm parameters were considerably enhanced in diabetic animals gavaged with AO extract. Testosterone levels were significantly elevated by administrating 500 mg kg-1 AO extract to the diabetic control rats (p <0.05). The morphological assessment of testis of treatment group (500 mg kg-1) indicated remarkable differences (p <0.05) by increasing the seminiferous tubules diameter (STD) and thickness of the seminiferous epithelium (TSE) compared with diabetic control rats.

CONCLUSION

As demonstrated by the results, AO extract ameliorated sperm damage and improved sperm morphology besides improving histological damage in the testis in diabetic rats. In addition, the dose of 500 mg kg-1 worked more efficiently than 200 mg kg-1.

Ethnobotany and the Role of Plant Natural Products in Antibiotic Drug Discovery

The crisis of antibiotic resistance necessitates creative and innovative approaches, from chemical identification and analysis to the assessment of bioactivity. Plant natural products (NPs) represent a promising source of antibacterial lead compounds that could help fill the drug discovery pipeline in response to the growing antibiotic resistance crisis. The major strength of plant NPs lies in their rich and unique chemodiversity, their worldwide distribution and ease of access, their various antibacterial modes of action, and the proven clinical effectiveness of plant extracts from which they are isolated. While many studies have tried to summarize NPs with antibacterial activities, a comprehensive review with rigorous selection criteria has never been performed. In this work, the literature from 2012 to 2019 was systematically reviewed to highlight plant-derived compounds with antibacterial activity by focusing on their growth inhibitory activity. A total of 459 compounds are included in this Review, of which 50.8% are phenolic derivatives, 26.6% are terpenoids, 5.7% are alkaloids, and 17% are classified as other metabolites. A selection of 183 compounds is further discussed regarding their antibacterial activity, biosynthesis, structure-activity relationship, mechanism of action, and potential as antibiotics. Emerging trends in the field of antibacterial drug discovery from plants are also discussed. This Review brings to the forefront key findings on the antibacterial potential of plant NPs for consideration in future antibiotic discovery and development efforts.

Flavone-Rich Fractions and Extracts from Oroxylum indicum and Their Antibacterial Activities against Clinically Isolated Zoonotic Bacteria and Free Radical Scavenging Effects

Oroxylum indicum extracts from the seeds collected from Lampang and Pattani provinces in Thailand, and young fruits and flowers exhibited in vitro display antioxidant and antibacterial activities against clinically isolated zoonotic bacteria including Staphylococcus intermedius, Streptococcus suis, Pseudomonas aeruginosa, β-hemolytic Escherichia coli and Staphylococcus aureus. The orange crystals and yellow precipitates were obtained from the preparation processes of the seed extracts. The orange-red crystals from the seeds collected from Lampang province exhibited strong in vitro 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging effects (EC50 value = 25.99 ± 3.30 μg/mL) and antibacterial effects on S. intermedius and β-hemolytic E. coli while the yellow precipitate from the same source exhibited only antioxidant activity. Quantitative analysis of phytochemicals in O. indicum samples by spectrophotometric and HPLC techniques showed that they contained different amounts of total phenolic, total flavonoid and three major flavones; baicalin, baicalein and chrysin contents. Young fruit extract, which contained low amounts of flavone contents, still promoted antibacterial effects against the tested bacteria with IC50 values lower than 1 mg/mL and MIC values between 4 to 10 mg/mL in S. intermedius, S. aureus and S suis while higher IC50 and MIC values against P. aeruginosa and β-hemolytic E. coli were found. From scanning electron microscopy, the extract of the young fruit of O. indicum promoted morphological changes in the bacterial cells by disrupting the bacterial cell walls, inducing leakage of the cellular content, and generating the abnormal accumulation of cells. The mechanism of action of the extract for this antibacterial effect may be the disruption of the cell membrane and abnormal cell aggregations. Regression analysis of the results suggests the correlation between total phenolic and total flavonoid contents and antioxidant and antibacterial effects. Baicalin was found to have a high correlation with an inhibitory effect against β-hemolytic E. coli while three unidentified peaks, which could be flavones, showed high correlations with an inhibitory effect against S. intermedius, S. suis, P. aeruginosa and S. aureus.

Efficacy Prediction of Four Pharmaceutical Formulations for Intramammary Administration Containing Aloe vera (L.) Burm. f. Combined With Ceftiofur or Cloxacillin in Lactating Cows as an Alternative Therapy to Treat Mastitis Caused by Staphylococcus aureus

Synergy or additive effect between Aloe vera (L.) Burm.f. and beta-lactam (β-lactam) antibiotics has been reported against Staphylococcus aureus, one of the most important etiological agents of cow mastitis. The goal of the present study was to predict the efficacy of intramammary formulations containing the Aloe vera gel extract in the combination with cloxacillin or ceftiofur at low concentrations in lactating cows as an alternative therapy. Each quarter of 20 healthy Holstein Friesian lactating cows were treated with a single dose of one of the following formulations, corresponding to one of these treatment groups: A1, A2, A3, and A4. A1 and A2 contained cloxacillin at 0.25 and 0.5 mg/ml, whereas A3 and A4 contained ceftiofur 0.25 and 0.5 mg/ml, respectively. In addition, all formulations contained 600 mg/ml of an alcoholic extract of Aloe vera. Milk samples were taken at predefined time points. Antibiotics and aloin (active compound of Aloe vera) concentrations were assessed by liquid chromatography mass spectrometry system (LC-MS/MS). Pharmacokinetic profiles were obtained, and the efficacy index, the fraction of dosing interval in which the antimicrobial concentration remains above the minimum inhibitory concentrations (MICs) (T > MIC) for each formulation, was calculated considering MIC values against Staphylococcus aureus ATCC 29213 as obtained for the combination Aloe vera + antibiotic and aloin concentration in the extract. Mammary gland safety assessment was performed for each combination. Values of the main efficacy index for this study, T > MIC (h) for Aloe vera were 23.29, 10.50, 27.50, and 13.89, whereas for cloxacillin or ceftiofur were 19.20, 10.9, 19.74, and 15.63, for A1, A2, A3, and A4, respectively. Only A1 and A3 reached aloin and antibiotic recommended values as predictors of clinical efficacy for cloxacillin, ceftiofur, and aloin (50, 70, and 60%, respectively), assuming a dose interval of 24 h. The efficacy index values obtained suggest that A1 and A3 might be an effective therapy to treat bovine mastitis caused by S. aureus after a single dose. Nevertheless, further trials in S. aureus mastitis clinical cases are mandatory to confirm the efficacy of Aloe vera formulations.

Propolis as a novel antibacterial agent

Propolis (bee glue) is a bee glue, sticky resinous material released from various plant sources such as bud exudates, flowers, and leaves modified by bee secretions and wax propolis is composed of resins, waxes, polyphenols, polysaccharides, volatile materials, and secondary metabolites that are responsible for various bioactivity such as antibacterial, anti-angiogenic, antiulcer, anti-inflammatory, antioxidant, and anti-viral activities. The physico-chemical characteristics and the natural properties of various kinds of propolis have been studied for the past decade. Novel active anti-microbial compounds have been identified in propolis. Those compounds positively modulated the antimicrobial resistance of multidrug resistant bacteria. Published research has indicated that propolis and its derivatives has many natural antimicrobial compounds with a broad spectrum against different types of bacteria and that it enhanced the efficacy of conventional antibiotics. Besides, the combination of propolis with other compounds such as honey has been studied whereby, such combinations have a synergistic effect against bacterial strains such as Escherichia coli and Staphylococcus aureus. The activity of propolis is very much dependent on seasonal and regional factors, and Middle Eastern propolis have shown best antibacterial efficacy. Propolis and its main flavonoids ingredients should not be overlooked and should be evaluated in clinical trials to better elucidate their potential application in various fields of medicine. Clinical antibacterial potential and its use in new drugs of biotechnological products should be conducted. This review aims at highlighting some of the recent scientific findings associated with the antibacterial properties of propolis and its components.

Antimicrobial flavonoids as a potential substitute for overcoming antimicrobial resistance

BACKGROUND

Infectious diseases are the leading cause of death in 21^st century due to antimicrobial resistance and scarcity of new molecules to undertake rising infections. There could be a multiple reasons behind antimicrobial resistance whether it is increased drug metabolism or bacterial endotoxins. The demand of effective medication is increasing day by day to treat microbial infections and combat antimicrobial resistance. In recent years most of the synthetic antimicrobials developed resistance so natural products could provide better options to fulfill this demand. There has been increasing interest in the research on flavonoids because various flavonoids were found to be effective against pathogenic microorganisms.

OBJECTIVE

The objective of this article will be to explore antimicrobial activity of flavonoids with special focus on their possible mechanism of action.

METHODS

The article reviewed recent literature related to flavonoids with antimicrobial activity, which were isolated from various sources and the compounds showing fairly good activity against tested microbial species were discussed.

RESULTS

By throughout literature review it has been found that flavonoids show antimicrobial effect by inhibiting virulence factors, efflux pump, biofilm formation, membrane disruption, cell envelop synthesis, nucleic acid synthesis, and bacterial motility inhibition.

CONCLUSION

Most of the antimicrobial drugs available now a days are ineffective due to development of resistance to them. Flavonoids have the potential to overcome this emerging crisis as this class of natural products showed the antimicrobial activity by different mechanisms than those of conventional drugs, so flavonoid could be an effective treatment of pathogenic infections.

Plant-Based Phytochemicals as Possible Alternative to Antibiotics in Combating Bacterial Drug Resistance

The unprecedented use of antibiotics that led to development of resistance affect human health worldwide. Prescription of antibiotics imprudently and irrationally in different diseases progressed with the acquisition and as such development of antibiotic resistant microbes that led to the resurgence of pathogenic strains harboring enhanced armors against existing therapeutics. Compromised the treatment regime of a broad range of antibiotics, rise in resistance has threatened human health and increased the treatment cost of diseases. Diverse on metabolic, genetic and physiological fronts, rapid progression of resistant microbes and the lack of a strategic management plan have led researchers to consider plant-derived substances (PDS) as alternative or in complementing antibiotics against the diseases. Considering the quantitative characteristics of plant constituents that attribute health beneficial effects, analytical procedures for their isolation, characterization and phytochemical testing for elucidating ethnopharmacological effects has being worked out for employment in the treatment of different diseases. With an immense potential to combat bacterial infections, PDSs such as polyphenols, alkaloids and tannins, present a great potential for use, either as antimicrobials or as antibiotic resistance modifiers. The present study focuses on the mechanisms by which PDSs help overcome the surge in resistance, approaches for screening different phytochemicals, methods employed in the identification of bioactive components and their testing and strategies that could be adopted for counteracting the lethal consequences of multidrug resistance.

Microbiota in vitro modulated with polyphenols shows decreased colonization resistance against Clostridioides difficile but can neutralize cytotoxicity

While the knowledge on gut microbiota - C. difficile interactions has improved over the years, the understanding of the underlying mechanisms providing colonization resistance as well as preventative measures against the infection remain incomplete. In this study the antibiotic clindamycin and polyphenol extracts from pomegranate and blueberries were used individually and in combination to modulate fecal microbial communities in minibioreactor arrays (MBRA). Modulated communities were inoculated with C. difficile (ribotype 027). Subsequent 7-day periodical monitoring included evaluation of C. difficile growth and activity of toxins TcdA and TcdB as well as analysis of MBRA bacterial community structure (V3V4 16 S metagenomics). Polyphenols affected multiple commensal bacterial groups and showed different synergistic and antagonistic effects in combination with clindamycin. Exposure to either clindamycin or polyphenols led to the loss of colonization resistance against C. difficile. The successful growth of C. difficile was most significantly correlated with the decrease in Collinsella and Lachnospiraceae. Additionally, we demonstrated that Clostridium sporogenes decreased the activity of both C. difficile toxins TcdA and TcdB. The feature was shown to be common among distinct C. sporogenes strains and could potentially be applicable as a non-antibiotic agent for the alleviation of C. difficile infection.

Antimicrobial polyphenol-rich extracts: Applications and limitations in the food industry

One of the common ways to prevent food spoilage throughout product's shelf life is by using artificial/synthetic preservatives. However, the growing negative perception of consumers over synthetic preservatives has encouraged the food industry to consider their natural alternatives. Plant extracts, increasingly recognized as consumer-friendly, represent a valuable source of active compounds, mostly polyphenols, with potent antimicrobial and antibiofilm activities. Hence, this article focuses mainly on the antimicrobial activity of plant-based polyphenol-rich extracts as well as on their potential use and limitations in the food industry. Some new trends such as antimicrobial food packaging combined with plant extracts and photodynamic inactivation (PDI) combined with a natural photosensitiser, curcumin, are discussed as well.

Antimicrobial Activity of Polyphenols and Alkaloids in Middle Eastern Plants

Antibiotic-resistant microorganisms have been an ever-growing concern over the past years. This has led researchers to direct their attention onto plants to be able to discover new possible antimicrobial compounds. The Middle East encompasses a wide spectrum of plant diversity with over 20,000 different species in habitats ranging from deserts to snow-capped mountains. Several plant secondary metabolites and their derivatives have been identified as possible antimicrobial agents. Among the secondary metabolites studied, alkaloids and polyphenols have shown strong antimicrobial activity. Polyphenols are one of the most numerous and diverse group of secondary metabolites; their antioxidant properties provide the basis for antimicrobial effects. Alkaloids provided the underlying structure for the development of several antibiotics with a diverse range of action. The ability of some plant secondary metabolites to act as resistance-modifying agents is a promising field in mitigating the spread of bacterial resistance.

Synthesis of a Series of Chalcones and Related Flavones and Evaluation of their Antibacterial and Antifungal Activities

Background:

A series of chalcones and flavones were synthesized from 2’-hydroxyacetophenone and substituted aromatic aldehydes via Simmons-Schmidt condensation followed by oxidative cyclization.

Methods:

Characterization of the obtained structures was established on the basis of their spectroscopic data. The synthesized compounds were screened for their antimicrobial activities against five bacterial strains (Citrobacter freundii, Staphylococcus aureus, Listeria monocytogenes, Salmonella braenderup, Escherichia coli.) and two fungal strains (Candida albicans, Candida krusei).

Results:

The in vitro bioassay results indicated that some target compounds displayed moderate (4d, 4e) to high (4a) antifungal activity against the pathogenic fungi C. albicans and C. krusei.

Conclusion:

For the antibacterial activity, only products 3d and 4d showed a weak antibacterial activity. These compounds can lead to the design of new drugs with specific antifungal activity.

Antibacterial activity of flavonoids and their structure-activity relationship: An update review

Based on World Health Organization reports, resistance of bacteria to well-known antibiotics is a major global health challenge now and in the future. Different strategies have been proposed to tackle this problem including inhibition of multidrug resistance pumps and biofilm formation in bacteria and development of new antibiotics with novel mechanism of action. Flavonoids are a large class of natural compounds, have been extensively studied for their antibacterial activity, and more than 150 articles have been published on this topic since 2005. Over the past decade, some promising results were obtained with the antibacterial activity of flavonoids. In some cases, flavonoids (especially chalcones) showed up to sixfold stronger antibacterial activities than standard drugs in the market. Some synthetic derivatives of flavonoids also exhibited remarkable antibacterial activities with 20- to 80-fold more potent activity than the standard drug against multidrug-resistant Gram-negative and Gram-positive bacteria (including Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus). This review summarizes the ever changing information on antibacterial activity of flavonoids since 2005, with a special focus on the structure-activity relationship and mechanisms of actions of this broad class of natural compounds.

A review on the ethnomedicinal uses, phytochemistry and pharmacology of Alpinia officinarum Hance

ETHNOPHARMACOLOGICAL RELEVANCE

Alpinia officinarum Hance is a perennial plant that has been traditionally used for many decades to treat several ailments including inflammation, pain, stomach-ache, cold, amongst others. Pharmacological studies over the years have demonstrated remarkable bioactivities that could be further explored for development of new therapeutic agents against various ailments.

AIM OF THE STUDY

The paper critically reviewed the ethno-medicinal uses, pharmacology, and phytochemistry of A. officinarum.

METHODS

Keywords including A. officinarum and its synonyms were searched using electronic databases including ISI web of knowledge, Science direct, Scopus, PubMed, Google scholar and relevant database for Masters and Doctoral theses.

RESULTS

A. officinarum is prepared in Asia, Turkey, Morocco and Iran as a decoction, infusion or juice as a single preparation or in combination with other herbs, food or drinks for the treatment of general health problems including cold, inflammation, digestive disorders, etc. Pharmacological studies revealed the potent in vitro and in vivo bioactivities of various parts of A. officinarum that include anti-inflammatory, cytotoxicity, homeostasis, lipid regulation, antioxidant, antiviral, antimicrobial, antiosteoporosis, etc. Over 90 phytochemical constituents have been identified and isolated from A. officinarum comprising vastly of phenolic compounds especially diarylheptanoids isolated from the rhizome and considered the most active bioactive components.

CONCLUSION

In vitro and in vivo studies have confirmed the potency of A. officinarum. However, further studies are required to establish the mechanisms mediating its bioactivities in relation to the medicinal uses as well as investigating any potential toxicity for future clinical studies.

The Synergy and Mode of Action of Cyperus rotundus L. Extract Plus Ampicillin against Ampicillin-Resistant Staphylococcus aureus

Cyperus rotundus L. has been used for pharmaceutical applications including antibacterial infections. Nevertheless, there is still no data regarding the mode of actions. This study aimed to determine the antibacterial activity and mode of actions of Cyperus rotundus extract (CRE) against ampicillin-resistant Staphylococcus aureus (ARSA) which poses a serious problem for hospitalized patients. The majority of chemical compounds of CRE were flavonoids and alkaloids. The minimum inhibitory concentrations (MICs) for ampicillin and CRE against all ARSA strains were 64 μg/ml and 0.5 mg/ml, respectively. Checkerboard assay revealed synergistic activity in the combination of ampicillin and CRE at the lowest fractional inhibitory concentration index (FICI) at 0.27. The killing curve assay had confirmed the synergistic and bactericidal activity of the combination against ARSA. Electron microscopic results showed that these ARSA cells treated with this combination caused peptidoglycan and cytoplasmic membrane (CM) damage and average cell areas significantly smaller than control. Also, this combination caused an increase in CM permeability of ARSA. CRE revealed the inhibitory activity against β-lactamase. It is normally known that some drugs are derived from flavonoids or alkaloids. So, this CRE proposes the potential to develop a novel adjunct phytopharmaceutical to ampicillin for the remedy of ARSA.

Plant phenolics and terpenoids as adjuvants of antibacterial and antifungal drugs

BACKGROUND

The intensive use of antibacterial and antifungal drugs has dramatically increased the microbial resistance and has led to a higher number of difficult-to-eradicate infections. Combination therapy with two or more antimicrobial drugs has emerged some years ago to overcome the issue, but it has proven to be not completely effective. Natural secondary metabolites of MW ≤ 500 represent promising adjuvants for antimicrobials and have been the object of several researches that have increased in the last two decades.

PURPOSE

The purpose of this Review is to do a literature search of the natural compounds that showed high enhancing capacity of antibacterials' and antifungals' effects against planktonic bacteria and fungi and to analyze which are the natural products most used in combination with a focus on polyphenols and terpenoids.

RESULTS

One hundred of papers were collected for reviewing. Fifty six (56) of them deal with combinations of low MW natural products with antibacterial drugs against planktonic bacteria and forty four (44) on natural products with antifungal drugs against planktonic fungi. Of the antibacterial adjuvants, 41 (73%) were either polyphenols (27; 48%) or terpenes (14; 25%). The remaining 15 papers (27%), deal with different class of natural products. Since most natural potentiators belong to the terpene or phenolic structural types, a more detailed description of the works dealing with these type of compounds is provided here. Bacterial and fungal resistance mechanisms, the modes of action of the main classes of antibacterial and antifungal drugs and the methodologies most used to assess the type of interactions in the combinations were included in the Review too.

CONCLUSIONS AND PERSPECTIVES

Several promising results on the potentiation effects of antifungals' and antibacterials' activities by low MW natural products mainly on polyphenols and terpenes were reported in the literature and, in spite of that most works included only in vitro assays, this knowledge opens a wide range of possibilities for the combination antimicrobial therapy. Further research including in vivo assays and clinical trials are required to determine the relevance of these antimicrobial enhancers in the clinical area and should be the focus of future studies in order to develop new antimicrobial combination agents that overpass the drawbacks of the existing antibiotics and antifungals in clinical use.

Antimicrobial Activity of Galangin and Its Effects on Murein Hydrolases of Vancomycin-Intermediate Staphylococcus aureus (VISA) Strain Mu50

Backgroud: Antibiotic treatment for infections caused by vancomycin-intermediate Staphylococcus aureus (VISA) strains is challenging, and only a few effective and curative methods have been developed to combat these strains. This study aimed to investigate the antimicrobial activity of galangin against S. aureus and its effects on the murein hydrolases of VISA strain Mu50. This is the first report on these effects of galangin, and it may help to improve the treatment for VISA infections by demonstrating the effective use of galangin.

METHODS

Firstly, the minimum inhibitory concentration (MIC) and growth curve were used to investigate the antimicrobial activity of galangin against S. aureus. Secondly, transmission electron microscopy (TEM) was used to observe morphological changes of VISA strain Mu50. Thirdly, Triton X-100-induced autolysis and cell wall hydrolysis assays were performed to determine the activities of the murein hydrolases of Mu50. Finally, fluorescence real-time quantitative PCR was used to investigate the expression of the murein hydrolase-related Mu50 genes.

RESULTS

The results indicated that the MIC of galangin was 32 μg/mL against ATCC25293, N315, and Mu50, and galangin could significantly suppress the bacterial growth (p < 0.05) with concentrations of 4, 8 and 16 μg/mL, compared with control group (0 μg/mL). To explore the possible reasons of bacteriostatic effects of galangin, we observed morphological changes using TEM which showed that the division of Mu50 daughter cells treated with galangin was obviously inhibited. Considering the vital role of murein hydrolases in cellular division, assays were performed, and galangin markedly decreased Triton X-100-induced autolysis and cell wall hydrolysis. Galangin also significantly inhibited the expression of the murein hydrolase genes (atl, lytM, and lytN) and their regulatory genes (cidR, cidA, and cidB).

CONCLUSIONS

Our findings indicated that galangin can effectively inhibit murein hydrolase activity as well as the growth of VISA strain Mu50.

Boesenbergia rotunda (L.) Mansf. extract potentiates the antibacterial activity of some β-lactams against β-lactam-resistant staphylococci

OBJECTIVES

The purpose of this study was to investigate the effect of Boesenbergia rotunda (L.) Mansf. extract (BRE) and peptidoglycan inhibitor antibiotics, alone and in combination, against β-lactam-resistant staphylococci.

METHODS

Antibacterial and synergistic activities of BRE alone and in combination with ampicillin (AMP), cloxacillin (CLX), cefazolin (CZO) or vancomycin (VAN) were evaluated against two β-lactam-resistant Staphylococcus aureus (BRSA) isolates and one β-lactam-resistant Staphylococcus epidermidis (BRSE) isolate. The activities were confirmed by killing curve assays. The preliminary antimicrobial action was elucidated by transmission electron microscopy (TEM) and cytoplasmic membrane (CM) permeability assay.

RESULTS

All tested staphylococci were inhibited by BRE at a minimum inhibitory concentration (MIC) of 16μg/mL. Two BRSA strains showed high resistance to CLX, AMP and CZO, whilst BRSE was resistant to CLX and AMP. All tested isolates remained susceptible to VAN. Chequerboard assay demonstrated a fractional inhibitory concentration index (FICI) of 0.50 for the BRE+CLX combination against the BRSA strains. Killing curve determinations confirmed the antibacterial and synergistic activities. TEM revealed collapse of the CM in BRE-treated cells and damage both of the CM and peptidoglycan (PG) in BRE+CLX-treated cells. The CM permeability assay showed that either BRE or nisin alone as well as BRE+CLX significantly induced leakage of OD_260nm-absorbing materials.

CONCLUSIONS

BRE potentiated the activity of β-lactams, particularly CLX, against β-lactam-resistant staphylococci by damaging the CM and PG layer, leading to leakage of intracellular material. Combination of BRE and β-lactams provides a potential way forward in developing novel antistaphylococcal agents.

Carbohydrate-Based Host-Guest Complexation of Hydrophobic Antibiotics for the Enhancement of Antibacterial Activity

Host-guest complexation with various hydrophobic drugs has been used to enhance the solubility, permeability, and stability of guest drugs. Physical changes in hydrophobic drugs by complexation have been related to corresponding increases in the bioavailability of these drugs. Carbohydrates, including various derivatives of cyclodextrins, cyclosophoraoses, and some linear oligosaccharides, are generally used as host complexation agents in drug delivery systems. Many antibiotics with low bioavailability have some limitations to their clinical use due to their intrinsically poor aqueous solubility. Bioavailability enhancement is therefore an important step to achieve the desired concentration of antibiotics in the treatment of bacterial infections. Antibiotics encapsulated in a complexation-based drug delivery system will display improved antibacterial activity making it possible to reduce dosages and overcome the serious global problem of antibiotic resistance. Here, we review the present research trends in carbohydrate-based host-guest complexation of various hydrophobic antibiotics as an efficient delivery system to improve solubility, permeability, stability, and controlled release.

Phytochemicals for human disease: An update on plant-derived compounds antibacterial activity

In recent years, many studies have shown that phytochemicals exert their antibacterial activity through different mechanisms of action, such as damage to the bacterial membrane and suppression of virulence factors, including inhibition of the activity of enzymes and toxins, and bacterial biofilm formation. In this review, we summarise data from the available literature regarding the antibacterial effects of the main phytochemicals belonging to different chemical classes, alkaloids, sulfur-containing phytochemicals, terpenoids, and polyphenols. Some phytochemicals, besides having direct antimicrobial activity, showed an in vitro synergistic effect when tested in combination with conventional antibiotics, modifying antibiotic resistance. Review of the literature showed that phytochemicals represent a possible source of effective, cheap and safe antimicrobial agents, though much work must still be carried out, especially in in vivo conditions to ensure the selection of effective antimicrobial substances with low side and adverse effects.

Synergism and the mechanism of action of the combination of α-mangostin isolated from Garcinia mangostana L. and oxacillin against an oxacillin-resistant Staphylococcus saprophyticus

Background

Globally, staphylococci have developed resistance to many antibiotics. New approaches to chemotherapy are needed and one such approach could be to use plant derived actives with conventional antibiotics in a synergestic way. The purpose of this study was to isolate α-mangostin from the mangosteen (Garcinia mangostana L.; GML) and investigate antibacterial activity and mechanisms of action when used singly and when combined with oxacillin against oxacillin-resistant Staphylococcus saprophyticus (ORSS) strains. The isolated α-mangostin was confirmed by HPLC chromatogram and NMR spectroscopy. The minimum inhibitory concentration (MIC), checkerboard and killing curve were determined. The modes of action of these compounds were also investigated by enzyme assay, transmission electron microscopy (TEM), confocal microscopic images, and cytoplasmic membrane (CM) permeabilization studies.

Results

The MICs of isolated α-mangostin and oxacillin against these strains were 8 and 128 μg/ml, respectively. Checkerboard assays showed the synergistic activity of isolated α-mangostin (2 μg/ml) plus oxacillin (16 μg/ml) at a fractional inhibitory concentration index (FICI) of 0.37. The kill curve assay confirmed that the viability of oxacillin-resistant Staphylococcus saprophyticus DMST 27055 (ORSS-27055) was dramatically reduced after exposure to isolated α-mangostin (2 μg/ml) plus oxacillin (16 μg/ml). Enzyme assays demonstrated that isolated α-mangostin had an inhibitory activity against β-lactamase in a dose-dependent manner. TEM results clearly showed that these ORSS-27055 cells treated with this combination caused peptidoglycan and cytoplasmic membrane damage, irregular cell shapes and average cell areas were significantly larger than the control. Clearly, confocal microscopic images confirmed that this combination caused considerable peptidoglycan damage and DNA leakage. In addition, the CM permeability of ORSS-27055 was also increased by this combination of actives.

Conclusions

These findings provide evidence that isolated α-mangostin alone has not only some activity but also shows the synergistic activity with oxacillin against ORSS-27055. The chromone and isoprenyl structures could play a significant role in its action. This synergistic activity may involve three mechanisms of action. Firstly, potential effects of cytoplasmic membrane disruption and increases permeability. Secondly, inhibit β-lactamase activity. Finally, also damage to the peptidoglycan structure. We proposes the potential to develop a novel adjunct phytopharmaceutical to oxacillin for the treatment of ORSS. Future studies require clinical trials to establish if the synergy reported can be translated to animals and humans.

The synergy and mode of action of quercetin plus amoxicillin against amoxicillin-resistant Staphylococcus epidermidis

Background

Staphylococcus epidermidis is one of the most multiple resistances to antibiotics in the recent years. Therefore, practically-prescribed antibiotics in the treatment of these strains are not effective. Plant-derived antibacterial is one of the most interesting sources of new therapeutics. The present study was to investigate antibacterial, synergy and modes of action of quercetin and amoxicillin against amoxicillin-resistant Staphylococcus epidermidis (ARSE).

Methods

The MICs, checkerboard assay, viability curves, cytoplasmic membrane (CM) permeability, enzyme assay, transmission electron microscopy, confocal microscopy and FT-IR microspectroscopy measurement was performed.

Results

The MICs of amoxicillin, penicillin, quercetin and kaempferol against all ARSE strains were 16, 200, 256-384 and >1024 μg/mL respectively. Synergistic effects were exhibited on amoxicillin plus quercetin and penicillin plus kaempferol against these strains at FIC index 0.50 and <0.38 respectively. The synergistic activity of quercetin plus amoxicillin was confirmed by the viable count. This combination increased CM permeability, caused marked morphological, peptidoglycan and cytoplasmic membrane damage, increased protein amide I and II, but decreased fatty acid in bacterial cells. The quercetin had an inhibitory activity against β-lactamase.

Conclusions

So, these findings are the first report that quercetin has the synergistic effect with amoxicillin against ARSE via four modes of actions, inhibit peptidoglycan synthesis and β-lactamases activity, increase CM permeability and protein amide I and II but decrease fatty acid in bacterial cells. Of course, this flavonol has the dominant potential to develop a brand-new collateral phytochemical agent plus amoxicillin to treat ARSE. Future work should focus on the bioavailability, efficacy and toxicity in animal and human studies, as well as, the synergistic effect on blood and tissue should be evaluated and achieved.

C-Geranylated flavonoids from Paulownia tomentosa fruits with antimicrobial potential and synergistic activity with antibiotics

Context C-6-Geranylated flavonoids possess promising biological activities. These substances could be a source of lead compounds for the development of therapeutics. Objective The study was designed to evaluate their antibacterial and antileishmanial activity. Materials and methods C-6-Geranylated flavanones were tested in micromolar concentrations against promastigote forms of Leishmania brazilensis, L. donovani, L. infantum, and L. panamensis against methicillin-resistant Staphylococcus aureus (MRSA); and synergistic potential with antibiotics was analyzed. IC50 values (after 72 h) were calculated and compared with that of miltefosine. Flow cytometry and DNA fragmentation analysis were used the mechanism of the effect. Geranylated flavanones or epigallocatechin gallate were combined with oxacillin, tetracycline, and ciprofloxacin, and the effects of these two-component combinations were evaluated. Minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) were established (after 24 h), the synergy was measured by the checkerboard titration technique, and the sums of the fractional inhibitory concentrations (∑FICs) were computed. Results 3'-O-Methyl-5'-O-methyldiplacone and 3'-O-methyldiplacone showed good antileishmanial activities (IC50 8-42 μM). 3'-O-Methyl-5'-hydroxydiplacone activates the apoptotic death at leishmanias, the effect of 3'-O-methyl-5'-O-methyldiplacone has another mechanism. The test of the antibacterial activity showed good effects of 3'-O-methyldiplacol and mimulone against MRSA (MIC 2-16 μg/mL), and in six cases, the results showed synergistic effects when combined with oxacillin. Synergistic effects were also found for the combination of epigallocatechin gallate with tetracycline or oxacillin. Conclusion This work demonstrates anti-MRSA and antileishmanial potential of geranylated flavanones and uncovers their promising synergistic activities with antibiotics. In addition, the mechanism of antileishmanial effect is proposed.

Synergy and Mode of Action of Ceftazidime plus Quercetin or Luteolin on Streptococcus pyogenes

Streptococcus pyogenes causes streptococcal toxic shock syndrome. The recommended therapy has been often failure through the interfering of beta-lactamase-producing bacteria (BLPB). The present study was to investigate antibacterial activity, synergy, and modes of action of luteolin and quercetin using alone and plus ceftazidime against S. pyogenes. The MICs of ceftazidime, luteolin, and quercetin against all S. pyogenes were 0.50, 128, and 128 µg mL⁻¹, respectively. A synergistic effect was exhibited on luteolin and quercetin plus ceftazidime against these strains at fractional inhibitory concentration indices 0.37 and 0.27, respectively, and was confirmed by the viable count. These combinations increased cytoplasmic membrane (CM) permeability, caused irregular cell shape, peptidoglycan, and CM damage, and decreased nucleic acid but increased proteins in bacterial cells. Enzyme assay demonstrated that these flavonoids had an inhibitory activity against β-lactamase. In summary, this study provides evidence that the inhibitory mode of action of luteolin and quercetin may be mediated via three mechanisms: (1) inhibiting of peptidoglycan synthesis, (2) increasing CM permeability, and (3) decreasing nucleic acid but increasing the protein contents of bacterial cells. So, luteolin and quercetin propose the high potential to develop adjunct to ceftazidime for the treatment of coexistence of the BLPB and S. pyogenes infections.

Synergy between baicalein and penicillins against penicillinase-producing Staphylococcus aureus

The combination of baicalein (the active constituent of Scutellaria baicalensis) with penicillin G/amoxicillin showed potent synergy against 20 clinical penicillinase-producing Staphylococcus aureus strains including 10 isolates that were additionally methicillin-resistant (MRSA). The fractional inhibitory concentration (FIC) indices of penicillins+baiclein ranged from 0.14 to 0.38. Baicalein protected penicillins (penicillin G and amoxicillin) from penicillinase and increased the susceptibility of penicillinase-supplemented S. aureus ATCC 29213 in a dose-dependent manner. The inhibition of penicillinase activity by baicalein should be responsible for the synergism and protective effect. These findings offer us good evidence that the penicillins combined with baicalein showed potent synergistic activity against penicillinase-producing S. aureus and penicillinase-producing MRSA in vitro and might provide promising implications for clinical treatment of these bacterial infections.

Combinatorial Activity of Flavonoids with Antibiotics Against Drug-Resistant Staphylococcus aureus

The use of resistance-modifying agents is a potential strategy that is used to prolong the effective life of antibiotics in the face of increasing antibiotic resistance. Since certain flavonoids are potent bacterial efflux pump inhibitors, we assessed morin, rutin, quercetin, hesperidin, and (+)-catechin for their combined activity with the antibiotics ciprofloxacin, tetracycline, erythromycin, oxacillin, and ampicillin against drug-resistant strains of Staphylococcus aureus, including methicillin-resistant S. aureus. Four established methods were used to determine the combined efficacy of each combination: microdilution checkerboard assays, time-kill determinations, the Etest, and dual disc-diffusion methods. The cytotoxicity of the flavonoids was additionally evaluated in a mouse fibroblast cell line. Quercetin and its isomer morin decreased by 3- to 16-fold the minimal inhibitory concentration of ciprofloxacin, tetracycline, and erythromycin against some S. aureus strains. Rutin, hesperidin, and (+)-catechin did not promote any potentiation of antibiotics. Despite the potential cytotoxicity of these phytochemicals at a high concentration (fibroblast IC50 of 41.8 and 67.5 mg/L, respectively), quercetin is commonly used as a supplement for several therapeutic purposes. All the methods, with exception of the time-kill assay, presented a high degree of congruence without any apparent strain specificity.

Anti-microbial principles of selected remedial plants from Southern India

OBJECTIVE

To examine the anti-bacterial activity of leaf extracts of Morus alba L. (Moraceae) and Piper betel L. (Piperaceae), and seed extracts of Bombax ceiba L. (Borabacaceae).

METHODS

We have partially purified plant extracts by solvent extraction method, and evaluated the effect of individual fractions on bacterial growth using Escherichia coli (E. coli), Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus) bacterial strains.

RESULTS

Compared with Morus and Bombax fractions, Piper fractions showed significant growth inhibition on all the three types of bacteria studied. The EtOAc-hexane fractions of Piper leaves exhibited significant anti-bacterial activity with minimum inhibitory concentrations (MIC) of 50 µg/mL culture against both gram-positive and gram-negative bacteria. The EtOAc-fractions I, II, and IV inhibited bacterial colony formation on soft agar in addition to growth inhibition. A combination treatment of piper fractions with ampicillin resulted in significant growth inhibition in E. coli and P. aeruginosa, and combination with anticancer drug geldanamycin (2µg/mL) showed selective growth inhibition against P. aeruginosa and S. aureus. Three major compounds, i.e., eugenol, 3-hexene-ol and stigmasterol, were primarily identified from Piper betel leaf extractions. Among the individual compounds, eugenol treatment showed improved growth inhibition compared with stigmasterol and 3-hexene-ol.

CONCLUSIONS

We are reporting potential anti-bacterial compounds from Piper betel against both gram-positive and gram-negative bacteria either alone or in combination with drug treatment.

Resources and biological activities of natural polyphenols

The oxidative stress imposed by reactive oxygen species (ROS) plays an important role in many chronic and degenerative diseases. As an important category of phytochemicals, phenolic compounds universally exist in plants, and have been considered to have high antioxidant ability and free radical scavenging capacity, with the mechanism of inhibiting the enzymes responsible for ROS production and reducing highly oxidized ROS. Therefore, phenolic compounds have attracted increasing attention as potential agents for preventing and treating many oxidative stress-related diseases, such as cardiovascular diseases, cancer, ageing, diabetes mellitus and neurodegenerative diseases. This review summarizes current knowledge of natural polyphenols, including resource, bioactivities, bioavailability and potential toxicity.

Synergistic activity and mechanism of action of Stephania suberosa Forman extract and ampicillin combination against ampicillin-resistant Staphylococcus aureus

Background

Ampicillin-resistant S. aureus (ARSA) now poses a serious problem for hospitalized patients, and their care providers. Plant-derived antibacterial that can reverse the resistance to well-tried agents which have lost their original effectiveness are the research objectives of far reaching importance. To this aim, the present study investigated antibacterial and synergistic activities of Stephania suberosa extracts (SSE) against ARSA when used singly and in combination with ampicillin.

Results

The majority chemical compounds of SSE were alkaloid (526.27 ± 47.27 mg/1 g of dried extract). The Minimum inhibitory concentration (MICs) for ampicillin and SSE against all ARSA strains were >512 μg/ml and 4 mg/ml, respectively. Checkerboard assay revealed synergistic activity in the combination of ampicillin (0.15 μg/ml) and SSE (2 mg/ml) at fractional inhibitory concentration index (FICI) <0.5. The killing curve assay had confirmed that the viability of ARSA was dramatically reduced from 5x10⁵ cfu/ml to 10³ cfu/ml within 6 h after exposure to SSE (2 mg/ml) plus ampicillin (0.15 μg/ml) combination. Electron microscopic study clearly revealed that these ARSA cells treated with this combination caused marked morphological damage, peptidoglycan and cytoplasmic membrane damage, and average cell areas significant smaller than control. Obviously, Immunofluorescence staining and confocal microscopic images confirmed that the peptidoglycan of these cells were undoubtedly disrupted by this combination. Furthermore, the CM permeability of ARSA was also increased by this combination. Enzyme assay demonstrated that SSE had an inhibitory activity against β-lactamase in concentrations manner.

Conclusions

So, these findings provide evidence that SSE has the high potential to reverse bacterial resistance to originate traditional drug susceptibility of it and may relate to three modes of actions of SSE: (1) inhibits peptidoglycan synthesis, resulting in morphological damage, (2) inhibits β-lactamases activity, and (3) increases CM permeability. It is widely recognized that many types of drugs are derived from alkaloids. So, this SSE offers the prominent potential to develop a novel adjunct phytopharmaceutical to ampicillin for the treatment of ARSA. Further active ingredients study, toxicity of it, and the synergistic effect on blood and tissue should be performed and confirmed in an animal test or in humans.

In vitro drug resistance of clinical isolated Brucella against antimicrobial agents

OBJECTIVE

To explore the antibiotic resistance of Brucella melitensis and instruct rational use of antimicrobial agents in clinical treatment of Brucella infection.

METHODS

Bacteria were cultured and identified by BACTEC9120 and VITEK II automicrobic system. E-test was used to detect the minimal inhibitory concentration (MIC) of antimicrobial agents in the drug susceptivity experiment.

RESULTS

A total of 19 brucella strains (all Brucella melitensis) were isolated from 19 patients, who had fever between January 2010 and June 2012, and 17 samples were blood, one was bone marrow, the other sample was cerebrospinal fluid. The MIC range of ceftazidime was 2.0-8.0 mg/L, rifampicin was 0.06-2.0 mg/L, amikacin was 4.0-12.0 mg/L, levofloxacin was 2.0-8.0 mg/L, doxycycline was 8.0-32.0 mg/L, sulfamethoxazole-trimethoprim was 4.0-16.0 mg/L, ampicillin was 1.5-2.0 mg/L and gentamicin was 0.50-0.75 mg/L.

CONCLUSIONS

The drugs used in this experiment cover common drugs for treating Brucella. Meanwhile, the results are consistent with clinical efficacy. It is suggested personalized regimen according to patients' status in treatment of Brucella.