Three flavonoids targeting the beta-hydroxyacyl-acyl carrier protein dehydratase from Helicobacter pylori: crystal structure characterization with enzymatic inhibition assay

Dietary flavonoids in health and diseases: A concise review of their role in homeostasis and therapeutics

Over the past few decades, extensive research has delved into the health advantages of flavonoids, exploring their physiological effects through cell-based assays, epidemiological studies, and human intervention trials. The regular intake of plant-derived flavonoids has shown therapeutic potential against noncommunicable pathophysiological conditions, including carcinoma and various inflammatory disorders. Among the myriads of flavonoids, many have been shown to inhibit the aggregation of amyloid-beta peptides in Alzheimer's disease, while anthocyanins exhibit cardioprotective effects by improving endothelial function and lowering blood pressure. In addition, their efficacy is known to manage infectious communicable diseases caused by various bacteria and viruses, such as S. pneumoniae and SARS-CoV-2. Currently, flavonoids are being used to develop new drugs for both communicable and noncommunicable diseases because of their intricate metabolism and bioavailability, leveraging their anti-inflammatory and antioxidant properties. This concise review provides insights into the potential of flavonoids for therapeutics and disease management, particularly with respect to cardiovascular health, neuroprotection, and antimicrobial action. The implications of these findings underscore the necessity for further exploration of flavonoid-rich diets and their incorporation into therapeutic practices to harness their full health benefits.

Potential Application of Origanum majorana Stabilized Silver Nanoparticles for Coating of Urinary Catheter

Introduction

Urinary tract infections related to catheters are one of the most common urinary infections and can affect patient outcomes. Hence, coating urinary catheters is an important issue against several resistant bacterial pathogens that can form a resistant biofilm. This study examined the antibacterial and antibiofilm properties of the coated catheter with green silver nanoparticles (AgNPs) made from Origanum majorana.

Methods

Aloe Vera, Ocimum basilicum, Matricaria chamomilla, Foeniculum vulgare, Glycyrrhiza glabra, Origanum majorana, Urtica urens, Salvia Rosmarinus, and Salvia officinalis hydro-alcoholic extracts were prepared and tested for their antibacterial activities utilizing the agar well diffusion technique. Furthermore, O. majorana extract was tested against biofilm formation using a microtiter plate assay. UPLC-ESI-Q-TOF was used for the profiling and tentative identification of biological compounds in the O. majorana extract. O. majorana was used to prepare AgNPs-MARJ, which were characterized for their size, charge, and shape. Further, AgNPs-MARJ were used to coat two types of urinary catheters. The coated catheters were tested for their resistance to bacterial biofilm formation and compared with non-coated catheters.

Results and Discussion

Initial antimicrobial screening tests showed that O. majorana extracts presented a significant (p<0.05; ANOVA/Tukey) antibacterial activity against the studied species of bacteria compared to the other plant extracts. O. majorana extract showed MIC value of 35.0 mg/mL for E. coli, Pseudomonas aeruginosa and K. pneumoniae and displayed the highest antibiofilm activity at 100 mg/mL. LC-MS analysis tentatively identified the presence of quinic acid and flavonoid-based constituents like apigenin which contribute to the antibiofilm activity. AgNPs-MARJ were efficiently prepared with a size and charge of 111.5 nm and -19.66 mV, respectively. The coated urinary catheters showed a significant (p<0.05) decrease in Pseudomonas aeruginosa biofilm formation compared to control non-coated catheters.

Conclusion

AgNPs-MARJ offer promising prospects for addressing biofilm-related challenges in urinary tract-related catheter infections.

Quercetin: Molecular Insights into Its Biological Roles

Quercetin, a prevalent plant flavonoid, demonstrates many biological functions through its interaction with distinct protein targets. Recent structural investigations of protein-quercetin complexes have elucidated the molecular mechanism behind these actions. This paper presents a thorough structural analysis of experimentally established protein-quercetin complex structures published to date. The structure of the protein-quercetin complex elucidates the molecular mechanism by which quercetin influences protein function. These structures illustrate how quercetin's chemical characteristics facilitate diverse modes of action by enabling particular interactions with the target protein. This structural knowledge provides the molecular foundation for comprehending quercetin's biological roles and indicates avenues for future structural investigations of flavonoid-protein complexes, especially those with ambiguous molecular processes.

Comparative antibacterial activity of clove extract against Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen belonging to the γ-proteobacteria family, known to cause pneumonia linked with ventilator use and nosocomial infections. With the increasing prevalence of antibiotic-resistant bacteria, there is a pressing need to identify alternatives to conventional antibiotics. Plant-derived substances (PDSs) offer potential not only as antibacterial agents but also as modulators of antibiotic resistance. In this study, diffusion assay using disc agar, and the minimum inhibitory concentration (MIC) assay of each imipenem, amoxicillin-clavulanic acid, and clove extract was determined. The clove extract was analyzed via the UHPLC/MS, and the checkerboard assay was employed to evaluate the potential synergistic effects of combining clove extract with both antibiotics. The combination of clove extract to each antibiotic led to a significant reduction in their respective MICs. Moreover, each antibiotic exhibited synergistic effects on the fractional inhibitory concentration value (FIC) of clove extract. The analysis identified seventeen components in the clove extract, predominantly flavonoids and phenolic compounds. The antibacterial efficacy of the Syzygium aromaticum Myrtaceae extract against P. aeruginosa indicated its potential as a promising antibacterial agent capable of enhancing the effectiveness of existing medications.

Isolation and identification of antifungal, antibacterial and nematocide agents from marine bacillus gottheilii MSB1

Pathogenic fungi employ numerous strategies to colonize plants, infect them, reduce crop yield and quality, and cause significant losses in agricultural production. The increasing use of chemical pesticides has led to various ecological and environmental issues, including the emergence of resistant weeds, soil compaction, and water pollution, all negatively impacting agricultural sustainability. Additionally, the extensive development of synthetic fungicides has adverse effects on animal and human health, prompting the exploration of alternative approaches and green strategies for phytopathogen control. Microorganisms living in sponges represent a promising source of novel bioactive secondary metabolites, potentially useful in developing new nematicidal and antimicrobial agents. This study focuses on extracting bioactive compounds from endosymbiotic bacteria associated with the marine sponge Hyrtios erect sp. (collected from NIOF Station, Hurghada, Red Sea, Egypt) using various organic solvents. Bacillus sp. was isolated and identified through 16 S rRNA gene sequencing. The biocidal activity of Bacillus gotheilii MSB1 extracts was screened against plant pathogenic bacteria, fungi, and nematodes. The n-butanol extract showed significant potential as a biological fungicide against Alternaria alternata and Fusarium oxysporum. Both n-hexane and ethyl acetate extracts exhibited negative impacts against the plant pathogenic bacteria Erwinia carotovora and Ralstonia solanacearum, whereas the n-butanol extract had a positive effect. Regarding nematicidal activity, ethyl acetate and n-butanol extracts demonstrated in-vitro activity against the root-knot nematode Meloidogyne incognita, which causes serious vegetable crop diseases, but the n-hexane extract showed no positive effects. The findings suggest that bioactive compounds from endosymbiotic bacteria associated with marine sponges, particularly B. gotheilii MSB1, hold significant potential as alternative biological control agents against plant pathogens. The n-butanol extract, in particular, displayed promising biocidal activities against various plant pathogenic fungi, bacteria, and nematodes. These results support further exploration and development of such bioactive compounds as sustainable, environmentally friendly alternatives to synthetic pesticides and fungicides in agricultural practices.

Plukenetia volubilis leaves as source of anti-Helicobacter pylori agents

INTRODUCTION

Helicobacter pylori infection is a major issue worldwide, with widespread prevalence, combined with its link to gastritis, peptic ulcers, gastric cancer, and mucosa-associated lymphoid tissue (MALT) lymphoma. Meanwhile, effectiveness of current treatment protocols is limited by increasing antibiotic resistance and patient compliance issues due to long regimens and side effects. Plukenetia volubilis, or sacha inchi, is a valuable source of bioactive molecules. However, studies on its antimicrobial activity, especially against H. pylori, are lacking.

METHODS

In this study, the anti-H. pylori activity of P. volubilis leaves water extract was explored using in vitro and in silico approaches. High-Performance Liquid Chromatography coupled to Electrospray Ionisation and Quadrupole Time-of-Flight Mass Spectrometry (HPLC-ESI- QTOF-MS-MS) analysis of the water extract from the leaves was used to characterise the chemical composition of the plant and allowed identification of some flavonoids, such as astragalin, and some phenolic compounds. Then, high-speed counter current chromatography (HSCCC) was used to fractionate the ethyl acetate partition obtained from the water extract from the leaves.

RESULTS AND DISCUSSION

The presence of flavonoids derived from kaempferol was confirmed and astragalin was isolated for the first time in P. volubilis. The P. volubilis water infusion, ethyl acetate extract and the isolated astragalin exhibited anti-bacterial activity against H. pylori J99 and two clinical isolates (e.g., minimum inhibitory concentrations of 0.53, 0.51 and 0.49 μg/mL, respectively, for clarithromycin-resistant clinical isolate SSR366). Then, using molecular docking for potential protein targets for H. pylori, it was verified that astragalin could interact with these proteins by in silico analysis.

CONCLUSION

These findings highlight that P. volubilis and astragalin produce a bacteriostatic activity against H. pylori and may have potential to be used in treatment against H. pylori, after further research.

Plant-Derived Antimicrobials and Their Crucial Role in Combating Antimicrobial Resistance

Antibiotic resistance emerged shortly after the discovery of the first antibiotic and has remained a critical public health issue ever since. Managing antibiotic resistance in clinical settings continues to be challenging, particularly with the rise of superbugs, or bacteria resistant to multiple antibiotics, known as multidrug-resistant (MDR) bacteria. This rapid development of resistance has compelled researchers to continuously seek new antimicrobial agents to curb resistance, despite a shrinking pipeline of new drugs. Recently, the focus of antimicrobial discovery has shifted to plants, fungi, lichens, endophytes, and various marine sources, such as seaweeds, corals, and other microorganisms, due to their promising properties. For this review, an extensive search was conducted across multiple scientific databases, including PubMed, Elsevier, ResearchGate, Scopus, and Google Scholar, encompassing publications from 1929 to 2024. This review provides a concise overview of the mechanisms employed by bacteria to develop antibiotic resistance, followed by an in-depth exploration of plant secondary metabolites as a potential solution to MDR pathogens. In recent years, the interest in plant-based medicines has surged, driven by their advantageous properties. However, additional research is essential to fully understand the mechanisms of action and verify the safety of antimicrobial phytochemicals. Future prospects for enhancing the use of plant secondary metabolites in combating antibiotic-resistant pathogens will also be discussed.

Screening Tests for the Interaction of Rubus idaeus and Rubus occidentalis Extracts with Antibiotics against Gram-Positive and Gram-Negative Human Pathogens

WHO (World Health Organization) reports from recent years warn about the growing number of antibiotic-resistant bacterial strains. Therefore, there is an urgent need to constantly search for new substances effective in the fight against microorganisms. Plants are a rich source of chemical compounds with antibacterial properties. These compounds, classified as secondary metabolites, may act independently or support the action of currently used antibiotics. Due to the large number of metabolites isolated from the plant kingdom and new plant species being studied, there is a need to develop new strategies/techniques or modifications of currently applied methods that can be used to select plant extracts or chemical compounds isolated from them that enter into positive, synergistic interactions with currently used antibiotics. One such method is the dual-disk synergy test (DDST). It involves the diffusion of active compounds in the agar environment and influencing the growth of microorganisms grown on it. The method was used to assess the interaction of extracts from the fruit and shoots of some cultivated varieties of Rubus idaeus and Rubus occidentalis with selected antibiotics. The research was conducted on strains of bacteria pathogenic to humans, including Staphylococcus aureus, Corynebacterium diphtheriae, Escherichia coli, Pseudomonas aeruginosa, Helicobacter pylori, and Candida albicans, showing synergy, antagonism, or lack of interaction of the tested substances-plant extract and antibiotic. As a result, it was found that the diffusion method is useful in screening tests to assess the impact of antibiotic-herbal substance interactions on Gram-positive and Gram-negative microorganisms.

TATA-Binding Protein-Based Virtual Screening of FDA Drugs Identified New Anti-Giardiasis Agents

Parasitic diseases, predominantly prevalent in developing countries, are increasingly spreading to high-income nations due to shifting migration patterns. The World Health Organization (WHO) estimates approximately 300 million annual cases of giardiasis. The emergence of drug resistance and associated side effects necessitates urgent research to address this growing health concern. In this study, we evaluated over eleven thousand pharmacological compounds sourced from the FDA database to assess their impact on the TATA-binding protein (TBP) of the early diverging protist Giardia lamblia, which holds medical significance. We identified a selection of potential pharmacological compounds for combating this parasitic disease through in silico analysis, employing molecular modeling techniques such as homology modeling, molecular docking, and molecular dynamics simulations. Notably, our findings highlight compounds DB07352 and DB08399 as promising candidates for inhibiting the TBP of Giardia lamblia. Also, these compounds and DB15584 demonstrated high efficacy against trophozoites in vitro. In summary, this study identifies compounds with the potential to combat giardiasis, offering the prospect of specific therapies and providing a robust foundation for future research.

Antimicrobial Metabolites of Caucasian Medicinal Plants as Alternatives to Antibiotics

This review explores the potential of antimicrobial metabolites derived from Caucasian medicinal plants as alternatives to conventional antibiotics. With the rise of antibiotic resistance posing a global health threat, there is a pressing need to investigate alternative sources of antimicrobial agents. Caucasian medicinal plants have traditionally been used for their therapeutic properties, and recent research has highlighted their potential as sources of antimicrobial compounds. Representatives of 15 families of Caucasian medicinal plant extracts (24 species) have been explored for their efficacy against these pathogens. The effect of these plants on Gram-positive and Gram-negative bacteria and fungi is discussed in this paper. By harnessing the bioactive metabolites present in these plants, this study aims to contribute to the development of new antimicrobial treatments that can effectively combat bacterial infections while minimizing the risk of resistance emergence. Herein we discuss the following classes of bioactive compounds exhibiting antimicrobial activity: phenolic compounds, flavonoids, tannins, terpenes, saponins, alkaloids, and sulfur-containing compounds of Allium species. The review discusses the pharmacological properties of selected Caucasian medicinal plants, the extraction and characterization of these antimicrobial metabolites, the mechanisms of action of antibacterial and antifungal plant compounds, and their potential applications in clinical settings. Additionally, challenges and future directions in the research of antimicrobial metabolites from Caucasian medicinal plants are addressed.

Sakuranetin ameliorates streptozotocin-induced diabetes in rodents by inhibiting caspase-3 activity, modulating hematological parameters, and suppressing inflammatory cytokines: a molecular docking and dynamics study

Diabetes affects people of all ages, regardless of gender and background. To date, there is no evidence for the effect of sakuranetin against the streptozotocin (STZ)-induced diabetes paradigm. The research was directed to evaluate the antidiabetic activity of sakuranetin in the STZ model invoking the diabetes-induced disease paradigm. STZ (I.P. 60 mg/kg) is directed to induce type 2 diabetes in experimental rats. Recent research pursued to regulate the anti-diabetic ability of sakuranetin at both 10 and 20 mg/kg in STZ-induced rats. Furthermore, molecular docking research was implemented to evaluate sakuranetin requisite attraction to inflammatory indicators. Various anti-diabetic [(glucose, hemoglobin A1c (HbA1c), and insulin)], lipid profile [triglycerides (TG), total cholesterol (TC), and high-density lipoproteins (HDL)], hematological parameters [Hemoglobin (HGB), packed cell volume (PCV), red blood cells (RBC), mean corpuscular volume (MCV), platelet (PLT), and white blood cells (WBC), pro-inflammatory cytokines [tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-6 (IL-6)], antioxidant level [catalase (CAT), superoxide dismutase (SOD), glutathione (GSH)], lipid oxidation, and caspase-3 were evaluated. Furthermore, molecular docking and dynamics were performed for TNF-α (2AZ5), IL-6 (1ALU), IL-1β (6Y8M), Caspase-3 (1NME) and serum insulin (4IBM) target ligands. Sakuranetin treatment at both doses restored the biochemical parameters i.e. blood glucose, insulin, HbA1c, lipid profile, hematological parameters, pro-inflammatory markers, antioxidant levels, lipid oxidation, and caspase-3 in the context of diabetic rats. It also showed favorable binding affinity on inflammatory markers. Sakuranetin binds to proteins 2AZ5, 1ALU, 6Y8M, 1NME, and 4IBM at -7.489, -6.381, -6.742, -7.202, and -8.166 Kcal/mol, respectively. All of the findings from the molecular dynamics simulations points toward a considerable change in the conformational dynamics of protein upon binding with sakuranetin. The potential use of sakuranetin as an alternative diabetes medication will aid future research as a potent anti-diabetic agent.

Wormwood-infused porous-CaCO3 for synthesizing antibacterial natural rubber latex

Wormwood leaf is a traditional Chinese herbal medicine with a high medicinal value and long application history and its essential oil is a high-purity plant oil extracted from Wormwood leaf. Pharmacological research reveals that Wormwood leaf and Wormwood essential oil are a broad-spectrum antibacterial and antiviral drug, which can inhibit and kill many bacteria and viruses. We loaded wormwood extract on porous calcium carbonate (Porous-CaCO3) and introduced it and Wormwood essential oil into Natural rubber latex (NRL), thus synthesizing NRL composites with excellent vitro and in vivo antibacterial effect, cell compatibility and mechanical properties. This NRL material can delay the light aging and thermal oxidation of some mechanical properties, which provides a broader avenue for its commercialization.

Interaction of sakuranetin with unsaturated lipids forming Langmuir monolayers at the air-water interface: A biomembrane model

This study investigates the interaction between sakuranetin, a versatile pharmaceutical flavonoid, and monolayers composed of unsaturated phospholipids, serving as a surrogate for cell membranes. The phospholipids were 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE). We conducted a series of experiments to comprehensively investigate this interaction, including surface pressure assessments, Brewster angle microscopy (BAM), and polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS). Our findings unequivocally demonstrate that sakuranetin interacts with these phospholipids, expanding the monomolecular films. Notably, regarding POPC, the presence of sakuranetin led to a reduction in stability and a decline in surface elasticity, which can likely be attributed to intricate molecular rearrangements at the interface. The visual evidence of aggregations in BAM images reinforces the interactions substantiated by PM-IRRAS, highlighting sakuranetin's interaction with the polar and nonpolar regions of POPC. However, it is worth noting that these aggregations do not appear to contribute significantly to the viscosity of the mixed film, and our investigations did not reveal any substantial hysteresis. In contrast, when examining POPE, we observed a minor reduction in thermodynamic stability, indicative of fewer rearrangements within the monolayer. This notion was further reinforced by the limited presence of aggregations in the BAM images. Sakuranetin also increased the rigidity of the lipid monolayer; nevertheless, the monolayer remained predominantly elastic, facilitating easy re-spreading on the surface, especially for the first lipid. PM-IRRAS analysis unveiled interactions between sakuranetin and POPE's polar and nonpolar segments, compellingly explaining the observed monolayer expansion. Taken together, our data suggest that sakuranetin was more effectively incorporated into the monomolecular layer of POPE, indicating that membranes comprised of POPC might exhibit a greater degree of interaction in the presence of this pharmacologically active compound.

DNA protection, molecular docking, antioxidant, antibacterial, enzyme inhibition, and enzyme kinetic studies for parietin, isolated from Xanthoria parietina (L.) Th. Fr

Parietin was isolated from Xanthoria parietina (L.) Th. Fr.' (methanol:chloroform) extract, using a silica column. 13 C NMR and 1H NMR were used to confirm the structure of the isolated parietin. For the first time, parietin was investigated for its antioxidant, antibacterial and DNA protective activities. Molecular docking was carried out to determine the binding affinity and interactions between the enzymes and our molecule. Inhibition and kinetic mechanism studies for the action of the enzymes were performed too. Parietin exhibited high metal chelating activity. The MIC values of parietin were sufficient to inhibit different bacterial strains; E. coli, P. aeruginosa, K. pneumoniae and S. aureus. Molecular docking applications exhibited that acetylcholinesterase (AChE), butyrylcholinesterase (BChE), lipase, and tyrosinase have high potential for binding with the parietin. Especially, the parietin's highest binding affinity was recorded with AChE and tyrosinase. These results were confirmed by the inhibition and kinetics results, where, parietin observed a potent inhibition with an IC50 values between 0.013-0.003 µM. Moreover, parietin acts' as a non-competitive inhibitor against AChE, BChE, and lipase, and as a competitive inhibitor against tyrosinase with a high rate of inhibition stability. The promising biological properties of parietin revealed its effectiveness in terms of suitability in the food and pharmaceutical industries.Communicated by Ramaswamy H. Sarma.

Phenylpropanoid Derivatives and Their Role in Plants' Health and as antimicrobials

Phenylpropanoids belong to a wide group of compounds commonly secreted by plants and involved in different roles related with plant growth and development and the defense against plant pathogens. Some key intermediates from shikimate pathway are used to synthesize these compounds. In this way, by the phenylpropanoid pathway several building blocks are achieved to obtain flavonoids, isoflavonoids, coumarins, monolignols, phenylpropenes, phenolic acids, stilbenes and stilbenoids, and lignin, suberin and sporopollenin for plant-microbe interactions, structural support and mechanical strength, organ pigmentation, UV protection and acting against pathogens. Some reviews have revised phenylpropanoid biosynthesis and regulation of the biosynthetic pathways. In this review, the most important chemical structures about phenylpropanoid derivatives are summarized grouping them in different sections according to their structure. We have put special attention on their different roles in plants especially in plant health, growth and development and plant-environment interactions. Their interaction with microorganisms is discussed including their role as antimicrobials. We summarize all new findings about new developed structures and their involvement in plants health.

Inhibitory mechanisms of promising antimicrobials from plant byproducts: A review

Plant byproducts and waste present enormous environmental challenges and an opportunity for valorization and industrial application. Due to consumer demands for natural compounds, the evident paucity of novel antimicrobial agents against foodborne pathogens, and the urgent need to improve the arsenal against infectious diseases and antimicrobial resistance (AMR), plant byproduct compounds have attracted significant research interest. Emerging research highlighted their promising antimicrobial activity, yet the inhibitory mechanisms remain largely unexplored. Therefore, this review summarizes the overall research on the antimicrobial activity and inhibitory mechanisms of plant byproduct compounds. A total of 315 natural antimicrobials from plant byproducts, totaling 1338 minimum inhibitory concentrations (MIC) (in μg/mL) against a broad spectrum of bacteria, were identified, and a particular emphasis was given to compounds with high or good antimicrobial activity (typically <100 μg/mL MIC). Moreover, the antimicrobial mechanisms, particularly against bacterial pathogens, were discussed in-depth, summarizing the latest research on using natural compounds to combat pathogenic microorganisms and AMR. Furthermore, safety concerns, relevant legislation, consumer perspective, and current gaps in the valorization of plant byproducts-derived compounds were comprehensively discussed. This comprehensive review covering up-to-date information on antimicrobial activity and mechanisms represents a powerful tool for screening and selecting the most promising plant byproduct compounds and sources for developing novel antimicrobial agents.

Phytochemicals as Invaluable Sources of Potent Antimicrobial Agents to Combat Antibiotic Resistance

Plants have been used for therapeutic purposes against various human ailments for several centuries. Plant-derived natural compounds have been implemented in clinics against microbial diseases. Unfortunately, the emergence of antimicrobial resistance has significantly reduced the efficacy of existing standard antimicrobials. The World Health Organization (WHO) has declared antimicrobial resistance as one of the top 10 global public health threats facing humanity. Therefore, it is the need of the hour to discover new antimicrobial agents against drug-resistant pathogens. In the present article, we have discussed the importance of plant metabolites in the context of their medicinal applications and elaborated on their mechanism of antimicrobial action against human pathogens. The WHO has categorized some drug-resistant bacteria and fungi as critical and high priority based on the need to develope new drugs, and we have considered the plant metabolites that target these bacteria and fungi. We have also emphasized the role of phytochemicals that target deadly viruses such as COVID-19, Ebola, and dengue. Additionally, we have also elaborated on the synergetic effect of plant-derived compounds with standard antimicrobials against clinically important microbes. Overall, this article provides an overview of the importance of considering phytogenous compounds in the development of antimicrobial compounds as therapeutic agents against drug-resistant microbes.

DEVELOPMENT OF APIGENIN LOADED GASTRORETENTIVE MICROSPONGE FOR THE TARGETING OF HELICO BACTER PYLORI

The goal of the present work was to invent an apigenin-stacked gastroretentive microsponge to target H. pylori. The quasi-emulsion technique was used to prepare microsponges, which were then tested for various physicochemical properties, in-vivo gastric retention, and in-vitro anti-H. pylori study. The microsponge that demonstrated a comparatively good product yield (76.23 ± 0.84), excellent entrapment efficiency (97.84 ± 0.85), sustained in-vitro gastric retention period, and prolonged drug release were chosen for further investigations. The microsponge's SEM analysis showed that it had a spherical form, porous surface, and interconnected spaces. No drug-polymer interactions were detected in the FTIR investigation. Apigenin was found to be dispersed in the microsponge's polymeric matrix according to DSC & XRD investigations. Moreover, the microsponge in the rat's stomach floated for 4 h, according to the ultrasonography. The antibacterial activity of apigenin against H. pylori was nearly two folds more than the pure apigenin and had a more sustained release in the best microsponge, according to the in vitro MIC data, when compared to pure apigenin. To sum up, the developed gastroretentive microsponge with apigenin offers a viable alternative for the efficient targeting of H. pylori. But more preclinical & clinical studies of our best microsponge would yield considerably more fruitful results.

Artemisia afra and Artemisia annua Extracts Have Bactericidal Activity against Mycobacterium tuberculosis in Physiologically Relevant Carbon Sources and Hypoxia

Mycobacterium tuberculosis (Mtb) is a deadly pathogen and causative agent of human tuberculosis, causing ~1.5 million deaths every year. The increasing drug resistance of this pathogen necessitates novel and improved treatment strategies. A crucial aspect of the host-pathogen interaction is bacterial nutrition. In this study, Artemisia annua and Artemisia afra dichloromethane extracts were tested for bactericidal activity against Mtb strain mc26230 under hypoxia and various infection-associated carbon sources (glycerol, glucose, and cholesterol). Both extracts showed significant bactericidal activity against Mtb, regardless of carbon source. Based on killing curves, A. afra showed the most consistent bactericidal activity against Mtb for all tested carbon sources, whereas A. annua showed the highest bactericidal activity in 7H9 minimal media with glycerol. Both extracts retained their bactericidal activity against Mtb under hypoxic conditions. Further investigations are required to determine the mechanism of action of these extracts and identify their active constituent compounds.

Sakuranetin and its therapeutic potentials - a comprehensive review

Sakuranetin (SKN), a naturally derived 7-O-methylated flavonoid, was first identified in the bark of the cherry tree (Prunus spp.) as an aglycone of sakuranin and then purified from the bark of Prunus puddum. It was later reported in many other plants including Artemisia campestris, Boesenbergia pandurata, Baccharis spp., Betula spp., Juglans spp., and Rhus spp. In plants, it functions as a phytoalexin synthesized from its precursor naringenin and is the only known phenolic phytoalexin in rice, which is released in response to different abiotic and biotic stresses such as UV-irradiation, jasmonic acid, cupric chloride, L-methionine, and the phytotoxin coronatine. Till date, SKN has been widely reported for its diverse pharmacological benefits including antioxidant, anti-inflammatory, antimycobacterial, antiviral, antifungal, antileishmanial, antitrypanosomal, glucose uptake stimulation, neuroprotective, antimelanogenic, and antitumor properties. Its pharmacokinetics and toxicological properties have been poorly understood, thus warranting further evaluation together with exploring other pharmacological properties such as antidiabetic, neuroprotective, and antinociceptive effects. Besides, in vivo studies or clinical investigations can be done for proving its effects as antioxidant and anti-inflammatory, antimelanogenic, and antitumor agent. This review summarizes all the reported investigations with SKN for its health-beneficial roles and can be used as a guideline for future studies.

Rice Phytoalexins: Half a Century of Amazing Discoveries; Part I: Distribution, Biosynthesis, Chemical Synthesis, and Biological Activities

Cultivated rice is a staple food for more than half of the world's population, providing approximately 20% of the world's food energy needs. A broad spectrum of pathogenic microorganisms causes rice diseases leading to huge yield losses worldwide. Wild and cultivated rice species are known to possess a wide variety of antimicrobial secondary metabolites, known as phytoalexins, which are part of their active defense mechanisms. These compounds are biosynthesized transiently by rice in response to pathogens and certain abiotic stresses. Rice phytoalexins have been intensively studied for over half a century, both for their biological role and their potential application in agronomic and pharmaceutical fields. In recent decades, the growing interest of the research community, combined with advances in chemical, biological, and biomolecular investigation methods, has led to a notable acceleration in the growth of knowledge on rice phytoalexins. This review provides an overview of the knowledge gained in recent decades on the diversity, distribution, biosynthesis, chemical synthesis, and bioactivity of rice phytoalexins, with particular attention to the most recent advances in this research field.

Bioassay-guided isolation and characterization of lead antimicrobial compounds from Acacia hydaspica plant extract

Acacia hydaspica possesses varied pharmacological attributes. We aimed to examine the antimicrobial potential and isolate the active antimicrobial metabolites. The plant extract was fractionated and the antimicrobial activity of the crude extract, fractions and compounds was tested by agar well diffusion and agar tube dilution and broth dilution methods. Bacterial strains selected for bioactivity testing were Staphylococcus aureus, Enterococcus faecalis, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Acinetobacter baumannii while selected strains from kingdom fungi were Candida albicans, Cryptococcus neoformans, Fusarium solani and Aspergillus. The active compounds were isolated from Acacia hydaspica by bioassay-guided fractionation and identified by nuclear magnetic resonance and spectroscopic techniques. S. aureus cell surface proteins, Autolysins (Atl), Clumping factor A (ClfA), and Fibronectin Binding Proteins (FnBP), were molecularly docked with Catechin 3-O-gallate (CG) and Methyl gallate (MG) and binding energy and molecular interactions between the proteins and compounds were analyzed. Ethyl acetate (AHE) and Butanol (AHB) fractions of A. hydaspica were the most active fractions against tested microbial strains. Therefore, both were subjected to bioassay-directed fractionation which led to the isolation of one pure active antimicrobial AHE and one active pure compound from AHB fraction besides active enriched isolates. Methyl-gallate (MG) and catechin-3-gallate (CG) are active compounds extracted from AHE and AHB fractions respectively. In antibacterial testing MG significantly inhibited the growth of E. coli (MIC₅₀ = 21.5 µg/ml), B. subtilus (MIC₅₀ = 23 µg/ml) and S. aureus (MIC₅₀ = 39.1 µg/ml) while moderate to low activity was noticed against other tested bacterial strains. Antifungal testing reveals that MG showed potent antifungal activity against F. solani (MIC₅₀ = 33.9 µg/ml) and A. niger (MIC₅₀ = 41.5 µg/ml) while lower antifungal activity was seen in other tested strains. AHB fractions and pure compound (CG) showed specific antibacterial activity against S. aureus only (MIC₅₀ = 10.1 µg/ml) while compound and enriched fractions showed moderate to no activity against other bacterial and fungal strains respectively. Molecular docking analysis revealed that CG interacted more strongly with the cell surface proteins than MG. Among these proteins, CG made a stronger complex with ClfA (binding affinity - 9.7) with nine hydrophobic interactions and five hydrogen bonds. Methyl gallate (MG) and catechin 3-O-gallate (CG) are the major antimicrobial compound from A. hydaspica that inhibit the growth of specific microbes. The occurrence of MG and CG endorse the traditional antimicrobial applicability of A. hydaspica, and it can be a legitimate alternative to control specific microbial infections.

Naringenin and Its Derivatives-Health-Promoting Phytobiotic against Resistant Bacteria and Fungi in Humans

Naringenin is a trihydroxyflavanone present in large amount in different citrus fruits, e.g., oranges, pomelos, grapefruits, but also in tomatoes, fenugreek and coffee. It has a wide range of pharmacological and biological effects beneficial to human health. Its antioxidant, anti-cancer, anti-inflammatory, antifungal and antimicrobial activity is frequently reported in scientific literature. In this review we presented the current state of knowledge on the antimicrobial activity of naringenin and its natural and synthetic derivatives as a phytobiotic against resistant Gram-positive and Gram-negative bacteria as well as fungi in humans. Most of the data reported here have been obtained from in vitro or in vivo studies. Over the past few years, due to the overuse of antibiotics, the occurrence of bacteria resistant to all available antibiotics has been growing. Therefore, the main focus here is on antibiotic resistant strains, which are a significant, worldwide problem in the treatment of infectious diseases. The situation is so alarming that the WHO has listed microbial resistance to drugs on the list of the 10 most important health problems facing humanity. In addition, based on scientific reports from recent years, we described the potential molecular mechanism of action of these bioflavonoids against pathogenic strains of microorganisms. As plant-derived substances have been pushed out of use with the beginning of the antibiotic era, we hope that this review will contribute to their return as alternative methods of preventing and treating infections in the epoch of drug resistance.

Natural products and their semi-synthetic derivatives against antimicrobial-resistant human pathogenic bacteria and fungi

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COVID-19 pandemic has traumatized the entire world. During this outbreak, an upsurge in MDR-associated pathogenic microbial organisms has been recorded.

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The increasing human microbial diseases pose a severe danger to global human safety.

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The infectious microbes have developed multiple tolerance strategies to overcome the negative drug impacts.

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Several naturally occurring chemicals produced from bacteria, plants, animals, marine species, and other sources with antimicrobial characteristics have been reviewed.

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These compounds show promise in minimizing the globally increasing microbial diseases.

Human infectious diseases caused by various microbial pathogens, in general, impact a large population of individuals every year. These microbial diseases that spread quickly remain to be a big issue in various health-related domains and to withstand the negative drug impacts, the antimicrobial-resistant pathogenic microbial organisms (pathogenic bacteria and pathogenic fungi) have developed a variety of resistance processes against many antimicrobial drug classes. During the COVID-19 outbreak, there seems to be an upsurge in drug and multidrug resistant-associated pathogenic microbial species. The preponderance of existing antimicrobials isn’t completely effective, which limits their application in clinical settings. Several naturally occurring chemicals produced from bacteria, plants, animals, marine species, and other sources are now being studied for antimicrobial characteristics. These natural antimicrobial compounds extracted from different sources have been demonstrated to be effective against a variety of diseases, although plants remain the most abundant source. These compounds have shown promise in reducing the microbial diseases linked to the development of drug tolerance and resistance. This paper offers a detailed review of some of the most vital and promising natural compounds and their derivatives against various human infectious microbial organisms. The inhibitory action of different natural antimicrobial compounds, and their possible mechanism of antimicrobial action against a range of pathogenic fungal and bacterial organisms, is provided. The review will be useful in refining current antimicrobial (antifungal and antibacterial) medicines as well as establishing new treatment strategies to tackle the rising number of human bacterial and fungal-associated infections.

Flavonoids-Rich Plant Extracts Against Helicobacter pylori Infection as Prevention to Gastric Cancer

Gastric cancer is the fifth most common and fourth type to cause the highest mortality rates worldwide. The leading cause is related to Helicobacter pylori (H. pylori) infection. Unfortunately, current treatments have low success rates, highlighting the need for alternative treatments against carcinogenic agents, specifically H. pylori. Noteworthy, natural origin products contain pharmacologically active metabolites such as flavonoids, with potential antimicrobial applications.

Objective: This article overviews flavonoid-rich extracts’ biological and pharmacological activities. It focuses on using these substances against Helicobacter pylori infection to prevent gastric cancer. For this, PubMed and Science Direct databases were searched for studies that reported the activity of flavonoids against H. pylori, published within a 10-year time frame (2010 to August 2020). It resulted in 1,773 publications, of which 44 were selected according to the search criteria. The plant family primarily found in publications was Fabaceae (9.61%). Among the flavonoids identified after extraction, the most prevalent were quercetin (19.61%), catechin (13.72), epicatechin (11.76), and rutin (11.76). The potential mechanisms associated with anti-H. pylori activity to the extracts were: inhibition of urease, damage to genetic material, inhibition of protein synthesis, and adhesion of the microorganism to host cells.

Conclusion: Plant extracts rich in flavonoids with anti-H. pylori potential proved to be a promising alternative therapy source, reinforcing the relevance of studies with natural products.

Sakuranetin interacting with cell membranes models: Surface chemistry combined with molecular simulation

Sakuranetin, a natural compound with activity in lipidic biointerfaces, was isolated from Baccharis retusa and studied with two models of lipid membranes: Langmuir monolayers and Molecular Simulation. For that, the mammalian lipid DPPC was chosen. Sakuranetin condensed the monolayers at high surface pressures, decreased the surface compressional modulus, reduced the molecular order of the acyl chains (diminution of all-trans/gauche conformers ratio), and increased the heterogeneity of the interface, forming aggregates. Molecular simulation data gave information on the bioactive compound's most favorable thermodynamic positions along the lipid monolayer, which was the lipid-air interface. These combined results lead to the conclusion that this lipophilic compound may interact with the lipidic layers, preferentially at the lipid-air interface, to minimize the free energy, and reaches this conformation disturbing the thermodynamic, structural, mechanical, rheological, and morphological properties of the well-packed DPPC monolayer.

Tackling Multiple-Drug-Resistant Bacteria With Conventional and Complex Phytochemicals

Emerging antibiotic resistance in bacteria endorses the failure of existing drugs with chronic illness, complicated treatment, and ever-increasing expenditures. Bacteria acquire the nature to adapt to starving conditions, abiotic stress, antibiotics, and our immune defense mechanism due to its swift evolution. The intense and inappropriate use of antibiotics has led to the development of multidrug-resistant (MDR) strains of bacteria. Phytochemicals can be used as an alternative for complementing antibiotics due to their variation in metabolic, genetic, and physiological fronts as well as the rapid evolution of resistant microbes and lack of tactile management. Several phytochemicals from diverse groups, including alkaloids, phenols, coumarins, and terpenes, have effectively proved their inhibitory potential against MDR pathogens through their counter-action towards bacterial membrane proteins, efflux pumps, biofilms, and bacterial cell-to-cell communications, which are important factors in promoting the emergence of drug resistance. Plant extracts consist of a complex assortment of phytochemical elements, against which the development of bacterial resistance is quite deliberate. This review emphasizes the antibiotic resistance mechanisms of bacteria, the reversal mechanism of antibiotic resistance by phytochemicals, the bioactive potential of phytochemicals against MDR, and the scientific evidence on molecular, biochemical, and clinical aspects to treat bacterial pathogenesis in humans. Moreover, clinical efficacy, trial, safety, toxicity, and affordability investigations, current status and developments, related demands, and future prospects are also highlighted.

The chemical ecology of the fungus-farming termite symbiosis

Covering: September 1972 to December 2020Explorations of complex symbioses have often elucidated a plethora of previously undescribed chemical compounds that may serve ecological functions in signalling, communication or defence. A case in point is the subfamily of termites that cultivate a fungus as their primary food source and maintain complex bacterial communities, from which a series of novel compound discoveries have been made. Here, we summarise the origins and types of 375 compounds that have been discovered from the symbiosis over the past four decades and discuss the potential for synergistic actions between compounds within the complex chemical mixtures in which they exist. We go on to highlight how vastly underexplored the diversity and geographic distribution of the symbiosis is, which leaves ample potential for natural product discovery of compounds of both ecological and medical importance.

Mechanisms, Anti-Quorum-Sensing Actions, and Clinical Trials of Medicinal Plant Bioactive Compounds against Bacteria: A Comprehensive Review

Bacterial strains have developed an ability to resist antibiotics via numerous mechanisms. Recently, researchers conducted several studies to identify natural bioactive compounds, particularly secondary metabolites of medicinal plants, such as terpenoids, flavonoids, and phenolic acids, as antibacterial agents. These molecules exert several mechanisms of action at different structural, cellular, and molecular levels, which could make them candidates or lead compounds for developing natural antibiotics. Research findings revealed that these bioactive compounds can inhibit the synthesis of DNA and proteins, block oxidative respiration, increase membrane permeability, and decrease membrane integrity. Furthermore, recent investigations showed that some bacterial strains resist these different mechanisms of antibacterial agents. Researchers demonstrated that this resistance to antibiotics is linked to a microbial cell-to-cell communication system called quorum sensing (QS). Consequently, inhibition of QS or quorum quenching is a promising strategy to not only overcome the resistance problems but also to treat infections. In this respect, various bioactive molecules, including terpenoids, flavonoids, and phenolic acids, exhibit numerous anti-QS mechanisms via the inhibition of auto-inducer releases, sequestration of QS-mediated molecules, and deregulation of QS gene expression. However, clinical applications of these molecules have not been fully covered, which limits their use against infectious diseases. Accordingly, the aim of the present work was to discuss the role of the QS system in bacteria and its involvement in virulence and resistance to antibiotics. In addition, the present review summarizes the most recent and relevant literature pertaining to the anti-quorum sensing of secondary metabolites and its relationship to antibacterial activity.

Impact of Propolis on Escherichia coli and Bacillus subtilis Based on Total DNA, RNA and Protein Levels

&lt;b&gt;Background and Objectives:&lt;/b&gt; Propolis is a natural product derived from plant resins and collected by honeybees to protect the colony against different pathogens. The antimicrobial properties of an ethanolic extract of propolis (EEP) were investigated in this study. &lt;b&gt;Materials and Methods:&lt;/b&gt; In the Egyptian Governorate of Giza, F1 carniolan honeybee (&lt;i&gt;Apis mellifera carnica&lt;/i&gt; P.) colonies collected propolis in the autumn, spring and summer of 2019-2020. We investigated the antibacterial activity of EEP against Gram-positive &lt;i&gt;B. subtilis&lt;/i&gt; and Gram-negative &lt;i&gt;E. coli&lt;/i&gt;. Propolis was evaluated and its effects on the amounts of total DNA, RNA and protein in &lt;i&gt;Bacillus subtilis&lt;/i&gt; and &lt;i&gt;Escherichia coli&lt;/i&gt; were investigated. &lt;b&gt;Results:&lt;/b&gt; Propolis inhibited the growth of &lt;i&gt;B. subtilis&lt;/i&gt;. At 5% concentration, the inhibition zones were 8.66, 10.66 and 8.52 mm for autumn, spring and summer propolis, respectively, at 10% concentration, they were 19.66, 21.33 and 18.0 mm, respectively. Propolis also inhibited the growth of &lt;i&gt;E. coli&lt;/i&gt; at a 5% concentration. The inhibition zones were 3.660, 4.00 and 4.33 mm for autumn, spring and summer propolis, respectively and at 10% concentration, they were 7.65, 8.33 and 7.33 mm, respectively. The inhibition zones were the largest (10.66 and 21.33 mm) for &lt;i&gt;B. subtilis&lt;/i&gt; at 5 and 10% propolis, respectively, whereas slightly low inhibition zones (4.0 and 8.33 mm) were observed for &lt;i&gt;E. coli&lt;/i&gt; (5 and 10% propolis, respectively) in spring. In &lt;i&gt;E. coli&lt;/i&gt; and &lt;i&gt;B. subtilis&lt;/i&gt;, propolis inhibited the replication of DNA-dependent RNA polymerase. &lt;b&gt;Conclusion:&lt;/b&gt; The study showed that total DNA, RNA and protein levels in &lt;i&gt;B. subtilis&lt;/i&gt; were reduced by 40, 15.52 and 52.6%, respectively, whereas those in &lt;i&gt;E. coli&lt;/i&gt; were reduced by 12, 15 and 8%, respectively. Furthermore, propolis activity was less effective against Gram-negative bacteria than Gram-positive bacteria.

Preparation, urease inhibition mechanisms, and anti-Helicobacter pylori activities of hesperetin-7-rhamnoglucoside

This work investigated the effects of the bioflavonoid hesperetin-7-rhamnoglucoside isolated from Citrus uranium fruit peel on Helicobacter pylori (H. pylori). Separation and purity, crystalline state, and urease inhibition assays were carried out. Then, molecular docking and molecular dynamics (MD) simulations were conducted with urease as the target protein. Hesp was isolated from citrus peel with a purity of 95.14 µg mg-1 of dry raw material. X-ray diffraction analysis, hydrogen-1 nuclear magnetic resonance, Fourier transform infrared spectroscopy, and differential scanning calorimetry revealed that pure Hesp had the same crystallinity rating as the Hesp standard. The kinetic inhibition study demonstrated that Hesp inhibited H. pylori urease in a competitive and concentration-dependent manner with jack bean urease. In addition, bioimaging studies with laser scanning confocal microscopy and scanning electron microscopy illustrated that Hesp interacted with bacterial cells and induced membrane disruption by creating holes in the outer membranes of the bacterial cells, resulting in the leakage of amino acids. Importantly, molecular docking and 20 ns MD simulations revealed that Hesp inhibited the target protein through slow-binding inhibition and hydrogen bond interactions with active site residues, namely, Gly11 (O⋯H distance = 2.2 Å), Gly13 (O⋯H distance = 2.4 Å), Ser12 (O⋯H distance = 3.3 Å), Lys14 (O⋯H distance = 3.3 Å), and Arg179 (O⋯H distance = 2.7 Å). This work presents novel anti- H. pylori agents from natural sources.

Anti-Helicobacter pylori Compounds from Oliveria decumbens Vent. through Urease Inhibitory In-vitro and In-silico Studies

Oliveria decumbens Vent. has been used by indigenous people of southwest Iran for treating peptic ulcers and gastrointestinal infections. This study aimed to investigate the antibacterial activity of Oliveria decumbens extract and fractions and to analyze the bioactive components of the fractions. Total plant extract and different fractions of Oliveria decumbens Vent. were prepared. Antibacterial activities were evaluated against the clinical strain of Helicobacter pylori and standard strains of Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, and Pseudomonas aeruginosa using agar dilution and disc diffusion methods. Phytochemical analysis of the fractions was performed using silica gel chromatography and 1D and 2D NMR spectroscopy. Moreover, the urease inhibitory effects of the isolated compounds were assessed in-vitro and in-silico. Three novel kaempferol derivatives and two thymol derivatives were isolated from Oliveria decumbens aerial parts, and the structures were determined by comparison with published data. The n-hexane fraction was found to exert the most significant anti-H. pylori activity with the minimum inhibitory concentration of 50 µg/mL. All fractions demonstrated antibacterial activity toward S. aureus. In-vitro urease inhibition assay showed that stigmasterol, tiliroside, and carvacrol were found to be the most potent enzyme inhibitors in the isolated compounds. Molecular interactions of the compounds with the active site of urease were supported by the molecular docking analysis. Novel bioactive compounds in Oliveria decumbens were described in this study. The antibacterial effects suggested the potential use of the compounds in pharmaceutical formulations inconsistent with the traditional use of the plant in the treatment of gastrointestinal infections.

Antimicrobial Potential of Plastic Films Incorporated with Sage Extract on Chicken Meat

The function of packaging is crucial in the maintenance of fresh meat product quality. This study aimed to assess the efficiency of six films added with coatings 2379L/220 and 2379L/221 (containing sage extracts) to inhibit Salmonella typhimurium, Staphylococcus aureus, and Escherichia coli, which showed that two of the six films had a significant effect. Additionally, the effects of the films on refrigerated skinless chicken breast meat were evaluated based on microbiological content, colour, weight loss, texture and pH. Four of the six films were examined could extend the storability of refrigerated chicken breast fillets for up to seven days. All six treated films improved the pH, colour stability, weight loss, and texture of the chicken fillets. Therefore, these findings suggested that the coatings containing sage extracts having different viscosities (2379L/220 and 2379L/221) were effective as antimicrobial adhesives in food packaging films and can be commercially applied in prolonging the storage of chicken breast meat without affecting their quality.

Fighting the Antibiotic Crisis: Flavonoids as Promising Antibacterial Drugs Against Helicobacter pylori Infection

Over half of the world’s population is estimated to be infected with Helicobacter pylori. Chronic infection with this microbial class I carcinogen is considered the most important risk factor for developing gastric cancer. The increasing antimicrobial resistance to first-line antibiotics mainly causes the failure of current eradication therapies, inducing refractory infections. The alarming increase in multidrug resistance in H. pylori isolates worldwide is already beginning to limit the efficacy of existing treatments. Consequently, the World Health Organization (WHO) has included H. pylori in its list of “priority pathogens” for which new antibiotics are urgently needed. Novel strategies must be followed to fight this antibiotic crisis, including properly exploiting the proven therapeutic potential of medicinal plants and plant-derived phytochemicals. In this mini-review, we overview the impressive properties of naturally occurring flavonoids as effective antimicrobial agents against H. pylori, which support the use of these plant-derived bioactive compounds as promising drug candidates for inclusion in novel and personalized combinatory therapies against H. pylori infection.

Stevia Genus: Phytochemistry and Biological Activities Update

The Stevia genus (Asteraceae) comprises around 230 species, distributed from the southern United States to the South American Andean region. Stevia rebaudiana, a Paraguayan herb that produces an intensely sweet diterpene glycoside called stevioside, is the most relevant member of this genus. Apart from S. rebaudiana, many other species belonging to the Stevia genus are considered medicinal and have been popularly used to treat different ailments. The members from this genus produce sesquiterpene lactones, diterpenes, longipinanes, and flavonoids as the main types of phytochemicals. Many pharmacological activities have been described for Stevia extracts and isolated compounds, antioxidant, antiparasitic, antiviral, anti-inflammatory, and antiproliferative activities being the most frequently mentioned. This review aims to present an update of the Stevia genus covering ethnobotanical aspects and traditional uses, phytochemistry, and biological activities of the extracts and isolated compounds.

Interactions with Microbial Proteins Driving the Antibacterial Activity of Flavonoids

Flavonoids are among the most abundant natural bioactive compounds produced by plants. Many different activities have been reported for these secondary metabolites against numerous cells and systems. One of the most interesting is certainly the antimicrobial, which is stimulated through various molecular mechanisms. In fact, flavonoids are effective both in directly damaging the envelope of Gram-negative and Gram-positive bacteria but also by acting toward specific molecular targets essential for the survival of these microorganisms. The purpose of this paper is to present an overview of the most interesting results obtained in the research focused on the study of the interactions between flavonoids and bacterial proteins. Despite the great structural heterogeneity of these plant metabolites, it is interesting to observe that many flavonoids affect the same cellular pathways. Furthermore, it is evident that some of these compounds interact with more than one target, producing multiple effects. Taken together, the reported data demonstrate the great potential of flavonoids in developing innovative systems, which can help address the increasingly serious problem of antibiotic resistance.

Antimicrobials from Medicinal Plants: An Emergent Strategy to Control Oral Biofilms

Oral microbial biofilms, directly related to oral diseases, particularly caries and periodontitis, exhibit virulence factors that include acidification of the oral microenvironment and the formation of biofilm enriched with exopolysaccharides, characteristics and common mechanisms that, ultimately, justify the increase in antibiotics resistance. In this line, the search for natural products, mainly obtained through plants, and derived compounds with bioactive potential, endorse unique biological properties in the prevention of colonization, adhesion, and growth of oral bacteria. The present review aims to provide a critical and comprehensive view of the in vitro antibiofilm activity of various medicinal plants, revealing numerous species with antimicrobial properties, among which, twenty-four with biofilm inhibition/reduction percentages greater than 95%. In particular, the essential oils of Cymbopogon citratus (DC.) Stapf and Lippia alba (Mill.) seem to be the most promising in fighting microbial biofilm in Streptococcus mutans, given their high capacity to reduce biofilm at low concentrations.

Biological nitrification inhibition in the rhizosphere: determining interactions and impact on microbially mediated processes and potential applications

Nitrification is the microbial conversion of reduced forms of nitrogen (N) to nitrate (NO3-), and in fertilized soils it can lead to substantial N losses via NO3- leaching or nitrous oxide (N2O) production. To limit such problems, synthetic nitrification inhibitors have been applied but their performance differs between soils. In recent years, there has been an increasing interest in the occurrence of biological nitrification inhibition (BNI), a natural phenomenon according to which certain plants can inhibit nitrification through the release of active compounds in root exudates. Here, we synthesize the current state of research but also unravel knowledge gaps in the field. The nitrification process is discussed considering recent discoveries in genomics, biochemistry and ecology of nitrifiers. Secondly, we focus on the 'where' and 'how' of BNI. The N transformations and their interconnections as they occur in, and are affected by, the rhizosphere, are also discussed. The NH4+ and NO3- retention pathways alternative to BNI are reviewed as well. We also provide hypotheses on how plant compounds with putative BNI ability can reach their targets inside the cell and inhibit ammonia oxidation. Finally, we discuss a set of techniques that can be successfully applied to solve unresearched questions in BNI studies.

The Interactions between Polyphenols and Microorganisms, Especially Gut Microbiota

This review presents the comprehensive knowledge about the bidirectional relationship between polyphenols and the gut microbiome. The first part is related to polyphenols' impacts on various microorganisms, especially bacteria, and their influence on intestinal pathogens. The research data on the mechanisms of polyphenol action were collected together and organized. The impact of various polyphenols groups on intestinal bacteria both on the whole "microbiota" and on particular species, including probiotics, are presented. Moreover, the impact of polyphenols present in food (bound to the matrix) was compared with the purified polyphenols (such as in dietary supplements) as well as polyphenols in the form of derivatives (such as glycosides) with those in the form of aglycones. The second part of the paper discusses in detail the mechanisms (pathways) and the role of bacterial biotransformation of the most important groups of polyphenols, including the production of bioactive metabolites with a significant impact on the human organism (both positive and negative).

Biochemical Characterization of a Flavonoid O-methyltransferase from Perilla Leaves and Its Application in 7-Methoxyflavonoid Production

Methylation is a common structural modification that can alter and improve the biological activities of natural compounds. O-Methyltransferases (OMTs) catalyze the methylation of a wide array of secondary metabolites, including flavonoids, and are potentially useful tools for the biotechnological production of valuable natural products. An OMT gene (PfOMT3) was isolated from perilla leaves as a putative flavonoid OMT (FOMT). Phylogenetic analysis and sequence comparisons showed that PfOMT3 is a class II OMT. Recombinant PfOMT3 catalyzed the methylation of flavonoid substrates, whereas no methylated product was detected in PfOMT3 reactions with phenylpropanoid substrates. Structural analyses of the methylation products revealed that PfOMT3 regiospecifically transfers a methyl group to the 7-OH of flavonoids. These results indicate that PfOMT3 is an FOMT that catalyzes the 7-O-methylation of flavonoids. PfOMT3 methylated diverse flavonoids regardless of their backbone structure. Chrysin, naringenin and apigenin were found to be the preferred substrates of PfOMT3. Recombinant PfOMT3 showed moderate OMT activity toward eriodictyol, luteolin and kaempferol. To assess the biotechnological potential of PfOMT3, the biotransformation of flavonoids was performed using PfOMT3-transformed Escherichia coli. Naringenin and kaempferol were successfully bioconverted to the 7-methylated products sakuranetin and rhamnocitrin, respectively, by E. coli harboring PfOMT3.

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.

Apigenin Attenuates the Allergic Reactions by Competitively Binding to ER With Estradiol

Apigenin (API) is a natural phytoestrogen with properties including anti-inflammatory and other abilities. This study aims to 1) systematically validate that excessive estrogen exacerbates allergic reactions; 2) explore the anti-allergic effects and mechanisms of API. We conduct a survey of college students, indicating that of the 505 effective results, 70 individuals were self-reported allergic and 74.1% of them were women, which proved the gender difference in allergic reactions. BALB/c mice are grouped into the negative control group (N-Ctrl), the OVA-sensitized group (P-Ctrl), the estrogenized OVA-sensitized group (E2), and three treatment groups administrating different dose of API (E2 + API/L/M/H). In vivo data indicated that API treatment significantly inhibited the enhancement of estradiol on clinical symptoms. Moreover, we found that high doses of API inhibited Th2 type humoral response and mast cell degranulation levels in vivo and in vitro. Additionally, medium, and high doses of API significantly reduced the potentiation of estradiol on ER expression, attenuated the transmission of estrogen/ER signaling, thereby inhibiting the phosphorylation of ERK1/2 and JNK1/2/3 in the MAPK. Besides, we found that API competitively bound to ER with estradiol, and showed a weak selectivity to ERβ. Overall, we identified API can be beneficial in allergic disease.

Antibacterial activity of Barbatimão (Stryphnodendron adstringens) against Staphylococcus aureus: in vitro and in silico studies

We evaluated the activity of the aqueous fraction and the ethyl acetate fraction of Stryphnodendron adstringens against Staphylococcus aureus and proposed their mechanism of action. The antibacterial activity of S. adstringens fractions was evaluated against S. aureus and the cell targets were rated by docking. The fractions showed moderate antibacterial activity against S. aureus without toxicity on two mammalian cell lines. They also showed synergistic antibacterial activity with tannic acid (TA). In silico assays indicated FabG, FabZ and FabI as probable targets. The metabolic pathway for fatty acid biosynthesis in S. aureus was affected by components of S. adstringens. The synergistic effect when combining TA with S. adstringens fractions suggests a natural alternative to S. aureus control. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first study describing the possible targets of action of Stryphnodendron adstringens on Staphylococcus aureus. Molecular dynamics simulations showed that the components of S. adstringens affected the metabolic pathway for fatty acid biosynthesis (FAS II) in S. aureus, inhibiting the FabI, FabG and FabZ enzymes. As tannic acid (TA) is a known inhibitor of some targets identified, we showed synergistic antibacterial activity of S. adstringens in combination with TA. This combination did not show toxicity against HaCaT and Vero cells and based on all these results we suggest that S. adstringens can be a natural and sustainable alternative to S. aureus control.

Sustainable and Ecofriendly Approach of Managing Soil Born Bacterium Ralstonia solanacearum (Smith) Using Dried Powder of Conyza canadensis

Bacterial wilt disease caused by Ralstonia solanacearum is a devastating plant disease that inflicts heavy losses to the large number of economic host plants it infects. The potential of dried powder of the Conyza canadensis to control bacterial wilt (BW) of tomato was explored in vitro and in planta. Three application times (16 days before transplanting (DBT), 8 DBT and 0 DBT), three plastic-mulch durations (10 days plastic mulching (DPM), 5DPM and 0DPM) and four doses viz. 0 g, 8 g, 16 g and 24 g of the plant powder were evaluated. SEM analysis was also conducted to observe the change in bacterial cell morphology. Ethanol extract of dried C. canadensis in different concentrations inhibited the in vitro growth of R. solanacearum by as much as 98% of that produced by ampicillin. As evident from the scanning electron micrograph, the highest concentration produced severe morphologic changes, such as rupture of the bacterial cell walls and cell contents leaked out. Results from application time and dose experiment demonstrated that the highest powder dose viz. 24 g kg⁻¹ mixed with infested soil 16 DBT gave maximum root length (34.0 ± 2.5 cm), plant height (74.3 ± 4.7 cm), fresh biomass (58.3 ± 4.3 g), reduction in bacterial population (1.52 log10) and resulted in lowest AUDPC value (1156.6). In case of mulching duration and dose experiment the maximum root length (39.6 ± 3.2 cm), plant height (78.3 ± 5.8 cm), fresh biomass (65.6 ± 4.9 g) reduction in bacterial population (1.59 log10) and lowest AUDPC value (1251.6) was achieved through the application of highest powder dose viz. 24 g kg⁻¹ and longest plastic mulching duration of 10 DPM. The better results of highest dose and longer application time can be explained on the basis of higher amounts of anti-microbial plant bio-active compounds in highest dose and the longer exposure time of the pathogen to these chemicals. The better results of longer mulching duration are due to faster and more complete decomposition (because of 10-days-long plastic-mulch-provided increased solar heat) of the dried powder which produced more amounts of volatile and non-volatile bactericidal compounds. Our results clearly suggest that the use of 24 g kg⁻¹ dried plant powder of C. canadensis plastic-mulched for two weeks could be used as a reliable component of the integrated disease management program against BW.

Interaction of Ziziphus mucronata subsp. mucronata Methanol Extract and First-Line Antibiotics is Synergistic In Vitro through Production of Reactive Oxygen Species

With the increased incidence of antibacterial resistance in microorganisms, combining natural products from plants with antibiotics may be considered interesting alternatives for synergy to attain multitarget effects. In this study, the antioxidant activity of the methanol extract of Ziziphus mucronata and its interactions with antibiotics against bacteria of clinical importance were investigated. While its phytochemicals and antioxidant activities were determined by free radical scavenging assays, the antibacterial activities of the extract and its interactions with the antibiotics were determined by macrobroth dilution and the checkerboard methods. From the results, total phenolic content was 29.67 ± 1.90 mg GAE/100 g, total flavonoid content was 8.72 ± 0.08 mg QE/100 g, and total proanthocyanidin content was 1.94 ± 0.00 mg CE/100 g of dry plant material. The inhibition concentration 50% (IC₅₀) of DPPH, BHT, and ascorbic acid was equal to 0.04 ± 0.02 mg/ml, respectively. Those of the ABTS, BHT, and ascorbic acid were equal to 0.02 ± 0.02, 0.04 ± 0.03, and 0.04 ± 0.02 mg/ml, respectively. The checkerboard assay showed that combining the extract with different antibiotics resulted in synergistic (38.75%), indifferent (30%), additive (28.75%), and antagonistic (2.5%) interactions. The interactions between the extract and antibiotics resulting in enhanced antibacterial activities could have resulted from the antioxidant activities of the extract mopping up the ROS generated by the antibiotics or the ability of both extract and antibiotics simultaneously producing reactive oxygen species with deleterious effects resulting in synergistic antibacterial effects.