Antibiofilm and Antioxidant Activity of Propolis and Bud Poplar Resins versus Pseudomonas aeruginosa

Organic extracts from sustainable hybrid poplar hairy root cultures as potential natural antimicrobial and antibiofilm agents

In order to meet growing consumer demands in terms of naturalness, the pharmaceutical, food, and cosmetic industries are looking for active molecules of plant origin. In this context, hairy roots are considered a promising biotechnological system for the sustainable production of compounds of interest. Poplars (genus Populus, family Salicaceae) are trees of ecological interest in temperate alluvial forests and are also cultivated for their industrial timber. Poplar trees also produce specialized metabolites with a wide range of bioactive properties. The present study aimed to assess the hybrid poplar hairy root extracts for antimicrobial and antibiofilm activities against four main life-threatening strains of Gram-positive (Staphylococcus aureus, Bacillus subtilis) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacteria. Ethyl acetate extracts from two hairy root lines (HP15-3 and HP A4-12) showed significant antibacterial properties as confirmed by disc diffusion assay. Antibiofilm activities were found to be dose dependent with significant biofilm inhibition (75-95%) recorded at 1000 µg.mL-1 in all the bacterial strains tested. Dose-dependent enhancement in the release of exopolysaccharides was observed in response to treatment with extracts, possibly because of stress and bacterial cell death. Fluorescence microscopy confirmed loss of cell viability of treated bacterial cells concomitant with increased production of reactive oxygen species compared to the untreated control. Overall, this study demonstrates for the first time a high potential of poplar hairy root extracts as a natural and safe platform to produce antimicrobial agents in pharmaceutical, food, industrial water management, or cosmetic industries.

A novel black poplar propolis extract with promising health-promoting properties: focus on its chemical composition, antioxidant, anti-inflammatory, and anti-genotoxic activities

Propolis is a resinous mixture produced by honeybees which has been used since ancient times for its useful properties. However, its chemical composition and bioactivity may vary, depending on the geographical area of origin and the type of tree bees use for collecting pollen. In this context, this research aimed to investigate the total phenolic content (using the Folin-Ciocalteu assay) and the total antioxidant capacity (using the FRAP, DPPH, and ABTS assays) of three black poplar (Populus nigra L.) propolis (BPP) solutions (S1, S2, and S3), as well as the chemical composition (HPLC-ESI-MSn) and biological activities (effect on cell viability, genotoxic/antigenotoxic properties, and anti-inflammatory activity, and effect on ROS production) of the one which showed the highest antioxidant activity (S1). The hydroalcoholic BPP solution S1 was a prototype of an innovative, research-type product by an Italian nutraceutical manufacturer. In contrast, hydroalcoholic BPP solutions S2 and S3 were conventional products purchased from local pharmacy stores. For the three extracts, 50 phenolic compounds, encompassing phenolic acids and flavonoids, were identified. In summary, the results showed an interesting chemical profile and the remarkable antioxidant, antigenotoxic, anti-inflammatory and ROS-modulating activities of the innovative BPP extract S1, paving the way for future research. In vivo investigations will be a possible line to take, which may help corroborate the hypothesis of the potential health benefits of this product, and even stimulate further ameliorations of the new prototype.

Advances in the phytochemical screening and biological potential of propolis

Propolis is a natural resinous product collected from different parts of plants by bees and mixed with their salivary secretions. The occurrence of more than 180 different chemotypes has flavonoids, phenolic acids, esters, and phenolic aldehydes, as well as balsamic resins, beeswax, pollen, and essential and aromatic oils, among others. Its biological potential documented throughout the world justifies the need, from time to time, to organize reviews on the subject, with the intention of gathering and informing about the update on propolis. In this review (CRD42020212971), phytochemical advances, in vitro, in vivo, and clinical biological assays of pharmacological interest are showcased. The focus of this work is to present propolis clinical safety assays, antitumor, analgesic, antioxidant, anti-inflammatory, and antimicrobial activities. This literature review highlights propolis' promising biological activity, as it also suggests that studies associating propolis with nanotechnology should be further explored for enhanced bioprocessing applications.

Structure based virtual screening and molecular dynamics of natural anti-biofilm compounds against SagS response regulator/sensor kinase in Pseudomonas aeruginosa

SagS sensor regulator plays a vital role in biofilm development of Pseudomonas aeruginosa which subsequently makes the cells more tolerant to various antimicrobials. The multidrug resistance (MDR) issue has risen substantially in recent years and is considered a global threat. Therefore, alternative compounds should be unearthed immediately to address the issues related to P. aeruginosa drug resistance for which SagS could be a candidate. The present study is an attempt to screen natural anti-biofilm compounds as the potent inhibitors of SagS. Twenty natural anti-biofilm/quorum sensing inhibiting compounds were retrieved from various literatures with significant inhibitory effects against P. aeruginosa biofilm from in-vitro experiments which were screened using various pharmacokinetic parameters. The screened and three standard drugs were docked against SagS-HisKA using AutoDock 4.2 tool, which were further analysed by MD simulations to understand the binding mode of compounds and dynamic behaviour of the complexes. Two potential anti-biofilm natural compounds, pinocembrin with binding affinity (-7.19 kcal/mol), vestitol (-7.18 kcal/mol) and the standard drug ceftazidime (-8.89 kcal/mol) were selected based on filtered parameters and better binding affinity. The trajectory analysis of MD simulations reflected Pinocembrin in stabilizing the system compared to ceftazidime. The existing reports state that the natural products represent promising source of therapy with least or almost nil adverse effect compared to synthetic drugs which is well collated with our in-silico findings. This investigation can save both time and cost required for in-vitro and in-vivo analysis for designing of a novel anti-biofilm agent against P. aeruginosa biofilm-associated infections.Communicated by Ramaswamy H. Sarma.

Bioactive compounds: a goldmine for defining new strategies against pathogenic bacterial biofilms?

Most human infectious diseases are caused by microorganisms growing as biofilms. These three-dimensional self-organized communities are embedded in a dense matrix allowing microorganisms to persistently inhabit abiotic and biotic surfaces due to increased resistance to both antibiotics and effectors of the immune system. Consequently, there is an urgent need for novel strategies to control biofilm-associated infections. Natural products offer a vast array of chemical structures and possess a wide variety of biological properties; therefore, they have been and continue to be exploited in the search for potential biofilm inhibitors with a specific or multi-locus mechanism of action. This review provides an updated discussion of the major bioactive compounds isolated from several natural sources - such as plants, lichens, algae, microorganisms, animals, and humans - with the potential to inhibit biofilm formation and/or to disperse established biofilms by bacterial pathogens. Despite the very large number of bioactive products, their exact mechanism of action often remains to be clarified and, in some cases, the identity of the active molecule is still unknown. This knowledge gap should be filled thus allowing development of these products not only as novel drugs to combat bacterial biofilms, but also as antibiotic adjuvants to restore the therapeutic efficacy of current antibiotics.

Bud-Poplar-Extract-Embedded Chitosan Films as Multifunctional Wound Healing Dressing

Wounds represent a major global health challenge. Acute and chronic wounds are sensitive to bacterial infection. The wound environment facilitates the development of microbial biofilms, delays healing, and promotes chronic inflammation processes. The aim of the present work is the development of chitosan films embedded with bud poplar extract (BPE) to be used as wound dressing for avoiding biofilm formation and healing delay. Chitosan is a polymer with antimicrobial and hydrating properties used in wound dressing, while BPE has antibacterial, antioxidative, and anti-inflammatory properties. Chitosan-BPE films showed good antimicrobial and antibiofilm properties against Gram-positive bacteria and the yeast Candida albicans. BPE extract induced an immunomodulatory effect on human macrophages, increasing CD36 expression and TGFβ production during M1/M2 polarization, as observed by means of cytofluorimetric analysis and ELISA assay. Significant antioxidant activity was revealed in a cell-free test and in a human neutrophil assay. Moreover, the chitosan-BPE films induced a good regenerative effect in human fibroblasts by in vitro cell migration assay. Our results suggest that chitosan-BPE films could be considered a valid plant-based antimicrobial material for advanced dressings focused on the acceleration of wound repair.

A comparative study of antimicrobial, anti-quorum sensing, anti-biofilm, anti-swarming, and antioxidant activities in flower extracts of pecan (Carya illinoinensis) and chestnut (Castanea sativa)

Antibiotic resistance, which has increased rapidly in recent years because of uncontrolled and unconscious antibiotic consumption, poses a major threat to public health. The inadequacy of existing antibiotics has increased the need for new, effective, and less toxic antibiotic raw materials or antibiotic derivatives. Pecan (Carya illinoinensis) and Chestnut (Castanea sativa) flowers possess abundant pollen contents and exhibit similar morphological features. The purpose of this study was to compare these two flower extracts in terms of their antimicrobial and antioxidant activities. Total phenolic content, total flavonoid contents, and phenolic components were also analyzed in aquatic and ethanolic extracts. Antioxidant activities were measured using ferric reducing/antioxidant capacity (FRAP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) methods. Antimicrobial and antifungal activities were compared by means of agar diffusion tests against bacteria including Staphylococcus aureus, Bacillus cereus, Mycobacterium smegmatis, Acinetobacter haemolyticus, and Chromobacterium violaceum, and the yeasts Candida albicans and Candida parapsilosis. Anti-quorum sensing (anti-QS), anti-biofilm, and anti-swarming (SW) activities were also studied against Chromobacterium violaceum ATCC 31532, Chromobacterium violaceum ATCC 12472, and Pseudomonas aeruginosa PA01, respectively. Both extracts were rich in ellagic acid and gallic acid and exhibited similar antioxidant properties. Both flower extracts exhibited high antimicrobial and antifungal activities as well as anti-biofilm, anti-QS, and anti-SW activities.

Antibiofilm and Anti-Quorum Sensing Potential of Cycloartane-Type Triterpene Acids from Cameroonian Grassland Propolis: Phenolic Profile and Antioxidant Activity of Crude Extract

Propolis is very popular for its beneficial health properties, such as antimicrobial activity and antioxidant effects. It is one of the most long-serving traditional medicines to mankind due to its interesting chemical diversity and therapeutic properties. The detailed chemical information of propolis samples is very necessary to guarantee its safety and for it to be accepted into health care systems. The phenolic profile of the hydroethanolic extract was determined using HPLC-DAD, and the antioxidant was evaluated using five complementary methods. Triterpenoids were isolated using column chromatography and characterized using 1H NMR and 13C NMR. The effects of the extract and the isolated compounds on quorum sensing mediated processes and biofilm formation in bacteria were evaluated. Protocatechic acid (40.76 ± 0.82 µg/g), 4-hydroxybenzoic acid (24.04 ± 0.21 µg/g), vanillic acid (29.90 ± 1.05 µg/g), quercetin (43.53 ± 1.10 µg/g), and luteolin (4.44 ± 0.48 µg/g) were identified and quantified. The extract showed good antioxidant activity in the DPPH•, ABTS•+, CUPRAC, and metal chelating assays, and this antioxidant effect was confirmed by cyclic voltammetry. 27-Hydroxymangiferonic acid (1), Ambolic acid (2), and Mangiferonic acid (3) were isolated from anti-quorum sensing activity at MIC, and it was indicated that the most active sample was the extract with inhibition diameter zone of 18.0 ± 1.0 mm, while compounds 1, 2, and 3 had inhibition zones of 12.0 ± 0.5 mm, 9.0 ± 1.0 mm, and 12.3 ± 1.0 mm, respectively. The samples inhibited the P. aeruginosa PA01 swarming motility at the three tested concentrations (50, 75, and 100 μg/mL) in a dose-dependent manner. The propolis extract was able to inhibit biofilm formation by S. aureus, E. coli, P. aeruginosa, C. albicans, and C. tropicalis at MIC concentration. Compound 1 proved biofilm inhibition on S. aureus, L. monocytogenes, E. faecalis, E. coli, and C. tropicalis at MIC and MIC/2; compound 2 inhibited the formation of biofilm at MIC on S. aureus, E. faecalis, E. coli, S. typhi, C. albicans, and C. tropicalis; and compound 3 inhibited biofilm formation on E. faecalis, E. coli, C. albicans, and C. tropicalis and further biofilm inhibition on E. coli at MIC/4 and MIC/8. The studied propolis sample showed important amounts of cycloartane-type triterpene acids, and this indicates that there can be significant intra-regional variation probably due to specific flora within the vicinity. The results indicate that propolis and its compounds can reduce virulence factors of pathogenic bacteria.

The Suitability of Propolis as a Bioactive Component of Biomaterials

Propolis is a resinous product collected by bees from plant exudates to protect and maintain hive homeostasis. Propolis has been used therapeutically for centuries as folk medicine. Modern research investigating the diversity of the chemical composition and plant sources, biological activity, extraction processes, analytical methods, and therapeutic properties in clinical settings have been carried out extensively since the 1980s. Due to its antimicrobial, anti-inflammatory, and immuno-modulator properties, propolis appears to be a suitable bioactive component to be incorporated into biomaterials. This review article attempts to analyze the potential application of propolis as a biomaterial component from the available experimental evidence. The efficacy and compabitility of propolis depend upon factors, such as types of extracts and types of biomaterials. Generally, propolis appears to be compatible with hydroxyapatite/calcium phosphate-based biomaterials. Propolis enhances the antimicrobial properties of the resulting composite materials while improving the physicochemical properties. Furthermore, propolis is also compatible with wound/skin dressing biomaterials. Propolis improves the wound healing properties of the biomaterials with no negative effects on the physicochemical properties of the composite biomaterials. However, the effect of propolis on the glass-based biomaterials cannot be generalized. Depending on the concentration, types of extract, and geographical sources of the propolis, the effect on the glass biomaterials can either be an improvement or detrimental in terms of mechanical properties such as compressive strength and shear bond strength. In conclusion, two of the more consistent impacts of propolis across these different types of biomaterials are the enhancement of the antimicrobial and the immune-modulator/anti-inflammatory properties resulting from the combination of propolis and the biomaterials.

Edible Xanthan/Propolis Coating and Its Effect on Physicochemical, Microbial, and Sensory Quality Indices in Mackerel Tuna (Euthynnus affinis) Fillets during Chilled Storage

Worldwide aquaculture production is increasing, but with this increase comes quality and safety related problems. Hence, there is an urgent need to develop potent technologies to extend the shelf life of fish. Xanthan gum is commonly used in the food industry because of its high-water solubility, stability of its aqueous solutions in a wide pH range, and high viscosity. One of its modern food applications is its use as a gelling agent in edible coatings building. Therefore, in this study, the effect of xanthan coating containing various concentrations (0, 1, 2%; w/v) of ethanolic extract of propolis (EEP) on physicochemical, microbial, and sensory quality indices in mackerel fillets stored at 2 °C for 20 days was evaluated. The pH, peroxide value, K-value, TVB-N, TBARS, microbiological and sensory characteristics were determined every 5 days over the storage period (20 days). Samples treated with xanthan (XAN) coatings containing 1 and 2% of EEP were shown to have the highest level of physicochemical protection and maximum level of microbial inhibition (p < 0.05) compared to uncoated samples (control) over the storage period. Furthermore, the addition of EEP to XAN was more effective in notably preserving (p < 0.05) the taste and odor of coated samples compared to control.

Propolis characterization and antimicrobial activities against Staphylococcus aureus and Candida albicans: A review

Propolis is a plant-based sticky substance that is produced by honeybees. It has been used traditionally by ancient civilizations as a folk medicine, and is known to have many pharmaceutical properties including antioxidant, antibacterial, antifungal, anti-inflammatory, antiviral, and antitumour effects. Worldwide, researchers are still studying the complex composition of propolis to unveil its biological potential, and especially its antimicrobial activity against a variety of multidrug-resistant microorganisms. This review explores scientific reports published during the last decade on the characterization of different types of propolis, and evaluates their antimicrobial activities against Staphylococcus aureus and Candida albicans. Propolis can be divided into different types depending on their chemical composition and physical properties associated with geographic origin and plant sources. Flavonoids, phenols, diterpenes, and aliphatic compounds are the main chemicals that characterize the different types of propolis (Poplar, Brazilian, and Mediterranean), and are responsible for their antimicrobial activity. The extracts of most types of propolis showed greater antibacterial activity against Gram-positive bacteria: particularly on S. aureus, as well as on C. albicans, as compared to Gram-negative pathogens. Propolis acts either by directly interacting with the microbial cells or by stimulating the immune system of the host cells. Some studies have suggested that structural damage to the microorganisms is a possible mechanism by which propolis exhibits its antimicrobial activity. However, the mechanism of action of propolis is still unclear, due to the synergistic interaction of the ingredients of propolis, and this natural substance has multi-target activity in the cell. The broad-spectrum biological potentials of propolis present it as an ideal candidate for the development of new, potent, and cost-effective antimicrobial agents.

Antimicrobial activity, in vitro anticancer effect (MCF-7 breast cancer cell line), antiangiogenic and immunomodulatory potentials of Populus nigra L. buds extract

PURPOSE

The aim of this study was to evaluate the antioxidant potential, antimicrobial activity, the in vitro anticancer effect (tested on MCF-7 breast cancer cell line), as well as the antiangiogenic and immunomodulatory potential of Populus nigra L. bud (Pg) extract collected from the western part of Romania.

RESULTS

Populus nigra L. bud extract presents an important antioxidant activity, due to the rich phytochemical composition. Regarding the biological activity, results have shown that poplar bud extract presents a significant inhibitory activity against Gram-positive bacteria and a dose-dependent decrease of MCF-7 tumor cell viability with an IC₅₀ of 66.26 μg/mL, while not affecting healthy cells. Phenomena of early apoptotic events at the maximum concentration tested (150 μg/mL) were detected by Annexin V-PI double staining. The extract induced G0/G1 phase cell cycle arrest. In addition, Pg extract showed antiangiogenic potential on the chorioallantoic membrane. Also, at the highest concentration (150 μg/mL), good tolerability and no signs of toxicity upon vascular plexus were observed. Moreover, in low concentrations, the Pg extract had immunomodulatory activity on primary human dendritic cells by upregulating IL-12 and IL-23 subunits.

CONCLUSION

The study concludes that poplar bud extract elicited antioxidant activity, antitumor properties on the breast cancer cell line, followed by an antiangiogenic effect and an immunomodulatory potential on human primary dendritic cells. The biological activity of Populus nigra L. buds extract may open new directions of research on the topic addressed.

The Potential Use of Propolis as a Primary or an Adjunctive Therapy in Respiratory Tract-Related Diseases and Disorders: A Systematic Scoping Review

Propolis is a resinous beehive product that is collected by the bees from plant resin and exudates, to protect and maintain hive homeostasis. Propolis has been used by humans therapeutically to treat many ailments including respiratory tract-related diseases and disorders. The aim of the present systematic scoping review is to evaluate the experimental evidence to support the use of propolis as a primary or an adjunctive therapy in respiratory tract-related diseases and disorders. After applying the exclusion criteria, 158 research publications were retrieved and identified from Scopus, Web of Science, Pubmed, and Google Scholar. The key themes of the included studies were pathogenic infection-related diseases and disorders, inflammation-related disorders, lung cancers, and adverse effects. Furthermore, the potential molecular and biochemical mechanisms of action of propolis in alleviating respiratory tract-related diseases and disorders are discussed. In conclusion, the therapeutic benefits of propolis have been demonstrated by various in vitro studies, in silico studies, animal models, and human clinical trials. Based on the weight and robustness of the available experimental and clinical evidence, propolis is effective, either as a primary or an adjunctive therapy, in treating respiratory tract-related diseases.

Evaluation of Total Phenolic and Flavonoid Contents, Antibacterial and Antibiofilm Activities of Hungarian Propolis Ethanolic Extract against Staphylococcus aureus

Propolis is a natural bee product that is widely used in folk medicine. This study aimed to evaluate the antimicrobial and antibiofilm activities of ethanolic extract of propolis (EEP) on methicillin-resistant and sensitive Staphylococcus aureus (MRSA and MSSA). Propolis samples were collected from six regions in Hungary. The minimum inhibitory concentrations (MIC) values and the interaction of EEP-antibiotics were evaluated by the broth microdilution and the chequerboard broth microdilution methods, respectively. The effect of EEP on biofilm formation and eradication was estimated by crystal violet assay. Resazurin/propidium iodide dyes were applied for simultaneous quantification of cellular metabolic activities and dead cells in mature biofilms. The EEP1 sample showed the highest phenolic and flavonoid contents. The EEP1 successfully prevented the growth of planktonic cells of S. aureus (MIC value = 50 µg/mL). Synergistic interactions were shown after the co-exposition to EEP1 and vancomycin at 108 CFU/mL. The EEP1 effectively inhibited the biofilm formation and caused significant degradation of mature biofilms (50-200 µg/mL), as a consequence of the considerable decrement of metabolic activity. The EEP acts effectively as an antimicrobial and antibiofilm agent on S. aureus. Moreover, the simultaneous application of EEP and vancomycin could enhance their effect against MRSA infection.

The antiviral and immunomodulatory activities of propolis: An update and future perspectives for respiratory diseases

Propolis is a complex natural product that possesses antioxidant, anti‐inflammatory, immunomodulatory, antibacterial, and antiviral properties mainly attributed to the high content in flavonoids, phenolic acids, and their derivatives. The chemical composition of propolis is multifarious, as it depends on the botanical sources from which honeybees collect resins and exudates. Nevertheless, despite this variability propolis may have a general pharmacological value, and this review systematically compiles, for the first time, the existing preclinical and clinical evidence of propolis activities as an antiviral and immunomodulatory agent, focusing on the possible application in respiratory diseases. In vitro and in vivo assays have demonstrated propolis broad‐spectrum effects on viral infectivity and replication, as well as the modulatory actions on cytokine production and immune cell activation as part of both innate and adaptive immune responses. Clinical trials confirmed propolis undeniable potential as an effective therapeutic agent; however, the lack of rigorous randomized clinical trials in the context of respiratory diseases is tangible. Since propolis is available as a dietary supplement, possible use for the prevention of respiratory diseases and their deleterious inflammatory drawbacks on the respiratory tract in humans is considered and discussed. This review opens up new perspectives on the clinical investigation of neglected propolis biological properties which, now more than ever, are particularly relevant with respect to the recent outbreaks of pandemic respiratory infections.

Activity of Ethanolic and Supercritical Propolis Extracts in Corynebacterium pseudotuberculosis and Its Associated Biofilm

Corynebacterium pseudotuberculosis is the etiological agent of caseous lymphadenitis in small ruminants, a chronic disease characterized by the development of granulomas in superficial and visceral lymph nodes as well as in several organs. An important characteristic of the infection with this bacterium is the formation of a biofilm and the absence of effective antibiotic therapy against the disease. From this scenario, the objective of this study was to evaluate the susceptibility of C. pseudotuberculosis to conventional antibiotics and to red, green, and brown propolis extracts obtained by the supercritical and ethanolic extraction methods as well as its activity in the bacterial biofilm. The results of the sensitivity test using antibiotics indicated a sensitivity of C. pseudotuberculosis strains to the antimicrobial agents. The ethanolic extract of green propolis and the supercritical red propolis extract showed the best antibacterial activities against planktonic C. pseudotuberculosis. A lower antimicrobial activity of the brown propolis extract was identified. Propolis extracts were effective in interfering with the formation of the C. pseudotuberculosis biofilm but had little activity on the consolidated biofilm. In conclusion, propolis extracts are more effective against C. pseudotuberculosis in the planktonic stage, being able to interfere with the formation of bacterial biofilm. However, the action of propolis extracts in a sessile and structured microbial biofilm is reduced.

Pharmaceutical Prospects of Bee Products: Special Focus on Anticancer, Antibacterial, Antiviral, and Antiparasitic Properties

Bee products have long been used in traditional healing practices to treat many types of disorders, including cancer and microbial-related diseases. Indeed, several chemical compounds found in bee products have been demonstrated to display anticancer, antibacterial, antiviral, and antiparasitic properties. With the improvement of research tools and in view of recent advances related to bee products, this review aims to provide broad yet detailed insight into the pharmaceutical prospects of bee products such as honey, propolis, bee pollen, royal jelly, bee bread, beeswax, and bee venom, in the domain of cancer and infectious disease management. Available literature confirms the efficacy of these bee products in the alleviation of cancer progression, inhibition of bacterial and viral proliferation, and mitigation of parasitic-related symptoms. With such potentials, bioactive components isolated from the bee products can be used as an alternative approach in the long-run effort to improve humans’ health at a personal and community level.

Extracts of Poplar Buds (Populus balsamifera L., Populus nigra L.) and Lithuanian Propolis: Comparison of Their Composition and Biological Activities

Balsam poplar and black poplar (Populus balsamifera L. and Populus nigra L.) buds that grow in Lithuania are the primary source of propolis, therefore it is proper to evaluate and compare the composition of these raw plant materials and propolis quantitatively and qualitatively. Propolis and balsamic poplar bud extract are dominated by p-coumaric acid and black poplar-caffeic acid. Antioxidant activity was evaluated by DPPH (2,2-diphenyl-1-picrylhydrazyl), ABTS (2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), FRAP (ferric-reducing antioxidant power) and CUPRAC (cupric reducing antioxidant capacity) methods and all extracts showed antioxidant activity, and obtained results correlated with the obtained amounts of phenolic compounds and flavonoids in the extracts. Studies of antimicrobial activity have shown that all extracts have a growth inhibitory effect against Staphylococcus aureus and Candida albicans, but the extract of balsam poplar buds showed the most significant effect of such kind. Considering the results of the research, it can be stated that balsam poplar buds cultured in Lithuania are the primary raw material of propolis, which is rich in phenolic compounds with antioxidant properties and is a promising raw material for pharmaceutical purposes.

Plant Sources Responsible for the Chemical Composition and Main Bioactive Properties of Poplar-Type Propolis

Propolis is a resinous mixture, made by the honeybees from substances collected from tree or other plant buds, plant exudates, or resins found in the stem, branches, or leaves of different plants. The geographical origin of propolis is given by plant sources from respective areas. Different studies have classified this bee product according to the vegetal material from the same areas. Poplar-type propolis has the widest spread in the world, in the temperate zones from Europe, Asia, or North America. The name is given by the main plant source from where the bees are collecting the resins, although other vegetal sources are present in the mentioned areas. Different Pinus spp., Prunus spp., Acacia spp. and also Betula pendula, Aesculus hippocastanum, and Salix alba are important sources of resins for "poplar-type" propolis. The aim of this review is to identify the vegetal material's chemical composition and activities of plant resins and balms used by the bees to produce poplar-type propolis and to compare it with the final product from similar geographical regions. The relevance of this review is to find the similarities between the chemical composition and properties of plant sources and propolis. The latest determination methods of bioactive compounds from plants and propolis are also reviewed.

Recent Advances Regarding the Phytochemical and Therapeutic Uses of Populus nigra L. Buds

Populus nigra L. (Salicaceae family) is one of the most popular trees that can be found in deciduous forests. Some particularities that characterize the Populus genus refer to the fact that it includes more than 40 species, being widespread especially in Europe and Asia. Many residues, parts of this tree can be used as a bioresource for different extracts as active ingredients in pharmaceuticals next to multiple benefits in many areas of medicine. The present review discusses the latest findings regarding the phytochemical composition and the therapeutic properties of Populus nigra L. buds. The vegetal product has been described mainly to contain phenolic compounds (phenols, phenolic acids and phenylpropanoids), terpenoids (mono and sesquiterpenoids), flavones (e.g., apigenol and crysin), flavanones (e.g., pinocembrin and pinostrombin), caffeic/ferulic acids and their derivates, and more than 48 phytocompounds in the essential oils. The resinous exudates present on the buds have been the major plant source used by bees to form propolis. Several studies depicted its antioxidant, anti-inflammatory, antibacterial, antifungal, antidiabetic, antitumor, hepatoprotective, hypouricemic properties and its effects on melanin production. All these lead to the conclusion that black poplar buds are a valuable and important source of bioactive compounds responsible for a wide range of therapeutic uses, being a promising candidate as a complementary and/or alternative source for a large number of health problems. The aim of the review is to gather the existing information and to bring an up to date regarding the phytochemical and therapeutic uses of Populus nigra L. buds.

Proteus mirabilis Biofilm: Development and Therapeutic Strategies

Proteus mirabilis is a Gram negative bacterium that is a frequent cause of catheter-associated urinary tract infections (CAUTIs). Its ability to cause such infections is mostly related to the formation of biofilms on catheter surfaces. In order to form biofilms, P. mirabilis expresses a number of virulence factors. Such factors may include adhesion proteins, quorum sensing molecules, lipopolysaccharides, efflux pumps, and urease enzyme. A unique feature of P. mirabilis biofilms that build up on catheter surfaces is their crystalline nature owing to their ureolytic biomineralization. This leads to catheter encrustation and blockage and, in most cases, is accompanied by urine retention and ascending UTIs. Bacteria embedded in crystalline biofilms become highly resistant to conventional antimicrobials as well as the immune system. Being refractory to antimicrobial treatment, alternative approaches for eradicating P. mirabilis biofilms have been sought by many studies. The current review focuses on the mechanism by which P. mirabilis biofilms are formed, and a state of the art update on preventing biofilm formation and reduction of mature biofilms. These treatment approaches include natural, and synthetic compounds targeting virulence factors and quorum sensing, beside other strategies that include carrier-mediated diffusion of antimicrobials into biofilm matrix. Bacteriophage therapy has also shown successful results in vitro for combating P. mirabilis biofilms either merely through their lytic effect or by acting as facilitators for antimicrobials diffusion.

Effect of Ethanol Extracts of Propolis (EEPs) against Staphylococcal Biofilm-Microscopic Studies

Staphylococci growing in the form of biofilm exhibit high resistance to a plethora of antibiotics. The aim of the study was to assess the influence of ethanolic extract of propolis (EEPs) on S. epidermidis ATCC 35984 biofilm using fluorescent microscopy. Propidium iodide (PI) and SYTO 9 were used for differentiation of live and dead cells, and calcofluor white was used to stain the extracellular matrix, the self-produced extracellular polymeric substances (EPS). The outcomes of the research confirm the promising potential of EEPs for eradication of staphylococcal biofilm. However, its activity cannot be classified as fully satisfactory, either in terms of the effectiveness of elimination of bacterial cells or disturbing the EPS structure. A two or even four times higher concentration of EEPs compared to MIC (Minimum Inhibitory Concentration) against planktonic cells (128 µg/mL) was necessary for effective (estimated for 90%) elimination of living cells from the biofilm structure. Unfortunately, even at that concentration of EEPs, the extracellular matrix was only partially disturbed and effectively protected the residual population of living cells of S. epidermidis ATCC 35984. In our opinion, a combination of EEPs with agents disrupting components of EPS, e.g., proteases, lysines, or enzymes degrading extracellular DNA or PIA (polysaccharide intercellular adhesin).

Antiviral effects of Brazilian green and red propolis extracts on Enterovirus surrogates

Propolis is a natural product of bees with biological activities that are mainly associated with bee type and geographic origin. Propolis extract has been proposed with several applications in environmental health. The ethanol extracts have shown good antimicrobial activity. The association of this technique with ultrasound-assisted extraction has been studied to improve the characteristics of the obtained extracts. Thus, the objective of this work is to verify the antiviral action against two strains of bacteriophages of two extracts of Brazilian propolis (green and red) obtained by conventional extraction and ultrasonic extraction. The activities of the propolis red and green extracts were confirmed by the significant ~3 and ~4.5 Log 10 PFU/mL reduction in the concentrations of the MS2 and Av-08 bacteriophages, respectively. It was found that ultrasound-assisted extraction is comparable to the maceration process and demonstrated the best antiviral activities. Brazilian red propolis was more effective than green propolis in viral reduction in all treatments.

Effects of Brazilian green propolis extract on planktonic cells and biofilms of multidrug-resistant strains of Klebsiella pneumoniae and Pseudomonas aeruginosa

Propolis could represent an alternative therapeutic agent for targeting multidrug-resistant bacteria due to its antimicrobial potential. The effect of Brazilian green propolis (BGP) aqueous extract (AqExt) was evaluated on eight multidrug-resistant clinical strains of Klebsiella pneumoniae and Pseudomonas aeruginosa, as well as on one reference strain for each bacterial species. The minimum bactericidal concentration (MBC) was determined and optimal concentrations were further evaluated in comparison with 0.12% chlorhexidine. The natural extract was chemically characterized by HPLC-DAD analysis. The MBC values ranged between 3.12 and 27.5 mg ml^-1. Analysis of bacterial metabolic activity after treatment for 5 min with BGP-AqExt revealed a strong antimicrobial potential, similar to chlorhexidine. The extract comprised several active compounds including quercetin, gallic acid, caffeic and p-coumaric acid, drupani, galangin, and artepillin C. Altogether, the findings suggest that BGP-AqExt is fast and effective against multidrug-resistant strains of K. pneumoniae and P. aeruginosa in planktonic cultures and biofilms.

Plant Phenolics and Phenolic-Enriched Extracts as Antimicrobial Agents against Food-Contaminating Microorganisms

Phenolic compounds and extracts with bioactive properties can be obtained from many kinds of plant materials. These natural substances have gained attention in the food research as possible growth inhibitors of foodborne pathogenic and spoilage bacteria. Many phenolic-enriched plant extracts and individual phenolics have promising anti-quorum sensing potential as well and can suppress the biofilm formation and toxin production of food-related pathogens. Various studies have shown that plant phenolics can substitute or support the activity of synthetic food preservatives and disinfectants, which, by the way, can provoke serious concerns in consumers. In this review, we will provide a brief insight into the bioactive properties, i.e., the antimicrobial, anti-quorum sensing, anti-biofilm and anti-enterotoxin activities, of plant phenolic extracts and compounds, with special attention to pathogen microorganisms that have food relation. Carbohydrase aided applications to improve the antimicrobial properties of phenolic extracts are also discussed.

Quorum sensing in food spoilage and natural-based strategies for its inhibition

Food can harbor a variety of microorganisms including spoilage and pathogenic bacteria. Many bacterial processes, including production of degrading enzymes, virulence factors, and biofilm formation are known to depend on cell density through a process called quorum sensing (QS), in which cells communicate by synthesizing, detecting and reacting to small diffusible signaling molecules - autoinducers (AI). The disruption of QS could decisively contribute to control the expression of many harmful bacterial phenotypes. Several quorum sensing inhibitors (QSI) have been extensively studied, being many of them of natural origin. This review provides an analysis on the role of QS in food spoilage and biofilm formation within the food industry. QSI from natural sources are also reviewed towards their putative future applications to prolong shelf life of food products and decrease foodborne pathogenicity.

Antibacterial Properties of Propolis

Researchers are continuing to discover all the properties of propolis due to its complex composition and associated broad spectrum of activities. This review aims to characterize the latest scientific reports in the field of antibacterial activity of this substance. The results of studies on the influence of propolis on more than 600 bacterial strains were analyzed. The greater activity of propolis against Gram-positive bacteria than Gram-negative was confirmed. Moreover, the antimicrobial activity of propolis from different regions of the world was compared. As a result, high activity of propolis from the Middle East was found in relation to both, Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) strains. Simultaneously, the lowest activity was demonstrated for propolis samples from Germany, Ireland and Korea.

Analysis of antibacterial and antibiofilm activity of purified recombinant Azurin from Pseudomonas aeruginosa

BACKGROUND AND OBJECTIVES

The aim of this study was to evaluate the antibacterial and antibiofilm activity of recombinant Azurin from Pseudomonas aeruginosa against different bacterial species.

MATERIALS AND METHODS

The azurin gene was cloned in the pET21a vector. The pET21a-azurin construct was transformed into Escherichia coli BL21. The recombinant Azurin was expressed and purified using affinity chromatography and confirmed by Western blotting. The cytotoxicity of rAzurin was assessed on peripheral blood mononuclear cells. Antibacterial and antibiofilm activity of rAzurin with different concentrations were determined by micro-broth dilution and crystal violet methods, respectively. The effect of rAzurin on bacterial species was statistically analyzed by t-test and spearman correlation.

RESULTS

The identity of purified protein was confirmed by blotting and distinguished as a 14 kDa band on 15% SDS-PAGE. The IC50 of rAzurin on Peripheral Blood Mononuclear Cell (PBMC) was determined as 377.91±0.5 μg/mL in 24 h. Vibrio cholerae and Campilobacter jejuni displayed the most sensitivity to rAzurin (27.5 and 55 μg/mL, respectively) and the highest resistance (220 μg/mL) was displayed by P. aeruginosa and E. coli. The MIC for other species was 110 μg/mL. The Minimum Biofilm Inhibition Concentration (MBIC) was determined as 220 μg/mL for Salmonella enterica and V. cholerae, 300 μg/mL for Shigella sonnei, Shigella flexneri and P. aeruginosa and 440 μg/mL for the other species. The antimicrobial effect of rAzurin on bacterial species were significant (p value<0.05) and correlation coefficient was negative.

CONCLUSION

The rAzurin appears to be an appropriate choice and a new strategy for prevention of bacterial infection. It inhibits bacterial growth and biofilm formation and candidates as antimicrobial peptides.

Antilisterial Activity of Polypropylene Film Coated with Chitosan with Propolis and/or Bee Pollen in Food Models

The aim of the study was to evaluate the effect of propylene film coated with solution of chitosan (CH), ethanolic extracts of propolis (EEP), and bee pollen (EEBP) and its combination on L. monocytogenes number in wrapped salmon, salami, and cheese. Sterile fragments of propylene film were coated with solution containing CH, CH+EEP, CH+EEBP, and CH+EEP+EEBP. The coated film was applied directly after preparation (AP) after 10 days of storage from preparation (AS). L. monocytogenes strains isolated from cheese, salmon, and salami were transferred on adequate food type. ATCC 19111 reference strain was placed on all examined slices. Contaminated slices were wrapped in the coated film. The film adhered strictly to the slices surface and was left for 0, 1, 6, 12, and 24 hours. Antilisterial activity of AP film was additionally assessed during 15-day storage of products wrapped in the coated film. In conclusion, the chitosan-coated film exhibited antibacterial activity. Incorporation of EPP and EEBP enhanced this activity. The antilisterial activity depended on the type and concentration of solutions, the types of food, and the origin of strains. This study proved that the time that passed since the use of coated film for packing food was of great importance.

Beneficial Effects of Poplar Buds on Hyperglycemia, Dyslipidemia, Oxidative Stress, and Inflammation in Streptozotocin-Induced Type-2 Diabetes

The effects of propolis on blood glucose regulation and the alleviation of various complications caused by diabetes have been widely studied. The main source of propolis in the northern temperate zone is poplar buds. However, there is limited research on the antidiabetic activity of poplar buds. In order to evaluate the effect of poplar buds on type-2 diabetes, crude extract and 50% fraction of poplar buds were used to feed streptozotocin-induced type-2 diabetic mice. The results showed that 50% fraction could increase insulin sensitivity and reduce insulin resistance, as well as decrease the levels of fasting blood glucose, glycated hemoglobin, and glycosylated serum proteins in diabetic mice. Compared with the model control group, the 50% fraction-treated group showed significant decreases of malondialdehyde (MDA) and increases of superoxide dismutase (SOD) in serum and liver homogenate. Moreover, 50% fraction could significantly decrease total cholesterol (TC), alleviate abnormal lipid metabolism, and enhance antioxidant capacity in the serum. For inflammatory factors, feeding of 50% fraction could also reduce the levels of interleukin 6 (IL-6), tumor necrosis factor α (TNF-α), monocyte chemotactic protein 1 (MCP-1), and cyclooxygenase-2 (COX-2) in liver homogenate. Taken together, our results suggest that crude extract and 50% fraction of poplar buds, particularly the latter, can decrease blood glucose levels and insulin resistance, and 50% fraction can significantly relieve dyslipidemia, oxidative stress, and inflammation caused by type-2 diabetes.

Propolis potentiates the effect of cranberry (Vaccinium macrocarpon) in reducing the motility and the biofilm formation of uropathogenic Escherichia coli

One strategy to prevent urinary tract infections is the use of natural products such as cranberry (Vaccinium macrocarpon) and propolis. The objective of this study was to evaluate the impact of these products alone and combined on the motility and biofilm formation of a collection of representative uropathogenic Escherichia coli (UPEC). Motility was evaluated by the swarming and swimming capacity of the isolates in presence/absence of cranberry ± propolis. Early and late biofilm formation was observed with the Biofilm Ring test (BioFilm Control) and the crystal violet method. Cranberry alone was seen to have a variable effect on motility and biofilm formation unrelated to bacterial characteristics, but a reduced motility and biofilm formation was observed for all the isolates in the presence of cranberry + propolis. These results suggest that cranberry alone doesn’t work on all the E. coli strains and propolis potentiates the effect of cranberry on UPEC, representing a new strategy to prevent recurrent urinary tract infections.

Real-time monitoring of Pseudomonas aeruginosa biofilm formation on endotracheal tubes in vitro

Background

Pseudomonas aeruginosa is an opportunistic bacterial pathogen responsible for both acute and chronic infections in humans. In particular, its ability to form biofilm, on biotic and abiotic surfaces, makes it particularly resistant to host’s immune defenses and current antibiotic therapies as well. Innovative antimicrobial materials, like hydrogel, silver salts or nanoparticles have been used to cover new generation catheters with promising results. Nevertheless, biofilm remains a major health problem. For instance, biofilm produced onto endotracheal tubes (ETT) of ventilated patients plays a relevant role in the onset of ventilation-associated pneumonia. Most of our knowledge on Pseudomonas aeruginosa biofilm derives from in vitro studies carried out on abiotic surfaces, such as polystyrene microplates or plastic materials used for ETT manufacturing. However, these approaches often provide underestimated results since other parameters, in addition to bacterial features (i.e. shape and material composition of ETT) might strongly influence biofilm formation.

Results

We used an already established biofilm development assay on medically-relevant foreign devices (CVC catheters) by a stably transformed bioluminescent (BLI)-Pseudomonas aeruginosa strain, in order to follow up biofilm formation on ETT by bioluminescence detection. Our results demonstrated that it is possible: i) to monitor BLI-Pseudomonas aeruginosa biofilm development on ETT pieces in real-time, ii) to evaluate the three-dimensional structure of biofilm directly on ETT, iii) to assess metabolic behavior and the production of microbial virulence traits of bacteria embedded on ETT-biofilm.

Conclusions

Overall, we were able to standardize a rapid and easy-to-perform in vitro model for real-time monitoring Pseudomonas aeruginosa biofilm formation directly onto ETT pieces, taking into account not only microbial factors, but also ETT shape and material. Our study provides a rapid method for future screening and validation of novel antimicrobial drugs as well as for the evaluation of novel biomaterials employed in the production of new classes of ETT.

Electronic supplementary material

The online version of this article (10.1186/s12866-018-1224-6) contains supplementary material, which is available to authorized users.

Impact of honey on dental erosion and adhesion of early bacterial colonizers

The aim was to investigate if honey causes erosion and if salivary pellicle modified with honey, or its components, or the by-product propolis has a protective effect against dental erosion and adhesion of early bacterial colonizers. The tested substances were: 3 types of honey, methylglyoxal (MGO), hydrogen peroxide, propolis. First in the erosion experiment, 120 human enamel specimens were covered with salivary pellicle and modified with the substances. Then they were eroded with 1% citric acid, pH 3.6 for 2 min, before surface hardness was measured. In the microbiological assay, the enamel specimens (n = 126) covered with modified salivary pellicle were contaminated with bacterial suspensions. The antimicrobial activity of each substance and their effect on early bacterial colonizer adhesion and biofilm formation were determined. Despite a low pH, honey did not cause erosion. On the other hand, pellicle modification with the tested solutions did not protect the enamel from erosion. Microbiologically, the 3 honeys inhibited species-specific growth of oral bacteria. Propolis decreased initial attachment of Streptococcus gordonii, while one honey inhibited demineralization of enamel by biofilm. In conclusion, pellicle modification with honey, or its components, or propolis did neither protect against erosion nor promote it. Propolis presented some bacterial adhesion inhibition.

Probiotic Cell-Free Supernatants Exhibited Anti-Inflammatory and Antioxidant Activity on Human Gut Epithelial Cells and Macrophages Stimulated with LPS

The incidence of inflammatory bowel disease is increasing all over the world, especially in industrialized countries. The aim of the present work was to verify the anti-inflammatory activity of metabolites. In particular, cell-free supernatants of Lactobacillus acidophilus, Lactobacillus casei, Lactococcus lactis, Lactobacillus reuteri, and Saccharomyces boulardii have been investigated. Metabolites produced by these probiotics were able to downregulate the expression of PGE-2 and IL-8 in human colon epithelial HT-29 cells. Moreover, probiotic supernatants can differently modulate IL-1β, IL-6, TNF-α, and IL-10 production by human macrophages, suggesting a peculiar anti-inflammatory activity. Furthermore, supernatants showed a significant dose-dependent radical scavenging activity. This study suggests one of the mechanisms by which probiotics exert their anti-inflammatory activity affecting directly the intestinal epithelial cells and the underlying macrophages. This study provides a further evidence to support the possible use of probiotic metabolites in preventing and downregulating intestinal inflammation as adjuvant in anti-inflammatory therapy.

Inhibitory Effect of Propolis on Platelet Aggregation In Vitro

Platelet hyperactivity plays an important role in arterial thrombosis and atherosclerosis. The present study was aimed to investigate the effects of different extracts of propolis and components of flavonoids on platelet aggregation. Platelet-rich plasma was prepared and incubated in vitro with different concentrations of the tested extracts and components of flavonoids. Platelets aggregation was induced by different agonists including adenosine diphosphate (ADP, 10 μM), thrombin receptor activator peptide (TRAP, 50 μM), and collagen (5 μg/mL). At 25 mg/L to 300 mg/mL, the water extract propolis (WEP) inhibited three agonists-induced platelet aggregations in a dose-dependent manner. The flavonoids isolated from the propolis also showed markedly inhibited platelet aggregation induced by collagen, ADP, and TRAP, respectively. The components including caffeic acid phenethyl ester (CAPE), galangin, apigenin, quercetin, kaempferol, ferulic acid, rutin, chrysin, pinostrobin, and pinocembrin and their abilities of inhibiting platelet aggregation were studied. It was concluded that propolis had an antiplatelet action in which flavonoids were mainly implicated.

Antioxidant and cytotoxic activity of propolis of Plebeia droryana and Apis mellifera (Hymenoptera, Apidae) from the Brazilian Cerrado biome

Propolis is a complex bioactive mixture produced by bees, known to have different biological activities, especially in countries where there is a rich biodiversity of plant species. The objective of this study was to determine the chemical composition and evaluate the antioxidant and cytotoxic properties of Brazilian propolis from the species Plebeia droryana and Apis mellifera found in Mato Grosso do Sul, Brazil. In the ethanolic extracts of P. droryana propolis (ExEP-P) and A. mellifera (ExEP-A) acids, phenolic compounds, terpenes and tocopherol were identified as major compounds. Both extracts presented antioxidant activity against the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical, the maximum activities being 500 μg/mL (ExEP-P) and 300 μg/mL (ExEP-A). However, only ExEP-A was able to inhibit lipid peroxidation induced by the oxidizing agent 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH), which inhibited oxidative hemolysis and reduced the levels of malondialdehyde (MDA) in human erythrocytes for 4 h of incubation. The extracts also reduced the cell viability of the K562 erythroleukemia tumour line, with a predominance of necrotic death. Thus, it is concluded that the propolis produced by P. droryana and A. mellifera contain important compounds capable of minimizing the action of oxidizing substances in the organism and reducing the viability of erythroleukemia cells.