Activity and synergistic interactions of stilbenes and antibiotic combinations against bacteria in vitro

Toxicological assessment of citral and geraniol: Efflux pump inhibition in Staphylococcus aureus and invertebrate toxicity

This study aimed to evaluate the antibacterial activity against multi-drug-resistant strains carrying efflux pumps and assess their toxicity on Drosophila melanogaster and Aedes aegypti models. Microdilution tests in broth were performed to determine the Minimum Inhibitory Concentration (MIC). The efflux pump inhibition was evaluated by analyzing the reduction in antibiotic MIC and Ethidium Bromide (EtBr) MIC when combined with the products. Mortality assay and negative geotaxis were conducted on D. melanogaster specimens, and insecticidal activity assays were performed on A. aegypti larvae. Only geraniol reduced the antibiotic MIC when combined, reducing from 64 µg/mL to 16 µg/mL in the 1199B strain of S. aureus. When combined with EtBr, both geraniol and citral reduced EtBr MIC, with geraniol decreasing from 64 µg/mL to 16 µg/mL and citral decreasing from 64 µg/mL to 32 µg/mL. Regarding the S. aureus K2068 strain, geraniol reduced the antibiotic MIC from 16 µg/mL to 8 µg/mL, and citral reduced it from 16 µg/mL to 4 µg/mL. In combination with EtBr, all monoterpenes reduced MIC from 64 µg/mL to 32 µg/mL. Both products exhibited toxicity in D. melanogaster; however, citral showed higher toxicity with a precisely determined LC50 of 2.478 μL. As for the insecticidal action on A. aegypti, both products demonstrated toxicity with cumulative effects and dose-dependent mortality.

Designing of new trans-stilbene derivative: An entry barrier of Zika virus in host cell

A large population in the world lives in tropical and subtropical regions, showing a high risk of Zika viral infection which leads to a situation of global health emergency and demands extensive research to create effective antiviral medicines. Herein, we introduce the design of a new derivatized trans-stilbene molecule to investigate the inhibition of Zika virus entry into the host cell by molecular docking approach. The synthesized compound has been characterized by different analytical techniques such as FTIR, 1H NMR,13C NMR and UV-visible spectroscopy as well as Mass spectrometry (MS). Moreover, the complete structure elucidation was achieved via X-ray crystallography and DFT analysis. The article describes the life cycle and genome of the Zika virus along with its mechanism of entry inhibition by illustrating the structure and function of the ZIKV envelop (E) protein. The docking studies disclosed that the newly synthesized stilbene compound confers an excellent inhibitory response towards the entry of Zika virus in host cells as supported by calculated docking score and its binding conformation with Zika virus E-protein. Further, the normal mode analysis (NMA) simulation technique is used to predict the conformational states of the target E-protein, which explains the potency of the compound to bind with the Zika virus E-protein. We hope that the present study will help and encourage researchers in the field of medicinal chemistry to develop potential drugs against the Zika virus.

Synergistic activity between conventional antifungals and chalcone-derived compound against dermatophyte fungi and Candida spp

The scarce antifungal arsenal, changes in the susceptibility profile of fungal agents, and lack of adherence to treatment have contributed to the increase of cases of dermatomycoses. In this context, new antimicrobial substances have gained importance. Chalcones are precursors of the flavonoid family that have multiple biological activities, have high tolerability by humans, and easy synthesis. In this study, we evaluated the in vitro antifungal activity, alone and in combination with conventional antifungal drugs, of the VS02-4'ethyl chalcone-derived compound against dermatophytes and Candida spp. Susceptibility testing was carried out by broth microdilution. Experiments for determination of the target of the compound on the fungal cell, time-kill kinetics, and toxicity tests in Galleria mellonella model were also performed. Combinatory effects were evaluated by the checkerboard method. Results showed high activity of the compound VS02-4'ethyl against dermatophytes (MIC of 7.81-31.25 μg/ml). The compound targeted the cell membrane, and the time-kill test showed the compound continues to exert gradual activity after 5 days on dermatophytes, but no significant activity on Candida. Low toxicity was observed at 250 mg/kg. Excellent results were observed in the combinatory test, where VS02-4'ethyl showed synergistic interactions with itraconazole, fluconazole, terbinafine, and griseofulvin, against all isolates tested. Although further investigation is needed, these results revealed the great potential of chalcone-derived compounds against fungal infections for which treatments are long and laborious.

In vitro and in silico effect of meldrum's acid-derived compounds on Staphylococcus aureus strains as NorA efflux pump inhibitors

The misuse of antibiotics has led to an alarming increase in bacterial strains resistant to these drugs. Efflux pumps, which expel antibiotics from bacterial cells, have emerged as one of the key mechanisms of bacterial resistance. In the quest to combat and mitigate bacterial resistance, researchers have turned their attention to efflux pump inhibitors as a potential solution. Meldrum's acid, a synthetic molecule widely utilized in the synthesis of bioactive compounds, has garnered significant interest in this regard. Hence, this study aims to investigate the antibacterial activity and evaluate the efficacy of three derivatives of meldrum's acid in inhibiting efflux mechanisms, employing both in silico and in vitro approaches. The antibacterial activity of the derivatives was assessed through rigorous broth microdilution testing. While the derivatives themselves did not exhibit direct antibacterial activity, they demonstrated remarkable potential in potentiating the effects of antibiotics. Additionally, fluorescence emission assays using ethidium bromide (EtBr) revealed fluorescence levels comparable to the positive control, indicating a possible blockade of efflux pumps. Molecular docking studies conducted in silico further supported these findings by revealing binding interactions similar to norfloxacin and CCCP, known efflux pump inhibitors. These results underscore the potential of meldrum's acid derivatives as effective inhibitors of efflux pumps. By inhibiting these mechanisms, the derivatives hold promise in enhancing the effectiveness of antibiotics and combatting bacterial resistance. This study contributes valuable insights into the development of novel strategies to address the pressing issue of bacterial resistance and paves the way for further research and exploration in this field.

Cuminaldehyde and Tobramycin Forestall the Biofilm Threats of Staphylococcus aureus: A Combinatorial Strategy to Evade the Biofilm Challenges

Staphylococcus aureus, an opportunistic Gram-positive pathogen, is known for causing various infections in humans, primarily by forming biofilms. The biofilm-induced antibiotic resistance has been considered a significant medical threat. Combinatorial therapy has been considered a reliable approach to combat antibiotic resistance by using multiple antimicrobial agents simultaneously, targeting bacteria through different mechanisms of action. To this end, we examined the effects of two molecules, cuminaldehyde (a natural compound) and tobramycin (an antibiotic), individually and in combination, against staphylococcal biofilm. Our experimental observations demonstrated that cuminaldehyde (20 μg/mL) in combination with tobramycin (0.05 μg/mL) exhibited efficient reduction in biofilm formation compared to their individual treatments (p < 0.01). Additionally, the combination showed an additive interaction (fractional inhibitory concentration value 0.66) against S. aureus. Further analysis revealed that the effective combination accelerated the buildup of reactive oxygen species (ROS) and increased the membrane permeability of the bacteria. Our findings also specified that the cuminaldehyde in combination with tobramycin efficiently reduced biofilm-associated pathogenicity factors of S. aureus, including fibrinogen clumping ability, hemolysis property, and staphyloxanthin production. The selected concentrations of tobramycin and cuminaldehyde demonstrated promising activity against the biofilm development of S. aureus on catheter models without exerting antimicrobial effects. In conclusion, the combination of tobramycin and cuminaldehyde presented a successful strategy for combating staphylococcal biofilm-related healthcare threats. This combinatorial approach holds the potential for controlling biofilm-associated infections caused by S. aureus.

Combinatorial effect of fluconazole, itraconazole, and terbinafine with different culture extracts of Candida parapsilosis and Trichophyton spp. against Trichophyton rubrum

Onychomycosis is a nail infection caused by dermatophytes, non-dermatophyte fungi, and yeasts, especially Candida species. The present study evaluated the combinatorial effect of different cultured extracts of Candida parapsilosis and Trichophyton mentagrophytes and Trichophyton rubrum with fluconazole, itraconazole, and terbinafine against clinical isolates of Trichophyton rubrum. In addition, investigation of the action of the extracts on the wall or membrane was performed. Pure and mixed cultures of Candida parapsilosis and dermatophytes were filtered through a 0.2-μm membrane and submitted to liquid-liquid extraction using ethyl acetate. After a checkerboard, trial with drugs was performed to evaluate the synergistic interaction with the extract. The results obtained for the minimum inhibitory concentration (MIC) of extracts against the T. rubrum strain in isolation were 500-8000 μg/mL. The MIC range for fluconazole, itraconazole, and terbinafine were 2-32 μg/mL, 0.25-0.5 μg/mL, 0.03-64 μg/mL, respectively. However, when the extract was combined with drugs, the MIC values decreased: extracts 1.9-1000 μg/mL, fluconazole 0.25-4, itraconazole 0.03-0.06 μg/mL, and terbinafine 0.001-0.02 μg/mL. The MIC values of the extracts in the Roswell Park Memorial Institute 1640 medium (RPMI) supplemented with sorbitol did not change, suggesting any action on the cell wall. However, in the presence of RPMI supplemented with ergosterol, MIC values of the extracts increased by up to 2×, indicating action on the fungal cell membrane. A synergistic action was observed between products and drugs, detecting a decrease in MIC values. There is potential and a new therapeutic perspective for fungal control.

Antimicrobial efficiency of bromhexine hydrochloride against endometritis-causing Escherichia coli and Trueperella pyogenes in bovines

In this study, the main agents associated with endometritis in cows in the state of Santa Catarina, Brazil, were identified and the resistance profile and virulence mechanisms of the bacterial isolates were evaluated. Isolates of Escherichia coli and Trueperella pyogenes were tested for their biofilm forming ability and the antimicrobial action of bromhexine hydrochloride in combination with other antimicrobials. A total of 37 uterine lavage samples were collected from cows with endometritis. Of the 55 bacteria isolated, 25.4% were identified as T. pyogenes and 16.3% as E. coli. The bacterial isolates showed greater resistance to sulfamethoxazole + trimethoprim (58.2%) and tetracycline (56.3%). Among the species, E. coli showed the highest resistance rates, with 100% of isolates showing resistance to amoxicillin, streptomycin, and gentamicin. The results of the minimum inhibitory concentration for the T. pyogenes isolates showed that 91.6% of the isolates were resistant to enrofloxacin and tetracycline, and 75% were resistant to ceftiofur and sulfamethoxazole + trimethoprim. All E. coli and T. pyogenes isolates showed biofilm forming ability. The plo, fimA, and nanH genes were identified in 100% of T. pyogenes isolates. In parallel, 100% of E. coli isolates had the fimH gene, and 11.1% had the csgD gene. Bromhexine hydrochloride showed antimicrobial activity against 100% of E. coli isolates and 66.6% of T. pyogenes isolates. Furthermore, when associated with antimicrobials, bromhexine hydrochloride has a synergistic and additive effect, proving to be an option in the treatment of endometritis in cows and an alternative for reducing the use of antimicrobials.

Meldrum's acid derivates are MepA efflux pump inhibitors: In vitro and in silico essays

Efflux pumps are proteins capable of expelling antibiotics from bacterial cells, have emerged as a major mechanism of bacterial resistance. In the ongoing pursuit to overcome and reduce bacterial resistance, novel substances are being explored as potential efflux pump inhibitors. Meldrum's acid, a synthetic molecule widely studied for its role in synthesizing bioactive compounds, holds promise in this regard. Therefore, the objective of this study is to evaluate the antibacterial activity of three derivatives of Meldrum's acid and assess their ability to inhibit efflux mechanisms, employing both in silico and in vitro approaches. The antibacterial activity of the derivatives was assessed using a broth microdilution testing method. Surprisingly, the derivatives did not exhibit direct antibacterial activity on their own. However, they displayed a significant effect in enhancing the efficacy of antibiotics, suggesting a potential role in potentiating their effects. Furthermore, fluorescence emission assays using ethidium bromide indicated that the derivatives could potentially block efflux pumps, as they exhibited fluorescence levels comparable to the positive control. To further investigate their inhibitory capacity, molecular docking studies were conducted in silico, revealing binding interactions similar to ciprofloxacin and carbonyl cyanide 3-chlorophenylhydrazone, known efflux pump inhibitors. These findings highlight the potential of Meldrum's acid derivatives as effective inhibitors of efflux pumps. By targeting these mechanisms, the derivatives offer a promising avenue to enhance the effectiveness of antibiotics and combat bacterial resistance. This study underscores the importance of exploring novel strategies in the fight against bacterial resistance and provides valuable insights into the potential of Meldrum's acid derivatives as efflux pump inhibitors. Further research and exploration in this field are warranted to fully exploit their therapeutic potential.

Evaluation of the antibacterial and inhibitory activity of the MepA efflux pump of Staphylococcus aureus by riparins I, II, III, and IV

The efflux pump mechanism contributes to the antibiotic resistance of widely distributed strains of Staphylococcus aureus. Therefore, in the present work, the ability of the riparins N-(4-methoxyphenethyl)benzamide (I), 2-hydroxy-N-[2-(4-methoxyphenyl)ethyl]benzamide (II), 2, 6-dihydroxy-N-[ 2-(4-methoxyphenyl)ethyl]benzamide (III), and 3,4,5-trimethoxy-N-[2-(4-methoxyphenethyl)benzamide (IV) as potential inhibitors of the MepA efflux pump in S. aureus K2068 (fluoroquinolone-resistant). In addition, we performed checkerboard assays to obtain more information about the activity of riparins as potential inhibitors of MepA efflux and also analyzed the ability of riparins to act on the permeability of the bacterial membrane of S. aureus by the fluorescence method with SYTOX Green. A molecular coupling assay was performed to characterize the interaction between riparins and MepA, and ADMET (absorption, distribution, metabolism, and excretion) properties were analyzed. We observed that I-IV riparins did not show direct antibacterial activity against S. aureus. However, combination assays with substrates of MepA, ciprofloxacin, and ethidium bromide (EtBr) revealed a potentiation of the efficacy of these substrates by reducing the minimum inhibitory concentration (MIC). Furthermore, increased EtBr fluorescence emission was observed for all riparins. The checkerboard assay showed synergism between riparins I, II, and III, ciprofloxacin, and EtBr. Furthermore, riparins III and IV exhibited permeability in the S. aureus membrane at a concentration of 200 μg/mL. Molecular docking showed that riparins I, II, and III bound in a different region from the binding site of chlorpromazine (standard pump inhibitor), indicating a possible synergistic effect with the reference inhibitor. In contrast, riparin IV binds in the same region as the chlorpromazine binding site. From the in silico ADMET prediction based on MPO, it could be concluded that the molecules of riparin I-IV present their physicochemical properties within the ideal pharmacological spectrum allowing their preparation as an oral drug. Furthermore, the prediction of cytotoxicity in liver cell lines showed a low cytotoxic effect for riparins I-IV.

Insight into the Antibacterial Action of Iodinated Imine, an Analogue of Rafoxanide: a Comprehensive Study of Its Antistaphylococcal Activity

In this study, we have focused on a multiparametric microbiological analysis of the antistaphylococcal action of the iodinated imine BH77, designed as an analogue of rafoxanide. Its antibacterial activity against five reference strains and eight clinical isolates of Gram-positive cocci of the genera Staphylococcus and Enterococcus was evaluated. The most clinically significant multidrug-resistant strains, such as methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant S. aureus (VRSA), and vancomycin-resistant Enterococcus faecium, were also included. The bactericidal and bacteriostatic actions, the dynamics leading to a loss of bacterial viability, antibiofilm activity, BH77 activity in combination with selected conventional antibiotics, the mechanism of action, in vitro cytotoxicity, and in vivo toxicity in an alternative animal model, Galleria mellonella, were analyzed. The antistaphylococcal activity (MIC) ranged from 15.625 to 62.5 μM, and the antienterococcal activity ranged from 62.5 to 125 μM. Its bactericidal action; promising antibiofilm activity; interference with nucleic acid, protein, and peptidoglycan synthesis pathways; and nontoxicity/low toxicity in vitro and in vivo in the Galleria mellonella model were found to be activity attributes of this newly synthesized compound. In conclusion, BH77 could be rightfully minimally considered at least as the structural pattern for future adjuvants for selected antibiotic drugs. IMPORTANCE Antibiotic resistance is among the largest threats to global health, with a potentially serious socioeconomic impact. One of the strategies to deal with the predicted catastrophic future scenarios associated with the rapid emergence of resistant infectious agents lies in the discovery and research of new anti-infectives. In our study, we have introduced a rafoxanide analogue, a newly synthesized and described polyhalogenated 3,5-diiodosalicylaldehyde-based imine, that effectively acts against Gram-positive cocci of the genera Staphylococcus and Enterococcus. The inclusion of an extensive and comprehensive analysis for providing a detailed description of candidate compound-microbe interactions allows the valorization of the beneficial attributes linked to anti-infective action conclusively. In addition, this study can help with making rational decisions about the possible involvement of this molecule in advanced studies or may merit the support of studies focused on related or derived chemical structures to discover more effective new anti-infective drug candidates.

Analytics, Properties and Applications of Biologically Active Stilbene Derivatives

Stilbene and its derivatives belong to the group of biologically active compounds. Some derivatives occur naturally in various plant species, while others are obtained by synthesis. Resveratrol is one of the best-known stilbene derivatives. Many stilbene derivatives exhibit antimicrobial, antifungal or anticancer properties. A thorough understanding of the properties of this group of biologically active compounds, and the development of their analytics from various matrices, will allow for a wider range of applications. This information is particularly important in the era of increasing incidence of various diseases hitherto unknown, including COVID-19, which is still present in our population. The purpose of this study was to summarize information on the qualitative and quantitative analysis of stilbene derivatives, their biological activity, potential applications as preservatives, antiseptics and disinfectants, and stability analysis in various matrices. Optimal conditions for the analysis of the stilbene derivatives in question were developed using the isotachophoresis technique.

Future Antimicrobials: Natural and Functionalized Phenolics

With incidence of antimicrobial resistance rising globally, there is a continuous need for development of new antimicrobial molecules. Phenolic compounds having a versatile scaffold that allows for a broad range of chemical additions; they also exhibit potent antimicrobial activities which can be enhanced significantly through functionalization. Synthetic routes such as esterification, phosphorylation, hydroxylation or enzymatic conjugation may increase the antimicrobial activity of compounds and reduce minimal concentrations needed. With potent action mechanisms interfering with bacterial cell wall synthesis, DNA replication or enzyme production, phenolics can target multiple sites in bacteria, leading to a much higher sensitivity of cells towards these natural compounds. The current review summarizes some of the most important knowledge on functionalization of natural phenolic compounds and the effects on their antimicrobial activity.

Phenotypic and in silico studies for a series of synthetic thiosemicarbazones as New Delhi metallo-beta-lactamase carbapenemase inhibitors

The past two decades have been marked by a global spread of bacterial resistance to β-lactam drugs and carbapenems derivatives are the ultimate treatment against multidrug-resistant bacteria. β-lactamase expression is related to resistance which demands the development of bacterial resistance blockers. Drug inhibitor combinations of serine-β-lactamase and β-lactam were successful employed in therapy despite their inactivity against New Delhi metallo-beta-lactamase (NDM). Until now, few compounds are active against NDM-producing bacteria and no specific inhibitors are available yet. The rational strategy for NDM inhibitors development starts with in vitro assays aiming to seek compounds that could act synergistically with β-lactam antibiotics. Thus, eight thiosemicarbazone derivatives were synthesized and investigated for their ability to reverse the resistant phenotype in NDM in Enterobacter cloacae. Phenotypic screening indicated that four isatin-beta-thiosemicarbazones showed Fractional Inhibitory Concentration (FIC) ≤ 250 µM in the presence of meropenem (4 µg/mL). The most promising compound (FIC= 31.25 µM) also presented synergistic effect (FICI = 0.34). Docking and molecular dynamics studies on NDM-thiosemicarbazone complex suggested that 2,3-dihydro-1H-indol-2-one subunit interacts with catalytic zinc and interacted through hydrogen bonds with Asp124 acting like a carboxylic acid bioisostere. Additionally, thiosemicarbazone tautomer with oxidized sulfur (thione) seems to act as a spacer rather than zinc chelator, and the aromatic moieties are stabilized by pi-pi and cation-pi interactions with His189 and Lys221 residues. Our results addressed some thiosemicarbazone structural changes to increase its biological activity against NDM and highlight its scaffold as promising alternatives to treat bacterial resistance.Communicated by Ramaswamy H. Sarma.

Comprehensive insight into anti-staphylococcal and anti-enterococcal action of brominated and chlorinated pyrazine-based chalcones

The greatest threat and medicinal impact within gram-positive pathogens are posed by two bacterial genera, Staphylococcus and Enterococcus. Chalcones have a wide range of biological activities and are recognized as effective templates in medicinal chemistry. This study provides comprehensive insight into the anti-staphylococcal and anti-enterococcal activities of two recently published brominated and chlorinated pyrazine-based chalcones, CH-0y and CH-0w. Their effects against 4 reference and 12 staphylococcal and enterococcal clinical isolates were evaluated. Bactericidal action, the activity in combination with selected conventional antibiotics, the study of post-antimicrobial effect (PAE, PAE/SME), and in vitro and in vivo toxicity, were included. In CH-0y, anti-staphylococcal activity ranging from MIC = 15.625 to 62.5 μM, and activity against E. faecium from 31.25 to 62.5 μM was determined. In CH-0w, anti-staphylococcal activity ranging from 31.25 to 125 μM, and activity against E. faecium and E. faecalis (62.5 μM) was revealed. Both CH-0y and CH-0w showed bactericidal action, beneficial impact on bacterial growth delay within PAE and PAE/SME studies, and non/low toxicity in vivo. Compared to CH-0w, CH-0y seems to have higher anti-staphylococcal and less toxic potential. In conclusion, chalcones CH-0y and CH-0w could be considered as structural pattern for future adjuvants to selected antibiotic drugs.

The antifungal and antibiofilm activity of Cymbopogon nardus essential oil and citronellal on clinical strains of Candida albicans

OBJECTIVE

This study investigated the antifungal and antibiofilm activity of Cymbopogon nardus essential oil (EO) and its major compound, citronellal, in association with miconazole and chlorhexidine on clinical strains of Candida albicans. The likely mechanism(s) of action of C. nardus EO and citronellal was further determined.

MATERIALS AND METHODS

The EO was chemically characterized by gas chromatography coupled with mass spectrometry (GC-MS). The antifungal activity (MIC/MFC) and antibiofilm effects of C. nardus EO and citronellal were determined by the microdilution method, and their likely mechanism(s) of action was determined by the sorbitol and ergosterol assays. Then, the samples were tested for a potential association with standard drugs through the checkerboard technique. Miconazole and chlorhexidine were used as positive controls and the assays were performed in triplicate.

RESULTS

The GC-MS analysis tentatively identified citronellal as the major compound in C. nardus EO. Both samples showed antifungal activity, with MIC of 256 µg/mL, as compared to 128 µg/mL and 8 µg/mL of miconazole and chlorhexidine, respectively. C. nardus EO and citronellal effectively inhibited biofilm formation (p < 0.05) and disrupted preformed biofilms (p < 0.0001). They most likely interact with the cell membrane, but not the cell wall, and did not present any synergistic activity when associated with standard drugs.

CONCLUSION

C. nardus EO and citronellal showed strong in vitro antifungal and antibiofilm activity on C. albicans.

CLINICAL RELEVANCE

Natural products have been historically bioprospected for novel solutions to control fungal biofilms. Our data provide relevant insights into the potential of C. nardus EO and citronellal for further clinical testing. However, additional bioavailability and toxicity studies must be carried out before these products can be used for the chemical control of oral biofilms.

pH-responsive Ag-Phy@ZIF-8 nanoparticles modified by hyaluronate for efficient synergistic bacteria disinfection

Zeolitic imidazolate framework-8 (ZIF-8) is a type of Metal-organic frameworks (MOFs), which shows promising application in the field of bacterial infection, owing to its excellent biocompatibility. Here, we report the encapsulation of silver nanoparticles (Ag NPs) in ZIF-8, accompanied with embedding of physcion (Phy) to obtain Ag-Phy@ZIF-8 with efficient and intelligent synergistic antimicrobial capabilities. Due to the micro-acidic environment around the bacteria, the release of silver and Phy shows a controlled released. Further, the Ag-Phy@ZIF-8 is modified by hyaluronate (HA), denoted as Ag-Phy@ZIF-8@HA, which has a strong inhibitory effect on the growth of both E. coli (99.1%) and S. aureus (99.5%), with no impacting on cell growth, showing good biocompatibility. Thus, these pH-responsive biocomposites have the potential application on smart wound excipients for bacterial infections.

Evaluation of antioxidant and antibacterial interactions between resveratrol and eugenol in carboxymethyl cellulose biodegradable film

The aim of present study was to compare the in vitro antioxidant and antibacterial properties of carboxymethyl cellulose (CMC) films containing resveratrol (RES) and eugenol (EUG), alone and in combination, and to calculate the dose interactions between them. At first, the total phenolic content of CMC films was evaluated. Then, their antioxidant and antibacterial effects of films were determined using DPPH, reducing power, disk diffusion, and broth dilution methods. Finally, concentrations of RES and EUG which showed better results in the CMC films were added in combination forms to calculate their antioxidant and antibacterial interactions. The results showed that addition of RES and/or EUG to CMC films increased the total phenolic content, free radicals scavenging activity, reducing power, and antibacterial activities of the films (p ≤ .05). Gram-positive bacteria were more susceptible than Gram-negatives. In addition, the combined use of RES and EUG in CMC films had synergistic antioxidant and antagonistic antibacterial effects. The best results belonged to the film containing RES (8 µg/ml) + EUG (8 mg/ml) (p ≤ .05). Considering the results of the present research, we can utilize CMC biodegradable film containing RES and EUG as a natural active packaging in food industry.

In vitroassessment of green polyhydroxybutyrate/chitosan blend loaded with kaempferol nanocrystals as a potential dressing for infected wounds

Despite the major medical advancements in recent decades, treating infected wounds successfully remains a challenge. In this research, a functional blend of Polyhydroxybutyrate (PHB) and Chitosan (Cs) was developed for wound infection mitigation with tailored biological and physicochemical properties. Water insoluble kaempferol (KPF) was pre-formulated to water soluble KPF nanocrystals (KPF-NCs) with fine particle size of 145 ± 11 nm, and high colloidal stability (-31 ± 0.4 mV) to improve its drug transdermal delivery. PHB-Cs-KPF-NCs (1:2 ratio) film owned the best physical properties in terms of high breathability, thermal stability and mechanical strength (33 ± 1 MPa). Besides, XRD and FTIR findings indicated the interaction between Cs, PHB and KPF, reducing the film crystallinity. The scanning electron microscopy of the film displayed a highly interconnected porous morphology. KPF-NCs were integrated in PHB-Cs matrix with a marked encapsulation efficiency of 96.6%. The enhanced drug-loading film showed a sustain release pattern of KPF-NCs over 48 h. Interestingly, the developed blend possessed an impressive blood clotting capacity within 20 min. Furthermore, we presented a new naturally-sourced mixture of Cs+KPF-NCs with powerful antibacterial effects against MDRStaphylococcus aureusandAcentibacter baumanniiat very low concentrations. The membrane evidenced a remarkable antibacterial naturein vitrowith almost 100% cell viability reduction against the study strains after 48 h. By virtue of these advantages, this green blend is highly proposed for optimal wound care.

Co-delivery of antibiotic and baicalein by using different polymeric nanoparticle cargos with enhanced synergistic antibacterial activity

To evaluate the effect of polymer structures on their unique characteristics and antibacterial activity, this study focused on developing amphiphilic copolymers by using three different molecules through RAFT polymerization. Three amphiphilic copolymers, namely, PBMA-b-(PDMAEMA-r-PPEGMA) (BbDrE), (PBMA-r-PDMAEMA)-b-PPEGMA (BrDbE), and PBMA-r-PDMAEMA-r-PPEGMA (BrDrE), are successfully self-assembled into spherical or oval shaped nanoparticles in aqueous solution and remain stable in PBS, LB, and 10% FBS solutions for at least 3 days. The critical micelle concentrations are 0.012, 0.025, and 0.041 mg/mL for BbDrE, BrDbE, and BrDrE, respectively. The zeta potential values under pH 5.5 and pH 7.4 conditions are 3.18/0.19, 8.57/0.046, and 2.54/-0.69 mV for BbDrE, BrDbE, and BrDrE nanoparticles, respectively. The three copolymers with similar monomer compositions show similar molecular weight and thermostability. Baicalein (BA) and ciprofloxacin (CPX) are encapsulated into the three nanoparticles to obtain BbDrE@BA/CPX, BrDbE@BA/CPX, and BrDrE@BA/CPX nanocomposites, with LC values of 63.9/78.3, 63.9/74.7, and 55.3/64.8, respectively. The two drugs are released from the three drug-loaded nanocomposites with 60%-95% release in pH 5.5 over 24 h and 15%-30% release in pH 7.4. The drug-loaded nanocomposites show synergistic antibacterial activity than the naked drug (2-8 fold reduction for CPX) or single drug-loaded nanocomposites (4-8 fold reduction for CPX) against Pseudomonas aeruginosa and Staphylococcus aureus. The drug-loaded nanocomposites inhibit the formation of bacterial biofilms above their MIC values and eliminate bacterial biofilms observed by fluorescent microscope. Finally, the nanocomposites improve the healing of infection induced by P. aeruginosa and S. aureus on rat dermal wounds. These results indicate that antimicrobial agents with different structures could be an alternative treatment strategy for bacteria-induced infection.

Resveratrol and Its Analogs as Functional Foods in Periodontal Disease Management

Periodontitis is a common chronic inflammatory disease driven by the interaction between a dysbiotic oral microbiome and the dysregulated host immune-inflammatory response. Naturally derived nutraceuticals, such as resveratrol and its analogs, are potential adjunctive therapies in periodontal treatment due to their antimicrobial and anti-inflammatory properties. Furthermore, different analogs of resveratrol and the choice of solvents used may lead to varying effects on therapeutic properties. This review presents the current findings and gaps in our understanding on the potential utility of resveratrol and its analogs in periodontal treatment.

Multivalent and synergistic chitosan oligosaccharide-Ag nanocomposites for therapy of bacterial infection

Chitosan oligosaccharide functionalized silver nanoparticles with synergistic bacterial activity were constructed as a multivalent inhibitor of bacteria. Placing the chitosan oligosaccharide on silver nanoparticles can dramatically enhance the adsorption to the bacterial membrane via multivalent binding. The multicomponent nanostructures can cooperate synergistically against gram-positive and gram-negative bacteria. The antibacterial activity was increased via orthogonal array design to optimize the synthesis condition. The synergistic bacterial activity was confirmed by fractional inhibitory concentration and zone of inhibition test. Through studies of antimicrobial action mechanism, it was found that the nanocomposites interacted with the bacteria by binding to Mg²⁺ ions of the bacterial surface. Then, the nanocomposites disrupted bacterial membrane by increasing the permeability of the outer membrane, resulting in leakage of cytoplasm. This strategy of chitosan oligosaccharide modification can increase the antibacterial activity of silver nanoparticles and accelerate wound healing at the same time. The nanomaterial without cytotoxicity has promising applications in bacteria-infected wound healing therapy.

Stilbenoids: A Natural Arsenal against Bacterial Pathogens

The escalating emergence of resistant bacterial strains is one of the most important threats to human health. With the increasing incidence of multi-drugs infections, there is an urgent need to restock our antibiotic arsenal. Natural products are an invaluable source of inspiration in drug design and development. One of the most widely distributed groups of natural products in the plant kingdom is represented by stilbenoids. Stilbenoids are synthesised by plants as means of protection against pathogens, whereby the potential antimicrobial activity of this class of natural compounds has attracted great interest in the last years. The purpose of this review is to provide an overview of recent achievements in the study of stilbenoids as antimicrobial agents, with particular emphasis on the sources, chemical structures, and the mechanism of action of the most promising natural compounds. Attention has been paid to the main structure modifications on the stilbenoid core that have expanded the antimicrobial activity with respect to the parent natural compounds, opening the possibility of their further development. The collected results highlight the therapeutic versatility of natural and synthetic resveratrol derivatives and provide a prospective insight into their potential development as antimicrobial agents.

The Implication of Oxidative Stress and AMPK-Nrf2 Antioxidative Signaling in Pneumonia Pathogenesis

It is widely recognized that chemical, physical, and biological factors can singly or synergistically evoke the excessive production of oxidative stress in pulmonary tissue that followed by pulmonary lesions and pneumonia. In addition, metabolic and endocrine disorder-induced diseases such as diabetes and obesity often expressed higher susceptibility to pulmonary infections, and presented severe symptoms which increasing the mortality rate. Therefore, the connection between the lesion of the lungs and the metabolic/endocrine disorders is an interesting and essential issue to be addressed. Studies have noticed a similar pathological feature in both infectious pneumonia and metabolic disease-intercurrent pulmonary lesions, that is, from the view of molecular pathology, the accumulation of excessive reactive oxygen species (ROS) in pulmonary tissue accompanying with activated pro-inflammatory signals. Meanwhile, Adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) and nuclear factor erythroid-2-related factor 2 (Nrf2) signaling plays important role in metabolic/endocrine homeostasis and infection response, and it's closely associated with the anti-oxidative capacity of the body. For this reason, this review will start from the summary upon the implication of ROS accumulation, and to discuss how AMPK-Nrf2 signaling contributes to maintaining the metabolic/endocrine homeostasis and attenuates the susceptibility of pulmonary infections.

Acidity-Activated Charge-Convertible Silver Nanocomposites for Enhanced Bacteria-Specific Aggregation and Antibacterial Activity

Bacterial infections has become an intractable problem to human health. To overcome this challenge, we developed an antimicrobial agent (AgNPs@PDPE) via the conjugation of a pH-responsive copolymer of PDMAEMA-b-PPEGMA onto AgNPs surface. The AgNPs@PDPE underwent an acidity-induced surface charge conversion that favored bacteria-specific aggregation and antibacterial activity improvement. The specific interaction between AgNPs@PDPE and bacteria under acidic conditions was confirmed via an electrochemical method using AgNPs@PDPE modified glassy carbon electrode as the working electrode. AgNPs@PDPE could efficiently aggregate and inhibit the growth of both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) under acidic condition. The AgNPs@PDPE could also selectively distinguish pathogenic bacteria from host cells, and this characteristic is benefical for reducing the damage to surrounding tissues in the host. Moreover, AgNPs@PDPE could promote the healing of E. coli- and S. aureus-induced infection, as proven by the histological and TNF-α immunohistochemical analyses of rat dermal wounds. The proposed antimicrobial agent could to be an alternative treatment strategy for the safe treatment of treat bacteria-induced infections in clinics.

The relationship between structure and in vitro antistaphylococcal effect of plant-derived stilbenes

Staphylococcus aureus is a major human pathogen that is responsible for both hospital- and community-acquired infections. Stilbenes are polyphenol compounds of plant origin known to possess a variety of pharmacological properties, such as antibacterial, antiviral, and antifungal effects. This study reports the in vitro growth-inhibitory potential of eight naturally occurring stilbenes against six standard strains and two clinical isolates of S. aureus, using a broth microdilution method, and expressing the results as minimum inhibitory concentrations (MICs). Pterostilbene (MICs = 32-128 μg/ml), piceatannol (MICs = 64-256 μg/ml), and pinostilbene (MICs = 128 μg/ml) are among the active compounds that possess the strongest activity against all microorganisms tested, followed by 3'-hydroxypterostilbene, isorhapontigenin, oxyresveratrol, and rhapontigenin with MICs 128-256 μg/ml. Resveratrol (MIC = 256 μg/ml) exhibited only weak inhibitory effect. Furthermore, structure-activity relationships were studied. Hydroxyl groups at ortho-position (B-3' and -4') played crucial roles for the inhibitory effect of hydroxystilbene piceatannol. Compounds with methoxy groups at ring A (3'-hydroxypterostilbene, pinostilbene, and pterostilbene) produced stronger effect against S. aureus than their analogues (isorhapontigenin and rhapontigenin) with methoxy groups at ring B. These findings provide arguments for further investigation of stilbenes as prospective leading structures for development of novel antistaphylococcal agents for topical treatment of skin infections.

Antibacterial and antioxidant activities for natural and synthetic dual-active compounds

Antimicrobial resistance is widely recognized as a grave threat to global health in the 21st century, since the past decades have seen a dramatic increase in human-pathogenic bacteria that are resistant to one or multiple antibiotics. New antimicrobial agents are urgently required, particularly in the treatment of chronic infections such as cystic fibrosis, often associated with persistent colonization by drug-resistant pathogens and epithelial damage by pulmonary oxidative stress. In such events, it would be favourable to find agents that could have antioxidant and antibacterial activities combined in one molecule. The discovery of compounds that can show a dual-target activity considerably increased in the last years, reflecting the growing confidence that this new approach could lead to better therapeutic solutions for complex multigenic diseases. The aim of this review is to report those natural and synthetic compounds displaying significant antioxidant and antibacterial activities. In recent years there has been a growing attention on plant-derived antimicrobials as an alternative to antibiotics, for their efficacy and low tendency in developing bacterial resistance. Moreover, it was found that some natural products could enhance the activity of common antibiotics displaying a synergistic effect. We then report some selected synthetic compounds with an in-built capacity to act on two targets or with the combination in a single structure of two pharmacophores with antioxidant and antibacterial activities. Recent literature instances were screened and the most promising examples of dual-active antibacterial-antioxidant molecules were highlighted.

Resveratrol-Potential Antibacterial Agent against Foodborne Pathogens

Bacterial foodborne pathogens are a significant health burden and the recent emergence of pathogenic resistant strains due to the excessive use of antibiotics makes it more difficult to effectively treat infections as a result of contaminated food. Awareness of this impending health crisis has spurred the search for alternative antimicrobials with natural plant antimicrobials being among the more promising candidates as these substances have good acceptability and likely low toxicity levels as they have long been used in traditional medicines. Resveratrol (3,5,4′-trihydroxystilbene) is a naturally occurring stilbenoid which has been gaining considerable attention in medical field due to its diverse biological activities - it has been reported to exhibit antioxidant, cardioprotective, anti-diabetic, anticancer, and antiaging properties. Given that resveratrol is phytoalexin, with increased synthesis in response to infection by phytopathogens, there has been interest in exploring its antimicrobial activity. This review aims to provide an overview of the published data on the antibacterial activity of resveratrol against foodborne pathogens, its mechanisms of action as well as its possible applications in food packing and processing; in addition we also summarize the current data on its potential synergism with known antibacterials and future research and applications.

Bactericidal Effect of Pterostilbene Alone and in Combination with Gentamicin against Human Pathogenic Bacteria

The antibacterial activity of pterostilbene in combination with gentamicin against six strains of Gram-positive and Gram-negative bacteria were investigated. The minimum inhibitory concentration and minimum bactericidal concentration of pterostilbene were determined using microdilution technique whereas the synergistic antibacterial activities of pterostilbene in combination with gentamicin were assessed using checkerboard assay and time-kill kinetic study. Results of the present study showed that the combination effects of pterostilbene with gentamicin were synergistic (FIC index < 0.5) against three susceptible bacteria strains: Staphylococcus aureus ATCC 25923, Escherichia coli O157 and Pseudomonas aeruginosa 15442. However, the time-kill study showed that the interaction was indifference which did not significantly differ from the gentamicin treatment. Furthermore, time-kill study showed that the growth of the tested bacteria was completely attenuated with 2 to 8 h treatment with 0.5 × MIC of pterostilbene and gentamicin. The identified combinations could be of effective therapeutic value against bacterial infections. These findings have potential implications in delaying the development of bacterial resistance as the antibacterial effect was achieved with the lower concentrations of antibacterial agents.

Functional Silver Nanoparticle as a Benign Antimicrobial Agent That Eradicates Antibiotic-Resistant Bacteria and Promotes Wound Healing

With the increased prevalence of antibiotic-resistant bacteria infections, there is a pressed need for innovative antimicrobial agent. Here, we report a benign ε-polylysine/silver nanoparticle nanocomposite (EPL-g-butyl@AgNPs) with polyvalent and synergistic antibacterial effects. EPL-g-butyl@AgNPs exhibited good stability in aqueous solution and effective antibacterial activity against both Gram-negative (P. aeruginosa) and Gram-positive (S. aureus) bacteria without emergence of bacterial resistance. Importantly, the nanocomposites eradicated the antibiotic-resistant bacteria without toxicity to mammalian cells. Analysis of the antibacterial mechanism confirmed that the nanocomposites adhered to the bacterial surface, irreversibly disrupted the membrane structure of the bacteria, subsequently penetrated cells, and effectively inhibited protein activity, which ultimately led to bacteria apoptosis. Notably, the nanocomposites modulated the relative level of CD3⁺ T cells and CD68⁺ macrophages and effectively promoted infected wound healing in diabetic rats. This work improves our understanding of the antibacterial mechanism of AgNPs-based nanocomposites and offers guidance to activity prediction and rational design of effective antimicrobial nanoparticles.

Discovery of potential anti-infectives against Staphylococcus aureus using a Caenorhabditis elegans infection model

Background

The limited antibiotic options for effective control of methicillin-resistant Staphylococcus aureus infections has led to calls for new therapeutic approaches to combat this human pathogen. An alternative approach to control MRSA is through the use of anti-infective agents that selectively disrupt virulence-mediated pathways without affecting microbial cell viability or by modulating the host natural immune defenses to combat the pathogen.

Methods

We established a C. elegans – S. aureus liquid-based assay to screen for potential anti-infectives against S. aureus. The assay was utilized to screen 37 natural extracts and 29 synthetic compounds for the ability to extend the lifespan of infected nematodes. Disc diffusion and MIC microdilution tests were used to evaluate the anti-microbial properties of these natural extracts and synthetic compounds whilst in vivo bacterial CFU within the C. elegans gut were also enumerated.

Results

We screened a total of 37 natural extracts and 29 synthetic compounds for anti-infective properties. The screen successfully revealed 14 natural extracts from six plants (Nypa fruticans, Swietenia macrophylla, Curcuma longa, Eurycoma longifolia, Orthosiphon stamineus and Silybum eburneum) and one marine sample (Faunus ater) that improved the survival of S. aureus-infected worms by at least 2.8-fold as well as 14 synthetic compounds that prolonged the survival of S. aureus-infected nematodes by 4-fold or greater. An anti-microbial screen of all positive hits demonstrated that 8/28 hits had no effect on S. aureus growth. Of these 8 candidates, 5 of them also protected the worms from MRSA infection. We also noted that worms exposed to N. fruticans root and O. stamineus leaf extracts showed reduced intestinal colonization by live S. aureus. This suggests that these extracts could possibly activate host immunity to eliminate the bacteria or interfere with factor/s that prevents pathogen accumulation.

Conclusion

We have successfully demonstrated the utility of this liquid-based screen to identify anti-infective substances that prolong S. aureus-infected host survival without affecting bacterial cell viability.

Synergistic antibacterial and antibiofilm effect between (+)-medioresinol and antibiotics in vitro

In this study, antibacterial effects of (+)-Medioresinol isolated from stem bark of Sambucus williamsii and its synergistic activities in combination with antibiotics such as ampicillin, cefotaxime, and chloramphenicol were tested by antibacterial susceptibility testing and checkerboard assay. (+)-Medioresinol possessed antibacterial effects against antibiotics-susceptible- or antibiotics-resistant strains. Most of combinations between (+)-Medioresinol and each antibiotic showed synergistic interaction (fractional inhibitory concentration index ≤ 0.5) against bacterial strains including antibiotics-resistant Pseudomonas aeruginosa. Furthermore, the antibiofilm effect of (+)-Medioresinol alone or in combination with each antibiotic was investigated. The results indicated that not only (+)-Medioresinol but also its combination with each antibiotic had antibiofilm activities. It concludes that (+)-Medioresinol has potential as a therapeutic agent and adjuvant for treatment of bacterial infection.