In vitroCombinatory Antimicrobial Effect of Plumbagin with Oxacillin and Tetracycline againstStaphylococcus aureus

Antibacterial phenolic compounds from the flowering plants of Asia and the Pacific: coming to the light

CONTEXT

The emergence of pan-resistant bacteria requires the development of new antibiotics and antibiotic potentiators.

OBJECTIVE

This review identifies antibacterial phenolic compounds that have been identified in Asian and Pacific Angiosperms from 1945 to 2023 and analyzes their strengths and spectra of activity, distributions, molecular masses, solubilities, modes of action, structures-activities, as well as their synergistic effects with antibiotics, toxicities, and clinical potential.

METHODS

All data in this review was compiled from Google Scholar, PubMed, Science Direct, Web of Science, and library search; other sources were excluded. We used the following combination of keywords: 'Phenolic compound', 'Plants', and 'Antibacterial'. This produced 736 results. Each result was examined and articles that did not contain information relevant to the topic or coming from non-peer-reviewed journals were excluded. Each of the remaining 467 selected articles was read critically for the information that it contained.

RESULTS

Out of ∼350 antibacterial phenolic compounds identified, 44 were very strongly active, mainly targeting the cytoplasmic membrane of Gram-positive bacteria, and with a molecular mass between 200 and 400 g/mol. 2-Methoxy-7-methyljuglone, [6]-gingerol, anacardic acid, baicalin, vitexin, and malabaricone A and B have the potential to be developed as antibacterial leads.

CONCLUSIONS

Angiosperms from Asia and the Pacific provide a rich source of natural products with the potential to be developed as leads for treating bacterial infections.

Interactions of plumbagin with five common antibiotics against Staphylococcus aureus in vitro

Staphylococcus aureus is the main culprit, causing a variety of severe clinical infections. At the same time, clinics are also facing the severe situation of antibiotic resistance. Therefore, effective strategies to address this problem may include expanding the antimicrobial spectrum by exploring alternative sources of drugs or delaying the development of antibiotic resistance through combination therapy so that existing antibiotics can continue to be used. Plumbagin (PLU) is a phytochemical that exhibits antibacterial activity. In the present study, we investigated the in vitro antibacterial activity of PLU. We selected five antibiotics with different mechanisms and inhibitory activities against S. aureus to explore their interaction with the combination of PLU. The interaction of combinations was evaluated by the Bliss independent model and visualized through response surface analysis. PLU exhibited potent antibacterial activity, with half maximal inhibitory concentration (IC50) and minimum inhibitory concentration (MIC) values against S. aureus of 1.73 μg/mL and 4 μg/mL, respectively. Synergism was observed when PLU was combined with nitrofurantoin (NIT), ciprofloxacin (CPR), mecillinam (MEC), and chloramphenicol (CHL). The indifference of the trimethoprim (TMP)-PLU pairing was demonstrated across the entire dose-response matrix, but significant synergy was observed within a specific dose region. In addition, no antagonistic interactions were indicated. Overall, PLU is not only a promising antimicrobial agent but also has the potential to enhance the growth-inhibitory activity of some antibiotics against S. aureus, and the use of the interaction landscape, along with the dose-response matrix, for analyzing and quantifying combination results represents an improved approach to comprehending antibacterial combinations.

Antibacterial activity of menadione alone and in combination with oxacillin against methicillin-resistant Staphylococcus aureus and its impact on biofilms

Introduction. Antibiotic resistance is a major threat to public health, particularly with methicillin-resistant Staphylococcus aureus (MRSA) being a leading cause of antimicrobial resistance. To combat this problem, drug repurposing offers a promising solution for the discovery of new antibacterial agents.Hypothesis. Menadione exhibits antibacterial activity against methicillin-sensitive and methicillin-resistant S. aureus strains, both alone and in combination with oxacillin. Its primary mechanism of action involves inducing oxidative stress.Methodology. Sensitivity assays were performed using broth microdilution. The interaction between menadione, oxacillin, and antioxidants was assessed using checkerboard technique. Mechanism of action was evaluated using flow cytometry, fluorescence microscopy, and in silico analysis.Aim. The aim of this study was to evaluate the in vitro antibacterial potential of menadione against planktonic and biofilm forms of methicillin-sensitive and resistant S. aureus strains. It also examined its role as a modulator of oxacillin activity and investigated the mechanism of action involved in its activity.Results. Menadione showed antibacterial activity against planktonic cells at concentrations ranging from 2 to 32 µg ml-1, with bacteriostatic action. When combined with oxacillin, it exhibited an additive and synergistic effect against the tested strains. Menadione also demonstrated antibiofilm activity at subinhibitory concentrations and effectively combated biofilms with reduced sensitivity to oxacillin alone. Its mechanism of action involves the production of reactive oxygen species (ROS) and DNA damage. It also showed interactions with important targets, such as DNA gyrase and dehydroesqualene synthase. The presence of ascorbic acid reversed its effects.Conclusion. Menadione exhibited antibacterial and antibiofilm activity against MRSA strains, suggesting its potential as an adjunct in the treatment of S. aureus infections. The main mechanism of action involves the production of ROS, which subsequently leads to DNA damage. Additionally, the activity of menadione can be complemented by its interaction with important virulence targets.

Antibacterial and antibiofilm efficacy of the preferred fractions and compounds from Euphorbia humifusa (herba euphorbiae humifusae) against Staphylococcus aureus

ETHNOPHARMACOLOGICAL RELEVANCE

Euphorbia humifusa Willd., known as Di-Jin-Cao in Chinese, has long been utilized as a traditional herb for the treatment of furuncles and carbuncles mainly caused by Staphylococcus aureus infection. Despite extensive chemical and pharmacological studies reported previously for E. humifusa, the antibacterial and antibiofilm activities against S. aureus as well as the related mechanism of action (MoA) remain largely obscure.

AIM OF THE STUDY

To investigate the antibacterial and antibiofilm activities of the preferred fractions and compounds from E. humifusa against S. aureus and assess the associated MoA.

MATERIALS AND METHODS

The bioactive fractions and compounds were obtained from the 75% ethanol extract of E. humifusa (75%-EEEH) with the assistance of the related antibacterial and antibiofilm screening. Their antibacterial activities were determined using the broth microdilution method, whilst the inhibition of biofilm formation and the disruption of preformed biofilm were assessed by crystal violet staining and confocal laser scanning microscopy (CLSM). To achieve more effective therapies, the combinatory effects of different components were also studied. The biofilm metabolic activities of isolated compounds were evaluated by 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) reduction assay. The scanning electron microscopy (SEM) and quantitative real-time polymerase chain reaction (qRT-PCR) were employed to explore the antibiofilm mechanism.

RESULTS

Fractions DJC06 and DJC07 collected from the ethyl acetate extract of the 75%-EEEH exhibited antibacterial activity (MIC = 256 μg/mL) against S. aureus and further separation of these two fractions led to the isolation and characterization of 22 compounds. Among the isolates, luteolin (LU), quercetin (QU), and kaempferol (KA) are the verified components associated with the antibacterial and antibiofilm activities by displaying individual or combinational MIC values of 8-128 μg/mL and 70.9-99.7% inhibition for biofilm formation. Importantly, QU and KA can work in synergy with LU to significantly enhance the efficacy via destroying cell integrity, increasing membrane permeability, and down-regulating the biofilm-related gene expression.

CONCLUSIONS

The preferred fractions and compounds from E. humifusa exerted desired antibacterial and antibiofilm efficacy against S. aureus via a MoA involving cell morphology disruption and altered genes expression. The findings herein not only support its traditional use in the treatment of furuncles and carbuncles, but reveal E. humifusa is a potential source for producing promising antibiofilm alternatives against S. aureus and highlight the isolated components (LU, QU, KA) that can potentiate the efficacy when used in synergy.

Structural Insights and Pharmaceutical Relevance of Plumbagin in Parasitic Disorders: A Comprehensive Review

Recently, natural products have been became the center of attraction for the scientific society and exploration of their biologically abilities is proceeding continuously. In search for novel antiparasitic agents with an objective of protecting humans from parasitic infections, the present work was focused on naphthoquinones possessing antiparasitic activity. Among naphthoquinones, plumbagin is one of the secondary metabolites exhibiting diverse biological properties such as antibacterial, antimalarial, antiinflammatory, insecticidal and antiparasitic. Plumbagin is reported to have antischistosomiasis, anti-haemonchosis, anti-fascioliasis, antiotoacariasis, anti-leishmaniasis, antimalaria, antiallergic and anthelmintic activities. Besides, various methods of extraction of plumbagin from different methods, their effectiveness against different parasites, and the structure-activity relationship reported by different researchers. This work highlight on recent advancements in the phytochemistry of plumbagin, studies associated with various biological activities. The structure-activity relationship studies have also been summarized. To conclude, present review could be beneficial for the scientific community to get better insight into medicinal research of plumbagin and may provide a new horizon for the rational design of plumbagin based compounds.

Redox ticklers and beyond: Naphthoquinone repository in the spotlight against inflammation and associated maladies

Cellular redox status has been considered as a focal point for the pathogenesis of multiple disorders. High and persistent levels of free radicals kick off inflammation and associated disorders. Though oxidative stress at high levels is harmful but at low levels it has been shown to exert cytoprotective effects. Therefore, cytoprotection by perturbation in cellular redox balance is a leading strategy for therapeutic interventions. Prooxidants are potent redox modifiers that generate mild oxidative stress leading to a spectrum of bioactivities. Naphthoquinones are a group of highly reactive organic chemical species that interact with biological systems owing to their prooxidants nature. Owing to the ability of naphthoquinones and its derivatives to perturb redox balance in a cell and modulate redox signaling, they have been in epicenter of drug development for plausible utilization in multiple clinical settings. The present review highlights the potential of 1,4-naphthoquinone and its natural derivatives (plumbagin, juglone, lawsone, menadione, lapachol and β-lapachone) as redox modifiers with anti-inflammatory, anti-cancer, anti-diabetic and anti-microbial activities for implication in therapeutic settings.

Napthoquinones from Neocosmospora sp.-Antibiotic Activity against Acidovorax citrulli, the Causative Agent of Bacterial Fruit Blotch in Watermelon and Melon

Bacterial fruit blotch (BFB) is a bacterial disease that devastates Cucurbitaceae crops worldwide, causing significant economic losses. Currently, there is no means to treat or control the disease. This study focused on exploring the antibacterial properties of endophytic fungi against Acidovorax citrulli (Aac), the causative agent of BFB. Based on disc diffusion, time kill and MIC microdilution broth assays, four endophytes showed promise in controlling Aac. Nonetheless, only one strain, Neocosmospora sp. MFLUCC 17-0253, reduced the severity of disease on watermelon and melon seedlings up to 80%. Structure analysis revealed production of several compounds by the fungus. Three of these secondary metabolites, including mixture of 2-methoxy-6-methyl-7-acetonyl-8-hydroxy-1,4-maphthalenedione and 5,8-dihydroxy-7-acetonyl-1,4-naphthalenedione, anhydrojavanicin, and fusarnaphthoquinones B exhibited antagonistic activity against Aac. The chemical profile data in planta experiment analyzed by LC-Q/TOF-MS suggested successful colonization of endophytic fungi in their host plant and different metabolic profiles between treated and untreated seedling. Biofilm assay also demonstrated that secondary metabolites of Neocosmospora sp. MFLUCC 17-0253 significantly inhibited biofilm development of Aac. To the best of our knowledge, secondary metabolites that provide significant growth inhibition of Aac are reported for the first time. Thus, Neocosmospora sp. MFLUCC 17-0253 possesses high potential as a biocontrol agent for BFB disease.

Antibacterial Effect of Caprylic Acid and Potassium Sorbate in Combination against Listeria monocytogenes ATCC 7644

ABSTRACT

Listeria monocytogenes is a common foodborne pathogen that cause life-threatening infection with high mortality rates. Biofilm development of L. monocytogenes decreases its sensitivity to antibiotics, which has long attracted attention globally. Caprylic acid (CA) and potassium sorbate (PS) are both widely used food preservatives, but their synergistic effect against L. monocytogenes has not been described. This study explored the antibacterial activities of the CA-PS combination against L. monocytogenes ATCC 7644 grown in planktonic or biofilm cultures. The fractional inhibitory concentration index values, determined by the checkerboard microdilution method, were 0.37 ± 0.03 and 0.31 ± 0.04, showing their synergistic antimicrobial effects against L. monocytogenes ATCC 7644 in planktonic and biofilm cultures, respectively. CA-PS effectively eradicated the biofilm biomass to 10.8% by crystal violet assay and to 8.63% by fluorescence microscopic analysis compared with the control. The apoptosis rates of microbial cells embedded within biofilm significantly increased to 51.4%. Subsequent analysis revealed that the combination inhibited biofilm formation by affecting extracellular DNA release and polysaccharide intercellular adhesion expression, which was decreased from 8.93 to 1.04 ng of extracellular DNA per relative biomass and to 54.7% of the control, respectively. In addition, the combination inhibited the growth of L. monocytogenes ATCC 7644 by up to 0.67 ± 0.05 and 0.30 ± 0.03 log CFU/cm2 in planktonic and biofilm modes on a carrot surface, respectively. The synergistic antibacterial effects of CA-PS against L. monocytogenes ATCC 7644 were statistically significant, and the combination is an excellent candidate to be a novel food preservative.

HIGHLIGHTS

In vitro antibacterial activity of plumbagin isolated from Plumbago zeylanica L. against methicillin-resistant Staphylococcus aureus

Plumbagin (5-hydroxy-2-methyl-1,4-napthoquinone) is a bicyclic naphthoquinone, found in three major plant families viz. Plumbaginaceae, Ebenceae and Droseraceae. The phytochemical is reported to exhibit various pharmacological properties. In this study, plumbagin isolated from Plumbago zeylanica L. was investigated for its in vitro activity against methicillin-resistant Staphylococcus aureus (MRSA). Against 100 MRSA isolates that included multi-drug-resistant phenotypes, plumbagin showed consistent activity with a narrow minimum inhibitory concentration (MIC) range of 4-8 μg ml^-1 . The time-kill study revealed 99% kill of a reference MRSA strain, 8 h after exposure to plumbagin. In the combination MIC study using the reference MRSA strain, plumbagin showed synergistic effect with ciprofloxacin and piperacillin while additive or indifference effect with other commonly used antibiotics. The transmission electron micrograph of the reference MRSA strain treated with plumbagin confirmed cell wall and cytoplasmic changes. Our results demonstrated potent anti-MRSA activity of plumbagin which was not impacted by multi-drug resistance. This is a first ever study that evaluated in vitro anti-MRSA activity of plumbagin employing large number of MRSA isolates. The findings of this study support the need for the further investigation on this phytochemical agent for therapeutic application. SIGNIFICANCE AND IMPACT OF THE STUDY: This study revealed phytochemical plumbagin's potent and consistent in vitro antibacterial activity against clinically problematic methicillin-resistant Staphylococcus aureus (MRSA) including multi-drug-resistant (MDR) phenotypes. The study results support further research to assess the clinical scope of plumbagin.

Discovery of natural products with metal-binding properties as promising antibacterial agents

INTRODUCTION

More than 50% of the clinically established antibiotics are either genuine natural products or derivatives thereof, featuring a mode of action decisively depending on their metal affinity and suitability as metal complex ligands. As their structural diversity and harvest from renewable sources is well-nigh inexhaustible, any future quest for affordable new antibiotics will have to concentrate on natural drugs with obvious metal ligating properties. Areas covered: The authors provide an overview of the promising developments in the field of antibiotic natural products with metal-binding properties with a specific focus on metal binders such as polyphenols, quinones, 3-acyltetramic and -tetronic acids. Works published by the authors are discussed in this manuscript as well as articles derived from PubMed and Scifinder. Expert opinion: Natural products with metal-binding properties possess a great potential for the development of drugs against various bacteria. There are many derivatives with great potential against multidrug-resistant bacteria as well. Synthetic approaches to structurally complex and/or rare natural products have added significantly to the cracking of synthetic problems. Thus, this field of scientific research appears attractive both to chemists and to clinicians.

Experimental and theoretical investigations of novel oxidovanadium(IV) juglone complex: DNA/HSA interaction and cytotoxic activity

A new oxidovanadium(IV) complex VO(L)(Jug) (HL = 5-methoxy-1,3-bis (1-methyl-1H-benzo[d]imidazol-2-yl)benzene, Jug = juglone) was synthesized and characterized. Interactions of the V(IV) complex with calf thymus DNA (CT DNA) and human serum albumin were studied using different techniques such as UV-vis and fluorescence emission spectroscopy. The experimental results were confirmed by the molecular docking study. The oxidovanadium(IV) complex can efficiently cleave pUC19 DNA in the presence of Hydrogen peroxide. Also, the in vitro cytotoxicity properties of the oxidovanadium(IV) complex was evaluated against MCF-7, HPG-2 and HT-29 cancer cell lines and HEK293 non-malignant fibroblasts were evaluated and compared with free ligands, VOSO₄ and cisplatin as reference drugs.Communicated by Ramaswamy H. Sarma.

Synergy of a combination of nisin and citric acid against Staphylococcus aureus and Listeria monocytogenes

Food-borne diseases caused by pathogens, such as Staphylococcus aureus and Listeria monocytogenes, have long attracted attention globally from researchers, food industries, and food safety authorities. Nisin (NS) is the only bacteriocin used worldwide as a generally recognised as safe (GRAS) food preservative, while citric acid (CA) has an unrestricted use in foods since it has GRAS status. In this study, synergistic interactions of NS combined with CA against S. aureus and L. monocytogenes were studied by the chequerboard microdilution method, with fractional inhibitory concentration index values ranging from 0.25 to 0.375 and 0.19 to 0.375, respectively. The positive interactions were verified by time-kill studies in pasteurised milk and disk diffusion assays. The mechanism of the synergistic antibacterial of NS and CA is proposed following SEM analysis and the determination of release of cell constituents. These results suggest that the cell walls and membrane are the probable main targets of this antimicrobial combination. These findings indicated that the combination of NS and CA not only could be used as a new promising naturally sourced food preservative, but may also reduce the problem of bacterial resistance.

Searching for a potential antibacterial lead structure against bacterial biofilms among new naphthoquinone compounds

AIMS

The aims of this study were to design, synthesize and to evaluate 2-hydroxy-3-phenylsulfanylmethyl-[1,4]-naphthoquinones against Gram-negative and Gram-positive bacterial strains, including methicillin-resistant Staphylococcus aureus (MRSA) and its biofilm, to probe for potential lead structures.

METHODS AND RESULTS

Thirty-six new analogues were prepared with good yields using a simple, fast, operational three-procedure reaction and a thiol addition to an ο-quinone methide using microwave irradiation. All compounds were tested against Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Proteus mirabilis ATCC 15290, Serratia marcescens ATCC 14756, Klebsiella pneumoniae ATCC 4352, Enterobacter cloacae ATCC 23355, Enterococcus faecalis ATCC 29212, S. aureus ATCC 25923, Staphylococcus simulans ATCC 27851, Staphylococcus epidermidis ATCC 12228 and a hospital strain of MRSA. Their antibacterial activity was determined using the disc diffusion method, revealing the activity of 19 compounds, mainly against Gram-positive strains. Interestingly, the minimal inhibitory concentration ranges detected for the hit molecules (32-128 μg ml^-1 ) were within Clinical and Laboratory Standards Institute levels. Promisingly, compound 15 affected the MRSA strain, with a reduction of up to 50% in biofilm formation, which is better than vancomycin as biofilm forms a barrier against the antibiotic that avoids its action.

CONCLUSIONS

After probing 36 naphthoquinones for a potential antibacterial lead structure against the bacterial biofilm, we found that compound 15 should be explored further and also should be structurally modified in the near future to test against Gram-negative strains.

SIGNIFICANCE AND IMPACT OF THE STUDY

Since vancomycin is one of the last treatment options currently available, and it is unable to inhibit biofilm, the research of new antimicrobials is urgent. In this context, 2-hydroxy-3-phenylsulfanylmethyl-[1,4]-naphthoquinones proved to be a promising lead structure against MRSA and bacterial biofilm.

In vitro synergistic effect of Hibiscus sabdariffa aqueous extract in combination with standard antibiotics against Helicobacter pylori clinical isolates

Context The increasing problem of drug-resistant strains has led to the failure of current treatment regimens of Helicobacter pylori (HP) infection. Recently, a new treatment strategy has been developed to overcome the problem by using natural products in combination with antibiotics to enhance the treatment efficacy. Objective The antimicrobial combinatory effect of the aqueous extract of Hibiscus sabdariffa L. (Malvaceae) (AEHS) with antibiotics (clarithromycin, CLA; amoxicillin, AMX; metronidazole, MTZ) has been evaluated in vitro against HP strains. Materials and methods Hibiscus calyces (35 g) were brewed in 250 mL of boiled water for 30 min, and minimum inhibitory concentrations (MICs) were determined by agar dilution method. The checkerboard assay was used to evaluate the antimicrobial combinatory effect according to the sum of fractional inhibitory concentration (∑FIC) indices. Results In this study, AEHS exerted remarkable bacteriostatic effect against all HP strains tested with MICs values ranging from 9.18 to 16.68 μg/mL. Synergy effect of AEHS with CLA or MTZ was obtained against four of seven HP strains tested with ∑FIC ranging from 0.21 to 0.39. The additive effect of AEHS with AMX was obtained against five of seven HP strains tested with ∑FIC ranging from 0.61 to 0.91. Conclusion This study presents AEHS as a potent therapeutic candidate alone, or in combination with antibiotics for the treatment of HP infection.

Plumbagin, a Plant-Derived Compound, Exhibits Antifungal Combinatory Effect with Amphotericin B against Candida albicans Clinical Isolates and Anti-hepatitis C Virus Activity

Plumbagin (5-hydroxy-2-methyl-1,4-naphthoquinone), the major active constituent of Plumbago indica L., has been shown to be effective against a wide range of infectious microbes. In this study, plumbagin has been evaluated in vitro for its antifungal combinatory effect with amphotericin B against Candida albicans (C. albicans) clinical isolates and anti-hepatitis C virus (HCV) activity. Antifungal activity was determined by broth microdilution method, and combinatory effect was evaluated by checkerboard assay according to ΣFIC indices, while cytotoxicity was determined by MTT assay. Anti-HCV activity was determined in infected Huh7.5 cells using quantitative real-time reverse transcription PCR, and cytotoxicity was evaluated by MTT assay. Plumbagin exerted inhibitory effect against all C. albicans strains with minimum inhibitory concentration values ranging from 7.41 to 11.24 µg/mL. The additive effect of plumbagin when combined with amphotericin B at concentrations of (0.12, 0.13 and 0.19, 1.81 µg/mL, respectively) was obtained against five of seven strains tested with ΣFIC ranging from 0.62 to 0.91. In addition, plumbagin was found to be used safely for topical application when combined with amphotericin B at concentrations corresponding to the additive effect. Plumbagin exerted anti-HCV activity compared with that of telaprevir with IC50 values of 0.57 and 0.01 μM/L, respectively, and selectivity indices SI = 53.7 and SI = 2127, respectively. Our results present plumbagin as a potential therapeutic agent in the treatment of C. albicans and HCV infections. Copyright © 2016 John Wiley & Sons, Ltd.

Towards targeting anticancer drugs: ruthenium(ii)–arene complexes with biologically active naphthoquinone-derived ligand systems

2-Hydroxy-[1,4]-naphthoquinone-derived ligands and their Ru^II(η⁶-p-cymene)Cl complexes were prepared with the aim to obtain multimodal anticancer agents.

Plumbagin and Its Role in Chronic Diseases

Plumbagin (5-hydroxy-2-methyl-1,4-naphthoquinone) is a plant-derived naphthoquinones obtained mainly from three families, including Plumbaginaceae, Droseraceae, and Ebenaceae. Plumbagin has exhibited its potential therapeutic benefits on numerous chronic diseases, i.e., breast cancer, non-small cell lung cancer, melanoma, ovarian, squamous cell carcinomas, pancreatic cancer, and prostate cancer. In addition, its anti-inflammatory and antimicrobial activities as well as control of diabetes and cardiovascular diseases have been reported. Thus, plumbagin is a promising agent for development as a new drug for the treatment or control of chronic diseases. Studies on controlled drug release or drug delivery systems have been involved for improvement of its therapeutic efficacy as well as for the reduction of its toxicity. However, most of the recent research information is from in vitro and in vivo studies. Further clinical studies are therefore required for its developments and applications as a novel drug used to treat chronic diseases.