Antibiofilm potential of 16-oxo-cleroda-3, 13(14) E-diene-15 oic acid and its five new γ-amino γ-lactone derivatives against methicillin resistant Staphylococcus aureus and Streptococcus mutans

Effects of bioconversion by Battus polydamas on the chemical composition of Aristolochia spp. and evaluation of antimicrobial activity and biocompatibility

Aristolochia plants are emblematic from an ethnopharmacological viewpoint and are know to possess numerous biological properties, including antiseptic. However, the medicinal potential of these species is debatable because of their representative chemical constituents, aristolochic acids (AAs) and aristolactams (ALs), which are associated, for instance, with nephropathy and cancer. These contrasting issues have stimulated the development of approaches intended to detoxification of aristoloquiaceous biomasses, among which is included the bioconversion method using larvae of the specialist phytophagous insect Battus polydamas, previously shown to be viable for chemical diversification and to reduce toxicity. Thus, eleven Aristolochia spp. were bioconverted, and the antimicrobial activities of the plant methanolic extracts and its respective bioconversion products were evaluated. The best results were found for Aristolochia esperanzae, Aristolochia gibertii, and Aristolochia ringens against Bacillus cereus, with MIC ranging from 7.8 to 31.25 μg/mL. These three species were selected for chemical, antioxidant, cytotoxic, hemolytic, and mutagenic analyses. Chemical analysis revealed 65 compounds, 21 of them possible bioconversion products. The extracts showed potential to inhibit the formation and degradation of B. cereus biofilms. Extracts of A. gibertii and its bioconverted biomass showed antioxidant activity comparable to dibutylhydroxytoluene (BHT) standard. Bioconversion decreased the hemolytic activity of A. esperanzae and the cytotoxicities of A. esperanzae and A. gibertii. None of the extracts was found to be mutagenic. The bioactivities of the fecal extracts were maintained, and biocompatibility was improved. Therefore, the results obtained in this study reveal positive expectations about the natural detoxification process of the Aristolochia species.

In vitro and in vivo antimicrobial potential of lithium complex against multi-drug resistant Acinetobacter baumannii

IMPORTANCE

Multi-drug resistance (MDR) by virtue of evolving resistance and virulence mechanisms among A. baumannii is a global concern which is responsible for lethal hospital-acquired infections. Therefore, it is crucial to develop new therapeutics against it. Metal complexes are compact structures with diverse mechanisms that the pathogens cannot evade easily which make them a strong drug candidate. In this study, we assessed the in vitro and in vivo efficacy of lithium complex {[Li(phen)2 sal]} against biofilm-forming MDR A. baumannii. The lithium complex displayed strong antimicrobial activity and reduced the pre-formed mature biofilm which is key barrier for antimicrobial action. Moreover, it employs oxidative stress as one of its mode of actions and causes cellular rupturing. Lithium complex was non-toxic and was significantly effective to overcome pneumonia in mice model. These results highlight the untapped potential of metal complexes that can be explored and utilized for combating notorious A. baumannii infections.

New Insights into the Antimicrobial Potential of Polyalthia longifolia-Antibiofilm Activity and Synergistic Effect in Combination with Penicillin against Staphylococcus aureus

Widespread antibiotic resistance has led to the urgent need for the identification of new antimicrobials. Plants are considered a valuable potential resource for new effective antimicrobial compounds. Therefore, in the present study, we focused on the antimicrobial activity of Polyalthia longifolia plants harvested from Cameroon using the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and time-kill assays. The mechanism of action was investigated by employing fluorescence and scanning electron microscopy. The anti-Staphylococcus aureus activity was studied using biofilm inhibition and checkerboard assays. Our results revealed that the tested extracts possess important antimicrobial activities, notably against Gram positive bacteria (MICs as low as 0.039 mg/mL). P. longifolia leaf extracts exhibited a significant bactericidal effect, with a total kill effect recorded after only 2 h of exposure at concentrations equivalent to MBC (0.078 and 0.156 mg/mL). The extracts showed a synergistic antibacterial activity in combination with penicillin against a MRSA clinical isolate and significantly inhibited S. aureus biofilm formation. The mechanism of action is related to the impairment of cell membrane integrity and cell lysis. All these findings suggest that P. longifolia could be an important source of reliable compounds used to develop new antimicrobials.

Novel Aporphine- and Proaporphine-Clerodane Hybrids Identified from the Barks of Taiwanese Polyalthia longifolia (Sonn.) Thwaites var. pendula with Strong Anti-DENV2 Activity

Hybrid natural products produced via mixed biosynthetic pathways are unique and often surprise one with unexpected medicinal properties in addition to their fascinating structural complexity/diversity. In view of chemical structures, hybridization is a way of diversifying natural products usually through dimerization of two similar or dissimilar subcomponents through a C-C or N-C covalent linkage. Here, we report four structurally attractive diterpene-alkaloid conjugates polyalongarins A-D (1-4), clerodane-containing aporphine and proaporphine alkaloids, the first of its kind from the barks of Taiwanese Polyalthia longifolia (Sonn.) Thwaites var. pendula. In addition to conventional spectroscopic analysis, single crystal X-ray crystallography was employed to determine the chemical structures and stereo-configurations of 1. Compounds 1-4 were subsequently subjected to in vitro antiviral examination against DENV2 by evaluating the expression level of the NS2B protein in DENV2-infected Huh-7 cells. These compounds display encouraging anti-DENV2 activity with superb EC₅₀ (2.8-6.4 μM) and CC₅₀ values (50.4-200 μM). The inhibitory mechanism of 1-4 on NS2B was further explored drawing on in-silico molecular docking analysis. Based on calculated binding affinities and predicted interactions between the functional groups of 1-4 and the allosteric-site residues of the DENV2 NS2B-NS3 protease, our analysis concludes that the clerodane-aporphine/proaporphine-type hybrids are novel and effective DENV NS2B-NS3 protease inhibitors.

Enoxacin-based derivatives: antimicrobial and antibiofilm agent: a biology-oriented drug synthesis (BIODS) approach

Background: To find alternative molecules against Klebsiella pneumonia, Proteus mirabilis and methicillin-resistant Staphylococcus aureus, new enoxacin derivatives were synthesized and screened. Methods: All derivatives exhibited promising antibacterial activities as compared to standard enoxacin (2 μg/ml) and standard cefixime (82 μg/ml). Compounds 2, 3 and 5 significantly downregulated the gene expression of biofilm-forming genes. Conclusion: Based on our results, these molecules may serve as potential drug candidates to cure several bacterial infections in the future.

Synthesis of gemifloxacin conjugated silver nanoparticles, their amplified bacterial efficacy against human pathogen and their morphological study via TEM analysis

Drug-loaded nanoparticles (NPs) allow specific accumulation and controlled release of drugs to infected tissues with minimal cytotoxicity. In this study, gemifloxacin conjugated silver nanoparticles (Gemi-AgNPs) were synthesized, and the amplification of their antibacterial potential against the human pathogen as well as their stability was monitored under physiological conditions. Fourier transform infrared spectroscopy (FTIR) analysis demonstrated the interaction between -NH₂ and -OH functional moiety and the metal surface. The morphological analyses via transmission electron microscopy revealed that Gemi-AgNPs has a round oval shape and average particle size of 22.23 ± 2 nm. The antibacterial and antibiofilm activities of these NPS showed that Gemi-AgNPs exhibit excellent antimicrobial and biofilm inhibition activity against human pathogens, namely, Proteus mirabilis (P. mirabilis) and methicillin-resistant Staphylococcus aureus (MRSA). A significant increase in the antibiofilm activity of Gemi-AgNPs was confirmed by crystal violet, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) staining, and microscopic analysis. Gemi-AgNPs exhibited the ability to inhibit urease with an IC₅₀ value of 57.4 ± 0.72 µg/mL. The changes in the bacterial cell morphology were analyzed via TEM, which revealed that cell membranes disrupted and completely destroyed the cell morphology by the treatment of Gemi-AgNPs.

Clerodane Diterpenoids from an Edible Plant Justicia insularis: Discovery, Cytotoxicity, and Apoptosis Induction in Human Ovarian Cancer Cells

OBJECTIVES

The toxicity of chemotherapeutic anticancer drugs is a serious issue in clinics. Drug discovery from edible and medicinal plants represents a promising approach towards finding safer anticancer therapeutics. Justicia insularis T. Anderson (Acanthaceae) is an edible and medicinal plant in Nigeria. This study aims to discover cytotoxic compounds from this rarely explored J. insularis and investigate their underlying mechanism of action.

METHODS

The cytotoxicity of the plant extract was evaluated in human ovarian cancer cell lines and normal human ovarian surface epithelia (HOE) cells using a sulforhodamine B assay. Bioassay-guided isolation was carried out using column chromatography including HPLC, and the isolated natural products were characterized using GC-MS, LC-HRMS, and 1D/2D NMR techniques. Induction of apoptosis was evaluated using Caspase 3/7, 8, and 9, and Annexin V and PI based flow cytometry assays. SwissADME and SwissTargetPrediction web tools were used to predict the molecular properties and possible protein targets of identified active compounds. Key finding: The two cytotoxic compounds were identified as clerodane diterpenoids: 16(α/β)-hydroxy-cleroda-3,13(14)Z-dien-15,16-olide (1) and 16-oxo-cleroda-3,13(14)E-dien-15-oic acid (2) from the Acanthaceous plant for the first time. Compound 1 was a very abundant compound (0.7% per dry weight of plant material) and was shown to be more potent than compound 2 with IC₅₀ values in the micromolar range against OVCAR-4 and OVCAR-8 cancer cells. Compounds 1 and 2 were less cytotoxic to HOE cell line. Both compounds induced apoptosis by increasing caspase 3/7 activities in a concentration dependent manner. Compound 1 further increased caspase 8 and 9 activities and apoptosis cell populations. Compounds 1 and 2 are both drug like, and compound 1 may target various proteins including a kinase.

CONCLUSIONS

Clerodane diterpenoids (1 and 2) in J. insularis were identified as cytotoxic to ovarian cancer cells via the induction of apoptosis, providing an abundant and valuable source of hit compounds for the treatment of ovarian cancer.

Antimicrobial and biofilm inhibiting potential of an amide derivative [N-(2', 4'-dinitrophenyl)-3β-hydroxyurs-12-en-28-carbonamide] of ursolic acid by modulating membrane potential and quorum sensing against colistin resistant Acinetobacter baumannii

Acinetobacter baumannii is Gram-negative, an opportunistic pathogen responsible for life-threatening ventilator-associated pneumonia. World Health Organization (WHO) enlisted it as a priority pathogen for which therapeutic options need speculations. Biofilm further benefits this pathogen and aids 100-1000 folds more resistant against antimicrobials and the host immune system. In this study, ursolic acid (1) and its amide derivatives (2-4) explored for their antimicrobial and antibiofilm potential against colistin-resistant A. baumannii (CRAB) reference and clinical strains. Viability, crystal violet, microscopic, and gene expression assays further detailed the active compounds' antimicrobial and biofilm inhibition potential. Compound 4 [N-(2',4'-dinitrophenyl)-3β-hydroxyurs-12-en-28-carbonamide)], a synthetic amide derivate of ursolic acid significantly inhibits bacterial growth with MIC in the range of 78-156 μg/mL against CRAB isolates. This compound failed to completely kill the CRAB isolates even at 500 μg/mL concentration, suggesting the compound's anti-virulence and bacteriostatic nature. Short and prolonged exposure of 4 inhibited or delayed the bacterial growth at sub MIC, MIC, and 2× MIC, as evident in time-kill and post-antibacterial assay. It significantly inhibited and eradicated >70% of biofilm formation at MIC and sub MIC levels compared to colistin required in high concentrations. Microscopic analysis showed disintegrated biofilm after treatment with the 4 further strengthened its antibiofilm potential. Atomic force microscopy (AFM) hinted the membrane disrupting effect of 4 at MIC's. Further it was confirmed by DiBAC4 using fluorescence-activating cells sorting (FACS), suggesting a depolarized membrane at MIC. Gene expression analysis also supported our data as it showed reduced expression of biofilm-forming (bap) and quorum sensing (abaR) genes after treatment with sub MIC of 4. The results suggest that 4 significantly inhibit bacterial growth and biofilm mode of colistin-resistant A. baumannii. Thus, further studies are required to decipher the complete mechanism of action to develop 4 as a new pharmacophore against A. baumannii.

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

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

Flow Injection-High Resolution-Electrospray Ionization-Mass Spectrometry (FI-HR-ESI-MS) Method for the Screening of Antimicrobial Pharmaceutical Drugs and Compounds against Klebsiella pneumoniae

The development of drug resistant microorganism is a global threat. Therefore, screening of more compounds for antimicrobial potentials is needed. Hence, a rapid method was developed for the screening of antimicrobial drugs and compounds against Klebsiella pneumoniae using Flow Injection Analysis-High Resolution-Mass Spectrometry. The method was optimized for bacterial culture time and concentration of drugs. IC₅₀ values for the drugs were calculated from the percent intensity of 704.5207 m/z of K. pneumoniae at 5 hrs incubation. This mass was proposed as diacylglycerophosphoethanolamine and observed as a potential biomarker of K. pneumoniae for the evaluation of inhibition potential of antimicrobial drugs and compounds. The calculated values for half maximal inhibitory concentration of cefixime, gentamicin and enrofloxacin were 0.052, 0.028 and 0.042 µg/mL, respectively. Ten compounds were also screened against the developed method, among them one compound (RSE-6) was found to be active with IC₅₀ value of 45.08 µg/mL. The obtained results were further compared with MIC values, obtained from micro dilution and Alamar blue assay after 24 hrs incubation. In comparison to these methods, developed method is sensitive, reproducible, rapid and robust for the determination of IC₅₀ value or inhibition potential of the drugs and compounds even at early incubation period of 5 hours.

A Clerodane Diterpene from Callicarpa americana Resensitizes Methicillin-Resistant Staphylococcus aureus to β-Lactam Antibiotics

The rise of antibiotic resistance presents a significant healthcare challenge and precludes the use of many otherwise valuable antibiotics. One potential solution to this problem is the use of antibiotics in combination with resistance-modifying agents, compounds that act synergistically with existing antibiotics to resensitize previously resistant bacteria. In this study, 12(S),16ξ-dihydroxycleroda-3,13-dien-15,16-olide, a clerodane diterpene isolated from the medicinal plant Callicarpa americana, was found to synergize with oxacillin against methicillin-resistant Staphylococcus aureus. This synergy was confirmed by checkerboard (fractional inhibitory concentration index (FICI) = 0.125) and time-kill assays, with a subinhibitory dose of 12(S),16ξ-dihydroxycleroda-3,13-dien-15,16-olide causing the effective concentration of oxacillin to fall below the susceptibility breakpoint for S. aureus, a >32-fold decrease in both cases.

Synthesis of new Enrofloxacin Derivatives as Potential Antibiofilm Drugs Against Staphylococcus Aureus and Klebsiella Pneumoniae

BACKGROUND

The antimicrobial resistance due to biofilm formation among bacteria is a significant problem in the healthcare and food industries.

OBJECTIVE

The current study describes the synthesis of enrofloxacin derivatives 2-17, and the evaluation of their anti-bacterial and anti-biofilm activities.

METHODS

Compounds 2-17 were synthesized through the acylation of enrofloxacin with thionyl chloride, followed by reaction with different aromatic amines. The new analogues identified among the sixteen compounds were 2-7, 11, 14, and 17.

RESULTS

Compound 2 appeared to be effective against pathogens S. aureus as well as K. pneumonia, whereas, compound 11 was found active against K. pneumonia only. Compound 2 inhibited >75% biofilm formation of S. aureus at 20 μg/mL and K. pneumonia at 10 μg/mL concentrations. These doses are far below the bactericidal concentration of compound 2, suggesting the anti-virulence mechanism of these compounds. Compound 11 inhibited 60% biofilm formation of K. pneumoniae at 70 μg/mL concentration. Compound 5 inhibited the biofilm of K. pneumoniae at 62 μg/mL concentration but also had bactericidal properties at this concentration. Interestingly, compound 2 eradicated the preformed biofilm of both the pathogens at much lower doses as compared to control drug, gentamycin and substrate, enrofloxacin. Cytotoxicity of compounds 2-17 was checked by a standard method using 3T3 normal cell lines (mouse fibroblast), all compounds were found to be noncytotoxic.

CONCLUSION

These compounds can be used alone or with FDA approved drugs to overcome biofilm related K. pneumoniae and S. aureus infections.

Antiamoebic activity of plant-based natural products and their conjugated silver nanoparticles against Acanthamoeba castellanii (ATCC 50492)

Acanthamoeba spp. are the causative agent of Acanthamoeba keratitis and granulomatous amoebic encephalitis (GAE). The current options to treat Acanthamoeba infections have limited success. Silver nanoparticles show antimicrobial effects and enhance the efficacy of their payload at the specific biological targets. Natural folk plants have been widely used for treating diseases as the phytochemicals from several plants have been shown to exhibit amoebicidal effects. Herein, we used natural products of plant or commercial sources including quercetin (QT), kolavenic acid (PGEA) isolated from plant extracts of Polyalthia longifolia var pendula and crude plant methanolic extract of Caesalpinia pulcherrima (CPFLM) as antiacanthamoebic agents. Furthermore, these plant-based materials were conjugated with silver nanoparticles (AgNPs) to determine the effects of the natural compounds and their nanoconjugates against a clinical isolate of A. castellanii from a keratitis patient (ATCC 50492) belonging to the T4 genotype. The compounds were conjugated with AgNPs and characterized by using ultraviolet visible spectrophotometry and atomic force microscopy. Quercetin coated silver nanoparticles (QT-AgNPs) showed characteristic surface plasmon resonance band at 443 nm and the average size distribution was found to be around 45 nm. The natural compounds alone and their nanoconjugates were tested for the viability of amoebae, encystation and excystation activity against A. castellanii. The natural compounds showed significant growth inhibition of A. castellanii while QT-AgNPs specifically exhibited enhanced antiamoebic effects as well as interrupted the encystation and excystation activity of the amoebae. Interestingly, these compounds and nanoconjugates did not exhibit in vitro cytotoxic effects against human cells. Plant-based compounds and extracts could be an interesting strategy in development of alternative therapeutics against Acanthamoeba infections.

Synthesis and sensitive detection of doxycycline with sodium bis 2-ethylhexylsulfosuccinate based silver nanoparticle

The monitoring of residual antibiotics in the environment has gained a significant importance for the effective control, because of the high risk to human health. A simple strategy was designed for the green synthesis and detection of doxycycline (Dox) by using anionic surfactant sodium bis 2-ethylhexylsulfosuccinate based silver nanoparticles (AOT-AgNPs). The chemical reduction and capping of Ag⁺¹ ions was achieved by sulfonyl and carbonyl functional groups of AOT molecule. The AOT-AgNPs were found to have excellent stability at variable environmental parameters (i.e. temperature, storage period, salt concentration and pH) possibly due to the strong emulsifying nature of the surfactant. Mechanism of interaction between the AOT-AgNPs and Dox was established with UV/visible, Fourier transform infrared (FTIR) spectroscopy, Atomic force microscopy (AFM) and Dynamic light scattering (DLS) techniques, which suggests the interaction via aggregates formation. The synthesize probe could detect the Dox within 15 min over a wide range of concentrations from 0.1 to 140μM with limit of detection (LOD) of 0.2 μM. As proof of strategy, we have illustrated that the AOT-AgNPs also detect Dox in biological and environmental samples with negligible interference and very significant recovery rates. Moreover, non-toxic nature against various tested cell lines (i.e. normal mouse fibroblast (NIH-3 T3) and cancerous non-small lung carcinoma (NCI-H460)) and significant antimicrobial, antibiofilm and biofilm eradicating potential of AOT-AgNPs were provide ideal nanomaterial for further applications.

Promising antibacterial agents against multidrug resistant Staphylococcus aureus

Rapid emergence of multidrug resistant Staphylococcus aureus infections has created a critical health menace universally. Resistance to all the available chemotherapeutics has been on rise which led to WHO to stratify Staphylococcus aureus as high tier priorty II pathogen. Hence, discovery and development of new antibacterial agents with new mode of action is crucial to address the multidrug resistant Staphylococcus aureus infections. The egressing understanding of new antibacterials on their biological target provides opportunities for new therapeutic agents. This review underlines on various aspects of drug design, structure activity relationships (SARs) and mechanism of action of various new antibacterial agents and also covers the recent reports on new antibacterial agents with potent activity against multidrug resistant Staphylococcus aureus. This review provides attention on in vitro and in vivo pharmacological activities of new antibacterial agents in the point of view of drug discovery and development.

Rifampicin conjugated silver nanoparticles: a new arena for development of antibiofilm potential against methicillin resistant Staphylococcus aureus and Klebsiella pneumoniae

Background: Infections caused by drug resistant bacteria are a major health concern worldwide and have prompted scientists to carry out efforts to overcome this challenge. Researchers and pharmaceutical companies are trying to develop new kinds of antimicrobial agents by using different physical and chemical methods to overcome these problems. Materials and methods: In the present study, rifampicin conjugated silver (Rif-Ag) nanoparticles have successfully been synthesized using a chemical method. Characterization of the nanoparticles was performed using a UV-Vis spectrophotometer, FTIR, SEM, TEM, and AFM. Results: The AFM, SEM, and TEM results showed that the average particle size of Rif-Ag nanoparticles was about 15-18±4 nm. The FTIR spectra revealed the conjugation of -NH2 and -OH functional moiety with silver nanoparticles surface. Considering the penetrating power of rifampicin, the free drug is compared with synthesized nanoparticle for antimicrobial, biofilm inhibition, and eradication potential. Synthesized nanoparticles were found to be significantly active as compared to drug alone. Conclusion: This study has shown greater biofilm inhibitory and eradicating potential against methicillin resistant Staphylococcus aureus and Klebsiella pneumoniae, as evident by crystal violet, MTT staining, and microscopic analysis. So, it will be further modified, and studies for the mechanism of action are needed.

The Current Status of O-Heterocycles: A Synthetic and Medicinal Overview

O-Heterocycles have been explored in the field of medicinal chemistry for a long time, but their significance has not been duly recognised and they are often shunned in favour of N-heterocycles. The design of bioactive molecules for nearly every pathophysiological condition is primarily focused on novel N-heterocycles. The main reasons for such bias include the ease of synthesis and possible mimicking of physiological molecules by N-heterocycles. But considering only this criterion rarely provides breakthrough molecules for a given disease condition, and instead the risks of toxicity or side effects are increased with such molecules. On the other hand, owing to improved synthetic feasibility, O-heterocycles have established themselves as equally potent lead molecules for a wide range of pathophysiological conditions. In the last decade there have been hundreds of reports validating the fact that equally potent molecules can be designed and developed by using O-heterocycles, and these are also expected to have comparably low toxicity. Even so, researchers tend to remain biased toward the use of N-heterocycles over O-heterocycles. Thus, this review provides a critical analysis of the synthesis and medicinal attributes of O-heterocycles, such as pyrones, oxazolones, furanones, oxetanes, oxazolidinones, and dioxolonones, and others, reported in the last five years, underlining the need for and the advantages guiding researchers toward them.