Gram-negative Antibacterial Activity Research Articles

Green Synthesis and Characterization of Hydrozincite Nanoparticles from Wild Passion Fruit

Abstract: Green synthesis of nano particles involves the use of whole plant or parts of plant for the bioreduction of metal ions into their elemental form. Hydrozincite nano particles were synthesized using the wild passion fruit. The fruit has got so many health benefits. The synthesized nano particles were characterized by X-Ray diffraction(XRD), Fourier Transform Infra-Red spectroscopy(FT-IR), UV-Vis absorption spectroscopy(UV), Scanning Electron Microscope(SEM) and Energy Dispersive X-Ray Diffraction(EDX). Using XRD the average particle size was found to be 14.032nm. The functional groups of the prepared sample were identified using FT-IR analysis. From UV the absorption peak was noticed at 302.199 nm which confirms the particle was in nano range. The surface morphology of the synthesized particles was noticied as bread spongy from the SEM analysis. The chemical compounds in the nano particles were identified using EDX analysis. Anti-microbial resistance is one of the greatest challenges to global health. The prepared nano particle shows a good effect for both gram-positive and gramnegative anti-bacterial activity.

RND Pump-Mediated Efflux of Amotosalen, a Compound Used in Pathogen Inactivation Technology to Enhance Safety of Blood Transfusion Products, May Compromise Its Gram-Negative Anti-Bacterial Activity.

Pathogen inactivation is a strategy to improve the safety of transfusion products. The only pathogen reduction technology for blood products currently approved in the US utilizes a psoralen compound, called amotosalen, in combination with UVA light to inactivate bacteria, viruses, and protozoa. Psoralens have structural similarity to bacterial multidrug efflux pump substrates. As these efflux pumps are often overexpressed in multidrug-resistant pathogens, we tested whether contemporary drug-resistant pathogens might show resistance to amotosalen and other psoralens based on multidrug efflux mechanisms through genetic, biophysical, and molecular modeling analysis. The main efflux systems in Enterobacterales, Acinetobacter baumannii, and Pseudomonas aeruginosa are tripartite resistance-nodulation-cell division (RND) systems, which span the inner and outer membranes of Gram-negative pathogens, and expel antibiotics from the bacterial cytoplasm into the extracellular space. We provide evidence that amotosalen is an efflux substrate for the E. coli AcrAB, Acinetobacter baumannii AdeABC, and P. aeruginosa MexXY RND efflux pumps. Furthermore, we show that the MICs for contemporary Gram-negative bacterial isolates for these species and others in vitro approached and exceeded the concentration of amotosalen used in the approved platelet and plasma inactivation procedures. These findings suggest that otherwise safe and effective inactivation methods should be further studied to identify possible gaps in their ability to inactivate contemporary, multidrug-resistant bacterial pathogens. IMPORTANCE Pathogen inactivation is a strategy to enhance the safety of transfused blood products. We identify the compound, amotosalen, widely used for pathogen inactivation, as a bacterial multidrug efflux substrate. Specifically, experiments suggest that amotosalen is pumped out of bacteria by major efflux pumps in E. coli, Acinetobacter baumannii, and Pseudomonas aeruginosa. Such efflux pumps are often overexpressed in multidrug-resistant pathogens. Importantly, the MICs for contemporary multidrug-resistant Enterobacterales, Acinetobacter baumannii, Pseudomonas aeruginosa, Burkholderia spp., and Stenotrophomonas maltophilia isolates approached or exceeded the amotosalen concentration used in approved platelet and plasma inactivation procedures, potentially as a result of efflux pump activity. Although there are important differences in methodology between our experiments and blood product pathogen inactivation, these findings suggest that otherwise safe and effective inactivation methods should be further studied to identify possible gaps in their ability to inactivate contemporary, multidrug-resistant bacterial pathogens.

Transforming Cross-Linked Cyclic Dimers of KR-12 into Stable and Potent Antimicrobial Drug Leads.

Is it possible to enhance structural stability and biological activity of KR-12, a truncated antimicrobial peptide derived from the human host defense peptide LL-37? Based on the mapping of essential residues in KR-12, we have designed backbone-cyclized dimers, cross-linked via a disulfide bond to improve peptide stability, while at the same time improving on-target activity. Circular dichroism showed that each of the dimers adopts a primarily alpha-helical conformation (55% helical content) when bound to lyso-phosphatidylglycerol micelles, indicating that the helical propensity of the parent peptide is maintained in the new cross-linked cyclic form. Compared to KR-12, one of the cross-linked dimers showed 16-fold more potent antimicrobial activity against human pathogens Pseudomonas aeruginosa, Staphylococcus aureus, and Candida albicans and 8-fold increased activity against Escherichia coli. Furthermore, these peptides retained antimicrobial activity at physiologically relevant conditions, including in the presence of salts and in human serum, and with selective Gram-negative antibacterial activity in rich growth media. In addition to giving further insight into the structure-activity relationship of KR-12, the current work demonstrates that by combining peptide stabilization strategies (dimerization, backbone cyclization, and cross-linking via a disulfide bond), KR-12 can be engineered into a potent antimicrobial peptide drug lead with potential utility in a therapeutic context.

Covalent DNA Binding Is Essential for Gram-Negative Antibacterial Activity of Broad Spectrum Pyrrolobenzodiazepines.

It is urgent to find new antibiotic classes against multidrug-resistant bacteria as the rate of discovery of new classes of antibiotics has been very slow in the last 50 years. Recently, pyrrolobenzodiazepines (PBDs) with a C8-linked aliphatic-heterocycle have been identified as a new broad-spectrum antibiotic class with activity against Gram-negative bacteria. The active imine moiety of the reported lead pyrrolobenzodiazepine compounds was replaced with amide to obtain the non-DNA binding and noncytotoxic dilactam analogues to understand the structure-activity relationship further and improve the safety potential of this class. The synthesised compounds were tested against panels of multidrug-resistant Gram-positive and Gram-negative bacteria, including WHO priority pathogens. Minimum inhibitory concentrations for the dilactam analogues ranged from 4 to 32 mg/L for MDR Gram-positive bacteria, compared to 0.03 to 2 mg/L for the corresponding imine analogues. At the same time, they were found to be inactive against MDR Gram-negative bacteria, with a MIC > 32 mg/L, compared to a MIC of 0.5 to 32 mg/L for imine analogues. A molecular modelling study suggests that the lack of imine functionality also affects the interaction of PBDs with DNA gyrase. This study suggests that the presence of N10-C11 imine moiety is crucial for the broad-spectrum activity of pyrrolobenzodiazepines.

Characteristics of Sargassum plagyophillum Extract as An Active Compound on Non-Alcoholic Hand Sanitizer

Excessive use of non-alcoholic hand sanitizers irritate to the skin, moreover a burning effect, that alternative natural active compound is required, namely Sargassum plagyophillum extract. S. plagyophillum extract contains secondary metabolites that can act as antibacterial and can moisturize the skin. This research aimed to determine the microbiological and physical characteristics of S. plagyophillum of the non-alcoholic hand sanitizer. The sample used in this research was 2% S. plagyophillum extract obtained by maceration using methanol. The production of non-alcoholic hand sanitizers was conducted using other ingredients such as carbopol, triethanolamine, methyl paraben, propilen glycol, and distilled water. The test parameters were testing for gram-positive and gram-negative antibacterial activity, pH, and viscosity. The results showed that non-alcoholic hand sanitizer containing 2% S. plagyophillum extract had characteristics in the form of a gel with gram positive antibacterial activity (Listeria monocytogenes) with an inhibition zone of 2.50 mm, while gram negative antibacterial activity (Pseudomonas aeruginosa) with an inhibition zone of 4.33 mm. Subsequently, the pH value produced from the hand sanitizer containing S. plagyophillum was in accordance with recommended skin pH of 7.33. Meanwhile, based on the value of the viscosity, the hand sanitizer containing S. plagyophillum had a viscosity value according to the viscosity standard, namely 2600 cPs.

Green synthesized pyridazinone derivatives as promising biologically active and anticancer drugs

An efficient synthesis of substituted 4-acetyl-5,6-diphenylpyridazin-3(2H)-one derivatives has been achieved using green chemistry tools such as grinding and microwave heating compared to conventional heating. In this work, 4-acetyl-5,6-diphenylpyridazin-3(2H)-one derivative attached to Schiff-bases, chalcones, pyridine, and pyrrole moieties have been prepared with the aim to possess engaging biological and pharmacological activities. The Schiff-base 2 was obtained by reacting 4-acetyl-5, 6-diphenylpyridazin-3(2H)-one 1 with p-amino acetophenone, and the corresponding chalcones 3a-d were obtained by reacting the Schiff-base 2 with the relevant aldehydes. Novel pyridinyl-pyridazinones 5a-h and pyrrole-pyridazinone derivatives 6a-h were synthesized by the reaction of chalcones 3a-d with different acetyls and aldehydes under grinding, microwave irradiations or under reflux conditions. The synthesized compounds were tested for both Gram-positive and Gram-negative antibacterial activity, antifungal, and anticancer activities. These substances were also evaluated using analytical and spectral data, such as 1HNMR and mass spectrum analysis.

Proteomic response of Escherichia coli to a membrane lytic and iron chelating truncated Amaranthus tricolor defensin

BackgroundPlant defensins are a broadly distributed family of antimicrobial peptides which have been primarily studied for agriculturally relevant antifungal activity. Recent studies have probed defensins against Gram-negative bacteria revealing evidence for multiple mechanisms of action including membrane lysis and ribosomal inhibition. Herein, a truncated synthetic analog containing the γ-core motif of Amaranthus tricolor DEF2 (Atr-DEF2) reveals Gram-negative antibacterial activity and its mechanism of action is probed via proteomics, outer membrane permeability studies, and iron reduction/chelation assays.ResultsAtr-DEF2(G39-C54) demonstrated activity against two Gram-negative human bacterial pathogens, Escherichia coli and Klebsiella pneumoniae. Quantitative proteomics revealed changes in the E. coli proteome in response to treatment of sub-lethal concentrations of the truncated defensin, including bacterial outer membrane (OM) and iron acquisition/processing related proteins. Modification of OM charge is a common response of Gram-negative bacteria to membrane lytic antimicrobial peptides (AMPs) to reduce electrostatic interactions, and this mechanism of action was confirmed for Atr-DEF2(G39-C54) via an N-phenylnaphthalen-1-amine uptake assay. Additionally, in vitro assays confirmed the capacity of Atr-DEF2(G39-C54) to reduce Fe3+ and chelate Fe2+ at cell culture relevant concentrations, thus limiting the availability of essential enzymatic cofactors.ConclusionsThis study highlights the utility of plant defensin γ-core motif synthetic analogs for characterization of novel defensin activity. Proteomic changes in E. coli after treatment with Atr-DEF2(G39-C54) supported the hypothesis that membrane lysis is an important component of γ-core motif mediated antibacterial activity but also emphasized that other properties, such as metal sequestration, may contribute to a multifaceted mechanism of action.

Design, Synthesis and Biological Evaluation of Biphenylglyoxamide-Based Small Molecular Antimicrobial Peptide Mimics as Antibacterial Agents.

There has been an increasing interest in the development of antimicrobial peptides (AMPs) and their synthetic mimics as a novel class of antibiotics to overcome the rapid emergence of antibiotic resistance. Recently, phenylglyoxamide-based small molecular AMP mimics have been identified as potential leads to treat bacterial infections. In this study, a new series of biphenylglyoxamide-based small molecular AMP mimics were synthesised from the ring-opening reaction of N-sulfonylisatin bearing a biphenyl backbone with a diamine, followed by the conversion into tertiary ammonium chloride, quaternary ammonium iodide and guanidinium hydrochloride salts. Structure–activity relationship studies of the analogues identified the octanesulfonyl group as being essential for both Gram-positive and Gram-negative antibacterial activity, while the biphenyl backbone was important for Gram-negative antibacterial activity. The most potent analogue was identified to be chloro-substituted quaternary ammonium iodide salt 15c, which possesses antibacterial activity against both Gram-positive (MIC against Staphylococcus aureus = 8 μM) and Gram-negative bacteria (MIC against Escherichia coli = 16 μM, Pseudomonas aeruginosa = 63 μM) and disrupted 35% of pre-established S. aureus biofilms at 32 μM. Cytoplasmic membrane permeability and tethered bilayer lipid membranes (tBLMs) studies suggested that 15c acts as a bacterial membrane disruptor. In addition, in vitro toxicity studies showed that the potent compounds are non-toxic against human cells at therapeutic dosages.

Discovery and Optimization of Phosphopantetheine Adenylyltransferase Inhibitors with Gram-Negative Antibacterial Activity.

In the preceding manuscript [ Moreau et al. 2018 , 10.1021/acs.jmedchem.7b01691 ] we described a successful fragment-based lead discovery (FBLD) strategy for discovery of bacterial phosphopantetheine adenylyltransferase inhibitors (PPAT, CoaD). Following several rounds of optimization two promising lead compounds were identified: triazolopyrimidinone 3 and 4-azabenzimidazole 4. Here we disclose our efforts to further optimize these two leads for on-target potency and Gram-negative cellular activity. Enabled by a robust X-ray crystallography system, our structure-based inhibitor design approach delivered compounds with biochemical potencies 4-5 orders of magnitude greater than their respective fragment starting points. Additional optimization was guided by observations on bacterial permeability and physicochemical properties, which ultimately led to the identification of PPAT inhibitors with cellular activity against wild-type E. coli.

Compound design guidelines for evading the efflux and permeation barriers of Escherichia coli with the oxazolidinone class of antibacterials: Test case for a general approach to improving whole cell Gram-negative activity

Previously we reported the results from an effort to improve Gram-negative antibacterial activity in the oxazolidinone class of antibiotics via a systematic medicinal chemistry campaign focused entirely on C-ring modifications. In that series we set about testing if the efflux and permeation barriers intrinsic to the outer membrane of Escherichia coli could be rationally overcome by designing analogs to reside in specific property limits associated with Gram-negative activity: i) low MW (<400), ii) high polarity (clogD7.4 <1), and iii) zwitterionic character at pH 7.4. Indeed, we observed that only analogs residing within these limits were able to overcome these barriers. Herein we report the results from a parallel effort where we explored structural changes throughout all three rings in the scaffold for the same purpose. Compounds were tested against a diagnostic MIC panel of Escherichia coli and Staphylococcus aureus strains to determine the impact of combining structural modifications in overcoming the OM barriers and in bridging the potency gap between the species. The results demonstrated that distributing the charge-carrying moieties across two rings was also beneficial for avoidance of the outer membrane barriers. Importantly, analysis of the structure-permeation relationship (SPR) obtained from this and the prior study indicated that in addition to MW, polarity, and zwitterionic character, having ≤4 rotatable bonds is also associated with evasion of the OM barriers. These combined results provide the medicinal chemist with a framework and strategy for overcoming the OM barriers in GNB in antibacterial drug discovery efforts.

Discovery and characterization of a novel class of pyrazolopyrimidinedione tRNA synthesis inhibitors.

A high-throughput phenotypic screen for novel antibacterial agents led to the discovery of a novel pyrazolopyrimidinedione, PPD-1, with preferential activity against methicillin-resistant Staphylococcus aureus (MRSA). Resistance mapping revealed the likely target of inhibition to be lysyl tRNA synthetase (LysRS). Preliminary structure-activity relationship (SAR) studies led to an analog, PPD-2, which gained Gram-negative antibacterial activity at the expense of MRSA activity and resistance to this compound mapped to prolyl tRNA synthetase (ProRS). These targets of inhibition were confirmed in vitro, with PPD-1 showing IC₅₀s of 21.7 and 35 μM in purified LysRS and ProRS enzyme assays, and PPD-2, 151 and 0.04 μM, respectively. The highly attractive chemical properties of these compounds combined with intriguing preliminary SAR suggest that further exploration of this compelling novel series is warranted.

Pyrrolopyrimidine inhibitors of DNA gyrase B (GyrB) and topoisomerase IV (ParE), Part II: Development of inhibitors with broad spectrum, Gram-negative antibacterial activity

The structurally related bacterial topoisomerases DNA gyrase (GyrB) and topoisomerase IV (ParE) have long been recognized as prime candidates for the development of broad spectrum antibacterial agents. However, GyrB/ParE targeting antibacterials with spectrum that encompasses robust Gram-negative pathogens have not yet been reported. Using structure-based inhibitor design, we optimized a novel pyrrolopyrimidine inhibitor series with potent, dual targeting activity against GyrB and ParE. Compounds were discovered with broad antibacterial spectrum, including activity against Pseudomonas aeruginosa, Acinetobacter baumannii and Escherichia coli. Herein we describe the SAR of the pyrrolopyrimidine series as it relates to key structural and electronic features necessary for Gram-negative antibacterial activity.

Pyridone Methylsulfone Hydroxamate LpxC Inhibitors for the Treatment of Serious Gram-Negative Infections

The synthesis and biological activity of a new series of LpxC inhibitors represented by pyridone methylsulfone hydroxamate 2a is presented. Members of this series have improved solubility and free fraction when compared to compounds in the previously described biphenyl methylsulfone hydroxamate series, and they maintain superior Gram-negative antibacterial activity to comparator agents.

Preparation, gram-negative antibacterial activity, and hydrolytic stability of novel siderophore-conjugated monocarbam diols.

A novel series of monocarbam compounds exhibiting promising antibacterial activity against multidrug resistant Gram-negative microorganisms is reported, along with the synthesis of one such molecule MC-1 (1). Also reported are structure-activity relationships associated with the in vitro and in vivo efficacy of 1 and related analogues in addition to the hydrolytic stability of such compounds and possible implications thereof.

Desirability-Based Methods of Multiobjective Optimization and Ranking for Global QSAR Studies. Filtering Safe and Potent Drug Candidates from Combinatorial Libraries

Up to now, very few applications of multiobjective optimization (MOOP) techniques to quantitative structure-activity relationship (QSAR) studies have been reported in the literature. However, none of them report the optimization of objectives related directly to the final pharmaceutical profile of a drug. In this paper, a MOOP method based on Derringer's desirability function that allows conducting global QSAR studies, simultaneously considering the potency, bioavailability, and safety of a set of drug candidates, is introduced. The results of the desirability-based MOOP (the levels of the predictor variables concurrently producing the best possible compromise between the properties determining an optimal drug candidate) are used for the implementation of a ranking method that is also based on the application of desirability functions. This method allows ranking drug candidates with unknown pharmaceutical properties from combinatorial libraries according to the degree of similarity with the previously determined optimal candidate. Application of this method will make it possible to filter the most promising drug candidates of a library (the best-ranked candidates), which should have the best pharmaceutical profile (the best compromise between potency, safety and bioavailability). In addition, a validation method of the ranking process, as well as a quantitative measure of the quality of a ranking, the ranking quality index (Psi), is proposed. The usefulness of the desirability-based methods of MOOP and ranking is demonstrated by its application to a library of 95 fluoroquinolones, reporting their gram-negative antibacterial activity and mammalian cell cytotoxicity. Finally, the combined use of the desirability-based methods of MOOP and ranking proposed here seems to be a valuable tool for rational drug discovery and development.

Synthesis and SAR of novel conformationally restricted oxazolidinones possessing Gram-positive and fastidious Gram-negative antibacterial activity. Part 2: Amino substitutions on heterocyclic D-ring system

A novel series of conformationally restricted oxazolidinones was synthesized, in which the heterocyclic D ring was substituted with various amino groups. Several analogs exhibited potent activity against both Gram-positive and fastidious Gram-negative organisms. Certain amino-substituted analogs also exhibited improved aqueous solubility compared to the corresponding un-substituted heterocyclic D-ring analogs.

Synthesis and SAR of novel conformationally-restricted oxazolidinones possessing Gram-positive and fastidious Gram-negative antibacterial activity. Part 1: Substituted pyrazoles

A novel series of conformationally-restricted oxazolidinones was synthesized which possess a fused pyrazole ring substituted with various alkyl, aryl and heteroaryl substituents. A number of analogs exhibited potent activity against both Gram-positive and fastidious Gram-negative organisms.

Structurally designed novel furogamma lactams as inhibitors for bacterial propagations

Some novel furogamma lactams have been synthesised by one step condensation of arylaminomalonates with substituted furyl acryloyl chlorides. The annulation of substituted monocyclic gammalactams followed by cyclization produced novel tricyclic furogamma lactams. Some of these furogammalactams are found to exhibit Gram-positive and Gram-negative antibacterial activity at very high concentrations.

6 alpha-hydroxypenicillanic acid-S(S)-oxide and analogues: synthesis and antimicrobial activity.

The synthesis and in vitro antibacterial activity of a series of 6-oxygenated penicillanic acid sulfoxides is described. 6 alpha-Hydroxypenicillanic acid-S(S)-oxide (1a) exhibits weak Gram-negative antibacterial activity and appears to be similar to amdinocillin (5) in its mode of action. 6 alpha-Hydroxypenicillanic acid-S(R)-oxide (4a) has a broader spectrum of activity, but again is rather weak. The corresponding 6 beta-hydroxy series is essentially devoid of activity.

ChemInform Abstract: MESOIONIC PYRIDAZINE RIBONUCLEOSIDES. A NOVEL BIOLOGICALLY ACTIVE NUCLEOSIDE METABOLITE

AbstractDargestellt und auf antibakterielle Wirkung getestet werden die Verbindungen (IV) und (V).