Antibiotics for emerging pathogens

Suppression of antibiotic resistance evolution by single-gene deletion

Antibiotic treatment generally results in the selection of resistant bacterial strains, and the dynamics of resistance evolution is dependent on complex interactions between cellular components. To better characterize the mechanisms of antibiotic resistance and evaluate its dependence on gene regulatory networks, we performed systematic laboratory evolution of Escherichia coli strains with single-gene deletions of 173 transcription factors under three different antibiotics. This resulted in the identification of several genes whose deletion significantly suppressed resistance evolution, including arcA and gutM. Analysis of double-gene deletion strains suggested that the suppression of resistance evolution caused by arcA and gutM deletion was not caused by epistatic interactions with mutations known to confer drug resistance. These results provide a methodological basis for combinatorial drug treatments that may help to suppress the emergence of resistant pathogens by inhibiting resistance evolution.

Structure and mechanism of a redesigned multidrug transporter from the Major Facilitator Superfamily

The rapid increase of multidrug resistance poses urgent threats to human health. Multidrug transporters prompt multidrug resistance by exporting different therapeutics across cell membranes, often by utilizing the H⁺ electrochemical gradient. MdfA from Escherichia coli is a prototypical H⁺ -dependent multidrug transporter belonging to the Major Facilitator Superfamily. Prior studies revealed unusual flexibility in the coupling between multidrug binding and deprotonation in MdfA, but the mechanistic basis for this flexibility was obscure. Here we report the X-ray structures of a MdfA mutant E26T/D34M/A150E, wherein the multidrug-binding and protonation sites were revamped, separately bound to three different substrates at resolutions up to 2.0 Å. To validate the functional relevance of these structures, we conducted mutational and biochemical studies. Our data elucidated intermediate states during antibiotic recognition and suggested structural changes that accompany the substrate-evoked deprotonation of E26T/D34M/A150E. These findings help to explain the mechanistic flexibility in drug/H⁺ coupling observed in MdfA and may inspire therapeutic development to preempt efflux-mediated antimicrobial resistance.

Colorimetric Assay of Bacterial Pathogens Based on Co3O4 Magnetic Nanozymes Conjugated with Specific Fusion Phage Proteins and Magnetophoretic Chromatography

It is important to detect pathogens rapidly, sensitively, and selectively for clinical medicine, homeland security, food safety, and environmental control. We report here a specific and sensitive colorimetric assay that incorporated a bovine serum albumin-templated Co₃O₄ magnetic nanozyme (Co₃O₄ MNE) with a novel specific fusion phage protein and magnetophoretic chromatography to detect Staphylococcus aureus. The Co₃O₄ MNE was conjugated to S. aureus-specific fusion-pVIII (Co₃O₄ MNE@fusion-pVIII), screened from the S. aureus-specific phage AQTFLGEQD (the phage monoclone is denoted by the peptide sequence). The as-prepared triple-functional Co₃O₄ MNE@fusion-pVIII particles were capable of capturing S. aureus in sterile milk, which were then isolated from milk magnetically. Assisted by polyethylene glycol, the Co₃O₄ MNE@fusion-pVIII@S. aureus complex was separated from the free Co₃O₄ MNE@fusion-pVIII by magnetophoretic chromatography in an external magnetic field. After transferring the isolated Co₃O₄ MNE@fusion-pVIII@S. aureus complexes into a 96-well plate, diammonium salt of 2,2'-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid) and H₂O₂ were added to develop color because of the peroxidase mimetics activity of the Co₃O₄ MNE. A S. aureus concentration within 10-10,000 cfu/mL in milk can be detected (detection limit: 8 cfu/mL). The as-developed method is simple, cost-efficient, and sensitive, which is useful for rapidly diagnosing pathogenic bacteria and helpful to prevent disease outbreaks induced by pathogens in developing countries.

Poly(lactic-co-glycolic) Acid-Lipid Hybrid Microparticles Enhance the Intracellular Uptake and Antibacterial Activity of Rifampicin

An urgent demand exists for the development of effective carrier systems that systematically enhance the cellular uptake and localization of antibiotic drugs for the treatment of intracellular pathogens. Commercially available antibiotics suffer from poor cellular penetration, restricting their efficacy against pathogens hosted and protected within phagocytic cells. In this study, the potency of the antibiotic rifampicin against intracellular small colony variants of Staphylococcus aureus was improved through encapsulation within a strategically engineered cell-penetrant delivery system, composed of lipid nanoparticles encapsulated within a poly(lactic-co-glycolic) acid (PLGA) nanoparticle matrix. PLGA-lipid hybrid (PLH) microparticles were synthesized through the process of spray drying, whereby rifampicin was loaded within both the polymer and lipid phases, to create a nanoparticle-in-microparticle system capable of efficient redispersion in aqueous biorelevant media and with programmable release kinetics. The ability of PLH particles to disintegrate into nanoscale agglomerates of the precursor nanoparticles was shown to be instrumental in optimizing rifampicin uptake in RAW264.7 macrophages, with a 7.2- and 1.6-fold increase in cellular uptake, when compared to the pure drug and PLGA microparticles (of an equivalent initial particle size), respectively. The enhanced phagocytosis and extended drug release mechanism (under the acidic macrophage environment) associated with PLH particles induced a 2.5-log reduction in colony forming units compared to initial colonies at 2.50 μg/mL rifampicin dose. Thus, the ability of PLH particles to reduce the intracellular viability of S. aureus, without demonstrating significant cellular toxicity, satisfies the requirements necessary for the safe and efficacious delivery of antibiotics to macrophages for the treatment of intracellular infections.

A Glycosylated Cationic Block Poly(β-peptide) Reverses Intrinsic Antibiotic Resistance in All ESKAPE Gram-Negative Bacteria

Carbapenem-resistant Gram-negative bacteria (GNB) are heading the list of pathogens for which antibiotics are the most critically needed. Many antibiotics are either unable to penetrate the outer-membrane or are excluded by efflux mechanisms. Here, we report a cationic block β-peptide (PAS8-b-PDM12) that reverses intrinsic antibiotic resistance in GNB by two distinct mechanisms of action. PAS8-b-PDM12 does not only compromise the integrity of the bacterial outer-membrane, it also deactivates efflux pump systems by dissipating the transmembrane electrochemical potential. As a result, PAS8-b-PDM12 sensitizes carbapenem- and colistin-resistant GNB to multiple antibiotics in vitro and in vivo. The β-peptide allows the perfect alternation of cationic versus hydrophobic side chains, representing a significant improvement over previous antimicrobial α-peptides sensitizing agents. Together, our results indicate that it is technically possible for a single adjuvant to reverse innate antibiotic resistance in all pathogenic GNB of the ESKAPE group, including those resistant to last resort antibiotics.

Chalcones, stilbenes and ketones have anti-infective properties via inhibition of bacterial drug-efflux and consequential synergism with antimicrobial agents

With antimicrobial resistance creating a major public health crisis, the designing of novel antimicrobial compounds that effectively combat bacterial infection is becoming increasingly critical. Interdisciplinary approaches integrate the best features of whole-cell phenotypic evaluation to validate novel therapeutic targets and discover new leads to combat antimicrobial resistance. In this project, whole-cell phenotypic evaluation such as testing inhibitors on bacterial growth, viability, efflux pump, biofilm formation and their interaction with other drugs were performed on a panel of Gram-positive, Gram-negative and acid-fast group of bacterial species. This enabled additional antimicrobial activities of compounds belonging to the flavonoid family including ketones, chalcones and stilbenes, to be identified. Flavonoids have received renewed attention in literature over the past decade, and a variety of beneficial effects of these compounds have been illuminated, including anti-cancer, anti-inflammatory, anti-tumour as well as anti-fungal and anti-bacterial. However, their mechanisms of action are yet to be identified. In this paper, we found that the compounds belonging to the flavonoid family exerted a range of anti-infective properties being identified as novel efflux pump inhibitors, whilst offering the opportunity to be used in combination therapy. The compound 2-phenylacetophenone displayed broad-spectrum efflux pump inhibition activity, whilst trans-chalcone, displayed potent activity against Gram-negative and mycobacterial efflux pumps causing inhibition higher than known potent efflux pump inhibitors, verapamil and chlorpromazine. Drug-drug interaction studies also highlighted that 2-phenylacetophenone not only has the potential to work additively with known antibacterial agents that affect the cell-wall and DNA replication but also trans-chalcone has the potential to work synergistically with anti-tubercular agents. Overall, this paper shows how whole-cell phenotypic analysis allows for the discovery of new antimicrobial agents and their consequent mode of action whilst offering the opportunity for compounds to be repurposed, in order to contribute in the fight against antimicrobial resistance.

Insight into the screening of potential beta-lactamase inhibitors as anti-bacterial chemical agents through pharmacoinformatics study

Drug resistance is an unsolved and major concern in the bacterial infection. Continuous development of drug-resistance to the antibiotics exponentially rises the danger of bacterial infections. Chemical components from the plants are becoming a major resource of potentially effective therapeutic chemical agents for the wide range of diseases including bacterial infections. In the current study, pharmacoinformatics methodologies were implemented on more than two hundred known phytochemicals to find promising beta-lactamase inhibitors for therapeutically effective anti-bacterial agents. Initially, the molecular docking-based score was used to reduce the chemical space of the selected dataset. Fourteen molecules were found to have more affinity towards the beta-lactamase in compared to the well-known anti-bacterial agent, Avibactam. Binding interactions analysis revealed the strong binding interactions between phytochemicals and catalytic amino residues. For further analysis, molecular dynamics (MD) simulations, density functional theory (DFT) and in silico pharmacokinetics studies were performed. Parameters from MD simulations studies suggested that selected molecules are strong enough to retain in the active site in different orientations of the beta-lactamase. The orbital energies obtained from the DFT study was undoubtedly explained the potentiality of the selected compounds for being effective beta-lactamase inhibitors. The drug-likeness and acceptable pharmacokinetics parameters were observed using in silico ADME analysis. Therefore, observations from the multiple pharmacoinformatics approach explained without any doubt that selected molecules are potential enough being promising anti-bacterial compounds. [Formula: see text] Communicated by Ramaswamy H. Sarma.

Cationic Organic Nanoaggregates as AIE Luminogens for Wash-Free Imaging of Bacteria and Broad-Spectrum Antimicrobial Application

The increase in the use of bactericides is a matter of grave concern and a serious threat to human health. The present situation demands rapid and efficient detection and elimination of antibiotic-resistant microbes. Herein, we report the synthesis of a simple C₃-symmetric molecular system (TGP) with an intrinsic positive charge through a single-step Schiff base condensation. In a water-dimethyl sulfoxide (DMSO) solvent mixture (80:20 v/v), TGP molecules self-aggregate to form spherical nanoparticles with a positively charged surface that displays efficient fluorescence owing to the aggregation-induced emission (AIE) phenomenon. Both Gram-positive and Gram-negative bacteria could be effectively detected through "turn-off" fluorescence spectroscopy as the electrostatic interaction of the resultant nanoaggregates with the negatively charged bacterial surface induced quenching of fluorescence of the nanoparticles. The fluorescence analysis and steady-state lifetime studies of TGP nanoparticles suggest that a nonradiative decay through photoinduced electron transfer from the nanoparticles to the bacterial surface leads to effective fluorescence quenching. Further, the TGP nanoaggregates demonstrate potent antimicrobial activity against microbes such as multidrug-resistant bacteria and fungi at a concentration as low as 74 μg/mL. A combination of factors including ionic surface characteristics of the nanoparticles for strong electrostatic binding on the bacterial surface followed by possible photoinduced electron transfer from the nanoaggregates to the bacterial membrane and enhanced oxidative stress in the membrane resulting from reactive oxygen species (ROS) generation is found accountable for the high antimicrobial activity of the TGP nanoparticles. The effective disruption of membrane integrity in both Gram-positive and Gram-negative bacteria upon interaction with the nanoaggregates can be observed from field emission scanning electron microscopy (FESEM) studies. The development of simple pathways for the molecular design of multifunctional broad-spectrum antimicrobial systems for rapid and real-time detection, wash-free imaging, and eradication of drug-resistant microbes might be crucial to combat pathogenic agents.

Multifunctional Antimicrobial Biometallohydrogels Based on Amino Acid Coordinated Self-Assembly

There is a real need for new antibiotics against self-evolving bacteria. One option is to use biofriendly broad-spectrum and mechanically tunable antimicrobial hydrogels that can combat multidrug-resistant microbes. Whilst appealing, there are currently limited options. Herein, broad-spectrum antimicrobial biometallohydrogels based on the self-assembly and local mineralization of Ag⁺ -coordinated Fmoc-amino acids are reported. Such biometallohydrogels have the advantages of localized delivery and sustained release, reduced drug dosage and toxicity yet improved bioavailability, prolonged drug effect, and tunable mechanical strength. Furthermore, they can directly interact with the cell walls and membrane, resulting in the detachment of the plasma membrane and leakage of the cytoplasm. This leads to cell death, triggering a significant antibacterial effect against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria in cells and mice. This study paves the way for developing a multifunctional integration platform based on simple biomolecules coordinated self-assembly toward a broad range of biomedical applications.

Structure-based design of guanosine analogue inhibitors targeting GTP cyclohydrolase IB towards a new class of antibiotics

GTP cyclohydrolase (GCYH-I) is an enzyme in the folate biosynthesis pathway that has not been previously exploited as an antibiotic target, although several pathogens including N. gonorrhoeae use a form of the enzyme GCYH-IB that is structurally distinct from the human homologue GCYH-IA. A comparison of the crystal structures of GCYH-IA and -IB with the nM inhibitor 8-oxo-GTP bound shows that the active site of GCYH-IB is larger and differently shaped. Based on this structural information, we designed and synthesized a small set of 8-oxo-G derivatives with ether linkages at O⁶ and O⁸ expected to displace water molecules from the expanded active site of GCYH-IB. The most potent of these compounds, G3, is selective for GCYH-IB, supporting the premise that potent and selective inhibitors of GCYH-IB could constitute a new class of small molecule antibiotics.

Suppression of the SOS response modifies spatiotemporal evolution, post-antibiotic effect, bacterial fitness and biofilm formation in quinolone-resistant Escherichia coli

Background

Suppression of the SOS response has been proposed as a therapeutic strategy for potentiating quinolones against susceptible, low-level quinolone-resistant (LLQR) and resistant Enterobacteriaceae.

Objectives

To monitor the functionality of the SOS response in the evolution towards clinical quinolone resistance and study its impact on the evolution of spatiotemporal resistance.

Methods

An isogenic collection of Escherichia coli (derived from the strain ATCC 25922) carrying combinations of chromosomally and plasmid-mediated quinolone resistance mechanisms (including susceptible, LLQR and resistant phenotypes) and exhibiting a spectrum of SOS activity was used. Relevant clinical parameters such as mutation rate, mutant prevention concentration (MPC), bacterial fitness, biofilm formation and post-antibiotic effect (PAE) were evaluated.

Results

Inactivating the SOS response (recA deletion) led to a decrease in mutation rate (∼103 fold) in LLQR compared with WT strains at ciprofloxacin concentrations of 1 mg/L (the EUCAST breakpoint for resistance) and 2.5 mg/L (Cmax), as well as a remarkable delay in the spatiotemporal evolution of quinolone resistance. For all strains, there was an 8-fold decrease in MPC in RecA-deficient strains, with values for LLQR strains decreasing below the Cmax of ciprofloxacin. Inactivation of the SOS response reduced competitive fitness by 33%-50%, biofilm production by 22%-80% and increased the PAE by ∼3-4 h at sub-MIC concentrations of ciprofloxacin.

Conclusions

Our data indicate that suppression of the SOS response affects key bacterial traits and is a promising strategy for reversing and tackling the evolution of antibiotic resistance in E. coli, including low-level and resistant phenotypes at therapeutic quinolone concentrations.

Heterologous production of porcine derived antimicrobial peptide PR-39 in Escherichia coli using SUMO and intein fusion systems

About half a century after antibiotics discovery, multi-antibiotic-resistant bacteria posed a new challenge to medicine. Attempts to discover new antibiotics have drawn the attention to Antimicrobial Peptides (AMPs). The rapid growth, besides its known genetic and manipulation systems, makes E. coli the preferred host system for production of recombinant proteins on an industrial scale. To produce AMPs in E. coli, the application of fusion-tags with the aim of stability, solubility, and prevention of antimicrobial activity is one of the best practices in this regard. In this study, we presented two different expression systems for the production of PR-39 in E. coli; one in fusion with intein-Chitin binding domain (CBD) and another in fusion with SUMO accompanied by polyhistidine affinity tag. Both were cloned in the NdeI-XhoI sites of pET-17b and transformed to E. coli BL21 (DE3) pLysS. Recombinant bacteria were cultured and induced with 0.4 mM IPTG at 30 °C. Expression and purification of target proteins were confirmed by Tricine- SDS-PAGE and dot blot analysis. Recovery of 250 μg PR-39/L from SUMO fusion system and 280 μg PR-39/L from the intein fusion system was achieved. Both purified peptides showed antibacterial activity using MIC/MBC demonstrating their functionality after SUMO and intein mediated purification.

Zn2+-assisted photothermal therapy for rapid bacteria-killing using biodegradable humic acid encapsulated MOFs

Bacterial infection is seriously threatening human health all over the world, especially with the emergence of increasing drug-fast bacteria. It is urgent to develop a drug-free strategy to kill bacteria rapidly and efficiently. In this work, humic acid (HuA) encapsulated zeolitic imidazole framework-8 (ZIF-8) (HuA@ZIF-8) nanocomposites are synthesized by the in-situ growth of ZIF-8 on the surface of polyvinylpyrrolidone (PVP)-modified HuA. The synthesized nanocomposites possesses good photothermal effects, i.e., the temperature increased to 59.4 °C under the particle concentration of 1000 μg/mL with 10 min NIR irradiation. In addition, NIR irradiation can also control the release of Zn²⁺ from the composites. The good photothermal effects originate from HuA that can effectively absorb NIR light. The controlled release of Zn²⁺ is ascribed to the induced-dissociation of ZIF-8 under NIR light irradiation. The synergistic action of photothermal therapy and release of zinc ions contributes to the excellent antibacterial efficiency of HuA@ZIF-8 within a short time, i.e. 99.59 % and 99.37 % against Staphylococcus aureus and Escherichia coli with 20 min NIR irradiation, respectively. This work provides a promising strategy to develop a light-responsive platform with good biodegradability and low cost for rapid and effective sterilization.

Gold-Decorated M13 I-Forms and S-Forms for Targeted Photothermal Lysis of Bacteria

With the emergence of multidrug-resistant bacteria, photothermal therapy has been proposed as an alternative to antibiotics for targeting and killing pathogens. In this study, two M13 bacteriophage polymorphs were studied as nanoscaffolds for plasmonic bactericidal agents. Receptor-binding proteins found on the pIII minor coat protein targeted Escherichia coli bacteria with F-pili (F⁺ strain), while a gold-binding peptide motif displayed on the pVIII major coat protein templated Au nanoparticles. Temperature-dependent exposure to a chloroform-water interface transformed the native filamentous phage into either rod-like or spheroid structures. The morphology, geometry, and size of the polymorphs, as well as the receptor-binding protein and host cell receptor interaction were studied using electron microscopy. Au/template structures were formed through incubation with Au colloid, and optical absorbance was measured. Despite the closely packed Au nanoparticle layer on the surface the viral scaffolds, electron microscopy confirmed that host receptor affinity was retained. Photothermal bactericidal studies were performed using 532 nm laser irradiation with a variety of powers and exposure times. Bacterial viability was assessed using colony count. With the shape-modified M13 scaffolds, up to 64% of E. coli were killed within 20 min. These studies demonstrate the promise of i-form and s-form polymorphs for the directed plasmonic-based photothermal killing of bacteria.

A Supramolecular Trap to Increase the Antibacterial Activity of Colistin

A strong interaction between colistin, a last‐resort antibiotic of the polymyxin family, and free lipopolysaccharide (LPS, also referred to as endotoxin), released from the Gram‐negative bacterial (GNB) outer membrane (OM), has been identified that can decrease the antibacterial efficacy of colistin, potentially increasing the dose of this antibiotic required for treatment. The competition between LPS in the GNB OM and free LPS for the interaction with colistin was prevented by using a supramolecular trap to capture free LPS. The supramolecular trap, fabricated from a subnanometer gold nanosheet with methyl motifs (SAuM), blocks lipid A, preventing the interaction between lipid A and colistin. This can minimize endotoxemia and maximize the antibacterial efficacy of colistin, enabling colistin to be used at lower doses. Thus, the potential crisis of colistin resistance could be avoided.

Exploration of (3-benzyl-5-hydroxyphenyl)carbamates as new antibacterial agents against Gram-positive bacteria

A series of (3-benzyl-5-hydroxyphenyl)carbamates were evaluated as new antibacterial agents. Several compounds showed potent inhibitory activity against sensitive and drug-resistant Gram-positive bacteria. The compounds are ineffective against all tested Gram-negative bacteria. The structure of the ester group exerted a profound effect on antibacterial activity. 4,4-Dimethylcyclohexanyl carbamate 6h exhibited the most potent inhibitory activity against the standard and clinically isolated Staphylococcus aureus, Staphylococcus epidermidis, and Enterococcus faecalis (minimum inhibitory concentration = 4-8 µg/ml) strains. The preliminary experimental evidence indicated that these carbamates target the bacterial cell wall and share a similar mechanism of action with vancomycin.

Hospital wastewater treatment scenario around the globe

Wastewaters generated from hospitals contain pharmaceuticals residues, pathogens, chemical reagents, radionuclide, and other harmful matter. The wastewater characteristics, quantity, and handling methods have not only variations among countries but also within a country. Some hazardous substances of hospital wastewaters (HWWs) may have a regulatory status and should be treated accordingly while others have characteristics similar to that of domestic sewage. At a global level, guidelines do exist for treatment of these HWWs. But literatures have shown that legislation has various loopholes in implementation. This chapter outlines the current status of management and handling of HWWs around the major industrial hubs of worlds in two categories of developed (the United States, United Kingdom, and Europe) and developing (India, China, Iran, and Bangladesh) countries. Various literatures and guidelines of these countries have been referred which mainly highlight different treatment scenarios and status of coverage of HWW management guidelines.

Three new compounds from the flower branch of Gastrodia elata Blume and anti-microbial activity

Three new compounds (1–3): gastrodinol (1), 2-(4′-hydroxybenzoyl)-3-hydroxyethyl indole (2) and 2-(4′-hydroxybenzoyl)-3-(4′′-hydroxybenzyl)indole (3) were isolated from the flower branch of G. elata, and anti-microbial activity.

Evolving Antibiotics against Resistance: a Potential Platform for Natural Product Development?

To avoid an antibiotic resistance crisis, we need to develop antibiotics at a pace that matches the rate of evolution of resistance. However, the complex functions performed by antibiotics-combining, e.g., penetration of membranes, counteraction of resistance mechanisms, and interaction with molecular targets-have proven hard to achieve with current methods for drug development, including target-based screening and rational design. Here, we argue that we can meet the evolution of resistance in the clinic with evolution of antibiotics in the laboratory. On the basis of the results of experimental evolution studies of microbes in general and antibiotic production in Actinobacteria in particular, we propose methodology for evolving antibiotics to circumvent mechanisms of resistance. This exploits the ability of evolution to find solutions to complex problems without a need for design. We review evolutionary theory critical to this approach and argue that it is feasible and has important advantages over current methods for antibiotic discovery.

Albumin Broadens the Antibacterial Capabilities of Nonantibiotic Small Molecule-Capped Gold Nanoparticles

Nonantibiotic small molecule-modified gold nanoparticles (Au NPs) show great potential as an alternative for commercial antibiotics, yet their narrow antibacterial spectrum hinders the wide application in clinics. We observe that Au NPs cofunctionalized with both bovine serum albumin (BSA) and 4,6-diamino-2-pyrimidinethiol (DAPT) can generate conjugates (Au_DAPT_BSA) with progressive antimicrobial activities, including decreased minimal inhibitory concentration against Gram-negative bacteria and extended antibacterial spectrum against Gram-positive bacteria compared with DAPT-capped Au NPs (Au_DAPT). Au_DAPT_BSA induces no drug resistance and can significantly decrease the number of bacteria in the biofilms formed by Pseudomonas aeruginosa and Staphylococcus aureus. In addition, Au_DAPT_BSA exhibit in vivo healing efficiency for mice with subcutaneous abscesses caused by clinically isolated, multidrug resistant Escherichia coli or S. aureus without inducing detectable toxicity to the mammalian cells/animals. Our findings provide a new strategy for strengthening nanomaterial-based bactericides such as Au NPs, especially against drug-resistant bacterial infections.

Electrospun nanofibers of polyelectrolyte-surfactant complexes for antibacterial wound dressing application

The development of polyelectrolyte-surfactant complexes (PESCs) has attracted extensive research interest in different fields of applications. However, the liquid state of PESCs has limited their utility in applications where solid materials are required. In this study, novel antibacterial fibers were fabricated via electrospinning PESCs in the solid state without any additives. The PESCs were prepared in aqueous mixtures of pre-hydrolyzed polyacrylonitrile (HPAN), a polyelectrolyte, and cetyltrimethyl ammonium chloride (CTAC), an antibacterial cationic surfactant, by taking advantage of the self-aggregation behavior of the polyelectrolyte and surfactant, which increased the antibacterial agent loading ability and, thus, the antibacterial activity of polymers. By release-killing and contact-killing mechanisms, the as-spun PESC nanofibrous membranes exhibited strong antibacterial ability against both Gram-positive and Gram-negative bacteria, killing 5 log CFU of E. coli and S. aureus within a contact time as short as 30 min. Furthermore, PESCs were blended with polycaprolactone (PCL) to prepare composite nanofibrous membranes as a novel wound dressing, which showed excellent antibacterial activity and favorable cytocompatibility, with the mechanical strength high enough to satisfy the clinical application requirements. The PESC fibers with durable antibacterial activity presented in the current work would be promising for medical applications.

Mitigation of acyl-homoserine lactone (AHL) based bacterial quorum sensing, virulence functions, and biofilm formation by yttrium oxide core/shell nanospheres: Novel approach to combat drug resistance

The present study evaluated the efficacy of Y2O3:Tb (core) and Y2O3:Tb@SiO2 nanospheres (core/shell NSs) against virulence functions regulated by quorum sensing (QS) and biofilm formation in pathogenic bacteria. Scanning electron microscope (SEM) images were used to study the size, shape, and morphology. The images clearly displayed spherical shaped, mono-dispersed particles with narrow size distribution and an average grain size of 110-130 nm. The chemical composition of the samples was determined by using energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS). We determined the impact of core and core/shell NSs on QS using sensor strains of Chromobacterium violaceum CVO26 and Pseudomonas aeruginosa PAO1 in a comparative study. Sub-MICs of core and core/shell NSs substantially suppressed QS-controlled violacein production in C. violaceum. Similar concentration-dependent effect of sub-MICs of synthesized core and core/shell NSs was observed in the QS-regulated virulence functions (elastase, total protease, pyocyanin production, swarming motility, and exopolysaccharide production) in PAO1. A concentration-dependent decrease (14-60%) was recorded in the biofilm forming capability of PAO1, upon treatment with core and core/shell NSs. Moreover, core/shell NSs were more effective in inhibiting biofilm at higher tested concentrations as compared to core-NSs. The synthesized NSs demonstrated significantly impaired attachment of cells to the microtiter plate indicating that NSs target biofilm inhibition at the attachment stage. Based on these results, we predict that core and core/shell NSs may be an alternative to combat the threat of drug-resistant pathogenic bacteria.

Structural Requirements of N-alpha-Mercaptoacetyl Dipeptide (NAMdP) Inhibitors of Pseudomonas Aeruginosa Virulence Factor LasB: 3D-QSAR, Molecular Docking, and Interaction Fingerprint Studies

The zinc metallopeptidase Pseudomonas elastase (LasB) is a virulence factor of Pseudomonas aeruginosa (P. aeruginosa), a pathogenic bacterium that can cause nosocomial infections. The present study relates the structural analysis of 118 N-alpha-mercaptoacetyl dipeptides (NAMdPs) as LasB inhibitors. Field-based 3D-QSAR and molecular docking methods were employed to describe the essential interactions between NAMdPs and LasB binding sites, and the chemical features that determine their differential activities. We report a predictive 3D-QSAR model that was developed according to the internal and external validation tests. The best model, including steric, electrostatic, hydrogen bond donor, hydrogen bond acceptor, and hydrophobic fields, was found to depict a three-dimensional map with the local positive and negative effects of these chemotypes on the LasB inhibitory activities. Furthermore, molecular docking experiments yielded bioactive conformations of NAMdPs inside the LasB binding site. The series of NAMdPs adopted a similar orientation with respect to phosphoramidon within the LasB binding site (crystallographic reference), where the backbone atoms of NAMdPs are hydrogen-bonded to the LasB residues N112, A113, and R198, similarly to phosphoramidon. Our study also included a deep description of the residues involved in the protein-ligand interaction patterns for the whole set of NAMdPs, through the use of interaction fingerprints (IFPs).

Adipostatins E-J, New Potent Antimicrobials Identified as Inhibitors of Coenzyme-A Biosynthesis

Phosphopantetheine is a key structural element in biological acyl transfer reactions found embedded within coenzyme A (CoA). Phosphopantothenoylcysteine synthetase (PPCS) is responsible for installing a cysteamine group within phosphopantetheine. Therefore, it holds considerable potential as a drug target for developing new antimicrobials. In this study, we adapted a biochemical assay specific for bacterial PPCS to screen for inhibitors of CoA biosynthesis against a library of marine microbial derived natural product extracts (NPEs). Analysis of the NPE derived from Streptomyces blancoensis led to the isolation of novel antibiotics (10-12, and 14) from the adipostatin class of molecules. The most potent molecule (10) displayed in vitro activity with IC50= 0.93 μM, against S. pneumoniae PPCS. The whole cell antimicrobial assay against isolated molecules demonstrated their ability to penetrate bacterial cells and inhibit clinically relevant pathogenic strains. This establishes the validity of PPCS as a pertinent drug target, and the value of NPEs to provide new antibiotics.

Exploration of the antibiotic resistome in a wastewater treatment plant by a nine-year longitudinal metagenomic study

The spread of antibiotic resistance genes (ARGs) is a growing global problem. Activated sludge (AS) in wastewater treatment plants (WWTPs) has been proposed as a hotspot for ARGs. However, few studies have been conducted to uncover the temporal dynamics of the resistome of AS in WWTPs by long-term longitudinal sampling. In this study, we quantified ARGs and identified their host microbiome in a Hong Kong WWTP in 97 monthly AS samples spanning 9 years. Throughout this analysis, we demonstrated that both the abundance and structures of the resistome changed significantly every two to three years, implying that there was a successive selection of resistomes in the AS system over the study period. The detection of genes of antibiotic-resistant pathogens that are emerging major threats to public health in the AS samples, including mcr, CRE (carbapenem-resistant Enterobacteriaceae) and MRSA (methicillin-resistant Staphylococcus aureus)-related genes, highlight the role of WWTPs as reservoirs of ARGs. In addition, the core resistome (abundant and persistent genes) in AS were found to overlap with those in other ecosystems such as urban sewage, livestock feces, and fishpond sediments, revealing the broad dissemination of ARGs in WWTPs and other environments. Annual variation of resistomes were explained via structural equation modeling (SEM), which deciphered the structural linkages of determining factors such as the operational parameters, microbial community composition and horizontal gene transfer (HGT). Specifically, potentially relevant antibiotic resistance bacteria (ARBs) were explored and discussed based on assembly-based analyses and network correlations. Moreover, consistent with the clear relationship between resistomes and mobile genetic elements (MGEs), it was found that there was a relatively high potential for gene exchange in AS in comparison with soil genomes, which could be explained by the engineering features of WWTPs. Based on these findings, longitudinal monitoring of WWTPs is warranted for risk assessment to reveal emerging ARGs, resistome evolution, correlations with ARBs, and the potential for spread in downstream environments and concomitant exposure risks for humans.

Antimicrobial Activity of Silver Containing Crosslinked Poly(Acrylic Acid) Fibers

Bacterial and fungal pathogens have caused serious problems to the human health. This is particularly true for untreatable infectious diseases and clinical situations where there is no reliable treatment for infected patients. To increase the antimicrobial activity of materials, we introduce silver nanoparticle (NP) patches in which the NPs are incorporated to the surface of smooth and uniform poly(acrylic acid) (PAA) nanofibers. The PAA nanofibers were thermally crosslinked with ethylene glycol via heat treatment through a mild method. The characterization of the resulting PAA-silver NP patches was done using scanning electron microscopy (SEM), UV spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). To demonstrate the antimicrobial activity of PAA, we incorporated the patches containing the silver NPs into strains of fungi such as Candida albicans (C. albican) and bacteria such as Methicillin-resistant Staphylococcus aureus (MRSA). The PAA-silver fibers achieved zones of inhibition against C. albicans and MRSA indicating their antimicrobial activity against both fungi and bacteria. We conclude that silver NP patches exhibited multiple inhibitory actions for the interruption and blockage of activity fungal and bacterial strains, which has the potential as an antimicrobial agent in infectious diseases. Moreover, the proposed material has the potential to be used in antimicrobial textile fabrics, food packaging films, and wound dressings.

Pharmacologically Aware Phage Therapy: Pharmacodynamic and Pharmacokinetic Obstacles to Phage Antibacterial Action in Animal and Human Bodies

The use of viruses infecting bacteria (bacteriophages or phages) to treat bacterial infections has been ongoing clinically for approximately 100 years. Despite that long history, the growing international crisis of resistance to standard antibiotics, abundant anecdotal evidence of efficacy, and one successful modern clinical trial of efficacy, this phage therapy is not yet a mainstream approach in medicine. One explanation for why phage therapy has not been subject to more widespread implementation is that phage therapy research, both preclinical and clinical, can be insufficiently pharmacologically aware. Consequently, here we consider the pharmacological obstacles to phage therapy effectiveness, with phages in phage therapy explicitly being considered to serve as drug equivalents. The study of pharmacology has traditionally been differentiated into pharmacokinetic and pharmacodynamic aspects. We therefore separately consider the difficulties that phages as virions can have in traveling through body compartments toward reaching their target bacteria (pharmacokinetics) and the difficulties that phages can have in exerting antibacterial activity once they have reached those bacteria (pharmacodynamics). The latter difficulties, at least in part, are functions of phage host range and bacterial resistance to phages. Given the apparently low toxicity of phages and the minimal side effects of phage therapy as practiced, phage therapy should be successful so long as phages can reach the targeted bacteria in sufficiently high numbers, adsorb, and then kill those bacteria. Greater awareness of what obstacles to this success generally or specifically can exist, as documented in this review, should aid in the further development of phage therapy toward wider use.

Antibacterial activity of lipo-α/sulfono-γ-AA hybrid peptides

Development of novel antimicrobial agents combating drug resistance is in an urgent need. Herein we report the design and synthesis of a series of short lipo-α/sulfono-γ-AA hybrid peptides. Several short peptides exhibit potent and broad-spectrum antimicrobial activity toward both Gram-positive and Gram-negative bacteria. Membrane depolarization and fluorescence microscopy studies indicate that these short lipo-α/sulfono-γ-AA hybrid peptides can mimic the mechanisms of HDPs to kill bacteria by disrupting bacterial membranes. In addition, these short peptides also show capability to eradicate the biofilm formation of E. coli even at very low concentration. The further development of lipidated α/sulofono-γ-AA hybrid peptides may lead to a new class of antibiotic agents to combat drug resistance.

Small Polar Hits against S. aureus: Screening, Initial Hit Optimization, and Metabolomic Studies

The global prevalence of antibacterial resistance requires new antibacterial drugs with novel chemical scaffolds and modes of action. It is also vital to design compounds with optimal physicochemical properties to permeate the bacterial cell envelope. We described an approach of combining and integrating whole cell screening and metabolomics into early antibacterial drug discovery using a library of small polar compounds. Whole cell screening of a diverse library of small polar compounds against Staphylococcus aureus gave compound 2. Hit expansion was carried out to determine structure-activity relationships. A selection of compounds from this series, together with other screened active compounds, was subjected to an initial metabolomics study to provide a metabolic fingerprint of the mode of action. It was found that compound 2 and its analogues have a different mode of action from some of the known antibacterial compounds tested. This early study highlighted the potential of whole cell screening and metabolomics in early antibacterial drug discovery. Future works will require improving potency and performing orthogonal studies to confirm the modes of action.

Bacteriophages as Potential Tools for Detection and Control of Salmonella spp. in Food Systems

The global problem of antibiotic resistance in bacteria is quickly developing in most antibiotics used in hospitals and livestock. Recently, the infections with multi-drug resistant (MDR) bacteria become a major cause of death worldwide. Current antibiotics are not very effective in treating MDR Salmonella infections, which have become a public health threat. Therefore, novel approaches are needed to rapidly detect and effectively control antibiotic-resistant pathogens. Bacteriophages (phages) have seen renewed attention for satisfying those requirements due to their host-specific properties. Therefore, this review aims to discuss the possibility of using phages as a detection tool for recognizing bacterial cell surface receptors and an alternative approach for controlling antibiotic-resistant pathogens in food systems.

Goals and Challenges in Bacterial Phosphoproteomics

Reversible protein phosphorylation at serine, threonine and tyrosine is a well-known dynamic post-translational modification with stunning regulatory and signalling functions in eukaryotes. Shotgun phosphoproteomic analyses revealed that this post-translational modification is dramatically lower in bacteria than in eukaryotes. However, Ser/Thr/Tyr phosphorylation is present in all analysed bacteria (24 eubacteria and 1 archaea). It affects central processes, such as primary and secondary metabolism development, sporulation, pathogenicity, virulence or antibiotic resistance. Twenty-nine phosphoprotein orthologues were systematically identified in bacteria: ribosomal proteins, enzymes from glycolysis and gluconeogenesis, elongation factors, cell division proteins, RNA polymerases, ATP synthases and enzymes from the citrate cycle. While Ser/Thr/Tyr phosphorylation exists in bacteria, there is a consensus that histidine phosphorylation is the most abundant protein phosphorylation in prokaryotes. Unfortunately, histidine shotgun phosphorproteomics is not possible due to the reduced phosphohistidine half-life under the acidic pH conditions used in standard LC-MS/MS analysis. However, considering the fast and continuous advances in LC-MS/MS-based phosphoproteomic methodologies, it is expected that further innovations will allow for the study of His phosphoproteomes and a better coverage of bacterial phosphoproteomes. The characterisation of the biological role of bacterial Ser/Thr/Tyr and His phosphorylations might revolutionise our understanding of prokaryotic physiology.

Nonpathogenic Bacteria as Targets in Antimicrobial High-Throughput Screening

Antimicrobial screening usually analyses the effects of natural or synthetic molecules against pathogens. McAuley et al. changed this paradigm, testing the effect of synthetic compounds against the sporulation of the nonpathogenic bacterium Streptomyces venezuelae. They discovered a novel DNA-targeting antibiotic effective against pathogens.

Monobactams: A Unique Natural Scaffold of Four-Membered Ring Skeleton, Recent Development to Clinically Overcome Infections by Multidrug- Resistant Microbes

Background:

Monobactam antibiotics have been testified to demonstrate significant antibacterial activity especially the treatment of infections by superbug microbes. Recently, research has been focused on the structural modifications, and new generation of this privileged natural scaffold.

Objective:

Efforts have been made to discover the structure-antibacterial relationship of monbactams in order to avoid the aimless work involving the ongoing generated analogues. This review aims to summarize the current knowledge and development of monobactams as a broad-spectrum antibacterial scaffolds. The recent structural modifications that expand the activity, especially in the infections by resistant-strains, combinational therapies and dosing, as well as the possibility of crosshypersensitivity/ reactivity/tolerability with penicillins and cephalosporins will also be summarized and inferred. Different approaches will be covered with emphasis on chemical methods and Structure- Activity Relationship (SAR), in addition to the proposed mechanisms of action. Clinical investigation of monobactams tackling various aspects will not be missed in this review.

Conclusion:

The conclusion includes the novels approaches, that could be followed to design new research projects and reduce the pitfalls in the future development of monobactams.

Evaluation of the Effect of Titatnium Dioxide Nanoparticles/Gelatin Composite on Infected Skin Wound Healing; An Animal Model Study

Objective:

To evaluate effects of titanium dioxide /gelatin nanocomposite on wound healing in mice as a model study.

Methods:

Fifty male rats were randomized into five groups of ten animals each. In group I, 0.1 mL sterile saline 0.9% solution was added to the wounds with no infection. In group II, the wounds were infected with MRSA and only treated with 0.1 mL the sterile saline 0.9% solution. In group III, infected wounds were treated with gelatin. In group IV, animals with infected wounds were treated with 0.1 mL titanium dioxide nanoparticles. In group V, animals with infected wounds were treated with titanium dioxide /gelatin nanocomposite. Wound size was measured on 2, 6, 10, 14, 18 and 20 days after surgery.

Results:

Reduction in wound area indicated that there was significant difference between group IV and other groups (p<0.05). Quantitative histological and morphometric studies and mean rank of the qualitative studies demonstrated that there was significant difference between group IV and other groups (P<0.05).

Conclusion:

Titatnium dioxide nanoparticles/gelatin composite offered potential advantages in wound healing acceleration and fibroblast proliferation on early days of healing phases. Acceleration in wound repair could be associated with earlier wound contraction and stability of damaged area by rearrangement of granulation tissue and collagen fibers.

Effects and formulation of silver nanoscaffolds on cytotoxicity dependent ion release kinetics towards enhanced excision wound healing patterns in Wistar albino rats

Wound tissue regeneration and angiogenesis are dynamic processes that send physiological signals to the body. Thus, designing novel nanoscaffolds by understanding their surface modifications and toxicological response in a biological system with a potent anti-inflammatory response is a viable solution. In this respect, inspired by the surface chemistry, in the present work we focus on the chemical optimization of silver nanoscaffolds using surface cappings in order to understand their kinetic release behaviour in simulated wound fluids (SWF), to analyze their blood compatibility in human lymphocytes and erythrocytes and then embed them in a chitosan-agarose matrix (CAM) as a productive drug delivery system to evaluate in vivo excision wound tissue regeneration efficiency in Wistar rats. In this regard, polyvinyl alcohol capped silver nanocomposites (PVA-AgNPs) exhibit a dominant antibacterial efficacy with the sustained and controlled release of silver ions and percentage cell mortality and percentage hemolysis of only 10% and 16% compared with uncapped-AgNPs or silver bandaids (SBDs). Also, PVA-AgNP impregnated CAM (PVA-CAM) shows positive effects through their anti-inflammatory and angiogenic properties, with a nearly 95% healing effect within 9 days. The complete development of collagen and fibroblast constituents was also monitored in PVA-CAM by hematoxylin & eosin (H & E) and Masson trichrome (MT) staining. These results provide a clear insight into the development of a potent therapeutic formulation using CAM as a scaffold incorporated with surface functionalized PVA-AgNPs as a bioeffective and biocompatible polymer for the fabrication of efficacious silver wound dressing scaffolds in clinical practice.

Enhanced Energy Transfer in a Donor-Acceptor Photosensitizer Triggers Efficient Photodynamic Therapy

Photosensitizers (PSs) play a vital role in photodynamic therapy (PDT) for combating bacterial resistance and treating tumor. In this study, we report new donor-acceptor porphyrin PSs with a cationic conjugated oligomer (OPV) as a donor unit and porphyrin (TPP) as an acceptor unit by covalent linkage and achieved a fluorescence resonance energy transfer efficiency of 99% owing to their strong spectral overlap and short distance. The ¹O₂ yield of porphyrin derivatives is 121% (rose bengal as the standard reference) by virtue of OPVs' excellent light-harvesting ability and high fluorescence resonance energy transfer efficiency, greatly exceeding those of oligomer and porphyrin derivatives reported in the literature. Additionally, the cationic donors significantly improved the water solubility, decreased the aggregation of porphyrin, and promoted the adherence of the PSs to cell membranes through electrostatic interactions. As a result, the D-A porphyrin PSs exhibit dramatic PDT treatment efficiency. The half-inhibitory concentration is as low as 33 and 88 nM for methicillin-resistant Staphylococcus aureus and Escherichia coli, respectively. Therefore, this study provides a new strategy to construct PSs with high ¹O₂ yield and an excellent treatment effect at a low dose of PSs, which is promising for application in PDT used to treat cancer and microbial infections.

Structure-activity relationships (SAR) of triazine derivatives: Promising antimicrobial agents

The emergence of drug resistance has created unmet medical need for the development of new classes of antibiotics. Innovation of new antibacterial agents with new mode of action remains a high priority universally. Triazines are six-membered, nitrogen-containing heterocyclic scaffold with a wide range of pharmaceutical properties such as antibacterial, antifungal, anticancer, antioxidants, antitubercular, antimalarial, anti-HIV, anticonvulsant, anti-inflammatory, antiulcer, and analgesic activities. The present review focuses on the recent developments in the area of medicinal chemistry to discover various chemical structures as potential antimicrobial agents and their structure-activity relationships (SAR) studies are also discussed for further rational design of this kind of derivatives.

Synthesis and antibacterial evaluation of novel oxazolidinone derivatives containing a piperidinyl moiety

In this article, a series of novel oxazolidinone derivatives containing a piperidinyl moiety was designed and synthesized. Their antibacterial activities were measured against S. aureus, MRSA, MSSA, LREF and VRE by MIC assay. Most of them exhibited potent activity against Gram-positive pathogens comparable to linezolid. Among them, compound 9h exhibited comparable activity with linezolid against human MAO-A for safety evaluation and showed moderate metabolism in human liver microsome. The most promising compound 9h, which showed remarkable antibacterial activity against S. aureus, MRSA, MSSA, LREF and VRE pathogens with MIC value of 0.25-1 μg/mL, was an interesting candidate for further investigation.

MetaMiner: A Scalable Peptidogenomics Approach for Discovery of Ribosomal Peptide Natural Products with Blind Modifications from Microbial Communities

Ribosomally synthesized and post-translationally modified peptides (RiPPs) are an important class of natural products that contain antibiotics and a variety of other bioactive compounds. The existing methods for discovery of RiPPs by combining genome mining and computational mass spectrometry are limited to discovering specific classes of RiPPs from small datasets, and these methods fail to handle unknown post-translational modifications. Here, we present MetaMiner, a software tool for addressing these challenges that is compatible with large-scale screening platforms for natural product discovery. After searching millions of spectra in the Global Natural Products Social (GNPS) molecular networking infrastructure against just eight genomic and metagenomic datasets, MetaMiner discovered 31 known and seven unknown RiPPs from diverse microbial communities, including human microbiome and lichen microbiome, and microorganisms isolated from the International Space Station.

Chitosan-based nitric oxide-releasing dressing for anti-biofilm and in vivo healing activities in MRSA biofilm-infected wounds

Bacterial biofilms on wounds impair the healing process and often lead to chronic wounds. Chitosan is a well-known biopolymer with antimicrobial and anti-biofilm effects. S-nitrosoglutathione (GSNO) has been identified as a promising nitric oxide (NO) donor to defend against pathogenic biofilms and enhance wound healing activities. In this study, we prepared NO-releasing chitosan film (CS/NO film) and evaluated its anti-biofilm activity and in vivo wound healing efficacy against methicillin-resistant Staphylococcus aureus (MRSA) biofilm-infected wounds in diabetic mice. The in vitro release study showed sustained release of NO over 3 days in simulated wound fluid. The CS/NO film significantly enhanced antibacterial activity against MRSA by > 3 logs reduction in bacterial viability. Moreover, CS/NO film exhibited a 3-fold higher anti-biofilm activity than the control and CS film. In in vivo MRSA biofilm-infected wounds, the CS/NO film-treated group showed faster biofilm dispersal, wound size reduction, epithelialization rates, and collagen deposition than the untreated and CS film-treated groups. Therefore, the CS/NO film investigated in this study could be a promising approach for the treatment of MRSA biofilm-infected wounds.

Evaluation of Structure-Function Relationships of Aggregation-Induced Emission Luminogens for Simultaneous Dual Applications of Specific Discrimination and Efficient Photodynamic Killing of Gram-Positive Bacteria

Bacterial infectious diseases, especially those caused by Gram-positive bacteria, have been seriously threatening human health. Preparation of a multifunctional system bearing both rapid bacterial differentiation and effective antibacterial effects is highly in demand, but remains a severe challenge. Herein, we rationally designed and successfully developed a sequence of aggregation-induced emission luminogens (AIEgens) with orderly enhanced D-A strength. Evaluation of structure-function relationships reveals that AIEgens having intrinsic positive charge and proper ClogP value are able to stain Gram-positive bacteria. Meanwhile, one of the presented AIEgens (TTPy) can generate reactive oxygen species (ROS) in extraordinarily high efficiency under white light irradiation due to the smaller singlet-triplet energy gap. Thanks to the NIR emission, excellent specificity to Gram-positive bacteria, and effective ROS generation efficiency, TTPy has been proved to perform well in selective photodynamic killing of Gram-positive bacteria in vitro, such as S. aureus and S. epidermidis, even in S. aureus-infected rat wounds.