Chemical Strategies To Target Bacterial Virulence

Compounds Derived from 5-Fluoropyridine and Benzo[b]thiophene: Killing Mycobacterium tuberculosis and Reducing its Virulence

The rise of drug-resistant Mycobacterium tuberculosis (Mtb) has extended the duration of tuberculosis (TB) treatment and reduced the likelihood of cure. One strategy to combat this issue is the development of inhibitors targeting the virulence factors of bacterial pathogens. Mtb' catalase (KatG) is crucial for its detoxification mechanisms and also serves as a significant virulence factor for the bacterium. In this study, twelve derivatives synthesized from 5-fluoropyridine and benzo[b]thiophene demonstrated antimycobacterial efficacy with minimum inhibitory concentrations (MICs) varying between 0.5 and 32 μg/mL. Compound 2, 1-(benzo[b]thiophen-2-ylmethylene) thiosemicarbazide, emerged as the most potent candidate. It effectively inhibited Mtb KatG, enhanced the production of reactive oxygen species (ROS) in Mtb, and achieved Mtb killing within 96 hours at a concentration of 2 μg/mL (4×MIC). Molecular docking simulations revealed that compound 2 binds tightly to the active site of Mtb-KatG with a docking score of 114, indicating that it may serve as a potent inhibitor of Mtb-KatG. The rabbit skin tuberculosis model was employed to assess the virulence of Mtb. Animal study results indicated that the granulomas induced by Mtb after treatment with compound 2 were reduced in size, exhibited a lower bacterial load, and the bacteria were no longer aggregated, in contrast to those caused by untreated Mtb. Hence, compound 2 can be regarded as a molecule capable of neutralizing the virulence factors of Mtb. This research offers insights into the design of anti-Mtb molecules with novel mechanisms of action.

A Review of Antibacterial Candidates with New Modes of Action

There is a lack of new antibiotics to combat drug-resistant bacterial infections that increasingly threaten global health. The current pipeline of clinical-stage antimicrobials is primarily populated by "new and improved" versions of existing antibiotic classes, supplemented by several novel chemical scaffolds that act on traditional targets. The lack of fresh chemotypes acting on previously unexploited targets (the "holy grail" for new antimicrobials due to their scarcity) is particularly unfortunate as these offer the greatest opportunity for innovative breakthroughs to overcome existing resistance. In recognition of their potential, this review focuses on this subset of high value antibiotics, providing chemical structures where available. This review focuses on candidates that have progressed to clinical trials, as well as selected examples of promising pioneering approaches in advanced stages of development, in order to stimulate additional research aimed at combating drug-resistant infections.

Sugar-Coated: Can Multivalent Glycoconjugates Improve upon Nature's Design?

Multivalent interactions between receptors and glycans play an important role in many different biological processes, including pathogen infection, self-recognition, and the immune response. The growth in the number of tools and techniques toward the assembly of multivalent glycoconjugates means it is possible to create synthetic systems that more and more closely resemble the diversity and complexity we observe in nature. In this Perspective we present the background to the recognition and binding enabled by multivalent interactions in nature, and discuss the strategies used to construct synthetic glycoconjugate equivalents. We highlight key discoveries and the current state of the art in their applications to glycan arrays, vaccines, and other therapeutic and diagnostic tools, with an outlook toward some areas we believe are of most interest for future work in this area.

Repurposing FDA-approved disulfiram for targeted inhibition of diphtheria toxin and the binary protein toxins of Clostridium botulinum and Bacillus anthracis

Many bacteria act pathogenic by the release of AB-type protein toxins that efficiently enter human or animal cells and act as enzymes in their cytosol. This leads to disturbed cell functions and the clinical symptoms characteristic for the individual toxin. Therefore, molecules that directly target and neutralize these toxins provide promising novel therapeutic options. Here, we found that the FDA-approved drug disulfiram (DSF), used for decades to treat alcohol abuse, protects cells from intoxication with diphtheria toxin (DT) from Corynebacterium diphtheria, the causative agent of diphtheria, lethal toxin (LT) from Bacillus anthracis, which contributes to anthrax, and C2 enterotoxin from Clostridium botulinum when applied in concentrations lower than those found in plasma of patients receiving standard DSF treatment for alcoholism (up to 20 µM). Moreover, this inhibitory effect is increased by copper, a known enhancer of DSF activity. LT and C2 are binary toxins, consisting of two non-linked proteins, an enzyme (A) and a separate binding/transport (B) subunit. To act cytotoxic, their proteolytically activated B subunits PA63 and C2IIa, respectively, form barrel-shaped heptamers that bind to their cellular receptors and form complexes with their respective A subunits LF and C2I. The toxin complexes are internalized via receptor-mediated endocytosis and in acidified endosomes, PA63 and C2IIa form pores in endosomal membranes, which facilitate translocation of LF and C2I into the cytosol, where they act cytotoxic. In DT, A and B subunits are located within one protein, but DT also forms pores in endosomes that facilitate translocation of the A subunit. If cell binding, membrane translocation, or substrate modification is inhibited, cells are protected from intoxication. Our results implicate that DSF neither affects cellular binding nor the catalytic activity of the investigated toxins to a relevant extend, but interferes with the toxin pore-mediated translocation of the A subunits of DT, LT and C2 toxin, as demonstrated by membrane-translocation assays and toxin pore conductivity experiments in the presence or absence of DSF. Since toxin translocation across intracellular membranes represents a central step during cellular uptake of many bacterial toxins, DSF might neutralize a broad spectrum of medically relevant toxins.

Catalytic Nanoparticles in Biomedical Applications: Exploiting Advanced Nanozymes for Therapeutics and Diagnostics

Catalytic nanoparticles (CNPs) as heterogeneous catalyst reveals superior activity due to their physio-chemical features, such as high surface-to-volume ratio and unique optical, electric, and magnetic properties. The CNPs, based on their physio-chemical nature, can either increase the reactive oxygen species (ROS) level for tumor and antibacterial therapy or eliminate the ROS for cytoprotection, anti-inflammation, and anti-aging. In addition, the catalytic activity of nanozymes can specifically trigger a specific reaction accompanied by the optical feature change, presenting the feasibility of biosensor and bioimaging applications. Undoubtedly, CNPs play a pivotal role in pushing the evolution of technologies in medical and clinical fields, and advanced strategies and nanomaterials rely on the input of chemical experts to develop. Herein, a systematic and comprehensive review of the challenges and recent development of CNPs for biomedical applications is presented from the viewpoint of advanced nanomaterial with unique catalytic activity and additional functions. Furthermore, the biosafety issue of applying biodegradable and non-biodegradable nanozymes and future perspectives are critically discussed to guide a promising direction in developing span-new nanozymes and more intelligent strategies for overcoming the current clinical limitations.

Mechanism-guided strategies for combating antibiotic resistance

Bacterial antibiotic resistance has been recognized as a global threat to public health. It challenges the antibiotics currently used in clinical practice and causes severe and often fatal infectious diseases. Fighting against antibiotic-resistant bacteria (ARB) is growing more urgent. While understanding the molecular mechanisms that underlie resistance is a prerequisite, several major mechanisms have been previously proposed including bacterial efflux systems, reduced cell membrane permeability, antibiotic inactivation by enzymes, target modification, and target protection. In this context, this review presents a panel of promising and potential strategies to combat antibiotic resistance/resistant bacteria. Different types of direct-acting and indirect resistance breakers, such as efflux pump inhibitors, antibiotic adjuvants, and oxidative treatments are discussed. In addition, the emerging multi-omics approaches for rapid resistance identification and promising alternatives to existing antibiotics are highlighted. Overall, this review suggests that continued effort and investment in research are required to develop new antibiotics and alternatives to existing antibiotics and translate them into environmental and clinical applications.

Electrically polarized nanoscale surfaces generate reactive oxygenated and chlorinated species for deactivation of microorganisms

Because of the decreasing supply of new antibiotics, recent outbreaks of infectious diseases, and the emergence of antibiotic-resistant microorganisms, it is imperative to develop new effective strategies for deactivating a broad spectrum of microorganisms and viruses. We have implemented electrically polarized nanoscale metallic (ENM) coatings that deactivate a wide range of microorganisms including Gram-negative and Gram-positive bacteria with greater than 6-log reduction in less than 10 minutes of treatment. The electrically polarized devices were also effective in deactivating lentivirus and Candida albicans. The key to the high deactivation effectiveness of ENM devices is electrochemical production of micromolar cuprous ions, which mediated reduction of oxygen to hydrogen peroxide. Formation of highly damaging species, hydroxyl radicals and hypochlorous acid, from hydrogen peroxide contributed to antimicrobial properties of the ENM devices. The electric polarization of nanoscale coatings represents an unconventional tool for deactivating a broad spectrum of microorganisms through in situ production of reactive oxygenated and chlorinated species.

Antimicrobial Strategies Proposed for the Treatment of S. pseudintermedius and Other Dermato-Pathogenic Staphylococcus spp. in Companion Animals: A Narrative Review

The treatment of dermato-pathogenic Staphylococcus spp., particularly Staphylococcus pseudintermedius, in companion animals presents significant challenges due to rising antimicrobial resistance. This review explores innovative strategies to combat these infections. We examined novel antimicrobials and the repurposing of existing drugs to enhance their efficacy against resistant strains. Additionally, we evaluate the potential of natural products, nanomaterials, and skin antiseptics as alternative treatments. The review also investigates the use of antimicrobial peptides and bacteriophages, highlighting their targeted action against staphylococcal pathogens. Furthermore, the role of adjuvants in antibiotic treatments, such as antimicrobial resistance breakers, is discussed, emphasizing their ability to enhance therapeutic outcomes. Our analysis underscores the importance of a multifaceted approach in developing effective antimicrobial strategies for companion animals, aiming to mitigate resistance and improve clinical management of staphylococcal skin infections.

Evaluating virulence features of Acinetobacter baumannii resistant to polymyxin B

The increasing resistance to polymyxins in Acinetobacter baumannii has made it even more urgent to develop new treatments. Anti-virulence compounds have been researched as a new solution. Here, we evaluated the modification of virulence features of A. baumannii after acquiring resistance to polymyxin B. The results showed lineages attaining unstable resistance to polymyxin B, except for Ab7 (A. baumannii polymyxin B resistant lineage), which showed stable resistance without an associated fitness cost. Analysis of virulence by a murine sepsis model indicated diminished virulence in Ab7 (A. baumannii polymyxin B resistant lineage) compared with Ab0 (A. baumannii polymyxin B susceptible lineage). Similarly, downregulation of virulence genes was observed by qPCR at 1 and 3 h of growth. However, an increase in bauE, abaI, and pgAB expression was observed after 6 h of growth. Comparison analysis of Ab0, Ab7, and Pseudomonas aeruginosa suggested no biofilm formation by Ab7. In general, although a decrease in virulence was observed in Ab7 when compared with Ab0, some virulence feature that enables infection could be maintained. In light of this, virulence genes bauE, abaI, and pgAB showed a potential relevance in the maintenance of virulence in polymyxin B-resistant strains, making them promising anti-virulence targets.

Discovery of Antibacterial Compounds against Xanthomonas citri subsp. citri from a Marine Fungus Aspergillus terreus SCSIO 41202 and the Mode of Action

Citrus canker, caused by Xanthomonas citri subsp. citri (Xcc), is a severe citrus disease. Currently, copper-containing pesticides are widely used to manage this disease, posing high risks to the environment and human health. This study reports the discovery of naturally occurring anti-Xcc compounds from a deep-sea fungus, Aspergillus terreus SCSIO 41202, and the possible mode of action. The ethyl acetate extract of A. terreus was subjected to bioassay-guided isolation, resulting in the discovery of eight anti-Xcc compounds (1-8) with minimum inhibitory concentrations (MICs) ranging from 0.078 to 0.625 mg/mL. The chemical structures of these eight metabolites were determined by integrative analysis of various spectroscopic data. Among these compounds, Asperporonin A (1) and Asperporonin B (2) were identified as novel compounds with a very unusual structural skeleton. The electronic circular dichroism was used to determine the absolute configurations of 1 and 2 through quantum chemical calculation. A bioconversion pathway involving pinacol rearrangement was proposed to produce the unusual compounds (1-2). Compound 6 exhibited an excellent anti-Xcc effect with a MIC value of 0.078 mg/mL, which was significantly more potent than the positive control CuSO4 (MIC = 0.3125 mg/mL). Compound 6 inhibited cell growth by disrupting biofilm formation, destroying the cell membrane, and inducing the accumulation of reactive oxygen species. In vivo tests indicated that compound 6 is highly effective in controlling citrus canker disease. These results indicate that compounds 1-8, especially 6, have the potential as lead compounds for the development of new, environmentally friendly, and efficient anti-Xcc pesticides.

Pore-Forming Toxin-Driven Recovery of Peroxidase-Mimicking Activity in Biomass Channels for Label-Free Electrochemical Bacteria Sensing

The development of sensitive, selective, and rapid methods to detect bacteria in complex media is essential to ensuring human health. Virulence factors, particularly pore-forming toxins (PFTs) secreted by pathogenic bacteria, play a crucial role in bacterial diseases and serve as indicators of disease severity. In this study, a nanochannel-based label-free electrochemical sensing platform was developed for the detection of specific pathogenic bacteria based on their secreted PFTs. In this design, wood substrate channels were functionalized with a Fe-based metal-organic framework (FeMOF) and then protected with a layer of phosphatidylcholine (PC)-based phospholipid membrane (PM) that serves as a peroxidase mimetic and a channel gatekeeper, respectively. Using Staphylococcus aureus (S. aureus) as the model bacteria, the PC-specific PFTs secreted by S. aureus perforate the PM layer. Now exposed to the FeMOF, uncharged 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) molecules in the electrolyte undergo oxidation to cationic products (ABTS•+). The measured transmembrane ionic current indicates the presence of S. aureus and methicillin-resistant S. aureus (MRSA) with a low detection limit of 3 cfu mL-1. Besides excellent specificity, this sensing approach exhibits satisfactory performance for the detection of target bacteria in the complex media of food.

Vibrio cholerae virulence and its suppression through the quorum-sensing system

Vibrio cholerae is a cholera-causing pathogen known to instigate severe contagious diarrhea that affects millions globally. Survival of vibrios depend on a combination of multicellular responses and adapt to changes that prevail in the environment. This process is achieved through a strong communication at the cellular level, the process has been recognized as quorum sensing (QS). The severity of infection is highly dependent on the QS of vibrios in the gut milieu. The quorum may exist in a low/high cell density (LCD/HCD) state to exert a positive or negative response to control the regulatory pathogenic networks. The impact of this regulation reflects on the transition of pathogenic V. cholerae from the environment to infect humans and cause outbreaks or epidemics of cholera. In this context, the review portrays various regulatory processes and associated virulent pathways, which maneuver and control LCD and HCD states for their survival in the host. Although several treatment options are existing, promotion of therapeutics by exploiting the virulence network may potentiate ineffective antibiotics to manage cholera. In addition, this approach is also useful in resource-limited settings, where the accessibility to antibiotics or conventional therapeutic options is limited.

A hydrogen-bonded curdlan-chitosan/polyvinyl alcohol edible dual functional hydrogel bandage against MRSA promotes wound healing

The most prevalent complication arising from skin injuries is bacterial infection, where pathogenic bacteria proliferate significantly at the wound site, leading to subsequent complications like septic shock and sepsis. Although antibiotics presently effectively manage wound infections caused by common bacteria, the escalating prevalence of antibiotic-resistant strains necessitates urgent novel approaches for addressing such infections. Here, we present CS9P1-RA, a dual functional hydrogel dressing, based on polyvinyl alcohol (PVA) matrix crosslinked through hydrogen bonding. CS9P1-RA combines chitosan (CS), a food-derived antibacterial agent, with the natural compound rosmarinic acid (RA) to specifically target skin injuries caused by MRSA. Computational and molecular biology assays illustrate RA's ability to selectively inhibit the activity of Staphylococcus aureus (S. aureus) serine/threonine phosphatase (Stp1), reducing the S. aureus pathogenicity. CS9P1-RA showcases exceptional antibacterial efficacy (MIC = 1 mg/mL) and demonstrates potency in reducing virulence (IC50 = 7.424 μM on Stp1). Notably, it effectively curbs bacterial growth and accelerates wound healing in the mice model, thereby fulfilling the practical requirements for clinical applications. Moreover, the mechanical properties of CS9P1-RA ensure user comfort during treatment. This work introduces a fresh design paradigm for dressing materials, offering a promising solution for treating skin injuries inflicted by antibiotic-resistant bacterial infections.

Plant-derived virulence arresting drugs as novel antimicrobial agents: Discovery, perspective, and challenges in clinical use

Antimicrobial resistance (AMR) emerges as a severe crisis to public health and requires global action. The occurrence of bacterial pathogens with multi-drug resistance appeals to exploring alternative therapeutic strategies. Antivirulence treatment has been a positive substitute in seeking to circumvent AMR, which aims to target virulence factors directly to combat bacterial infections. Accumulated evidence suggests that plant-derived natural products, which have been utilized to treat infectious diseases for centuries, can be abundant sources for screening potential virulence-arresting drugs (VADs) to develop advanced therapeutics for infectious diseases. This review sums up some virulence factors and their actions in various species of bacteria, as well as recent advances pertaining to plant-derived natural products as VAD candidates. Furthermore, we also discuss natural VAD-related clinical trials and patents, the perspective of VAD-based advanced therapeutics for infectious diseases and critical challenges hampering clinical use of VADs, and genomics-guided identification for VAD therapeutic. These newly discovered natural VADs will be encouraging and optimistic candidates that may sustainably combat AMR.

Ag+-Adsorbing Semiconducting Polymer Nanosponge for Smart Local Treatment of Wound Infection

Nanoplatform combined with photothermal therapy (PTT) and silver nanoparticles have been widely used to combat bacterial infections. However, the development of environmentally benign antibacterial nanoplatforms with controllable and long-term antibacterial activity is still challenging. Herein, we synthesized an Ag+-adsorbing organic semiconducting polymeric nanosponge (PDPP3T NPe@Ag+) to realize Ag+ enhanced photothermal anti-infective therapy. Furthermore, the PDPP3T NPe@Ag+ sponge can also spatiotemporally release silver ions in a pH/NIR light-responsive manner for controllable and long-term antimicrobial therapy. Owing to good biocompatibility and controlled release of silver ions, PDPP3T NPe@Ag+ can effectively kill bacteria in vitro and promote wound healing in vivo. We expect that this antimicrobial platform could be utilized as a robust antibacterial agent for infective therapy.

Coupling a Virulence-Targeting Moiety with Ru-Based AMP Mimics Efficiently Improved Its Anti-Infective Potency and Therapeutic Index

The surge of antibiotic resistance in Staphylococcus aureus calls for novel drugs that attack new targets. Developing antimicrobial peptides (AMPs) or antivirulence agents (AvAs) is a promising strategy to tackle this challenge. However, AMPs, which kill bacteria by disrupting cell membranes, suffer from low stability and high synthesis cost, while AvAs, which inhibit toxin secretion, have relatively poor bactericidal activity. Here, to address their respective shortcomings, we combined these two different antibacterial activities on the same molecular scaffold and developed a Ru-based metalloantibiotic, termed Ru1. Notably, Ru1 exerted remarkable bactericidal activity (MICS = 460 nM) and attenuated bacterial virulence as well. Mechanistic studies demonstrated that Ru1 had two independent targets: CcpA and bacterial membrane integrity. Based on its dual mechanism of action, Ru1 effectively overcame S. aureus resistance and showed high efficacy in a mouse infection model against S. aureus. This study provides a promising approach to confronting bacterial infections.

Anti-Vibrio parahaemolyticus compounds from Streptomyces parvus based on Pan-genome and subtractive proteomics

Introduction

Vibrio parahaemolyticus is a foodborne pathogen commonly found in seafood, and drug resistance poses significant challenges to its control. This study aimed to identify novel drug targets for antibacterial drug discovery.

Methods

To identify drug targets, we performed a pan-genome analysis on 58 strains of V. parahaemolyticus genomes to obtain core genes. Subsequently, subtractive proteomics and physiochemical checks were conducted on the core proteins to identify potential therapeutic targets. Molecular docking was then employed to screen for anti-V. parahaemolyticus compounds using a in-house compound library of Streptomyces parvus, chosen based on binding energy. The anti-V. parahaemolyticus efficacy of the identified compounds was further validated through a series of experimental tests.

Results and Discussion

Pangenome analysis of 58 V. parahaemolyticus genomes revealed that there were 1,392 core genes. After Subtractive proteomics and physiochemical checks, Flagellar motor switch protein FliN was selected as a therapeutic target against V. parahaemolyticus. FliN was modeled and docked with Streptomyces parvus source compounds, and Actinomycin D was identified as a potential anti-V. parahaemolyticus agent with a strong binding energy. Experimental verification confirmed its effectiveness in killing V. parahaemolyticus and significantly inhibiting biofilm formation and motility. This study is the first to use pan-genome and subtractive proteomics to identify new antimicrobial targets for V. parahaemolyticus and to identify the anti-V. parahaemolyticus effect of Actinomycin D. These findings suggest potential avenues for the development of new antibacterial drugs to control V. parahaemolyticus infections.

Molecular mechanism of green tea polyphenol epicatechin gallate attenuating Staphylococcus aureus pathogenicity by targeting Ser/Thr phosphatase Stp1

In this study, through virtual screening and in vitro bioactivity assays, we discovered that (-)-epicatechin gallate (ECG), a polyphenol compound extracted from green tea, demonstrated marked anti-Ser/Thr phosphatase (Stp1) activity towards Staphylococcus aureus (S. aureus) with an IC₅₀ value of 8.35 μM. By targeting S. aureus Stp1, ECG prevented the up-regulation of virulence gene and the formation of antibody membrane and protected the mice from S. aureus infection. Through MD simulation, the allosteric inhibitory mechanism of ECG on Stp1 was determined. The Stp1-ECG complex model underwent a significant change in conformation; its flap subdomain changed from opening to closing, whereas Stp1 activity was lost when bound to ECG. In addition, the MD simulation results of Stp1 and several tea polyphenol compounds showed that gallate groups and fewer adjacent phenolic hydroxyl groups contributed to the binding of Stp1 and inhibitors. As an inhibitor targeting S. aureus Stp1, ECG reduced the pathogenicity of S. aureus without inhibiting S. aureus, which largely reduced the possibility of drug resistance. Our findings demonstrated a novel molecular mechanism of green tea as the usual drink against S. aureus infection and elucidated the future design of allosteric inhibitors targeting Stp1.

Selective killing of the human gastric pathogen Helicobacter pylori by mitochondrial respiratory complex I inhibitors

Respiratory complex I is a multicomponent enzyme conserved between eukaryotic cells and many bacteria, which couples oxidation of electron donors and quinone reduction with proton pumping. Here, we report that protein transport via the Cag type IV secretion system, a major virulence factor of the Gram-negative bacterial pathogen Helicobacter pylori, is efficiently impeded by respiratory inhibition. Mitochondrial complex I inhibitors, including well-established insecticidal compounds, selectively kill H. pylori, while other Gram-negative or Gram-positive bacteria, such as the close relative Campylobacter jejuni or representative gut microbiota species, are not affected. Using a combination of different phenotypic assays, selection of resistance-inducing mutations, and molecular modeling approaches, we demonstrate that the unique composition of the H. pylori complex I quinone-binding pocket is the basis for this hypersensitivity. Comprehensive targeted mutagenesis and compound optimization studies highlight the potential to develop complex I inhibitors as narrow-spectrum antimicrobial agents against this pathogen.

AIEgen-Based Nanomaterials for Bacterial Imaging and Antimicrobial Applications: Recent Advances and Perspectives

Microbial infections have always been a thorny problem. Multi-drug resistant (MDR) bacterial infections rendered the antibiotics commonly used in clinical treatment helpless. Nanomaterials based on aggregation-induced emission luminogens (AIEgens) recently made great progress in the fight against microbial infections. As a family of photosensitive antimicrobial materials, AIEgens enable the fluorescent tracing of microorganisms and the production of reactive oxygen (ROS) and/or heat upon light irradiation for photodynamic and photothermal treatments targeting microorganisms. The novel nanomaterials constructed by combining polymers, antibiotics, metal complexes, peptides, and other materials retain the excellent antimicrobial properties of AIEgens while giving other materials excellent properties, further enhancing the antimicrobial effect of the material. This paper reviews the research progress of AIEgen-based nanomaterials in the field of antimicrobial activity, focusing on the materials' preparation and their related antimicrobial strategies. Finally, it concludes with an outlook on some of the problems and challenges still facing the field.

Isoflavone glucoside genistin, an inhibitor targeting Sortase A and Listeriolysin O, attenuates the virulence of Listeria monocytogenes in vivo and in vitro

As a common intracellular facultative anaerobic Gram-positive bacterium, Listeria monocytogenes (L. monocytogenes) exhibits strong resistance to extreme environments, such as low temperature and a wide range of pH values, causing contamination in food production and processing. Sortase A (SrtA) and listeriolysin O (LLO), two crucial virulence factors of L. monocytogenes, are widely recognized as potential targets for the development of anti-L. monocytogenes infection drugs. In this study, we found that genistin simultaneously inhibits the peptidase activity of SrtA and the hemolytic activity of LLO without affecting the growth of L. monocytogenes, alleviating concerns about developing resistance. Furthermore, we demonstrated that genistin reduces L. monocytogenes biofilm formation and invasion of human colorectal cancer (Caco-2) cells. Subsequent mechanistic studies revealed that genistin inhibited LLO-mediated Caco-2 cell damage by blocking LLO oligomerization. Fluorescence quenching assay revealed the potential binding mode of SrtA and LLO to genistin. Genistin might bind to the active pocket of SrtA through residues Leu33, Asn29, and Met40, interacting with D1 domain of LLO involved in oligomerization and pore formation through residues Asn259. Studies in infection models revealed that genistin reduces mortality and pathological damage in mice infected with L. monocytogenes. These results indicate that genistin is a promising anti-virulence agent that could be considered an alternative candidate for the treatment of L. monocytogenes infection.

In Situ Structure Transformation of a Sprayed Gel for pH-Ultrasensitive Nano-Catalytic Antibacterial Therapy

Nano-catalytic bacterial killing provides new opportunities to address ever-increasing antibiotic resistance. However, the intrinsic catalytic activity usually depends on a much lower pH conditions (pH = 2-5) than that in the weakly acidic bacterial microenvironments (pH = 6-7) for reactive oxygen species production by Fenton reactions. Herein, a MnSiO₃ -based pH-ultrasensitive "in situ structure transformation" is first reported to significantly promote the adhesion between material and bacteria, and shorten the diffusion distance (<20 nm) to compensate ultra-short life (<200 ns) of ·OH generated by Mn²⁺ -mediated Fenton-like reaction, finally enhancing its nano-catalytic antibacterial performance in weakly acidic conditions. A separated spray bottle is further designed to achieve in situ gelation at the wound site, which demonstrates excellent shape adaptability to complicated and rough surfaces of wounds, allowing for long-term nano-catalyst release. As a result, bacterial-infected wound healing is efficiently promoted. Herein, the in situ sprayed nano-catalytic antibacterial gel presents a promising paradigm for bacterial infection treatment.

Synthesis and antibiofilm evaluation of N-acyl-2-aminopyrimidine derivatives against Acinetobacter baumannii

The overuse of antibiotics will led to the increase of drug resistance. Especially, the multidrug-resistant A. baumannii became the leading cause of nosocomial infections with high rates of morbimortality. The drug resistance of A. baumannii is greatly attributed to its biofilm. To alleviate the burden of drug resistance, the anti-virulence signaling strategies was developed. By specifically interfering with the ability of the bacteria to recognize host signals that are needed to establish infection, the bacteria are less able to colonize the host. In this paper, 39 N-acyl-2-aminopyrimidine derivatives were synthesized and tested for their biofilm inhibition efficacy. The screening results reveal that some of the analogues (3ac, 8d) efficiently inhibited the biofilm formation of A. baumannii (IC₅₀ as low as 3.8 μM), and the biofilm inhibition ability was further demonstrated with laser confocal results and extracellular polysaccharides inhibition test. Further motility test reveals our compounds are quorum sensing inhibitors. Besides, the synergistic effect of compounds 3ac and 8d with different antibiotics suggest its potential clinical significance, which was further enhanced by the long time biofilm inhibition test after coating with PLGA. Finally, we also look into the safety of the compounds with cytotoxicity assay.

Hyperglycemia in Diabetic Skin Infections Promotes Staphylococcus aureus Virulence Factor Aureolysin: Visualization by Molecular Imaging

Bacterial skin infections are common in diabetic patients, with Staphylococcus aureus (S. aureus) being the most commonly isolated, causing comorbidities such as increased mortality and long-term hospitalization. While precise mechanisms remain to be determined, hyperglycemia represents an important pathogenetic factor responsible for the increased risk of S. aureus infection. Herein, we constructed a series of ratiometric fluorescent molecular probes for aureolysin (Aur), a major virulence factor in S. aureus. Using probe 1, we were able to determine specific Aur activity in both cells and tissues. We also observed that elevated glucose levels led to 2-fold higher Aur expression in S. aureus cultures. In a diabetic mouse model, we used molecular imaging to demonstrate that hyperglycemia tripled S. aureus Aur virulence compared to nondiabetic mice, resulting in more severe infections.

Progress and prospects of nanomaterials against resistant bacteria

Drug-resistant bacterial infections are increasingly heightening, which lead to more severe illness, higher cost of treatment and increased risk of death. Nanomaterials-based therapy, an "outrider", serving as a kind of innovative antimicrobial therapeutics, showing promise in replacing antimicrobial agents and enhancing the activity of antibiotics, generally bases on the various inorganic and/or organic materials. When the size of those materials is below to a certain nano-level and the content of nanomaterials is above a certain amount, they are lethal to the resistant bacteria, which bypass the traditional bacterial resistance mechanisms. This review highlights the effect of nanomaterials in combating extracellular/intracellular bacteria and eradicating biofilms. Based on the studies searched on the Web of Science through relevant keywords, this review article starts with analyzing the current situation, resistance mechanisms, and treatment difficulties of bacteria resistance. Then, the efficacy of nanomaterials against resistant bacteria and their mechanisms (e.g., physical impairment, biofilm lysis, regulating bacterial metabolism, protein and DNA replication as well as enhancing the antibiotics concentration in infected cells) are collected. Lastly, the factors affecting the antibacterial efficacy are argued from the side of nanomatrials and bacterium, which followed by the emerging challenges and recent perspectives of achieving higher targeting released nanomaterials as antibacterial therapeutics.

Investigation of Salicylanilides as Botulinum Toxin Antagonists

Botulinum neurotoxin serotype A (BoNT/A) is recognized by the Centers for Disease Control and Prevention (CDC) as the most potent toxin and as a Tier 1 biowarfare agent. The severity and longevity of botulism stemming from BoNT/A is of significant therapeutic concern, and early administration of antitoxin-antibody therapy is the only approved pharmaceutical treatment for botulism. Small molecule therapeutic strategies have targeted both the heavy chain (HC) and the light chain (LC) catalytic active site and α-/β-exosites. The LC translocation mechanism has also been studied, but an effective, nontoxic inhibitor remains underexplored. In this work, we screened a library of salicylanilides as potential translocation inhibitors. Potential leads following a primary screen were further scrutinized to identify sal30, which has a cellular minimal concentration of a drug that is required for 50% inhibition (IC50) value of 141 nM. The inquiry of salicylanilide sal30's mechanism of action was explored through a self-quenched fluorogenic substrate conjugated to bovine serum albumin (DQ-BSA) fluorescence, confocal microscopy, and vacuolar H+-ATPase (V-ATPase) inhibition assays. The summation of these findings imply that endolysosomal proton translocation through the protonophore mechanism of sal30 causes endosome pH to increase, which in turn prevents LC translocation into cytosol, a process that requires an acidic pH. Thus, the inhibition of BoNT/A activity by salicylanilides likely occurs through disruption of pH-dependent endosomal LC translocation. We further probed BoNT inhibition by sal30 using additivity analysis studies with bafilomycin A1, a known BoNT/A LC translocation inhibitor, which indicated the absence of synergy between the two ionophores.

N-acylhomoserine lactonase-based hybrid nanoflowers: a novel and practical strategy to control plant bacterial diseases

BACKGROUND

The disease caused by plant pathogenic bacteria in the production, transportation, and storage of many crops has brought huge losses to agricultural production. N-acylhomoserine lactonases (AHLases) can quench quorum-sensing (QS) by hydrolyzing acylhomoserine lactones (AHLs), which makes them the promising candidates for controlling infections of QS-dependent pathogenic bacteria. Although many AHLases have been isolated and considered as a potentially effective preventive and therapeutic agents for bacterial diseases, the intrinsically poor ambient stability has seriously restricted its application.

RESULTS

Herein, we showed that a spheroid enzyme-based hybrid nanoflower (EHNF), AhlX@Ni₃(PO₄)₂, can be easily synthesized, and it exhibited 10 times AHL (3OC8-HSL) degradation activity than that with free AhlX (a thermostable AHL lactonase). In addition, it showed intriguing stability even at the working concentration, and retained ~ 100% activity after incubation at room temperature (25 °C) for 40 days and approximately 80% activity after incubation at 60 °C for 48 h. Furthermore, it exhibited better organic solvent tolerance and long-term stability in a complicated ecological environment than that of AhlX. To reduce the cost and streamline production processes, CSA@Ni₃(PO₄)₂, which was assembled from the crude supernatants of AhlX and Ni₃(PO₄)₂, was synthesized. Both AhlX@Ni₃(PO₄)₂ and CSA@Ni₃(PO₄)₂ efficiently attenuated pathogenic bacterial infection.

CONCLUSIONS

In this study, we have developed N-acylhomoserine lactonase-based hybrid nanoflowers as a novel and efficient biocontrol reagent with significant control effect, outstanding environmental adaptability and tolerance. It was expected to overcome the bottlenecks of poor stability and limited environmental tolerance that have existed for over two decades and pioneered the practical application of EHNFs in the field of biological control.

Bacterial AB toxins and host-microbe interactions

AB toxins are protein virulence factors secreted by many bacterial pathogens, contributing to the pathogenicity of the cognate bacteria. AB toxins consist of two functionally distinct components: the enzymatic "A" component for pathogenicity and the receptor-binding "B" component for toxin delivery. Consistently, unlike other virulence factors such as effectors, AB toxins do not require additional systems to deliver them to the target host cells. Target host cells are located in the infection site and/or located distantly from infected host cells. The first part of this review discusses the structural and functional features of single-peptide and multiprotein AB toxins in the context of host-microbe interactions, using several well-characterized examples. The second part of this review discusses toxin neutralization strategies, as well as applications of AB toxins relevant to developing intervention strategies against diseases.

Combatting Antibiotic Resistance Using Supramolecular Assemblies

Antibiotic resistance has posed a great threat to human health. The emergence of antibiotic resistance has always outpaced the development of new antibiotics, and the investment in the development of new antibiotics is diminishing. Supramolecular self-assembly of the conventional antibacterial agents has been proved to be a promising and versatile strategy to tackle the serious problem of antibiotic resistance. In this review, the recent development of antibacterial agents based on supramolecular self-assembly strategies will be introduced.

Secondary Ammonium-Based Hyperbranched Poly(amidoamine) with Excellent Membrane-Active Property for Multidrug-Resistant Bacterial Infection

With the rapid emergence of microbial infections induced by "superbugs", public health and the global economy are threatened by the lack of effective and biocompatible antibacterial agents. Herein, we systematically design a series of secondary ammonium-based hyperbranched poly(amidoamine) (SAHBP) with different alkyl chain lengths for probing high-efficacy antibacterial agents. SAHBP modified with alkyl tails at the hyperbranched core could efficiently kill Escherichia coli and Staphylococcus aureus, two types of clinically important bacteria worldwide. The best SAHBP with 12-carbon-long alkyl tails (SAHBP-12) also showed high activity against problematic multidrug-resistant bacteria, including Pseudomonas aeruginosa and methicillin-resistant S. aureus (MRSA). Based on ζ potential, isothermal titration microcalorimetry (ITC), and membrane integrity assays, it is found that SAHBP-12 could attach to the cell membrane via electrostatic adsorption and hydrophobic interactions, following which the integrity of the bacterial cell wall and the cell membrane is disrupted, resulting in severe cell membrane damage and the leakage of cytoplasmic contents, finally causing bacterial cell death. Impressively, benefiting from excellent membrane-active property, SAHBP-12 exhibited robust therapeutic efficacy in MRSA-infected mice wounds. Moreover, SAHBP-12 also showed excellent biosafety in vitro and in vivo, which undoubtedly distinguished it as a potent weapon in combating the growing threat of problematic multidrug-resistant bacterial infections.

Fluorescent dyes with multiple quaternary ammonium centers for specific image discrimination and Gram-positive antibacterial activity

Three quaternary ammonium compounds (QACs), TPQA, T2PQA, and T3PQA, were synthesized and employed in antimicrobial tests against E. coli and S. aureus. It was confirmed that they exhibit selective bacteriostasis against S. aureus. The antibacterial activities of the compounds were evaluated via determining their minimum inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) against S. aureus using the 2,3,5-triphenyltetrazolium chloride (TTC) coloration method. Notably, T2PQA exhibited far better properties than TPQA and T3PQA, with the activity found to be dependent on the structure of the QA and the exposed hydrophobic groups. All three compounds showed promising potential for killing Gram-positive bacteria, efficiently guided by fluorescence imaging.

The antibacterial activity of quinazoline and quinazolinone hybrids

Bacterial infections cause substantial morbidity and mortality across the world and pose serious threats to humankind. Drug resistance, especially multidrug resistance resulting from different defensive mechanisms in bacteria, is the leading cause of failure the chemotherapy, making it an urgent need to develop more effective antibacterials. Quinazoline and quinazolinone frameworks have received considerable attention due to their diversified therapeutic potential. In particular, quinazoline/quinazolinone hybrids could exert antibacterial activity through various mechanisms and are useful scaffolds for the discovery of novel antibacterials. This review principally emphases on the antibacterial potential, structure-activity relationships (SARs), and mechanism of action of quinazoline and quinazolinone hybrids, covering articles published between 2017 and 2021.

Versatile polymer-based strategies for antibacterial drug delivery systems and antibacterial coatings

Human health damage and economic losses due to bacterial infections are very serious worldwide. Excessive use of antibiotics has caused an increase in bacterial resistance. Fortunately, various non-antibiotic antibacterial materials...

Natural Berberine-derived Azolyl Ethanols as New Structural Antibacterial Agents against Drug-Resistant Escherichia coli

Natural berberine-derived azolyl ethanols as new structural antibacterial agents were designed and synthesized for fighting with dreadful bacterial resistance. Partial target molecules exhibited potent activity against the tested strains, particularly, nitroimidazole derivative 4d and benzothiazole-2-thoil compound 18b, with low cytotoxicity both exerted strong antibacterial activities against multidrug-resistant Escherichia coli at low concentrations as 0.007 and 0.006 mM, respectively. Meanwhile, the active compounds 4d and 18b possessed the ability to rapidly kill bacteria and observably eradicate the E. coli biofilm by reducing exopolysaccharide content to prevent bacterial adhesion, which was conducive to alleviating the development of E. coli resistance. Preliminary mechanistic explorations suggested that the excellent antibacterial potential of molecules 4d and 18b might be attributed to their ability to disintegrate membrane, accelerate ROS accumulation, reduce bacterial metabolism, and intercalate into DNA groove. These results provided powerful information for the further exploitation of natural berberine derivatives against bacterial pathogens.

Multicharged Supramolecular Assembly Mediated by Polycationic Cyclodextrin for Efficiently Photodynamic Antibacteria

Supramolecular antimicrobial materials based on synthetic macrocycles have recently aroused enormous interests due to their controllable and effective antibacterial treatment. Herein, a multicharged supramolecular assembly was fabricated employing the moderate host-guest interaction between hexa-adamantane-appended ruthenium polypyridyl (Ru2) and polycationic cyclodextrin (CD-QAS) in water. The positively multicharged feature of supramolecular assembly could remarkably enhance the specific intercalation and accumulation in negatively charged bacteria membrane leading to the physical membrane damage. Subsequently, the assembly could efficiently initiate the significant generation of singlet oxygen (¹O₂) in situ when irradiated with white light thus exhibiting a highly efficient antibacterial capability. Significantly, antibacterial experiments indicated that Ru2/CD-QAS displayed less effect on suppressing the growth of E. coli only about 25% in the absence of light while they exhibited excellent killing efficiency more than 99% toward E. coli under light irradiation. This work provides a simple approach for constructing supramolecular antimicrobial materials for synergistic photodynamic antibacteria.

Bacterial virulence factors: a target for heterocyclic compounds to combat bacterial resistance

Antibiotic resistance is one of the most important challenges of the 21st century. However, the growing understanding of bacterial pathogenesis and cell-to-cell communication has revealed many potential strategies for the discovery of drugs that can be used for the treatment of bacterial infections. Interfering with bacterial virulence and/or quorum sensing could be a particularly interesting approach, because it is believed to exert less selective pressure on the bacterial resistance than with traditional strategies, geared toward killing bacteria or preventing their growth. Here, we discuss the mechanism of bacterial virulence, presenting promising strategies and recently synthesized heterocyclic compounds to combat future bacterial infections.

Effective Antibacterial and Antihemolysin Activities of Ellipticine Hydrochloride against Streptococcus suis in a Mouse Model

Streptococcal toxic shock-like syndrome (STSLS) caused by the epidemic strain of Streptococcus suis leads to severe inflammation and high mortality. The life and health of humans and animals are also threatened by the increasingly severe antimicrobial resistance in Streptococcus suis There is an urgent need to discover novel strategies for the treatment of S. suis infection. Suilysin (SLY) is considered to be an important virulence factor in the pathogenesis of S. suis In this study, ellipticine hydrochloride (EH) was reported as a compound that antagonizes the hemolytic activity of SLY. In vitro, EH was found to effectively inhibit SLY-mediated hemolytic activity. Furthermore, EH had a strong affinity for SLY, thereby directly binding to SLY to interfere with the hemolytic activity. Meanwhile, it was worth noting that EH was also found to have a significant antibacterial activity. In vivo, compared with traditional ampicillin, EH not only significantly improved the survival rate of mice infected with S. suis 2 strain Sc19 but also relieved lung pathological damage. Furthermore, EH effectively decreased the levels of inflammatory cytokines (interleukin-6 [IL-6], tumor necrosis factor alpha [TNF-α]) and blood biochemistry enzymes (alanine transaminase [ALT], aspartate transaminase [AST], creatine kinase [CK]) in Sc19-infected mice. Additionally, EH markedly reduced the bacterial load of tissues in Sc19-infected mice. In conclusion, our findings suggest that EH can be a potential compound for treating S. suis infection in view of its antibacterial and antihemolysin activity.IMPORTANCE In recent years, the inappropriate use of antibiotics has unnecessarily caused the continuous emergence of resistant bacteria. The antimicrobial resistance of Streptococcus suis has also become an increasingly serious problem. Targeting virulence can reduce the selective pressure of bacteria on antibiotics, thereby alleviating the development of bacterial resistance to a certain extent. Meanwhile, the excessive inflammatory response caused by S. suis infection is considered the primary cause of acute death. Here, we found that ellipticine hydrochloride (EH) exhibited effective antibacterial and antihemolysin activities against S. suisin vitroIn vivo, compared with ampicillin, EH had a significant protective effect on S. suis serotype 2 strain Sc19-infected mice. Our results indicated that EH, with dual antibacterial and antivirulence effects, will contribute to treating S. suis infections and alleviating the antimicrobial resistance of S. suis to a certain extent. More importantly, EH may develop into a promising drug for the prevention of acute death caused by excessive inflammation.

Antivirulence Properties of a Low-Molecular-Weight Quaternized Chitosan Derivative against Pseudomonas aeruginosa

The co-occurrence of increasing rates of resistance to current antibiotics and the paucity of novel antibiotics pose major challenges for the treatment of bacterial infections. In this scenario, treatments targeting bacterial virulence have gained considerable interest as they are expected to exert a weaker selection for resistance than conventional antibiotics. In a previous study, we demonstrated that a low-molecular-weight quaternized chitosan derivative, named QAL, displays antibiofilm activity against the major pathogen Pseudomonas aeruginosa at subinhibitory concentrations. The aim of this study was to investigate whether QAL was able to inhibit the production of relevant virulence factors of P. aeruginosa. When tested in vitro at subinhibiting concentrations (0.31-0.62 mg/mL), QAL markedly reduced the production of pyocyanin, pyoverdin, proteases, and LasA, as well as inhibited the swarming motility of three out of four P. aeruginosa strains tested. Furthermore, quantitative reverse transcription PCR (qRT-PCR) analyses demonstrated that expression of lasI and rhlI, two QS-related genes, was highly downregulated in a representative P. aeruginosa strain. Confocal scanning laser microscopy analysis suggested that FITC-labelled QAL accumulates intracellularly following incubation with P. aeruginosa. In contrast, the reduced production of virulence factors was not evidenced when QAL was used as the main polymeric component of polyelectrolyte-based nanoparticles. Additionally, combination of sub-MIC concentrations of QAL and tobramycin significantly reduced biofilm formation of P. aeruginosa, likely due to a synergistic activity towards planktonic bacteria. Overall, the results obtained demonstrated an antivirulence activity of QAL, possibly due to polymer intracellular localization and QS-inhibition, and its ability to inhibit P. aeruginosa growth synergizing with tobramycin.

Polymeric Nanoparticles for Antimicrobial Therapies: An Up-To-Date Overview

Despite the many advancements in the pharmaceutical and medical fields and the development of numerous antimicrobial drugs aimed to suppress and destroy pathogenic microorganisms, infectious diseases still represent a major health threat affecting millions of lives daily. In addition to the limitations of antimicrobial drugs associated with low transportation rate, water solubility, oral bioavailability and stability, inefficient drug targeting, considerable toxicity, and limited patient compliance, the major cause for their inefficiency is the antimicrobial resistance of microorganisms. In this context, the risk of a pre-antibiotic era is a real possibility. For this reason, the research focus has shifted toward the discovery and development of novel and alternative antimicrobial agents that could overcome the challenges associated with conventional drugs. Nanotechnology is a possible alternative, as there is significant evidence of the broad-spectrum antimicrobial activity of nanomaterials and nanoparticles in particular. Moreover, owing to their considerable advantages regarding their efficient cargo dissolving, entrapment, encapsulation, or surface attachment, the possibility of forming antimicrobial groups for specific targeting and destruction, biocompatibility and biodegradability, low toxicity, and synergistic therapy, polymeric nanoparticles have received considerable attention as potential antimicrobial drug delivery agents. In this context, the aim of this paper is to provide an up-to-date overview of the most recent studies investigating polymeric nanoparticles designed for antimicrobial therapies, describing both their targeting strategies and their effects.

Investigational Studies on a Hit Compound Cyclopropane-Carboxylic Acid Derivative Targeting O-Acetylserine Sulfhydrylase as a Colistin Adjuvant

Antibacterial adjuvants are of great significance, since they allow the therapeutic dose of conventional antibiotics to be lowered and reduce the insurgence of antibiotic resistance. Herein, we report that an O-acetylserine sulfhydrylase (OASS) inhibitor can be used as a colistin adjuvant to treat infections caused by Gram-positive and Gram-negative pathogens. A compound that binds OASS with a nM dissociation constant was tested as an adjuvant of colistin against six critical pathogens responsible for infections spreading worldwide, Escherichia coli, Salmonella enterica serovar Typhimurium, Klebisiella pneumoniae, Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, and Staphylococcus pseudintermedius. The compound showed promising synergistic or additive activities against all of them. Knockout experiments confirmed the intracellular target engagement supporting the proposed mechanism of action. Moreover, compound toxicity was evaluated by means of its hemolytic activity against sheep defibrinated blood cells, showing a good safety profile. The 3D structure of the compound in complex with OASS was determined at 1.2 Å resolution by macromolecular crystallography, providing for the first time structural insights about the nature of the interaction between the enzyme and this class of competitive inhibitors. Our results provide a robust proof of principle supporting OASS as a potential nonessential antibacterial target to develop a new class of adjuvants and the structural basis for further structure-activity relationship studies.

Exploring the future of infectious disease treatment in a post-antibiotic era: A comparative review of alternative therapeutics

Antibiotic resistance is projected to be one of the greatest healthcare challenges of the 21st century. As the efficacy of these critical drugs wanes and the discovery of new antibiotics stagnates, exploration of alternative therapies could offer a much needed solution. Although numerous alternative therapies are currently under investigation, three in particular appear poised for long-term success, namely antimicrobial oligonucleotides, monoclonal antibodies and phage therapy. Antimicrobial oligonucleotides could conceivably offer the greatest spectrum of activity while having the lowest chance of unrecoverable resistance. Bacteriophages, while most susceptible to resistance, are inexhaustible, inexpensive and exceptionally adept at eliminating biofilm-associated infections. And although monoclonal antibodies may have limited access to such recalcitrant bacteria, these agents are uniquely able to neutralise exotoxins and other diffusible virulence factors. This comparative review seeks to illuminate these promising therapies and to encourage the scientific and financial support necessary to usher in the next generation of infectious disease treatment.

Thioether-linked dihydropyrrol-2-one analogues as PqsR antagonists against antibiotic resistant Pseudomonas aeruginosa

The Pseudomonas quinolone system (pqs) is one of the key quorum sensing systems in antibiotic-resistant P. aeruginosa and is responsible for the production of virulence factors and biofilm formation. Thus, synthetic small molecules that can target the PqsR (MvfR) receptor can be utilized as quorum sensing inhibitors to treat P. aeruginosa infections. In this study, we report the synthesis of novel thioether-linked dihydropyrrol-2-one (DHP) analogues as PqsR antagonists. Compound 7g containing a 2-mercaptopyridyl linkage effectively inhibited the pqs system with an IC₅₀ of 32 µM in P. aeruginosa PAO1. Additionally, these inhibitors significantly reduced bacterial aggregation and biofilm formation without affecting planktonic growth. The molecular docking study suggest that these inhibitors bind with the ligand binding domain of the MvfR as a competitive antagonist.

Does targeting Arg98 of FimH lead to high affinity antagonists?

Bacterial resistance has become an important challenge in the treatment of urinary tract infections. The underlying resistance mechanisms can most likely be circumvented with an antiadhesive approach, antagonizing the lectin FimH located at the tip of fimbriae of uropathogenic E. coli. Here we report on a novel series of FimH antagonists based on the 1-(α-d-mannopyranosyl)-4-phenyl-1,2,3-triazole scaffold, designed to incorporate carboxylic acid or ester functions to interact with FimH Arg98. The most potent representative of the series, ester 11e, displayed a K_d value of 7.6 nM for the lectin domain of FimH with a general conclusion that all esters outperform carboxylates in terms of affinity. Surprisingly, all compounds from this new series exhibited improved binding affinities also for the R98A mutant, indicating another possible interaction contributing to binding. Our study on 1-(α-d-mannopyranosyl)-4-phenyl-1,2,3-triazole-based FimH antagonists offers proof that targeting Arg98 side chain by a "chemical common sense", i.e. by introduction of the acidic moiety to form ionic bond with Arg98 is most likely unsuitable approach to boost FimH antagonists' potency.

Bacterial Resistance: Antibiotics of Last Generation used in Clinical Practice and the Arise of Natural Products as New Therapeutic Alternatives

Bacterial resistance to therapeutical drugs has been a serious issue over the last decades. In fact, the quick development of resistance mechanisms by the microorganisms has been fatal for millions of people around the world, turning into a public health issue. The major cause of the resistance mechanisms is the overuse of antimicrobials. European countries try to implement mechanisms to overcome antimicrobial resistance in the community through the rational use of antimicrobials. The scientific community has been exhaustively dedicated to the discovering of new, safer and efficient drugs, being the exploitation of natural resources, mainly plants and fungi, considered as a hot topic in the field of antimicrobial agents. Innumerous reports have already shown the promising capacity of natural products or molecules extracted from these natural resources, to act as bacteriostatic and bactericidal agents. More importantly, these natural agents present significantly lower harmful effects. Bearing that in mind, this review aims at giving a contribution to the knowledge about the synthetic antibiotics of the last generation. Moreover, it is intended to provide information about the last advances regarding the discovery of new antimicrobial agents. Thus, a compilation of the chemical characteristics, efficiency, harmful outcomes and resistance mechanisms developed by the microorganisms can be consulted in the following sections together with a critical discussion, in line with the recent approaches. Furthermore, modern strategies for the prospection of novel anti-infective compounds for tackling resistant bacteria have been considered as also a current synopsis of plants and mushrooms with relevant antimicrobial potentials.

Indole/isatin-containing hybrids as potential antibacterial agents

The emergence and worldwide spread of drug-resistant bacteria have already posed a serious threat to human life, creating the urgent need to develop potent and novel antibacterial drug candidates with high efficacy. Indole and isatin (indole-2,3-dione) present a wide structural and mechanistic diversity, so their derivatives possess various pharmacological properties and occupy a salient place in the development of new drugs. Indole/isatin-containing hybrids, which demonstrate a promising activity against a panel of clinically important Gram-positive and Gram-negative bacteria, are privileged scaffolds for the discovery of novel antibacterial candidates. This review, covering articles published between January 2015 and May 2020, focuses on the development and structure-activity relationship (SAR) of indole/isatin-containing hybrids with potential application for fighting bacterial infections, to facilitate further rational design of novel drug candidates.