Immobilization of antibacterial dihydropyrrol-2-ones on functional polymer supports to prevent bacterial infections in vivo

Disruption of Communication: Recent Advances in Antibiofilm Materials with Anti-Quorum Sensing Properties

Biofilm contamination presents a significant threat to public health, the food industry, and aquatic/marine-related applications. In recent decades, although various methods have emerged to combat biofilm contamination, the intricate and persistent nature of biofilms makes complete eradication challenging. Therefore, innovative alternative solutions are imperative for addressing biofilm formation. Instead of solely focusing on the eradication of mature biofilms, strategically advantageous measures involve the delay or prevention of biofilm formation on surfaces. Quorum sensing, a communication system enabling bacteria to coordinate their behavior based on population density, plays a pivotal role in biofilm formation for numerous microbial species. Materials possessing antibiofilm properties that target quorum sensing have gained considerable attention for their potential to prevent biofilm formation. This Review consolidates recent research progress on the utilization of materials with antiquorum sensing properties for combating biofilm formation. These materials can be categorized into three distinct types: (i) antibiofilm nanomaterials, (ii) antibiofilm surfaces, and (iii) antibiofilm hydrogels with antiquorum sensing capabilities. Finally, the Review concludes with a brief discussion of current challenges and outlines potential avenues for future research.

Iron-Mediated C-H Functionalization of Unactivated Alkynes for the Synthesis of Derivatized Dihydropyrrolones: Regioselectivity Under Thermodynamic Control

Cyclopentadienyliron dicarbonyl-based complexes present opportunities for underexplored disconnections in synthesis. Access to challenging dihydropyrrolone products is achieved by propargylic C-H functionalization of alkynes for the formation of cyclic organoiron species. Excellent regioselectivity for unsymmetrical alkynes is observed in many cases. Notably, regioselectivity under these stoichiometric conditions diverges from those observed previously under catalysis, occurring at the more-substituted terminus of the alkyne, allowing for methine functionalization and the formation of quaternary centers. Divergent demetallation of the intermediate organoiron complexes gives access to chemically diverse products which are amenable to further functionalization.

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.

Structure-activity relationships of furanones, dihydropyrrolones and thiophenones as potential quorum sensing inhibitors

Since their initial isolation from the marine alga Delisea pulchra, bromofuranones have been investigated as potential inhibitors of quorum sensing (QS) in various bacterial strains. QS is an important mechanism by which bacteria co-ordinate their molecular response to the environment. QS is intrinsically linked to bacterial antibiotic resistance. Inspired by nature, chemists have developed a wide variety of synthetic analogs in an effort to elucidate the structure-activity relationships of these compounds, and to ultimately develop novel antimicrobial agents. In this work, we describe advances in this field while paying particular attention to apparent structure-activity relationships. This review is organized according to the main ring systems under investigation, namely furanones, dihydropyrrolones and thiophenones.

Combating Implant Infections: Shifting Focus from Bacteria to Host

The widespread use of biomaterials to support or replace body parts is increasingly threatened by the risk of implant-associated infections. In the quest for finding novel anti-infective biomaterials, there generally has been a one-sided focus on biomaterials with direct antibacterial properties, which leads to excessive use of antibacterial agents, compromised host responses, and unpredictable effectiveness in vivo. This review sheds light on how host immunomodulation, rather than only targeting bacteria, can endow biomaterials with improved anti-infective properties. How antibacterial surface treatments are at risk to be undermined by biomaterial features that dysregulate the protection normally provided by critical immune cell subsets, namely, neutrophils and macrophages, is discussed. Accordingly, how the precise modification of biomaterial surface biophysical cues, or the incorporation of immunomodulatory drug delivery systems, can render biomaterials with the necessary immune-compatible and immune-protective properties to potentiate the host defense mechanisms is reviewed. Within this context, the protective role of host defense peptides, metallic particles, quorum sensing inhibitors, and therapeutic adjuvants is discussed. The highlighted immunomodulatory strategies may lay a foundation to develop anti-infective biomaterials, while mitigating the increasing threat of antibacterial drug resistance.

Recent progress and strategies to develop antimicrobial contact lenses and lens cases for different types of microbial keratitis

Although contact lenses are widely used for vision correction, they are also the primary cause of a number of ocular diseases such as microbial keratitis (MK), etc. and inflammatory events such as infiltrative keratitis (IK), contact lens acute red eye (CLARE), contact lens-induced peripheral ulcer (CLPU), etc. These diseases and infiltrative events often result from microbial contamination of lens care solutions and lens cases that can be exacerbated by unsanitary lens care and extended lens wear. The treatment of microbial biofilms (MBs) on lens cases and contact lenses are complicated and challenging due to their resistance to conventional antimicrobial lens care solutions. More importantly, MK caused by MBs can lead to acute visual damage or even vision impairment. Therefore, the development of lens cases, lens care solutions, and contact lenses with effective antimicrobial performance against MK will contribute to the safe use of contact lenses. This review article summarizes and discusses different chemical approaches for the development of antimicrobial contact lenses and lens cases employing passive surface modifications, antimicrobial peptides, free-radical fabricating agents, quorum sensing quenchers, antibiotics, antifungal drugs and various metals and coatings with antimicrobial nanomaterials. The benefits and shortcomings of these approaches are assessed, and alternative solutions for future developments are discussed.

The Role of Orientation of Surface Bound Dihydropyrrol-2-ones (DHP) on Biological Activity

Quorum sensing (QS) signaling system is important for bacterial growth, adhesion, and biofilm formation resulting in numerous infectious diseases. Dihydropyrrol-2-ones (DHPs) represent a novel class of antimicrobial agents that inhibit QS, and are less prone to develop bacterial resistance due to their non-growth inhibition mechanism of action which does not cause survival pressure on bacteria. DHPs can prevent bacterial colonization and quorum sensing when covalently bound to substrates. In this study, the role of orientation of DHP compounds was investigated after covalent attachment by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)/N-hydroxysuccinimide (NHS) coupling reaction to amine-functionalized glass surfaces via various positions of the DHP scaffold. The functionalized glass surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and contact angle measurements and tested for their in vitro biological activity against S. aureus and P. aeruginosa. DHPs attached via the N-1 position resulted in the highest antibacterial activities against S. aureus, while no difference was observed for DHPs attached either via the N-1 position or the C-4 phenyl ring against P. aeruginosa.

Dihydropyrrolones as bacterial quorum sensing inhibitors

Bacteria regulate their pathogenicity and biofilm formation through quorum sensing (QS), which is an intercellular communication system mediated by the binding of signaling molecules to QS receptors such as LasR. In this study, a range of dihydropyrrolone (DHP) analogues were synthesized via the lactone-lactam conversion of lactone intermediates. The synthesized compounds were tested for their ability to inhibit QS, biofilm formation and bacterial growth of Pseudomonas aeruginosa. The compounds were also docked into a LasR crystal structure to rationalize the observed structure-activity relationships. The most active compound identified in this study was compound 9i, which showed 63.1% QS inhibition of at 31.25 µM and 60% biofilm reduction at 250 µM with only moderate toxicity towards bacterial cell growth.

Molecular topology: A new strategy for antimicrobial resistance control

The control of antimicrobial resistance (AMR) seems to have come to an impasse. The use and abuse of antibacterial drugs has had major consequences on the genetic mutability of both pathogenic and nonpathogenic microorganisms, leading to the development of new highly resistant strains. Because of the complexity of this situation, an in silico strategy based on QSAR molecular topology was devised to identify synthetic molecules as antimicrobial agents not susceptible to one or several mechanisms of resistance such as: biofilms formation (BF), ionophore (IA) activity, epimerase (EI) activity or SOS system (RecA inhibition). After selecting a group of 19 compounds, five of them showed significant antimicrobial activity against several strains of Staphylococcus (2 S. aureus, including 1 methicillin resistant, and 1 S. epidermidis), with MIC values between 16 and 32 mg/L. Among the compounds active on RecA, one showed a marked activity in decreasing RecA gene expression in Escherichia coli.

Quorum sensing inhibitory activities of surface immobilized antibacterial dihydropyrrolones via click chemistry

Device-related infection remains a major barrier to the use of biomaterial implants as life-saving devices. This study aims to examine the effectiveness and mechanism of action of surface attached dihydropyrrolones (DHPs), a quorum sensing (QS) inhibitor, against bacterial colonization. DHPs were covalently attached on glass surfaces via copper-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC) click reaction. The covalent attachment of DHP surfaces was confirmed by X-ray photoelectron spectroscopy (XPS) and contact angle measurements, and the antimicrobial efficacy of the DHP coatings was assessed by confocal laser scanning microscopy (CLSM) and image analysis. The results demonstrated that covalently bound DHP compounds are effective in reducing the adhesion by up to 97% (p < 0.05) for both Pseudomonas aeruginosa and Staphylococcus aureus. Furthermore, using the green fluorescent protein (Gfp)-based reporter technology, it is demonstrated that surface attached DHPs were able to repress the expression of a lasB-gfp reporter fusion of P. aeruginosa by 72% (p < 0.001) without affecting cell viability. This demonstrates the ability of the covalently bound QS inhibitor to inhibit QS and suggests the existence of a membrane-based pathway(s) for QS inhibition. Hence, strategies based on incorporation of QS inhibitors such as DHPs represent a potential approach for prevention of device-related infections.

Characterization of chemoselective surface attachment of the cationic peptide melimine and its effects on antimicrobial activity

Antimicrobial peptides (AMPs) are promising alternatives to current treatments for bacterial infections. However, our understanding of the structural-functional relationship of tethered AMPs still requires further investigation to establish a general approach for obtaining consistent antimicrobial surfaces. In this study, we have systematically examined the effects of surface orientation of a broad-spectrum synthetic cationic peptide, melimine, on its antibacterial activity against Gram-positive and Gram-negative bacteria. The attachment of melimine to maleimide-functionalized glass was facilitated by addition of a single cysteine amino acid into the peptide sequence at the N-terminus (CysN) or C-terminus (CysC), or at position 13 (Cys13, approximately central). The successful attachment of the modified melimine was monitored using X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry (ToF-SIMS) with principle component analysis. The ToF-SIMS analysis clearly demonstrated structural difference between the three orientations. The peptide density for the modified surfaces was found to be between 3.5-4.0×10(-9)molcm(-2) using a modified Bradford assay. The ability of the surfaces to resist Pseudomonas aeruginosa and Staphylococcus aureus colonization was compared using fluorescence confocal microscopy. Reductions in total P. aeruginosa and S. aureus adhesion of 70% (p<0.001) and 83% (p<0.001), respectively, after 48h were observed for the melimine samples when compared to the blank control. We found that melimine attached via the N-terminus was the most effective in reducing total bacterial adhesion and bacterial viability with two- and four times (p<0.001) more activity than melimine attached via the C-terminus for P. aeruginosa and S. aureus, respectively. Furthermore, for Cys13, despite having the highest measured peptide density of the three surfaces, the higher concentration did not confer the greatest antibacterial effect. This highlights the importance of orientation of the peptides on the surface to efficacy. Our results suggest that the optimal orientation of the cationic residues is essential for maximum surface activity, whereby the optimal activity is obtained when the cationic portion is more available to interact with colonizing bacteria.