Fluoroquinolone-Transition Metal Complexes: A Strategy to Overcome Bacterial Resistance

A Review of the Resistance Mechanisms for β-Lactams, Macrolides and Fluoroquinolones among Streptococcus pneumoniae

Streptococcus pneumoniae (S. pneumoniae) is a bacterial species often associated with the occurrence of community-acquired pneumonia (CAP). CAP refers to a specific kind of pneumonia that occurs in individuals who acquire the infection outside of a healthcare setting. It represents the leading cause of both death and morbidity on a global scale. Moreover, the declaration of S. pneumoniae as one of the 12 leading pathogens was made by the World Health Organization (WHO) in 2017. Antibiotics like β-lactams, macrolides, and fluoroquinolones are the primary classes of antimicrobial medicines used for the treatment of S. pneumoniae infections. Nevertheless, the efficacy of these antibiotics is diminishing as a result of the establishment of resistance in S. pneumoniae against these antimicrobial agents. In 2019, the WHO declared that antibiotic resistance was among the top 10 hazards to worldwide health. It is believed that penicillin-binding protein genetic alteration causes β-lactam antibiotic resistance. Ribosomal target site alterations and active efflux pumps cause macrolide resistance. Numerous factors, including the accumulation of mutations, enhanced efflux mechanisms, and plasmid gene acquisition, cause fluoroquinolone resistance. Furthermore, despite the advancements in pneumococcal vaccinations and artificial intelligence (AI), it is not feasible for individuals to rely on them indefinitely. The ongoing development of AI for combating antimicrobial resistance necessitates more research and development efforts. A few strategies can be performed to curb this resistance issue, including providing educational initiatives and guidelines, conducting surveillance, and establishing new antibiotics targeting another part of the bacteria. Hence, understanding the resistance mechanism of S. pneumoniae may aid researchers in developing a more efficacious antibiotic in future endeavors.

Antibacterial Properties of Mesoporous Silica Nanoparticles Modified with Fluoroquinolones and Copper or Silver Species

Antibiotic resistance is a global problem and bacterial biofilms contribute to its development. In this context, this study aimed to perform the synthesis and characterization of seven materials based on silica mesoporous nanoparticles functionalized with three types of fluoroquinolones, along with Cu2+ or Ag+ species to evaluate the antibacterial properties against Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, and Pseudomonas aeruginosa, including clinical and multi-drug-resistant strains of S. aureus and P. aeruginosa. In addition, in order to obtain an effective material to promote wound healing, a well-known proliferative agent, phenytoin sodium, was adsorbed onto one of the silver-functionalized materials. Furthermore, biofilm studies and the generation of reactive oxygen species (ROS) were also carried out to determine the antibacterial potential of the synthesized materials. In this sense, the Cu2+ materials showed antibacterial activity against S. aureus and E. coli, potentially due to increased ROS generation (up to 3 times), whereas the Ag+ materials exhibited a broader spectrum of activity, even inhibiting clinical strains of MRSA and P. aeruginosa. In particular, the Ag+ material with phenytoin sodium showed the ability to reduce biofilm development by up to 55% and inhibit bacterial growth in a "wound-like medium" by up to 89.33%.

A perception into binary and ternary copper (II) complexes: synthesis, characterization, DFT modeling, antimicrobial activity, protein binding screen, and amino acid interaction

Ensuring healthy lives and promoting well-being for all at all ages is the third goal of the sustainable development plan, so it was necessary to identify the most important problems that threaten health in our world. The World Health Organization declared that antibiotic resistance is one of the uppermost global public health threats facing humanity and searching for new antibiotics is slow. This problem can be approached by improving available drugs to combat various bacterial threats. To circumvent bacterial resistance, three copper(II) complexes based on the pefloxacin drug were prepared and characterized using analytical, spectroscopic, and thermal techniques. The resulting data suggested the formation of one octahedral binary and two distorted square pyramidal ternary complexes. Fluorescence spectra results revealed the formation of a turn-on fluorophore for amino acid detection. Computational calculations investigated quantum and reactivity parameters. Molecular electrostatic potential profiles and noncovalent bond interaction-reduced density gradient analysis indicated the active sites on the complex surface. The complexes were subjected to six microbial species, where the octahedral binary complex provoked its antimicrobial potency in comparison with ternary complexes. The enhanced antimicrobial activity against gram-negative bacterium E-coli compared to gentamicin was exhibited by the three complexes. Docking simulation was performed based on the crystal structure of E. coli and S. pneumoniae receptors using 5I2D and 6O15 codes. The binary complex exhibited a potent fitness score with 5I2D (TBE = - 107 kcal/mol) while ternary complexes displayed the highest docked score of fitness with 6O15.

Dynamic Intramolecular Cap for Preserving Metallodrug Integrity─A Case of Catalytic Fluoroquinolones

A library of eight new fluoroquinolone-nuclease conjugates containing a guanidinoethyl or aminoethyl auxiliary pendant on the cyclen moiety was designed and synthesized to investigate their potential for overcoming the general issue of "metallodrug vulnerability" under physiological conditions. The Cu(II) and Co(III) complexes of the new designer compounds were synthesized, and their potential to operate a dynamic, intramolecular cap with DNase activity was explored. The lead Co(III)-cyclen-ciprofloxacin conjugate showed excellent in vitro hydrolytic DNase activity, which was retained in the presence of strong endogenous chelators and exhibited enhanced antibacterial activity relative to the metal-free ligand (in the absence of any adjuvants), thereby demonstrating a "proof of concept" in vitro and ex vivo, respectively, for the dynamic cap hypothesis. The lead conjugate nicked supercoiled plasmid DNA within the fluoroquinolone-gyrase-DNA ternary complex and thereby disabled the function of gyrase, a new mode of action not previously reported for any fluoroquinolone.

Instantaneous synthesis and full characterization of organic-inorganic laccase-cobalt phosphate hybrid nanoflowers

A novel approach termed the "concentrated method" was developed for the instant fabrication of laccase@Co₃(PO₄)₂•hybrid nanoflowers (HNFs). The constructed HNFs were obtained by optimizing the concentration of cobalt chloride and phosphate buffer to reach the highest activity recovery. The incorporation of 30 mM CoCl₂ and 160 mM phosphate buffer (pH 7.4) resulted in a fast anisotropic growth of the nanomaterials. The purposed method did not involve harsh conditions and prolonged incubation of precursors, as the most reported approaches for the synthesis of HNFs. The catalytic efficiency of the immobilized and free laccase was 460 and 400 M⁻¹S⁻¹, respectively. Also, the enzymatic activity of the prepared biocatalyst was 113% of the free enzyme (0.5 U mL⁻¹). The stability of the synthesized HNFs was enhanced by 400% at pH 6.5–9.5 and the elevated temperatures. The activity of laccase@Co₃(PO₄)₂•HNFs declined to 50% of the initial value after 10 reusability cycles, indicating successful immobilization of the enzyme. Structural studies revealed a 32% increase in the α-helix content after hybridization with cobalt phosphate, which improved the activity and stability of the immobilized laccase. Furthermore, the fabricated HNFs exhibited a considerable ability to remove moxifloxacin as an emerging pollutant. The antibiotic (10 mg L⁻¹) was removed by 24% and 75% after 24 h through adsorption and biodegradation, respectively. This study introduces a new method for synthesizing HNFs, which could be used for the fabrication of efficient biocatalysts, biosensors, and adsorbents for industrial, biomedical, and environmental applications.

A Combination of Pharmacophore-Based Virtual Screening, Structure-Based Lead Optimization, and DFT Study for the Identification of S. epidermidis TcaR Inhibitors

The transcriptional regulator (TcaR) enzyme plays an important role in biofilm formation. Prevention of TcaR-DNA complex formation leads to inhibit the biofilm formation is likely to reveal therapeutic ways for the treatment of bacterial infections. To identify the novel ligands for TcaR and to provide a new idea for drug design, two efficient drug design methods, such as pharmacophore modeling and structure-based drug design, were used for virtual screening of database and lead optimization, respectively. Gemifloxacin (FDA-approved drug) was considered to generate the pharmacophore model for virtual screening of the ZINC database, and five hits, namely ZINC77906236, ZINC09550296, ZINC77906466, ZINC09751390, and ZINC01269201, were identified as novel inhibitors of TcaR with better binding energies. Using structure-based drug design, a set of 7a–7p inhibitors of S. epidermidis were considered, and Mol34 was identified with good binding energy and high fitness score with improved pharmacological properties. The active site residues ARG110, ASN20, HIS42, ASN45, ALA38, VAL63, VAL68, ALA24, VAL43, ILE57, and ARG71 are playing a promising role in inhibition process. In addition, we performed DFT simulations of final hits to understand the electronic properties and their significant role in driving the inhibitor to adopt apposite bioactive conformations in the active site. Conclusively, the newly identified and designed hits from both the methods are promising inhibitors of TcaR, which can hinder biofilm formation.

Advances in Nanostructures for Antimicrobial Therapy

Microbial infections caused by a variety of drug-resistant microorganisms are more common, but there are fewer and fewer approved new antimicrobial chemotherapeutics for systemic administration capable of acting against these resistant infectious pathogens. Formulation innovations of existing drugs are gaining prominence, while the application of nanotechnologies is a useful alternative for improving/increasing the effect of existing antimicrobial drugs. Nanomaterials represent one of the possible strategies to address this unfortunate situation. This review aims to summarize the most current results of nanoformulations of antibiotics and antibacterial active nanomaterials. Nanoformulations of antimicrobial peptides, synergistic combinations of antimicrobial-active agents with nitric oxide donors or combinations of small organic molecules or polymers with metals, metal oxides or metalloids are discussed as well. The mechanisms of actions of selected nanoformulations, including systems with magnetic, photothermal or photodynamic effects, are briefly described.