Overcoming the rising incidence and evolving mechanisms of antibiotic resistance by novel drug delivery approaches - An overview

Development of novel bisphenol derivatives with a membrane-targeting mechanism as potent gram-positive antibacterial agents

Antibiotic resistance is becoming increasingly severe. The development of small molecular antimicrobial peptides is regarded as a promising design strategy for antibiotics. Here, a series of bisphenol derivatives with amphiphilic structures were designed and synthesized as antibacterial agents by imitating the design strategy of antimicrobial peptides. After a series of structural optimizations, lead compound 43 was identified, which exhibited excellent antibacterial activity against Gram-positive bacterial strains (MICs = 0.78-1.56 μg/mL), poor hemolytic activity (HC50 > 200 μg/mL), and low cytotoxicity (CC50 > 100 μg/mL). Further biological evaluation results indicated that 43 exerted antibacterial effects by directly destroying bacterial cell membranes and displayed rapid bactericidal properties (within 0.5-1 h), leading to a very low probability of drug resistance. Moreover, in a murine model of corneal infection, 43 exhibited a strong in vivo antibacterial efficacy. These findings indicate that 43 is a promising candidate compound for the treatment of bacterial infections.

Machine Learning Tools to Assist the Synthesis of Antibacterial Carbon Dots

Introduction

The emergence and rapid spread of multidrug-resistant bacteria (MRB) caused by the excessive use of antibiotics and the development of biofilms have been a growing threat to global public health. Nanoparticles as substitutes for antibiotics were proven to possess substantial abilities for tackling MRB infections via new antimicrobial mechanisms. Particularly, carbon dots (CDs) with unique (bio)physicochemical characteristics have been receiving considerable attention in combating MRB by damaging the bacterial wall, binding to DNA or enzymes, inducing hyperthermia locally, or forming reactive oxygen species.

Methods

Herein, how the physicochemical features of various CDs affect their antimicrobial capacity is investigated with the assistance of machine learning (ML) tools.

Results

The synthetic conditions and intrinsic properties of CDs from 121 samples are initially gathered to form the raw dataset, with Minimum inhibitory concentration (MIC) being the output. Four classification algorithms (KNN, SVM, RF, and XGBoost) are trained and validated with the input data. It is found that the ensemble learning methods turn out to be the best on our data. Also, ε-poly(L-lysine) CDs (PL-CDs) were developed to validate the practical application ability of the well-trained ML models in a laboratory with two ensemble models managing the prediction.

Discussion

Thus, our results demonstrate that ML-based high-throughput theoretical calculation could be used to predict and decode the relationship between CD properties and the anti-bacterial effect, accelerating the development of high-performance nanoparticles and potential clinical translation.

Toxin-triggered liposomes for the controlled release of antibiotics to treat infections associated with the gram-negative bacterium, Aggregatibacter actinomycetemcomitans

Antibiotic resistance has become an urgent threat to health care in recent years. The use of drug delivery systems provides advantages over conventional administration of antibiotics and can slow the development of antibiotic resistance. In the current study, we developed a toxin-triggered liposomal antibiotic delivery system, in which the drug release is enabled by the leukotoxin (LtxA) produced by the Gram-negative pathogen, Aggregatibacter actinomycetemcomitans. LtxA has previously been shown to mediate membrane disruption by promoting a lipid phase change in nonlamellar lipids, such as 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-methyl (N-methyl-DOPE). In addition, LtxA has been observed to bind strongly and nearly irreversibly to membranes containing large amounts of cholesterol. Here, we designed a liposomal delivery system composed of N-methyl-DOPE and cholesterol to take advantage of these interactions. Specifically, we hypothesized that liposomes composed of N-methyl-DOPE and cholesterol, encapsulating antibiotics, would be sensitive to LtxA, enabling controlled antibiotic release. We observed that liposomes composed of N-methyl-DOPE were sensitive to the presence of low concentrations of LtxA, and cholesterol increased the extent and kinetics of content release. The liposomes were stable under various storage conditions for at least 7 days. Finally, we showed that antibiotic release occurs selectively in the presence of an LtxA-producing strain of A. actinomycetemcomitans but not in the presence of a non-LtxA-expressing strain. Together, these results demonstrate that the designed liposomal vehicle enables toxin-triggered delivery of antibiotics to LtxA-producing strains of A. actinomycetemcomitans.

Magnetically actuated pandanus fruit-like nanorobots for enhanced pH-stimulated drug release and targeted biofilm elimination in wound healing

Conventional antibiotic treatment struggles to eliminate biofilms in wounds due to the formation compact barrier. Herein, we fabricate magnetic pandanus fruit-like nanorobots (NRs) that function as drug carriers while exhibit excellent maneuverability for enhanced antibacterial tasks. Specifically, zeolitic imidazolate framework-8 (ZIF-8) is self-assembled on the surface of Fe3O4 nanoparticles, loaded with a small quantity of ciprofloxacin, and covered with a layer of polydopamine (PDA). Energized by external magnetic fields, the NRs (F@Z/C/P) are steered in defined direction to penetrate the infection tissues, and effectively arrive targeted areas for pH stimulated drug release and near-infrared triggered phototherapy, contributing to an antibacterial rate of >99.9 %. The Zn2+ in ZIF-8 and the catechol group in PDA form catechol-ZIF-8-drug structures, which effectively reduce drug release by 11 % in high pH environments and promote rapid drug release by 14 % in low pH environments compared to NRs without PDA. Additionally, F@Z/C/P can remove the biofilms and bacteria in Staphylococcus aureus infected wounds, and eventually be discharged from the infected site after treatment, leading to faster healing with an intact epidermis and minimal harm to surrounding tissues and organs. The study provides a promising strategy for tackling biofilm-associated infections in vivo through the use of multi-functional NRs.

Strategies to Promote the Journey of Nanoparticles Against Biofilm-Associated Infections

Biofilm-associated infections are one of the most challenging healthcare threats for humans, accounting for 80% of bacterial infections, leading to persistent and chronic infections. The conventional antibiotics still face their dilemma of poor therapeutic effects due to the high tolerance and resistance led by bacterial biofilm barriers. Nanotechnology-based antimicrobials, nanoparticles (NPs), are paid attention extensively and considered as promising alternative. This review focuses on the whole journey of NPs against biofilm-associated infections, and to clarify it clearly, the journey is divided into four processes in sequence as 1) Targeting biofilms, 2) Penetrating biofilm barrier, 3) Attaching to bacterial cells, and 4) Translocating through bacterial cell envelope. Through outlining the compositions and properties of biofilms and bacteria cells, recent advances and present the strategies of each process are comprehensively discussed to combat biofilm-associated infections, as well as the combined strategies against these infections with drug resistance, aiming to guide the rational design and facilitate wide application of NPs in biofilm-associated infections.

In vivo biodistribution and ototoxicity assessment of cationic liposomal-ceftriaxone via noninvasive trans-tympanic delivery in chinchilla models: Implications for otitis media therapy

OBJECTIVES

We report the in vivo biodistribution and ototoxicity of cationic liposomal-ceftriaxone (CFX) delivered via ear drop formulation in adult chinchilla.

METHODS

CFX was encapsulated in liposomes with size of ∼100 nm and surface charge of +20 mV. 100 μl liposomes or free drug was applied twice daily in both external ear canals of adult chinchillas for either 3 or 10 days. Study groups included free ceftriaxone (CFX, Day 3: n = 4, Day 10: n = 8), liposomal ceftriaxone (CFX-Lipo, Day 3: n = 4, Day 10: n = 8), and a systemic control group (Day 3: n = 4, Day 10: n = 4). Ceftriaxone delivery to the middle ear and systemic circulation was quantified by HPLC assays. Liposome transport was visualized via confocal microscopy. Auditory brainstem response (ABR) tests and cochlear histology were used to assess ototoxicity.

RESULTS

Liposomal ceftriaxone (CFX-Lipo) displayed a ∼658-fold increase in drug delivery efficiency in the middle ear relative to the free CFX (8.548 ± 0.4638% vs. 0.013 ± 0.0009%, %Injected dose, Mean ± SEM). CFX measured in blood serum (48.2 ± 7.78 ng/ml) following CFX-Lipo treatment in ear was 41-fold lower compared to systemic free-CFX treatment (1990.7 ± 617.34 ng/ml). ABR tests and histological analysis indicated no ototoxicity due to the treatment.

CONCLUSION

Cationic liposomal encapsulation results in potent drug delivery across the tympanic membrane to the middle ear with minimal systemic exposure and no ototoxicity.

In situ peptide assemblies for bacterial infection imaging and treatment

Bacterial infections, especially antibiotic-resistant ones, remain a major threat to human health. Advances in nanotechnology have led to the development of numerous antimicrobial nanomaterials. Among them, in situ peptide assemblies, formed by biomarker-triggered self-assembly of peptide-based building blocks, have received increasing attention due to their unique merits of good spatiotemporal controllability and excellent disease accumulation and retention. In recent years, a variety of "turn on" imaging probes and activatable antibacterial agents based on in situ peptide assemblies have been developed, providing promising alternatives for the treatment and diagnosis of bacterial infections. In this review, we introduce representative design strategies for in situ peptide assemblies and highlight the bacterial infection imaging and treatment applications of these supramolecular materials. Besides, current challenges in this field are proposed.

Fabrication of poly(β-amino ester) and hyaluronic acid based pH responsive nanocomplex as an antibiotic release system

World Health Organization (WHO) warns about antimicrobial resistance (AMR) considered as the most serious threats to global health, food security, and development. There are various efforts for elimination of this serious issue. These efforts include education of individuals, new policies, development of new antimicrobials and new materials for effective delivery. Novel drug delivery systems with ability of local and on-demand delivery are one of the promising approaches for prevention of AMR. In this regard, a pH-responsive antibiotic delivery system based on pH-responsive poly(β-amino ester) (PBAE) and enzyme responsive hyaluronic acid (HA). The polymeric nanocomplexes were obtained via electrostatic complexation of PBAE and HA in the presence of a model antibiotics, colistin and vancomycin. The particle sizes at pH 7.4 were determined in the range of 131-730 nm and 120-400 nm by DLS and STEM, respectively. When pH was switched from 7.4 to 5.5, the hydrodynamic diameter increased 2.5-32 fold. The drug release performances were tested using FITC-labeled antibiotics via fluorescence spectroscopy. The nanocomplexes released the drugs more at pH 5.5 compared to pH 7.4. Antibacterial activity of the system was evaluated on various bacteria. The nanocomplex loaded with the antibiotics exhibited significantly greater efficacy against E. coli and S. aureus.

Evaluation of Expanded 2-Aminobenzothiazole Library for Inhibition of Pseudomonas aeruginosa Virulence Phenotypes

Bacterial resistance to antibiotics is a rapidly increasing threat to human health. New strategies to combat resistant organisms are desperately needed. One potential avenue is targeting two-component systems, which are the main bacterial signal transduction pathways used to regulate development, metabolism, virulence, and antibiotic resistance. These systems consist of a homodimeric membrane-bound sensor histidine kinase, and a cognate effector, the response regulator. The high sequence conservation in the catalytic and adenosine triphosphate-binding (CA) domain of histidine kinases and their essential role in bacterial signal transduction could enable broad-spectrum antibacterial activity. Through this signal transduction, histidine kinases regulate multiple virulence mechanisms including toxin production, immune evasion, and antibiotic resistance. Targeting virulence, as opposed to development of bactericidal compounds, could reduce evolutionary pressure for acquired resistance. Additionally, compounds targeting the CA domain have the potential to impair multiple two-component systems that regulate virulence in one or more pathogens. We conducted structure-activity relationship studies of 2-aminobenzothiazole-based inhibitors designed to target the CA domain of histidine kinases. We found these compounds have anti-virulence activities in Pseudomonas aeruginosa, reducing motility phenotypes and toxin production associated with the pathogenic functions of this bacterium.

Prospects and Challenges of Bacteriophage Substitution for Antibiotics in Livestock and Poultry Production

The overuse and misuse of antibiotics in the livestock and poultry industry has led to the development of multi-drug resistance in animal pathogens, and antibiotic resistance genes (ARGs) in bacteria transfer from animals to humans through the consumption of animal products, posing a serious threat to human health. Therefore, the use of antibiotics in livestock production has been strictly controlled. As a result, bacteriophages have attracted increasing research interest as antibiotic alternatives, since they are natural invaders of bacteria. Numerous studies have shown that dietary bacteriophage supplementation could regulate intestinal microbial composition, enhance mucosal immunity and the physical barrier function of the intestinal tract, and play an important role in maintaining intestinal microecological stability and normal body development of animals. The effect of bacteriophages used in animals is influenced by factors such as species, dose, and duration. However, as a category of mobile genetic elements, the high frequency of gene exchange of bacteriophages also poses risks of transmitting ARGs among bacteria. Hence, we summarized the mechanism and efficacy of bacteriophage therapy, and highlighted the feasibility and challenges of bacteriophage utilization in farm animal production, aiming to provide a reference for the safe and effective application of bacteriophages as an antibiotic alternative in livestock and poultry.

Synergistic Antibacterial Efficacy of Melittin in Combination with Oxacillin against Methicillin-Resistant Staphylococcus aureus (MRSA)

Methicillin-resistant Staphylococcus aureus (MRSA) often cause infections with high mortality rates. Antimicrobial peptides are a source of molecules for developing antimicrobials; one such peptide is melittin, a fraction from the venom of the Apis mellifera bee. This study aimed to evaluate the antibacterial and antibiofilm activities of melittin and its association with oxacillin (mel+oxa) against MRSA isolates, and to investigate the mechanisms of action of the treatments on MRSA. Minimum inhibitory concentrations (MICs) were determined, and synergistic effects of melittin with oxacillin and cephalothin were assessed. Antibiofilm and cytotoxic activities, as well as their impact on the cell membrane, were evaluated for melittin, oxacillin, and mel+oxa. Proteomics evaluated the effects of the treatments on MRSA. Melittin mean MICs for MRSA was 4.7 μg/mL and 12 μg/mL for oxacillin. Mel+oxa exhibited synergistic effects, reducing biofilm formation, and causing leakage of proteins, nucleic acids, potassium, and phosphate ions, indicating action on cell membrane. Melittin and mel+oxa, at MIC values, did not induce hemolysis and apoptosis in HaCaT cells. The treatments resulted in differential expression of proteins associated with protein synthesis and energy metabolism. Mel+oxa demonstrated antibacterial activity against MRSA, suggesting a potential as a candidate for the development of new antibacterial agents against MRSA.

Isolation and identification of bioactive compounds from Antrodia camphorata against ESKAPE pathogens

Antimicrobial resistance is a major threat to human health globally. Antrodia camphorata was grown in a malt/yeast extract broth liquid medium for 15 days. Then, 4-L fermentation broth was harvested, yielding 7.13 g of the ethyl acetate extract. By tracing the antimicrobial activity, 12.22 mg of the antimicrobial compound was isolated. The structure of 5-methyl-benzo [1,3]-dioxole-4,7-diol (MBBD) was elucidated using NMR and MS data analyses. The antibacterial activity of MBBD was detected through the microbroth dilution method. MBBD exhibited broad-spectrum antibacterial activity. The minimum inhibitory concentration (MIC) range of MBBD for drug-resistant pathogenic bacteria was 64-256 μg/mL, with the lowest MIC observed for Acinetobacter baumannii (64 μg/mL), followed by Pseudomonas aeruginosa (MIC = 128 μg/mL). Klebsiella pneumoniae, Staphylococcus aureus, Enterococcus faecalis, and Escherichia coli were also sensitive, with an MIC of 256 μg/mL. The MIC range of MBBD against 10 foodborne pathogens was 12.5-100 μg/mL. Based on the results of this study, MBBD exhibits broad-spectrum antibacterial activity, particularly demonstrating excellent inhibitory effects against A. baumannii. MBBD will be good candidates for new antimicrobial drugs.

Antimicrobial Resistance in Bacteria from Meat and Meat Products: A One Health Perspective

According to the 2030 Agenda of the United Nations, one of the sustainable development goals is to ensure sustainable consumption and production patterns. The need to ensure food safety includes, other than microbiological hazards, concerns with antimicrobial-resistant (AMR) bacteria. The emergence of resistant bacteria in the food industry is essentially due to the abusive, and sometimes incorrect, administration of antimicrobials. Although not allowed in Europe, antimicrobials are often administered to promote animal growth. Each time antimicrobials are used, a selective pressure is applied to AMR bacteria. Moreover, AMR genes can be transmitted to humans through the consumption of meat-harbouring-resistant bacteria, which highlights the One Health dimension of antimicrobial resistance. Furthermore, the appropriate use of antimicrobials to ensure efficacy and the best possible outcome for the treatment of infections is regulated through the recommendations of antimicrobial stewardship. The present manuscript aims to give the current state of the art about the transmission of AMR bacteria, particularly methicillin-resistant S. aureus, ESBL-producing Enterobacteriaceae, and vancomycin-resistant Enterococcus spp., along with other ESKAPE bacteria, from animals to humans through the consumption of meat and meat products, with emphasis on pork meat and pork meat products, which are considered the most consumed worldwide.

The increasing importance of novel deep eutectic solvents as potential effective antimicrobials and other medicinal properties

With the rise of antibiotic resistance globally, coupled with evolving and emerging infectious diseases, there is an urgent need for the development of novel antimicrobials. Deep eutectic solvents (DES) are a new generation of eutectic mixtures that depict promising attributes with several biological implications. DES exhibit unique properties such as low toxicity, biodegradability, and high thermal stability. Herein, the antimicrobial properties of DES and their mechanisms of action against a range of microorganisms, including bacteria, amoebae, fungi, viruses, and anti-cancer properties are reviewed. Overall, DES represent a promising class of novel antimicrobial agents as well as possessing other important biological attributes, however, future studies on DES are needed to investigate their underlying antimicrobial mechanism, as well as their in vivo effects, for use in the clinic and public at large.

Enhancing Surgical Outcomes: A Critical Review of Antibiotic Prophylaxis in Orthopedic Surgery

The postoperative burden remains significant due to the possibility of prolonged hospitalization, escalated healthcare costs, and patient distress caused by postorthopedic surgical site infections (SSIs). Orthopedic surgery is likewise faced with a significant challenge posed by these conditions. A positive association has been observed between the presence of postorthopedic SSIs and heightened susceptibility to adverse health outcomes, along with elevated rates of morbidity and mortality. Systemic antibiotic prophylaxis (SAP) reduces the risk of acquiring an SSI. Closed fractures, open fractures, arthroplasty, and percutaneous fixation each possess distinct attributes that impact the data and antimicrobial therapy. When implementing SAP, it is crucial to strike a delicate equilibrium between maintaining effective antibiotic stewardship protocols and preventing the occurrence of SSIs. This practice effectively prevents both the incidence of negative consequences and the emergence of antibiotic resistance. The objective of this study was to examine the existing literature on the use of surgical antibiotic prophylaxis in orthopedic surgery and explore the potential consequences associated with the inappropriate administration of antibiotics.

Toxin-Triggered Liposomes for the Controlled Release of Antibiotics to Treat Infections Associated with Gram-Negative Bacteria

Antibiotic resistance has become an urgent threat to health care in recent years. The use of drug delivery systems provides advantages over conventional administration of antibiotics and can slow the development of antibiotic resistance. In the current study, we developed a toxin-triggered liposomal antibiotic delivery system, in which the drug release is enabled by the leukotoxin (LtxA) produced by the Gram-negative pathogen, Aggregatibacter actinomycetemcomitans. LtxA has previously been shown to mediate membrane disruption by promoting a lipid phase change in nonlamellar lipids, such as 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-methyl (N-methyl-DOPE). In addition, LtxA has been observed to bind strongly and nearly irreversibly to membranes containing large amounts of cholesterol. Here, we designed a liposomal delivery system composed of N-methyl-DOPE and cholesterol to take advantage of these interactions. Specifically, we hypothesized that liposomes composed of N-methyl-DOPE and cholesterol, encapsulating antibiotics, would be sensitive to LtxA, enabling controlled antibiotic release. We observed that liposomes composed of N-methyl-DOPE were sensitive to the presence of low concentrations of LtxA, and cholesterol increased the extent and kinetics of content release. The liposomes were stable under various storage conditions for at least 7 days. Finally, we showed that antibiotic release occurs selectively in the presence of an LtxA-producing strain of A. actinomycetemcomitans but not in the presence of a non-LtxA-expressing strain. Together, these results demonstrate that the designed liposomal vehicle enables toxin-triggered delivery of antibiotics to LtxA-producing strains of A. actinomycetemcomitans.

Novel Antibacterial Materials and Coatings-A Perspective by the Editors

The fight between humans and bacteria has escalated to a new level.

Evaluation of Poly(vinyl alcohol)-Xanthan Gum Hydrogels Loaded with Neomycin Sulfate as Systems for Drug Delivery

In recent years, multidrug-resistant bacteria have developed the ability to resist multiple antibiotics, limiting the available options for effective treatment. Raising awareness and providing education on the appropriate use of antibiotics, as well as improving infection control measures in healthcare facilities, are crucial steps to address the healthcare crisis. Further, innovative approaches must be adopted to develop novel drug delivery systems using polymeric matrices as carriers and support to efficiently combat such multidrug-resistant bacteria and thus promote wound healing. In this context, the current work describes the use of two biocompatible and non-toxic polymers, poly(vinyl alcohol) (PVA) and xanthan gum (XG), to achieve hydrogel networks through cross-linking by oxalic acid following the freezing/thawing procedure. PVA/XG-80/20 hydrogels were loaded with different quantities of neomycin sulfate to create promising low-class topical antibacterial formulations with enhanced antimicrobial effects. The inclusion of neomycin sulfate in the hydrogels is intended to impart them with powerful antimicrobial properties, thereby facilitating the development of exceptionally efficient topical antibacterial formulations. Thus, incorporating higher quantities of neomycin sulfate in the PVA/XG-80/20-2 and PVA/XG-80/20-3 formulations yielded promising cycling characteristics. These formulations exhibited outstanding removal efficiency, exceeding 80% even after five cycles, indicating remarkable and consistent adsorption performance with repeated use. Furthermore, both PVA/XG-80/20-2 and PVA/XG-80/20-3 formulations outperformed the drug-free sample, PVA/XG-80/20, demonstrating a significant enhancement in maximum compressive stress.

Unraveling the atomic-level vacancy modulation in Cu9S5 for NIR-driven efficient inhibition of drug-resistant bacteria: Key role of Cu vacancy position

Cu₉S₅ possesses high hole concentration and potential superior electrical conductivity as a novel p-type semiconductor, whose biological applications remain largely unexploited. Encouraged by our recent work that Cu₉S₅ has enzyme-like antibacterial activity in the absence of light, which may further enhance the near infrared (NIR) antibacterial performance. Moreover, vacancy engineering can modulate the electronic structure of the nanomaterials and thus optimize their photocatalytic antibacterial activities. Here, we designed two different atomic arrangements with same V_CuSCu vacancies of Cu₉S₅ nanomaterials (CSC-4 and CSC-3) determined by positron annihilation lifetime spectroscopy (PALS). Aiming at CSC-4 and CSC-3 as a model system, for the first time, we investigated the key role of different copper (Cu) vacancies positions in vacancy engineering toward optimizing the photocatalytic antibacterial properties of the nanomaterials. Combined with the experimental and theoretical approach, CSC-3 exhibited stronger absorption energy of surface adsorbate (LPS and H₂O), longer lifetime of photogenerated charge carriers (4.29 ns), and lower reaction active energy (0.76 eV) than those of CSC-4, leading to the generation of abundant ·OH for attaining rapid drug-resistant bacteria killed and wound healed under NIR light irradiation. This work provided a novel insight for the effective inhibition of drug-resistant bacteria infection via vacancy engineering at the atomic-level modulation.

New antifungal strategies: drug combination and co-delivery

The growing occurrence of invasive fungal infections and the mounting rates of drug resistance constitute a significant menace to human health. Antifungal drug combinations have garnered substantial interest for their potential to improve therapeutic efficacy, reduce drug doses, reverse, or ameliorate drug resistance. A thorough understanding of the molecular mechanisms underlying antifungal drug resistance and drug combination is key to developing new drug combinations. Here we discuss the mechanisms of antifungal drug resistance and elucidate how to discover potent drug combinations to surmount resistance. We also examine the challenges encountered in developing such combinations and discuss prospects, including advanced drug delivery strategies.

Double network hydrogel based on curdlan and flaxseed gum with photothermal antibacterial properties for accelerating infectious wound healing

The healing of infected wounds has always been a clinical challenge. With the increasing threat of drug resistance due to antibiotic overuse, it is imperative to improve antibacterial wound dressings. In this study, we designed a double network (DN) hydrogel via a "one pot method" with antibacterial activity, and natural polysaccharides with the potential to promote skin wound healing were used. That is, a DN hydrogel matrix was formed by the hydrogen bond crosslinking of curdlan and the covalent crosslinking of flaxseed gum under the action of borax. We added ε-polylysine (ε-PL) as a bactericide. Tannic acid/ferric ion (TA/Fe³⁺) complex was also introduced into the hydrogel network as a photothermal agent to induce photothermal antibacterial properties. The hydrogel had fast self-healing, tissue adhesion, mechanical stability, good cell compatibility and photothermal antibacterial activity. In vitro studies of hydrogel showed its ability to inhibit S. aureus and E. coli. In vivo experiments also demonstrated the significant healing effect of hydrogel when used to treat wounds infected by S. aureus by promoting collagen deposition and accelerating the formation of skin appendage. This work provides a new design for the preparation of safe antibacterial hydrogel wound dressings and demonstrates great potential for promoting wound healing of bacterial infections.

Molecular Dipole Modulation of Porphyrins to Enhance Photocatalytic Oxidation Activity for Inactivation of Intracellular Bacteria

The regulation of molecular structures of porphyrin-based photosensitizers is crucial for yielding the effective singlet oxygen as one of the efficient photocatalytic reactive oxidation species. Here, we select methoxy substitution as an electron donor to decorate the porphyrin rings. Introducing a series of metal ions into porphyrin centers further prepares the methoxy-substituted metalloporphyrins (MPs, M = Co, Ni, Cu, Zn), with the hope of modulating their molecular dipole moments and photocatalytic activity. The theoretical calculation analyses show that the metal-free porphyrin center possesses a higher transition dipole and more delocalized orbitals, leading to efficient charge transfer and improved photocatalytic activity. The metalloporphyrin samples are then polymerized by poly(D, l-lactide-co-glycolide) to be applied to in vitro sterilization experiments. As expected, metal-free porphyrin has good antibacterial ability and good biocompatibility. Moreover, the highly effective bacteriostatic metal-free porphyrin achieves satisfactory photodynamic therapeutic outcomes against intracellular pathogens in cancer cells. This work demonstrates that the molecular dipole modulation of porphyrins is critical for their photocatalytic oxidation and antibacterial ability.

Nanomaterials to address the genesis of antibiotic resistance in Escherichia coli

Escherichia is a genus of prokaryotic gram-negative bacteria which forms a vital component of the gut microbiota of homeotherms including humans. Many members of this genus are commensals and pathogenic strains, which are responsible for some of the most common bacterial infections and can be fatal, particularly in the case of newborns and children. The fecal matter in wastewater treatment plants serves as major environmental sinks for the accumulation of Escherichia. The rise in antibiotic pollution and the lateral gene exchange of antibiotic-resistant genes have created antibiotic-resistant Escherichia strains that are often called superbugs. Antibiotic resistance has reached a crisis level that nowadays existing antibiotics are no longer effective. One way of tackling this emerging concern is by using nanomaterials. Punitively, nanomaterials can be used by conjugating with antibodies, biomolecules, and peptides to reduce antibiotic usage, whereas, preventatively, they can be used as either nano-antimicrobial additives or nano-photocatalytic sheets to reduce the microbial population and target the superbugs of environmental Escherichia. In this review, we have explored the threat posed by pathogenic Escherichia strains in the environment, especially in the context of antibiotic-resistant strains. Along with this, we have discussed some nanomaterial-mediated strategies in which the problem can be addressed by using nanomaterials as nanophotocatalytics, antimicrobial additives, drugs, and drug conjugates. This review also presents a brief overview of the ecological threats posed by the overuse of nanomaterials which warrants a balanced and judicious approach to the problem.

New N4-Donor Ligands as Supramolecular Guests for DNA and RNA: Synthesis, Structural Characterization, In Silico, Spectrophotometric and Antimicrobial Studies

The present work reports the synthesis of new N4-donor compounds carrying p-xylyl spacers in their structure. Different Schiff base aliphatic N-donors were obtained synthetically and subsequently evaluated for their ability to interact with two models of nucleic acids: calf-thymus DNA (CT-DNA) and the RNA from yeast Saccharomyces cerevisiae (herein simply indicated as RNA). In more detail, by condensing p-xylylenediamine and a series of aldehydes, we obtained the following Schiff base ligands: 2-thiazolecarboxaldehyde (L1), pyridine-2-carboxaldehyde (L2), 5-methylisoxazole-3-carboxaldehyde (L3), 1-methyl-2-imidazolecarboxaldehyde (L4), and quinoline-2-carboxaldehyde (L5). The structural characterisation of the ligands L1-L5 (X-ray, ¹H NMR, ¹³C NMR, elemental analysis) and of the coordination polymers {[CuL1]PF₆}_n (herein referred to as Polymer1) and {[AgL1]BF₄}_n, (herein referred to as Polymer2, X-ray, ¹H NMR, ESI-MS) is herein described in detail. The single crystal X-ray structures of complexes Polymer1 and Polymer2 were also investigated, leading to the description of one-dimensional coordination polymers. The spectroscopic and in silico evaluation of the most promising compounds as DNA and RNA binders, as well as the study of the influence of the 1D supramolecular polymers Polymer1 and Polymer2 on the proliferation of Escherichia coli bacteria, were performed in view of their nucleic acid-modulating and antimicrobial applications. Spectroscopic measurements (UV-Vis) combined with molecular docking calculations suggest that the thiazolecarboxaldehyde derivative L1 is able to bind CT-DNA with a mechanism different from intercalation involving the thiazole ring in the molecular recognition and shows a binding affinity with DNA higher than RNA. Finally, Polymer2 was shown to slow down the proliferation of bacteria much more effectively than the free Ag(I) salt.

Functionally modified halloysite nanotubes for personalized bioapplications

Halloysite nanotubes (HNTs) are naturally aluminosilicate clay minerals that have the benefits of large surface areas, high mechanical properties, easy functionalization, and high biocompatibility, HNTs have been developed as multifunctional nanoplatforms for various bioapplications. Although some reviews have summarized the properties and bioapplications of HNTs, it remains unclear how to functionalize the modifications of HNTs for their personalized bioapplications. In this review, based on the physicochemical properties of HNTs, we summarized the methods of functionalized modifications (surface modification and structure modification) on HNTs. Also, we highlighted their personalized bioapplications (anti-bacterial, anti-inflammatory, wound healing, cancer theranostics, bone regenerative, and biosensing) by stressing on the main roles of HNTs. Finally, we provide perspectives on the future of functionalized modifications of HNTs for docking specific biological applications.

Molecular characterization and antimicrobial susceptibility of human Brucella in Northeast China

Introduction

Northeast China has always been an area with severe brucellosis prevalence. This study will identify Brucella in Northeast China and test its resistance to antibiotics, in order to clarify its resistance mechanism. Brucella is a widespread and highly pathogenic bacteria that poses serious threats to public health and animal husbandry.

Methods

In this study, 61 Brucella isolates were identified by abortus-melitensis-ovis-suis polymerase chain reaction (AMOS-PCR) for biotypes and epidemic potential was clarified by multi-locus sequence analysis. Whole-genome sequencing (WGS) was performed and the antibiotic susceptibility of the Brucella strains against 13 antibiotics was detected with the use of E-test strips.

Results

The results showed that all of the isolates were Brucella melitensis ST8, group CC4 with little genetic variation and obvious geographical characteristics. All 61 Brucella isolates were sensitive to doxycycline, tetracycline, minocycline, levofloxacin, ciprofloxacin, gentamicin, and streptomycin, while 24.6%, 86.9%, 65.6%, 27.9%, 3.3%, and 1.6% were resistant to rifampin, azithromycin, cefepime, cefoperazone/sulbactam, cefotaxime, and meperidine/sulfamethoxazole, respectively. This is the first report of cephalosporin-resistant B. melitensis in China. The WGS results indicated that about 60% of the antibiotic resistance genes were associated with efflux pumps (mainly the resistance nodulation division family).

Discussion

Brucellosis is usually treated with antibiotics for several months, which can easily lead to the emergence of antibiotic resistance. To ensure the effectiveness and safety of antibiotics for treatment of brucellosis, continuous surveillance of antibiotic susceptibility is especially important.

The Effect of Operating Strategies on the Anaerobic Digestion of Gentamicin Mycelial Residues: Insights into the Enhancement of Methane Production and Attenuation of Gentamicin Resistance

Anaerobic digestion (AD) has been widely employed for converting various biowastes into renewable energy. However, AD of gentamicin mycelial residues (GMRs, a byproduct of gentamicin production) is limited by ammonia inhibition and antimicrobial resistance risk. Compared to mesophilic AD (MMAD) of GMRs, this study looked into three semicontinuous AD processes, i.e., codigestion with wheat straw, thermophilic digestion (TAcoD), and AD at shortened retention time (RT). Results showed that a stable and safe AD could be achieved under suitable operating conditions. Co-digestion could effectively mitigate the adverse effect of ammonia inhibition. The methane production increased by 35.86% in TAcoD compared to that in MMAD and 43.99% of hazardous waste was reduced in TAcoD. Concerning the antimicrobial resistance of AD system, gentamicin was degraded efficiently and the degradation process was not involved in the expression of antibiotic resistance genes (ARGs) related to modifying enzyme. Effective removal of ARGs under three operating strategies was associated with a higher reduction in bacterial abundance of potential hosts. In addition, the changes in the relevant proteins for transformation and conjugation as predicted by PICRUSt suggested that thermophilic condition and shorter RT were conducive to the reduction of the dissemination risks of ARGs.

Mussel-Inspired Polydopamine-Based Multilayered Coatings for Enhanced Bone Formation

Repairing bone defects remains a challenge in clinical practice and the application of artificial scaffolds can enhance local bone formation, but the function of unmodified scaffolds is limited. Considering different application scenarios, the scaffolds should be multifunctionalized to meet specific demands. Inspired by the superior adhesive property of mussels, polydopamine (PDA) has attracted extensive attention due to its universal capacity to assemble on all biomaterials and promote further adsorption of multiple external components to form PDA-based multilayered coatings with multifunctional property, which can induce synergistic enhancement of new bone formation, such as immunomodulation, angiogenesis, antibiosis and antitumor property. This review will summarize mussel-inspired PDA-based multilayered coatings for enhanced bone formation, including formation mechanism and biofunction of PDA coating, as well as different functional components. The synergistic enhancement of multiple functions for better bone formation will also be discussed. This review will inspire the design and fabrication of PDA-based multilayered coatings for different application scenarios and promote deeper understanding of their effect on bone formation, but more efforts should be made to achieve clinical translation. On this basis, we present a critical conclusion, and forecast the prospects of PDA-based multilayered coatings for bone regeneration.

Microbial Resistance to Antibiotics and Effective Antibiotherapy

Currently, the efficacy of antibiotics is severely affected by the emergence of the antimicrobial resistance phenomenon, leading to increased morbidity and mortality worldwide. Multidrug-resistant pathogens are found not only in hospital settings, but also in the community, and are considered one of the biggest public health concerns. The main mechanisms by which bacteria develop resistance to antibiotics include changes in the drug target, prevention of entering the cell, elimination through efflux pumps or inactivation of drugs. A better understanding and prediction of resistance patterns of a pathogen will lead to a better selection of active antibiotics for the treatment of multidrug-resistant infections.

Alginate-based aerogels as wound dressings for efficient bacterial capture and enhanced antibacterial photodynamic therapy

The development of novel wound dressings, such as aerogels, with rapid hemostasis and bactericidal capacities for pre-hospital care is necessary. To prevent the occurrence of bacterial resistance, antibacterial photodynamic therapy (aPDT) with broad-spectrum antibacterial ability and negligible bacterial resistance has been intensively studied. However, photosensitizers often suffer from poor water solubility, short singlet oxygen (¹O₂) half-life and restricted ¹O₂ diffusion distance. Herein, sodium alginate was covalently modified by photosensitizers and phenylboronic acid, and cross-linked by Ca(II) ions to generate SA@TPAPP@PBA aerogel after lyophilization as an antibacterial photodynamic wound dressing. Afterwards, its photodynamic and bacterial capture activities were intensively evaluated. Furthermore, its hemostasis and bactericidal efficiency against Staphylococcus aureus were assessed via in vitro and in vivo assays. First, chemical immobilization of photosensitizers led to an enhancement of its solubility. Moreover, it showed an excellent hemostasis capacity. Due to the formation of reversible covalent bonds between phenylboronic acid and diol groups on bacterial cell surface, the aerogel could capture S. aureus tightly and dramatically enhance aPDT. To sum up, the prepared aerogel illustrated excellent hemostasis capacity and antibacterial ability against S. aureus. Therefore, they have great potential to be utilized as wound dressing in clinical trials.

Ofloxacin-loaded HMPB NPs for K. pneumoniae eradication in the surgical wound with the combination of PTT

Klebsiella pneumoniae (K. pneumoniae) is a common bacterium whose drug-resistant can cause surgical failures and incurable infections in hospital patients. Thus, how to reverse or delay the resistance induction has become a great challenge for development anti-resistant drug. Recently, the combination of nanomaterial-loaded antibiotics with photothermal therapy showed the efficient anti-bacteria ability under low dosage of antibiotics. In this work, a nanocomposite of HMPB NPs with inherent photothermal therapy capability was used to eradicate K. pneumoniae after loading with Ofloxacin, an antibiotic against K. pneumoniae in vitro and in vivo. The nanocomplexes named as Ofloxacin@HMPB@HA NPs showed higher effect against K. pneumoniae by destroying cell integrity and inducing ATP leakage with the assistance of laser irradiation, compared with sole Ofloxacin@HMPB@HA NPs or laser irradiation. Surgical wound infection assay further demonstrated the efficient killing K. pneumoniae and promoting the formation of new tissues, as well, which was reflected by the rapid healing of surgical wound. In summary, these results indicate the great potential of this combinational tactic based on Ofloxacin@HMPB@HA NPs for preventing the failure caused by K. pneumoniae infection. This article is protected by copyright. All rights reserved.

Considerations on the Controlled Delivery of Bioactive Compounds through Hyaluronic Acid Membrane

(1) Background: The standard treatment for periodontal disease, a chronic inflammatory state caused by the interaction between biofilms generated by organized oral bacteria and the local host defense response, consists of calculus and biofilm removal through mechanical debridement, associated with antimicrobial therapy that could be delivered either systemically or locally. The present study aimed to determine the effectiveness of a hyaluronic acid membrane matrix as a carrier for the controlled release of the active compounds of a formulation proposed as a topical treatment for periodontal disease, and the influence of pH on the complex system’s stability. (2) Methods: The obtained hyaluronic acid (HA) hydrogel membrane with dispersed melatonin (MEL), metronidazole (MZ), and tetracycline (T) was completely characterized through FTIR, XRD, thermal analysis, UV-Vis and fluorescence spectroscopy, fluorescence microscopy, zeta potential and dielectric analysis. The MTT viability test was applied to check the cytotoxicity of the obtained membranes, while the microbiological assessment was performed against strains of Staphylococcus spp. and Streptococcus spp. The spectrophotometric investigations allowed to follow up the release profile from the HA matrix for MEL, MZ, and T present in the topical treatment considered. We studied the behavior of the active compounds against the pH of the generated environment, and the release profile of the bioactive formulation based on the specific comportment towards pH variation. The controlled delivery of the bioactive compounds using HA as a supportive matrix was modeled applying Korsmeyer–Peppas, Higuchi, first-order kinetic models, and a newly proposed pseudo-first-order kinetic model. (3) Results: It was observed that MZ and T were released at higher active concentrations than MEL when the pH was increased from 6.75, specific for patients with periodontitis, to a pH of 7.10, characterizing the healthy patients. Additionally, it was shown that for MZ, there is a burst delivery up to 2.40 × 10⁻⁵ mol/L followed by a release decrease, while for MEL and T a short release plateau was recorded up to a concentration of 1.80 × 10⁻⁵ mol/L for MEL and 0.90 × 10⁻⁵ mol/L for T, followed by a continuous release; (4) Conclusions: The results are encouraging for the usage of the HA membrane matrix as releasing vehicle for the active components of the proposed topical treatment at a physiological pH.

Synthesis, Biological Activity and Molecular Docking Studies of Novel Nicotinic Acid Derivatives

In our research, we used nicotinic acid as a starting compound, which was subjected to a series of condensation reactions with appropriate aldehydes. As a result of these reactions, we were able to obtain a series of twelve acylhydrazones, two of which showed promising activity against Gram-positive bacteria (MIC = 1.95-15.62 µg/mL), especially against Staphylococcus epidermidis ATCC 12228 (MIC = 1.95 µg/mL). Moreover, the activity of compound 13 against the Staphylococcus aureus ATCC 43300 strain, i.e., the MRSA strain, was MIC = 7.81 µg/mL. Then, we subjected the entire series of acylhydrazones to a cyclization reaction in the acetic anhydride, thanks to which we were able to obtain twelve new 3-acetyl-2,5-disubstituted-1,3,4-oxadiazoline derivatives. Obtained 1,3,4-oxadiazolines were also tested for antimicrobial activity. The results showed high activity of compound 25 with a 5-nitrofuran substituent, which was active against all tested strains. The most promising activity of this compound was found against Gram-positive bacteria, in particular against Bacillus subtilis ATCC 6633 and Staphylococcus aureus ATCC 6538 (MIC = 7.81 µg/mL) and ATCC 43300 MRSA strains (MIC = 15.62 µg/mL). Importantly, the best performing compounds did not show cytotoxicity against normal cell lines. It seems practical to use some of these compounds or their derivatives in the future in the prevention and treatment of infections caused by some pathogenic or opportunistic microorganisms.