Recent Developments in Antibacterial Therapy: Focus on Stimuli-Responsive Drug-Delivery Systems and Therapeutic Nanoparticles

Targeted Stimuli-Responsive Mesoporous Silica Nanoparticles for Bacterial Infection Treatment

The rise of antibiotic resistance and the growing number of biofilm-related infections make bacterial infections a serious threat for global human health. Nanomedicine has entered into this scenario by bringing new alternatives to design and develop effective antimicrobial nanoweapons to fight against bacterial infection. Among them, mesoporous silica nanoparticles (MSNs) exhibit unique characteristics that make them ideal nanocarriers to load, protect and transport antimicrobial cargoes to the target bacteria and/or biofilm, and release them in response to certain stimuli. The combination of infection-targeting and stimuli-responsive drug delivery capabilities aims to increase the specificity and efficacy of antimicrobial treatment and prevent undesirable side effects, becoming a ground-breaking alternative to conventional antibiotic treatments. This review focuses on the scientific advances developed to date in MSNs for infection-targeted stimuli-responsive antimicrobials delivery. The targeting strategies for specific recognition of bacteria are detailed. Moreover, the possibility of incorporating anti-biofilm agents with MSNs aimed at promoting biofilm penetrability is overviewed. Finally, a comprehensive description of the different scientific approaches for the design and development of smart MSNs able to release the antimicrobial payloads at the infection site in response to internal or external stimuli is provided.

Dual drug delivery system based on pH-sensitive silk fibroin/alginate nanoparticles entrapped in PNIPAM hydrogel for treating severe infected burn wound

Herein, the pH-sensitive vancomycin (VANCO) loaded silk fibroin-sodium alginate nanoparticles (NPs) embedded in poly(N-isopropylacrylamide) (PNIPAM) hydrogel containing epidermal growth factor (EGF) are introduced for treating chronic burn wound infections. The hybrid system was developed to control the release rates of an antibiotic and growth factor for optimal treatment of burn infections. VANCO had a pH responsive release behavior from the nanoparticle (NP) and showed higher release rate in an alkaline pH compared to the neutral pH during 10 d. About 30% of EGF was also released from the hydrogel within 20 d. The released VANCO and EGF preserved their bioactivity more than ∼ 80%. The suitable physico-chemical properties and cellular behaviors of PNIPAM hydrogel supported the proliferation and growth of the fibroblast cells. Furthermore, the higher re-epithelialization with good wound contraction rate, neovascular formation, and expression of transforming growth factor-beta were observed in S. aureus infected rat burn wound by using the hydrogel containing VANCO and EGF compared with untreated wounds and hydrogel alone. The wound infection was also significantly reduced in the groups treated with the hydrogels containing VANCO. Overall, in vitro and in vivo results suggested that developed hybrid system would be a promising construct to treat severe wound infection.

Sustained Release of Linezolid from Prepared Hydrogels with Polyvinyl Alcohol and Aliphatic Dicarboxylic Acids of Variable Chain Lengths

A series of hydrogels with a specific release profile of linezolid was successfully synthesized. The hydrogels were synthesized by cross-linking polyvinyl alcohol (PVA) and aliphatic dicarboxylic acids, which include succinic acid (SA), glutaric acid (GA), and adipic acid (AA). The three crosslinked hydrogels were prepared by esterification and characterized by equilibrium swelling ratio, infrared spectroscopy, thermogravimetric analysis, mechanical properties, and scanning electron microscopy. The release kinetics studies of the linezolid from prepared hydrogels were investigated by cumulative drug release and quantified by chromatographic techniques. Mathematical models were carried out to understand the behavior of the linezolid release. These data revealed that the sustained release of linezolid depends on the aliphatic dicarboxylic acid chain length, their polarity, as well as the hydrogel crosslinking degree and mechanical properties. The in vitro antibacterial assay of hydrogel formulations was assessed in an Enterococcus faecium bacterial strain, showing a significant activity over time. The antibacterial results were consistent with cumulative release assays. Thus, these results demonstrated that the aliphatic dicarboxylic acids used as crosslinkers in the PVA hydrogels were a determining factor in the antibiotic release profile.

Tackling Multidrug Resistance in Streptococci - From Novel Biotherapeutic Strategies to Nanomedicines

The pyogenic streptococci group includes pathogenic species for humans and other animals and has been associated with enduring morbidity and high mortality. The main reason for the treatment failure of streptococcal infections is the increased resistance to antibiotics. In recent years, infectious diseases caused by pyogenic streptococci resistant to multiple antibiotics have been raising with a significant impact to public health and veterinary industry. The rise of antibiotic-resistant streptococci has been associated to diverse mechanisms, such as efflux pumps and modifications of the antimicrobial target. Among streptococci, antibiotic resistance emerges from previously sensitive populations as result of horizontal gene transfer or chromosomal point mutations due to excessive use of antimicrobials. Streptococci strains are also recognized as biofilm producers. The increased resistance of biofilms to antibiotics among streptococci promote persistent infection, which comprise circa 80% of microbial infections in humans. Therefore, to overcome drug resistance, new strategies, including new antibacterial and antibiofilm agents, have been studied. Interestingly, the use of systems based on nanoparticles have been applied to tackle infection and reduce the emergence of drug resistance. Herein, we present a synopsis of mechanisms associated to drug resistance in (pyogenic) streptococci and discuss some innovative strategies as alternative to conventional antibiotics, such as bacteriocins, bacteriophage, and phage lysins, and metal nanoparticles. We shall provide focused discussion on the advantages and limitations of agents considering application, efficacy and safety in the context of impact to the host and evolution of bacterial resistance.

Nanoparticle-Based Strategies to Combat COVID-19

Coronavirus disease 2019 (COVID-19) is the worst pandemic disease of the current millennium. This disease is caused by the highly contagious severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which first exhibited human-to-human transmission in December 2019 and has infected millions of people within months across 213 different countries. Its ability to be transmitted by asymptomatic carriers has put a massive strain on the currently available testing resources. Currently, there are no clinically proven therapeutic methods that clearly inhibit the effects of this virus, and COVID-19 vaccines are still in the development phase. Strategies need to be explored to expand testing capacities, to develop effective therapeutics, and to develop safe vaccines that provide lasting immunity. Nanoparticles (NPs) have been widely used in many medical applications, such as biosensing, drug delivery, imaging, and antimicrobial treatment. SARS-CoV-2 is an enveloped virus with particle-like characteristics and a diameter of 60-140 nm. Synthetic NPs can closely mimic the virus and interact strongly with its proteins due to their morphological similarities. Hence, NP-based strategies for tackling this virus have immense potential. NPs have been previously found to be effective tools against many viruses, especially against those from the Coronaviridae family. This Review outlines the role of NPs in diagnostics, therapeutics, and vaccination for the other two epidemic coronaviruses, the 2003 severe acute respiratory syndrome (SARS) virus and the 2012 Middle East respiratory syndrome (MERS) virus. We also highlight nanomaterial-based approaches to address other coronaviruses, such as human coronaviruses (HCoVs); feline coronavirus (FCoV); avian coronavirus infectious bronchitis virus (IBV); coronavirus models, such as porcine epidemic diarrhea virus (PEDV), porcine reproductive and respiratory syndrome virus (PRRSV), and transmissible gastroenteritis virus (TGEV); and other viruses that share similarities with SARS-CoV-2. This Review combines the salient principles from previous antiviral studies with recent research conducted on SARS-CoV-2 to outline NP-based strategies that can be used to combat COVID-19 and similar pandemics in the future.

Recent Advances in Polymeric Nanoparticle-Encapsulated Drugs against Intracellular Infections

Polymeric nanocarriers (PNs) have demonstrated to be a promising alternative to treat intracellular infections. They have outstanding performance in delivering antimicrobials intracellularly to reach an adequate dose level and improve their therapeutic efficacy. PNs offer opportunities for preventing unwanted drug interactions and degradation before reaching the target cell of tissue and thus decreasing the development of resistance in microorganisms. The use of PNs has the potential to reduce the dose and adverse side effects, providing better efficiency and effectiveness of therapeutic regimens, especially in drugs having high toxicity, low solubility in the physiological environment and low bioavailability. This review provides an overview of nanoparticles made of different polymeric precursors and the main methodologies to nanofabricate platforms of tuned physicochemical and morphological properties and surface chemistry for controlled release of antimicrobials in the target. It highlights the versatility of these nanosystems and their challenges and opportunities to deliver antimicrobial drugs to treat intracellular infections and mentions nanotoxicology aspects and future outlooks.

Intrinsic stimuli-responsive nanocarriers for smart drug delivery of antibacterial agents-An in-depth review of the last two decades

Antibiotic resistance due to suboptimal targeting and inconsistent antibiotic release at bacterial infection sites has driven the formulation of stimuli-responsive nanocarriers for antibacterial therapy. Unlike conventional nanocarriers, stimuli-responsive nanocarriers have the ability to specifically enhance targeting and drug release profiles. There has been a significant escalation in the design and development of novel nanomaterials worldwide; in particular, intrinsic stimuli-responsive antibiotic nanocarriers, due to their enhanced activity, improved targeted delivery, and superior potential for bacterial penetration and eradication. Herein, we provide an extensive and critical review of pH-, enzyme-, redox-, and ionic microenvironment-responsive nanocarriers that have been reported in literature to date, with an emphasis on the mechanisms of drug release, the nanomaterials used, the nanosystems constructed and the antibacterial efficacy of the nanocarriers. The review also highlights further avenues of research for optimizing their potential and commercialization. This review confirms the potential of intrinsic stimuli-responsive nanocarriers for enhanced drug delivery and antibacterial killing. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Advances in Antimicrobial Microneedle Patches for Combating Infections

Skin infections caused by bacteria, viruses and fungi are difficult to treat by conventional topical administration because of poor drug penetration across the stratum corneum. This results in low bioavailability of drugs to the infection site, as well as the lack of prolonged release. Emerging antimicrobial transdermal and ocular microneedle patches have become promising medical devices for the delivery of various antibacterial, antifungal, and antiviral therapeutics. In the present review, skin anatomy and its barriers along with skin infection are discussed. Potential strategies for designing antimicrobial microneedles and their targeted therapy are outlined. Finally, biosensing microneedle patches associated with personalized drug therapy and selective toxicity toward specific microbial species are discussed.

Fabrication and Characterization of Ceftizoxime-Loaded Pectin Nanocarriers

Ceftizoxime (C13H12N5NaO5S2)is a parenteral, third-generationcephalosporin antibiotic used to treat bacterial infections including ear, nose, and throat infections. In this work, pectin has been used as a nanocarrier for ceftizoxime due to its high biocompatibility and non-toxicity with tunable surface properties. Ceftizoxime-loaded pectin nanocarriers (CPN) were successfully synthesized by the solvent displacement method. Optimization of nanoformulation was done by response surface methodology using Design-Expert software. The optimized formulation examined various in-vitro characterizations such as particle size, morphology, and FTIR studies. TEM results revealed irregular shape nanoparticles within the range of 29-110 nm. The in-vitro drug release using the dialysis method was performed after 24h where nanoformulation showed sustained drug release. Drug-loaded nanoparticles revealed good antimicrobial activity against Bacillus cereus, Bacilluspolymyxa, Enterobacteraerogenes, andPseudomonasaeruginosa.

Towards Robust Delivery of Antimicrobial Peptides to Combat Bacterial Resistance

Antimicrobial peptides (AMPs), otherwise known as host defence peptides (HDPs), are naturally occurring biomolecules expressed by a large array of species across the phylogenetic kingdoms. They have great potential to combat microbial infections by directly killing or inhibiting bacterial activity and/or by modulating the immune response of the host. Due to their multimodal properties, broad spectrum activity, and minimal resistance generation, these peptides have emerged as a promising response to the rapidly concerning problem of multidrug resistance (MDR). However, their therapeutic efficacy is limited by a number of factors, including rapid degradation, systemic toxicity, and low bioavailability. As such, many strategies have been developed to mitigate these limitations, such as peptide modification and delivery vehicle conjugation/encapsulation. Oftentimes, however, particularly in the case of the latter, this can hinder the activity of the parent AMP. Here, we review current delivery strategies used for AMP formulation, focusing on methodologies utilized for targeted infection site release of AMPs. This specificity unites the improved biocompatibility of the delivery vehicle with the unhindered activity of the free AMP, providing a promising means to effectively translate AMP therapy into clinical practice.

pH-Responsive Micelles From an Oleic Acid Tail and Propionic Acid Heads Dendritic Amphiphile for the Delivery of Antibiotics

The aim of this study was to synthesize a novel biocompatible pH-responsive oleic acid-based dendritic lipid amphiphile (OLA-SPDA) which self-assembled into stable micelles (OLA-SPDA -micelles) with a relatively low critical micelle concentration (CMC) of 5.6 × 10^-6 M. The formulated micelles had particle size, polydispersity index (PDI) and zeta potential (ZP) of 84.16 ± 0.184 nm, 0.199 ± 0.011 and -42.6 ± 1.98 mV, respectively, at pH 7.4. The vancomycin (VCM) encapsulation efficiency was 78.80 ± 3.26%. The micelles demonstrated pH-responsiveness with an increase in particle size to 141.1 ± 0.0707 nm and a much faster release profile at pH 6.0, as compared to pH 7.4. The minimum inhibitory concentration (MIC) of VCM-OLA-SPDA-micelle against methicillin-resistant staphylococcus aureus (MRSA) was 8-fold lower compared to bare VCM, and the formulation had a 4-fold lower MIC at pH 6.0 when compared to the formulation's MIC at pH 7.4. MRSA viability assay showed the micelles had a percentage killing of 93.39% when compared bare-VCM (58.21%) at the same MIC (0.98 μg/mL). In vivo mice (BALB/c) skin infection models showed an 8-fold reduction in MRSA burden after treatment with VCM-OLA-SPDA-micelles when compared with bare VCM. The above results suggest that pH-responsive VCM-OLA-SPDA-micelles has the potential to be an effective carrier to enhance therapeutic outcomes against infections characterised by low pH.

Farnesol-Containing Macromolecular Systems for Antibiofilm Strategies

Farnesol is a natural sesquiterpenoid and an interesting quorum-sensing molecule. Its insolubility in water is the biggest obstacle to its application for bacterial biofilm treatments since it compromises the bioavailability. Recently, an increasing interest in farnesol encapsulation or loading in polymeric materials may be noted due to the prolonged action of the active macromolecular systems. In this short review, we present an overview of methods leading to improved interactions between farnesol and microbial biofilms.

The global preclinical antibacterial pipeline

Antibacterial resistance is a great concern and requires global action. A critical question is whether enough new antibacterial drugs are being discovered and developed. A review of the clinical antibacterial drug pipeline was recently published, but comprehensive information about the global preclinical pipeline is unavailable. This Review focuses on discovery and preclinical development projects and has found, as of 1 May 2019, 407 antibacterial projects from 314 institutions. The focus is on Gram-negative pathogens, particularly bacteria on the WHO priority bacteria list. The preclinical pipeline is characterized by high levels of diversity and interesting scientific concepts, with 135 projects on direct-acting small molecules that represent new classes, new targets or new mechanisms of action. There is also a strong trend towards non-traditional approaches, including diverse antivirulence approaches, microbiome-modifying strategies, and engineered phages and probiotics. The high number of pathogen-specific and adjunctive approaches is unprecedented in antibiotic history. Translational hurdles are not adequately addressed yet, especially development pathways to show clinical impact of non-traditional approaches. The innovative potential of the preclinical pipeline compared with the clinical pipeline is encouraging but fragile. Much more work, focus and funding are needed for the novel approaches to result in effective antibacterial therapies to sustainably combat antibacterial resistance.

Nano-Based Drug Delivery or Targeting to Eradicate Bacteria for Infection Mitigation: A Review of Recent Advances

Pathogenic bacteria infection is a major public health problem due to the high morbidity and mortality rates, as well as the increased expenditure on patient management. Although there are several options for antimicrobial therapy, their efficacy is limited because of the occurrence of drug-resistant bacteria. Many conventional antibiotics have failed to show significant amelioration in overall survival of infectious patients. Nanomedicine for delivering antibiotics provides an opportunity to improve the efficiency of the antibacterial regimen. Nanosystems used for antibiotic delivery and targeting to infection sites render some benefits over conventional formulations, including increased solubility, enhanced stability, improved epithelium permeability and bioavailability, prolonged antibiotic half-life, tissue targeting, and minimal adverse effects. The nanocarriers' sophisticated material engineering tailors the controllable physicochemical properties of the nanoparticles for bacterial targeting through passive or active targeting. In this review, we highlight the recent progress on the development of antibacterial nanoparticles loaded with antibiotics. We systematically introduce the concepts and amelioration mechanisms of the nanomedical techniques for bacterial eradication. Passive targeting by modulating the nanoparticle structure and the physicochemical properties is an option for efficient drug delivery to the bacteria. In addition, active targeting, such as magnetic hyperthermia induced by iron oxide nanoparticles, is another efficient way to deliver the drugs to the targeted site. The nanoparticles are also designed to respond to the change in environment pH or enzymes to trigger the release of the antibiotics. This article offers an overview of the benefits of antibacterial nanosystems for treating infectious diseases.

Dual-crosslinked nanocomposite hydrogels based on quaternized chitosan and clindamycin-loaded hyperbranched nanoparticles for potential antibacterial applications

Bacterial infections caused by S. aureus are prevalent all over the world. Antibiotic-loaded hydrogel has been reported as a promising drug delivery system for the treatment. However, the direct incorporation of antibiotics into the hydrogel leads to quick initial burst release, which results in a sub-inhibition concentration of antibiotics in local environment and induces the antibiotic resistance of bacteria. In this work, a novel dual-crosslinked nanocomposite hydrogel (imine bond and nanoparticle crosslinking) was prepared based on quaternized chitosan and clindamycin-loaded hyperbranched nanoparticles. Dual-crosslinked nanocomposite structure endowed the hydrogel with considerable mechanical and injectable properties. Dual pH responses were introduced into the hydrogel, and a controlled clindamycin release was observed in the acidic environment, which might avoid inducing the antibiotic resistance of bacteria. What's more, the antibacterial results demonstrated an excellent antibacterial activity of the hydrogel for not only E. coli and S. aureus, but also Methicillin-resistant S. aureus (MRSA). Nearly 90% of bacteria was killed after contacting with the hydrogel. In addition, the in vitro cell cytotoxicity test results showed that the hydrogel owned good biocompatibility. The in vitro cell viability was >90%. Above all, this dual-crosslinked nanocomposite hydrogel owned possibility for potential antibacterial applications.

A pH-sensitive delivery system based on N-succinyl chitosan-ZnO nanoparticles for improving antibacterial and anticancer activities of curcumin

Inherent selective cytotoxicity, antibacterial activity and unique physicochemical properties of ZnO nanostructures and chitosan (CS) make them promising candidates for drug delivery. In this study, ZnO nanoparticles functionalized by N-succinyl chitosan as a pH-sensitive delivery system were synthesized to enhance the therapeutic potential of curcumin (CUR). CS coated-ZnO nanoparticles were synthesized by a co-precipitation method in the presence of CS. Chemical modification of CS-ZnO particles was performed by succinic anhydride for introducing -COOH functional groups which were then activated using 1,1'‑carbonyldiimidazole for CUR conjugation. The spherical-like CUR-conjugated system (CUR-CS-ZnO) with the average particle size of 40 nm presented significantly enhanced water dispersibility versus free CUR. The experimental study of CUR release from the system showed a pH-sensitive release profile, which enabled drug delivery to tumors and infection sites. MTT and Annexin-V FITC/PI assays revealed the superior anticancer activity of CUR-CS-ZnO compared to free CUR against breast cancer cells (MDA-MB-231) by inducing the apoptotic response with no cytotoxic effects on HEK293 normal cells. Moreover, CUR conjugation to the system notably dropped the MIC (25 to 50-fold) and MBC values (10 to 40-fold) against S. aureus and E. coli. The features qualify the formulation for anticancer and antimicrobial applications in the future.

Recent advances in pH-responsive nanomaterials for anti-infective therapy

The design and synthesis of pH-responsive antibacterial nanomaterials and their applications in anti-infective therapy.

Erythrocyte-Coated Nanoparticles Block Cytotoxic Effects of Group B Streptococcus β-Hemolysin/Cytolysin

Group B Streptococcus (GBS) emerged as a leading cause of invasive infectious disease in neonates in the 1970s, but has recently been identified as an escalating public health threat in non-pregnant adults, particularly those of advanced aged or underlying medical conditions. GBS infection can rapidly develop into life-threatening disease despite prompt administration of effective antibiotics and initiation of state-of-the-art intensive care protocols and technologies due to deleterious bacterial virulence factors, such as the GBS pore-forming toxin β-hemolysin/cytolysin (β-H/C). β-H/C is known to have noxious effects on a wide range of host cells and tissues, including lung epithelial cell injury, blood brain barrier weakening, and immune cell apoptosis. Neonatal and adult survivors of GBS infection are at a high risk for substantial long-term health issues and neurologic disabilities due to perturbations in organ systems caused by bacterial- and host- mediated inflammatory stressors. Previously engineered anti-virulence inhibitors, such as monoclonal antibodies and small molecular inhibitors, generally require customized design for each different pathogenic toxin and do not target deleterious host pro-inflammatory responses that may cause organ injury, septic shock, or death. By simply wrapping donor red blood cells (RBCs) around polymeric cores, we have created biomimetic "nanosponges." Because nanoparticles retain the same repertoire of cell membrane receptors as their host cell, they offer non-specific and all-purpose toxin decoy strategies with a broad ability to sequester and neutralize various bacterial toxins and host pro-inflammatory chemokines and cytokines to attenuate the course of infectious disease. This proof-of-concept study successfully demonstrated that intervention with nanosponges reduced the hemolytic activity of live GBS and stabilized β-H/C in a dose-dependent manner. Nanosponge treatment also decreased lung epithelial and macrophage cell death following exposure to live GBS bacteria and stabilized β-H/C, improved neutrophil killing of GBS, and diminished GBS-induced macrophage IL-1β production. Our results, therefore, suggest biomimetic nanosponges provide a titratable detoxification therapy that may provide a first-in-class treatment option for GBS infection by sequestering and inhibiting β-H/C activity.