Enhanced killing of methicillin-resistant Staphylococcus aureus in human macrophages by liposome-entrapped vancomycin and teicoplanin

Advancements in Nanoparticle-Based Strategies for Enhanced Antibacterial Interventions

The escalating global threat of antibiotic resistance underscores the urgent need for innovative antimicrobial strategies. This review explores the cutting-edge applications of nanotechnology in combating bacterial infections, addressing a critical healthcare challenge. We critically assess the antimicrobial properties and mechanisms of diverse nanoparticle systems, including liposomes, polymeric micelles, solid lipid nanoparticles, dendrimers, zinc oxide, silver, and gold nanoparticles, as well as nanoencapsulated essential oils. These nanomaterials offer distinct advantages, such as enhanced drug delivery, improved bioavailability, and efficacy against antibiotic-resistant strains. Recent advancements in nanoparticle synthesis, functionalization, and their synergistic interactions with conventional antibiotics are highlighted. The review emphasizes biocompatibility considerations, stressing the need for rigorous safety assessments in nanomaterial applications. By synthesizing current knowledge and identifying emerging trends, this review provides crucial insights for researchers and clinicians aiming to leverage nanotechnology for next-generation antimicrobial therapies. The integration of nanotechnology represents a promising frontier in combating infectious diseases, underscoring the timeliness and imperative of this comprehensive analysis.

Nanoparticles-based therapeutics for the management of bacterial infections: A special emphasis on FDA approved products and clinical trials

Microbial resistance has increased in recent decades as a result of the extensive and indiscriminate use of antibiotics. The World Health Organization listed antimicrobial resistance as one of ten major global public health threats in 2021. In particular, six major bacterial pathogens, including third-generation cephalosporin-resistant Escherichia coli, methicillin-resistant Staphylococcus aureus, carbapenem-resistant Acinetobacter baumannii, Klebsiella pneumoniae, Streptococcus pneumoniae, and Pseudomonas aeruginosa, were found to have the highest resistance-related death rates in 2019. To respond to this urgent call, the creation of new pharmaceutical technologies based on nanoscience and drug delivery systems appears to be the promising strategy against microbial resistance in light of recent advancements, particularly the new knowledge of medicinal biology. Nanomaterials are often defined as substances having sizes between 1 and 100 nm. If the material is used on a small scale; its properties significantly change. They come in a variety of sizes and forms to help provide distinguishing characteristics for a wide range of functions. The field of health sciences has demonstrated a strong interest in numerous nanotechnology applications. Therefore, in this review, prospective nanotechnology-based therapeutics for the management of bacterial infections with multiple medication resistance are critically examined. Recent developments in these innovative treatment techniques are described, with an emphasis on preclinical, clinical, and combinatorial approaches.

Exploring Nanotechnology as a Strategy to Circumvent Antimicrobial Resistance in Bone and Joint Infections

Bone and joint infections (BJIs) are difficult to treat, necessitating antimicrobial therapy at high doses for an extended period of time, in some cases different from our local guidelines. As a consequence of the rise in antimicrobial-resistant organisms, drugs that were previously reserved for last-line defense are now being used as first line treatment, and the pill burden and adverse effects on patients are leading to nonadherence, encouraging antimicrobial resistance (AMR) to these last-resort medicines. Nanodrug delivery is the field of pharmaceutical sciences and drug delivery which combines nanotechnology with chemotherapy and/or diagnostics to improve treatment and diagnostic outcomes by targeting specific cells or tissues affected. Delivery systems based on lipids, polymers, metals, and sugars have been used in an attempt to provide a way around AMR. This technology has the potential to improve drug delivery by targeting the site of infection and using the appropriate amount of antibiotics to treat BJIs caused by highly resistant organisms. This Review aims to provide an in-depth examination of various nanodrug delivery systems used to target the causative agents in BJI.

Microbial resistance to nanotechnologies: An important but understudied consideration using antimicrobial nanotechnologies in orthopaedic implants

Microbial resistance to current antibiotics therapies is a major cause of implant failure and adverse clinical outcomes in orthopaedic surgery. Recent developments in advanced antimicrobial nanotechnologies provide numerous opportunities to effective remove resistant bacteria and prevent resistance from occurring through unique mechanisms. With tunable physicochemical properties, nanomaterials can be designed to be bactericidal, antifouling, immunomodulating, and capable of delivering antibacterial compounds to the infection region with spatiotemporal accuracy. Despite its substantial advancement, an important, but under-explored area, is potential microbial resistance to nanomaterials and how this can impact the clinical use of antimicrobial nanotechnologies. This review aims to provide a better understanding of nanomaterial-associated microbial resistance to accelerate bench-to-bedside translations of emerging nanotechnologies for effective control of implant associated infections.

Nanomaterials: The New Antimicrobial Magic Bullet

Bacterial infections are a significant cause of mortality and morbidity worldwide, despite decades of use of numerous existing antibiotics and constant efforts by researchers to discover new antibiotics. The emergence of infections associated with antibiotic-resistant bacterial strains, has amplified the pressure to develop additional bactericidal therapies or new unorthodox approaches that can deal with antimicrobial resistance. Nanomaterial-based strategies, particularly those that do not rely on conventional small-molecule antibiotics, offer promise in part due to their ability to dodge existing mechanisms used by drug-resistant bacteria. Therefore, the use of nanomaterial-based formulations has attracted attention in the field of antibiotic therapy. In this Review, we highlight novel and emerging nanomaterial-based formulations along with details about the mechanisms by which nanoparticles can target bacterial infections and antimicrobial resistance. A detailed discussion about types and the activities of nanoparticles is presented, along with how they can be used as either delivery systems or as inherent antimicrobials, or a combination of both. Lastly, we highlight some toxicological concerns for the use of nanoparticles in antibiotic therapies.

Infection microenvironment-related antibacterial nanotherapeutic strategies

The emergence and spread of antibiotic resistance is one of the biggest challenges in public health. There is an urgent need to discover novel agents against the occurrence of multidrug-resistant bacteria, such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci. The drug-resistant pathogens are able to grow and persist in infected sites, including biofilms, phagosomes, or phagolysosomes, which are more difficult to eradicate than planktonic ones and also foster the development of drug resistance. For years, various nano-antibacterial agents have been developed in the forms of antibiotic nanocarriers. Inorganic nanoparticles with intrinsic antibacterial activity and inert nanoparticles assisted by external stimuli, including heat, photon, magnetism, or sound, have also been discovered. Many of these strategies are designed to target the unique microenvironment of bacterial infections, which have shown potent antibacterial effects in vitro and in vivo. This review summarizes ongoing efforts on antibacterial nanotherapeutic strategies related to bacterial infection microenvironments, including targeted antibacterial therapy and responsive antibiotic delivery systems. Several grand challenges and future directions for the development and translation of effective nano-antibacterial agents are also discussed. The development of innovative nano-antibacterial agents could provide powerful weapons against drug-resistant bacteria in systemic or local bacterial infections in the foreseeable future.

Nano-enabled strategies to combat methicillin-resistant Staphylococcus aureus

The emergence of methicillin-resistant Staphylococcus aureus (MRSA) has become a threat to global health because of limited treatments. MRSA infections are difficult to treat due to increasingly developing resistance in combination with protective biofilms of Staphylococcus aureus (S. aureus). Nanotechnology-based research revealed that effective MRSA treatments could be achieved through targeted nanoparticles (NPs) that withstand biological films and drug resistance. Thus, the principal aim towards improving MRSA treatment is to advance drug delivery tools, which successfully address the delivery-related problems. These potential delivery tools would also carry drugs to the desired sites of therapeutic action to overcome the adverse effects. This review focused on different types of nano-engineered carriers system for antimicrobial agents with improved therapeutic efficacy of entrapped drugs. The structural characteristics that play an essential role in the effectiveness of delivery systems have also been addressed with a description of recent scientific advances in antimicrobial treatment, emphasizing challenges in MRSA treatments. Consequently, existing gaps in the literature are highlighted, and reported contradictions are identified, allowing for the development of roadmaps for future research.

Exploring the possible targeting strategies of liposomes against methicillin-resistant Staphylococcus aureus (MRSA)

Multi antibiotic-resistant bacterial infections are on the rise due to the overuse of antibiotics. Methicillin-resistant Staphylococcus aureus (MRSA) is one of the pathogens listed under the category of serious threats where vancomycin remains the mainstay treatment despite the availability of various antibacterial agents. Recently, decreased susceptibility to vancomycin from clinical isolates of MRSA has been reported and has drawn worldwide attention as it is often difficult to overcome and leads to increased medical costs, mortality, and longer hospital stays. Development of antibiotic delivery systems is often necessary to improve bioavailability and biodistribution, in order to reduce antibiotic resistance and increase the lifespan of antibiotics. Liposome entrapment has been used as a method to allow higher drug dosing apart from reducing toxicity associated with drugs. The surface of the liposomes can also be designed and enhanced with drug-release properties, active targeting, and stealth effects to prevent recognition by the mononuclear phagocyte system, thus enhancing its circulation time. The present review aimed to highlight the possible targeting strategies of liposomes against MRSA bacteremia systemically while investigating the magnitude of this effect on the minimum inhibitory concentration level.

Application of Nanotechnology in Immunity against Infection

The immune system has a physiological defense function, protecting the body from infectious diseases. Antibiotics have long been one of the most important means to treat infectious diseases, but in recent years, with the emergence of more and more multidrug-resistant (MDR) bacteria, it has become urgent to find new ways or drugs to treat infectious diseases. Nanoparticles (NPs) have attracted extensive attention owing to the special properties within the particle size range of 1–100 nanometers. In addition, NPs also have special shape symmetry and relative structural stability. The emergence of nanotechnology has brought new light to the widespread existence of MDR by its different antibacterial mechanisms. In addition to antibiotic nanocarriers being able to improve the antibacterial effect of antibiotics, some NPs also have certain antibacterial effect. What is more interesting is that linking functional groups on the surface of NPS as coatings can improve the stability of the whole system and improve the biocompatibility. The present review overviews the development of antimicrobial agents, so as to better understand the causes and mechanisms of antibiotic resistance in most microbial species, and to better think and explore new strategies to solve the problem. At the same time, this review introduces how nanotechnology can be applied to anti-infection immunity and its practical application and advantages in the treatment of infection.

Novel approaches for the treatment of methicillin-resistant Staphylococcus aureus: Using nanoparticles to overcome multidrug resistance

Methicillin-resistant Staphylococcus aureus (MRSA) causes serious infections in both community and hospital settings, with high mortality rates. Treatment of MRSA infections is challenging because of the rapidly evolving resistance mechanisms combined with the protective biofilms of S. aureus. Together, these characteristic resistance mechanisms continue to render conventional treatment modalities ineffective. The use of nanoformulations with unique modes of transport across bacterial membranes could be a useful strategy for disease-specific delivery. In this review, we summarize treatment approaches for MRSA, including novel techniques in nanoparticulate designing for better therapeutic outcomes; and facilitate an understanding that nanoparticulate delivery systems could be a robust approach in the successful treatment of MRSA.

Lipid-based nanosystems for targeting bone implant-associated infections: current approaches and future endeavors

Bone infections caused by Staphylococcus aureus are a major concern in medical care, particularly when associated with orthopedic-implant devices. The ability of the bacteria to form biofilms and their capacity to invade and persist within osteoblasts turn the infection eradication into a huge challenge. The reduction of antibiotic penetration through bacterial biofilms associated with the presence of persistent cells, ability to survive in the host, and high tolerance to antibiotics are some of the reasons for the difficult treatment of these infections. Effective therapeutic approaches are urgently needed. In this sense, lipid-based nanosystems, such as liposomes, have been investigated as an innovative and alternative strategy for the treatment of implant-associated S. aureus infections, due to their preferential accumulation at infected sites and interaction with S. aureus. This review highlights the recent advances on antibiotic-loaded liposome formulations both in vitro and in vivo and how the interaction with S. aureus biofilms may be improved by modulating the liposomal external surface. Graphical Abstract.

Multi-functionalized nanocarriers targeting bacterial reservoirs to overcome challenges of multi drug-resistance

INTRODUCTION

Infectious diseases associated with intracellular bacteria such as Staphylococcus aureus, Salmonella typhimurium and Mycobacterium tuberculosis are important public health concern. Emergence of multi and extensively drug-resistant bacterial strains have made it even more obstinate to offset such infections. Bacteria residing within intracellular compartments provide additional barriers to effective treatment.

METHOD

Information provided in this review has been collected by accessing various electronic databases including Google scholar, Web of science, Scopus, and Nature index. Search was performed using keywords nanoparticles, intracellular targeting, multidrug resistance, Staphylococcus aureus; Salmonella typhimurium; Mycobacterium tuberculosis. Information gathered was categorized into three major sections as 'Intracellular targeting of Staphylococcus aureus, Intracellular targeting of Salmonella typhimurium and Intracellular targeting of Mycobacterium tuberculosis' using variety of nanocarrier systems.

RESULTS

Conventional management for infectious diseases typically comprises of long-term treatment with a combination of antibiotics, which may lead to side effects and decreased patient compliance. A wide range of multi-functionalized nanocarrier systems have been studied for delivery of drugs within cellular compartments where bacteria including Staphylococcus aureus, Salmonella typhimurium and Mycobacterium tuberculosis reside. Such carrier systems along with targeted delivery have been utilized for sustained and controlled delivery of drugs. These strategies have been found useful in overcoming the drawbacks of conventional treatments including multi-drug resistance.

CONCLUSION

Development of multi-functional nanocargoes encapsulating antibiotics that are proficient in targeting and releasing drug into infected reservoirs seems to be a promising strategy to circumvent the challenge of multidrug resistance. Graphical abstract.

Anti-Methicillin-Resistant Staphylococcus aureus Nanoantibiotics

Nanoparticle-based antibiotic constructs have become a popular area of investigation in the biomedical sciences. Much of this work has pertained to human diseases, largely in the cancer therapy arena. However, considerable research has also been devoted to the nanochemistry for controlling infectious diseases. Among these are ones due to bacterial infections, which can cause serious illnesses leading to death. The onset of multi-drug-resistant (MDR) infections such as those caused by the human pathogen Staphylococcus aureus has created a dearth of problems such as surgical complications, persistent infections, and lack of available treatments. In this article, we set out to review the primary literature on the design and development of new nanoparticle materials for the potential treatment of S. aureus infections, and areas that could be further expanded upon to make nanoparticle antibiotics a mainstay in clinical settings.

Recent insights on nanomedicine for augmented infection control

Antimicrobial agents have been widely investigated for protecting against microbial infections in modern health. Drug-related limitations, poor bioavailability, toxicity to mammalian cells, and frequent bacteria drug resistance are major challenges faced when exploited in nanomedicine forms. Specific attention has been paid to control nanomaterial-based infection against numerous challenging pathogens in addition to improved drug delivery, targeting, and pharmacokinetic (PK) profiles, and thus, efficient antimicrobials have been fabricated using diverse components (metals, metal oxides, synthetic and semisynthetic polymers, natural or biodegradable polymers, etc). The present review covers several nanocarriers delivered through various routes of administration, highlighting major findings to control microbial infection as compared to using the free drug. Results over the past decade support the consistent development of various nanomedicines capable of improving biological significance and therapeutic benefits against an array of microbial strains. Depending on the intended application of nanomedicine, infection control will be challenged by various factors such as weighing the risk-benefits in healthcare settings, nanomaterial-induced (eco)toxicological hazards, frequent development of antibiotic resistance, scarcity of in vivo toxicity data, and a poor understanding of microbial interactions with nanomedicine at the molecular level. This review summarizes well-established informative data for nanomaterials used for infection control and safety concerns of nanomedicines to healthcare sectors followed by the significance of a unique "safe-by-design" approach.

Antibiotic-Derived Lipid Nanoparticles to Treat Intracellular Staphylococcus aureus

Intracellular survival of pathogenic bacteria leads to high chances of bacterial persistence and relapse in the bacteria-infected host. However, many antibiotics fail to clear the intracellular bacteria due to their low internalization by cells. In order to increase delivery of antibiotics in cells and eliminate intracellular bacteria, we developed antibiotic-derived lipid nanoparticles. First, we synthesized antibiotic-derived lipid conjugates using two widely used antibiotics including penicillin G (PenG) and levofloxacin (Levo). Then, we formulated them into antibiotic-derived lipid nanoparticles and evaluated their antibacterial effects. We found that penicillin G derived phospholipid nanoparticles (PenG-PL NPs) were able to enhance cellular uptake of penicillin G as compared with free penicillin G and eliminate up to 99.9998% of ~10^8.5 intracellular methicillin sensitive Staphylococcus aureus (S. aureus) in infected A549 cells, a lung epithelial cell line. The PenG-PL NPs showed the potential for inhibiting intracellular S. aureus and are promising to be further studied for in vivo antibacterial applications.

Recent Advances in the Development of Antimicrobial Nanoparticles for Combating Resistant Pathogens

The rapid growth of harmful pathogens and their multidrug-resistance poses a severe challenge for health professionals and for the development of new healthcare products. Various strategies are exploited for the development of effective antimicrobial agents, and nanoparticles are a particularly promising class of materials in this respect. This review summarizes recent advances in antimicrobial metallic, polymeric, and lipid-based nanoparticles such as liposomes, solid lipid nanoparticles, and nanostructured lipid carriers. The latter materials in particular are engineered for antimicrobial agent delivery and act by encapsulation, receptor-based binding, and disruption of microbial adherence to cellular substrates. Potential strategies for the design of multifunctional antimicrobial nanocarriers, combining material chemistry and biological interface science, are also discussed.

Emerging Nanomedicine Therapies to Counter the Rise of Methicillin-Resistant Staphylococcus aureus

In a recent report, the World Health Organisation (WHO) classified antibiotic resistance as one of the greatest threats to global health, food security, and development. Methicillin-resistant Staphylococcus aureus (MRSA) remains at the core of this threat, with persistent and resilient strains detectable in up to 90% of S. aureus infections. Unfortunately, there is a lack of novel antibiotics reaching the clinic to address the significant morbidity and mortality that MRSA is responsible for. Recently, nanomedicine strategies have emerged as a promising therapy to combat the rise of MRSA. However, these approaches have been wide-ranging in design, with few attempts to compare studies across scientific and clinical disciplines. This review seeks to reconcile this discrepancy in the literature, with specific focus on the mechanisms of MRSA infection and how they can be exploited by bioactive molecules that are delivered by nanomedicines, in addition to utilisation of the nanomaterials themselves as antibacterial agents. Finally, we discuss targeting MRSA biofilms using nano-patterning technologies and comment on future opportunities and challenges for MRSA treatment using nanomedicine.

Self-enhanced targeted delivery of a cell wall- and membrane-active antibiotics, daptomycin, against staphylococcal pneumonia

Considering that some antibacterial agents can identify the outer structure of pathogens like cell wall and/or cell membrane, we explored a self-enhanced targeted delivery strategy by which a small amount of the antibiotic molecules were modified on the surface of carriers as targeting ligands of certain bacteria while more antibiotic molecules were loaded inside the carriers, and thus has the potential to improve the drug concentration at the infection site, enhance efficacy and reduce potential toxicity. In this study, a novel targeted delivery system against methicillin-resistant Staphylococcus aureus (MRSA) pneumonia was constructed with daptomycin, a lipopeptide antibiotic, which can bind to the cell wall of S. aureus via its hydrophobic tail. Daptomycin was conjugated with N-hydroxysuccinimidyl–polyethylene glycol–1,2-distearoyl-sn-glycero-3-phosphoethanolamine to synthesize a targeting compound (Dapt–PEG–DSPE) which could be anchored on the surface of liposomes, while additional daptomycin molecules were encapsulated inside the liposomes. These daptomycin-modified, daptomycin-loaded liposomes (DPD-L[D]) showed specific binding to MRSA as detected by flow cytometry and good targeting capabilities in vivo to MRSA-infected lungs in a pneumonia model. DPD-L[D] exhibited more favorable antibacterial efficacy against MRSA than conventional PEGylated liposomal daptomycin both in vitro and in vivo. Our study demonstrates that daptomycin-modified liposomes can enhance MRSA-targeted delivery of encapsulated antibiotic, suggesting a novel drug delivery approach for existing antimicrobial agents.

Nanoparticulate platforms for targeting bone infections: meeting a major therapeutic challenge

Bone infections are devastating complications in orthopedics due to biofilm formation. Treatment requires high antibiotic doses, which may lead to systemic toxicity thus limiting the drug therapeutic effectiveness. In this context, nanoparticles are well-known controlled release drug carriers that are able to modulate release rate, versatile in terms of administration routes and may be used as local delivery systems. Regarding bone infections, although nanoparticles are a promising strategy for overcoming biofilm tolerance, there are clearly technical, safety, regulatory and clinical challenges that need to be overcome before such nanomedicines may be translated into clinical use. In this paper, we present a critical overview on the high expectations against the real potential of the nanotechnological approaches to bone infection treatment.

Toward an optimized treatment of intracellular bacterial infections: input of nanoparticulate drug delivery systems

Intracellular pathogenic bacteria can lead to some of the most life-threatening infections. By evolving a number of ingenious mechanisms, these bacteria have the ability to invade, colonize and survive in the host cells in active or latent forms over prolonged period of time. A variety of nanoparticulate systems have been developed to optimize the delivery of antibiotics. Main advantages of nanoparticulate systems as compared with free drugs are an efficient drug encapsulation, protection from inactivation, targeting infection sites and the possibility to deliver drugs by overcoming cellular barriers. Nevertheless, despite the great progresses in treating intracellular infections using nanoparticulate carriers, some challenges still remain, such as targeting cellular subcompartments with bacteria and delivering synergistic drug combinations. Engineered nanoparticles should allow controlling drug release both inside cells and within the extracellular space before reaching the target cells.

Nanoengineered drug delivery systems for enhancing antibiotic therapy

Formulation scientists are recognizing nanoengineered drug delivery systems as an effective strategy to overcome limitations associated with antibiotic drug therapy. Antibiotics encapsulated into nanodelivery systems will contribute to improved management of patients with various infectious diseases and to overcoming the serious global burden of antibiotic resistance. An extensive review of several antibiotic-loaded nanocarriers that have been formulated to target drugs to infectious sites, achieve controlled drug release profiles, and address formulation challenges, such as low-drug entrapment efficiencies, poor solubility and stability is presented in this paper. The physicochemical properties and the in vitro/in vivo performances of various antibiotic-loaded delivery systems, such as polymeric nanoparticles, micelles, dendrimers, liposomes, solid lipid nanoparticles, lipid-polymer hybrid nanoparticles, nanohybirds, nanofibers/scaffolds, nanosheets, nanoplexes, and nanotubes/horn/rods and nanoemulsions, are highlighted and evaluated. Future studies that will be essential to optimize formulation and commercialization of these antibiotic-loaded nanosystems are also identified. The review presented emphasizes the significant formulation progress achieved and potential that novel nanoengineered antibiotic drug delivery systems have for enhancing the treatment of patients with a range of infections.

Novel formulations for antimicrobial peptides

Peptides in general hold much promise as a major ingredient in novel supramolecular assemblies. They may become essential in vaccine design, antimicrobial chemotherapy, cancer immunotherapy, food preservation, organs transplants, design of novel materials for dentistry, formulations against diabetes and other important strategical applications. This review discusses how novel formulations may improve the therapeutic index of antimicrobial peptides by protecting their activity and improving their bioavailability. The diversity of novel formulations using lipids, liposomes, nanoparticles, polymers, micelles, etc., within the limits of nanotechnology may also provide novel applications going beyond antimicrobial chemotherapy.

Biodegradable nanoparticles for intracellular delivery of antimicrobial agents

Biodegradable nanoparticles have emerged as a promising strategy for ferrying antimicrobial agents into specific cells due to their unique properties. This review discusses the current progress and challenges of biodegradable nanoparticles for intracellular antimicrobial delivery to understand design principles for the development of ideal nanocarriers. The intracellular delivery performances of biodegradable nanoparticles for diverse antimicrobial agents are first summarized. Second, the cellular internalization and intracellular trafficking, degradation and release kinetics of nanoparticles as well as their relation with intracellular delivery of encapsulated antimicrobial agents are provided. Third, the influences of nanoparticle properties on the cellular internalization and intracellular fate of nanoparticles and their payload antimicrobial agents are discussed. Finally, the challenges and perspectives of nanoparticles for intracellular delivery of antimicrobial agents are addressed. The review will be helpful to the scientists who are interested in searching for more efficient nanosystem strategies for intracellular delivery of antimicrobial agents.

Nanotechnology and pulmonary delivery to overcome resistance in infectious diseases

Used since ancient times especially for the local treatment of pulmonary diseases, lungs and airways are a versatile target route for the administration of both local and systemic drugs. Despite the existence of different platforms and devices for the pulmonary administration of drugs, only a few formulations are marketed, partly due to physiological and technological limitations.

Respiratory infections represent a significant burden to health systems worldwide mainly due to intrahospital infections that more easily affect immune-compromised patients. Moreover, tuberculosis (TB) is an endemic infectious disease in many developing nations and it has resurged in the developed world associated with the human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) epidemic.

Currently, medicine faces the specter of antibiotic resistance. Besides the development of new anti-infectious drugs, the development of innovative and more efficient delivery systems for drugs that went off patent appears as a promising strategy pursued by the pharmaceutical industry to improve the therapeutic outcomes and to prolong the utilities of their intellectual property portfolio. In this context, nanotechnology-based drug delivery systems (nano-DDS) emerged as a promising approach to circumvent the limitations of conventional formulations and to treat drug resistance, opening the hypothesis for new developments in this area.

Nano-technology for targeted drug delivery to combat antibiotic resistance

Several microbes have evolved clinically significant resistance against almost every available antibiotic. Yet the development of new classes of antibiotics has lagged far behind our growing need. Frequent and suboptimal use of antibiotics particularly in developing countries aggravated the problem by increasing the rate of resistance. Therefore, developing new and multidimensional strategies to combat microbial infections is warranted. These include i) modification of existing antibiotics, ii) searching new and novel antibiotics, iii) development and improvement of antibiotics carrier system to reduce amount and frequency of antibiotic doses, iv) development of targeted antibiotic delivery systems. Here, the authors discuss trends and development of nano-materials and alternative antimicrobials to solve the problem of antibiotic resistance.

Liposomal encapsulation of vancomycin improves killing of methicillin-resistant Staphylococcus aureus in a murine infection model

OBJECTIVES

Methicillin-resistant Staphylococcus aureus (MRSA) poses a major problem to public health worldwide. MRSA strains with increased resistance to vancomycin cause infections that are associated with greater morbidity and threaten the use of this once gold-standard antistaphylococcal drug. We investigated whether encapsulation of vancomycin within liposomes could improve its antistaphylococcal activity.

METHODS

Two liposomal formulations of vancomycin were prepared using a rehydration-dehydration method. MICs and MBCs of the liposomal vancomycin for strains of MRSA were determined. The efficacy of one of the liposomal vancomycin formulations was also investigated in a time-kill assay in vitro and in a murine systemic infection model.

RESULTS

Encapsulation in either liposome preparation decreased the vancomycin MICs and MBCs for MRSA strains by approximately 2-fold. Liposomal vancomycin increased killing of MRSA in vitro in a kinetic study. In a systemic murine infection model, treatment with a 50 mg/kg intraperitoneal injection of liposomal vancomycin improved kidney clearance of a USA300 strain by 1 log compared with an injection of 50 mg/kg of free vancomycin.

CONCLUSIONS

Our findings suggest that entrapment within liposomes could improve the antistaphylococcal efficacy of vancomycin.

Lipase-sensitive polymeric triple-layered nanogel for "on-demand" drug delivery

We report a new strategy for differential delivery of antimicrobials to bacterial infection sites with a lipase-sensitive polymeric triple-layered nanogel (TLN) as the drug carrier. The TLN was synthesized by a convenient arm-first procedure using an amphiphilic diblock copolymer, namely, monomethoxy poly(ethylene glycol)-b-poly(ε-caprolactone), to initiate the ring-opening polymerization of the difunctional monomer 3-oxapentane-1,5-diyl bis(ethylene phosphate). The hydrophobic poly(ε-caprolactone) (PCL) segments collapsed and surrounded the polyphosphoester core, forming a hydrophobic and compact molecular fence in aqueous solution which prevented antibiotic release from the polyphosphoester core prior to reaching bacterial infection sites. However, once the TLN sensed the lipase-secreting bacteria, the PCL fence of the TLN degraded to release the antibiotic. Using Staphylococcus aureus (S. aureus) as the model bacterium and vancomycin as the model antimicrobial, we demonstrated that the TLN released almost all the encapsulated vancomycin within 24 h only in the presence of S. aureus, significantly inhibiting S. aureus growth. The TLN further delivered the drug into bacteria-infected cells and efficiently released the drug to kill intracellular bacteria. This technique can be generalized to selectively deliver a variety of antibiotics for the treatment of various infections caused by lipase-secreting bacteria and thus provides a new, safe, effective, and universal approach for the treatment of extracellular and intracellular bacterial infections.

Development and stability studies of novel liposomal vancomycin formulations

A promising strategy to improve the therapeutic efficiency of antimicrobial agents is targeted therapy. Although vancomycin has been considered a gold standard for the therapy of MRSA pneumonia, clinical failure rates have also been reported owing to its slow, time-dependent bactericidal activity, variable lung tissue penetration and poor intracellular penetration into macrophages. Liposomal encapsulation has been established as an alternative for antimicrobial delivery to infected tissue macrophages and offers enhanced pharmacodynamics, pharmacokinetics and decreased toxicity compared to standard preparations. The aim of the present work is to prepare vancomycin in two different liposomal formulations, conventional and PEGylated liposomes using different methods. The prepared formulations were optimized for their particle size, encapsulation efficiency and physical stability. The dehydration-rehydration was found to be the best preparation method. Both the conventional and PEGylated liposomal formulations were successfully formulated with a narrow particle size and size distribution and % encapsulation efficiency of 9 ± 2 and 12 ± 3, respectively. Both the formulations were stable at 4°C for 3 months. These formulations were successfully used to evaluate for their intracellular killing of MRSA and in vivo pharmacokinetic and bio-distribution studies.

PEGylated liposome encapsulation increases the lung tissue concentration of vancomycin

Pneumonia due to methicillin-resistant Staphylococcus aureus (MRSA) often cannot be cured by vancomycin treatment. Poor lung tissue and intracellular penetration limits the ability to achieve effective bactericidal levels, particularly in alveolar macrophages, where MRSA can evade phagocytic killing. Compared to standard formulations, liposome encapsulation has been shown to enhance vancomycin intracellular killing of MRSA. In this murine pharmacokinetic and biodistribution study, PEGylated liposomal vancomycin, compared to standard and non-PEGylated formulations, significantly prolonged blood circulation time and increased deposition in lung, liver, and spleen and yet reduced accumulation in kidney tissue. As a result of optimizing antimicrobial targeting of infected lung tissue and limiting renal parenchymal exposure, administration of PEGylated liposomal vancomycin may improve the efficacy of treatment of MRSA pneumonia and reduce the risk of nephrotoxicity.

"Nanoantibiotics": a new paradigm for treating infectious diseases using nanomaterials in the antibiotics resistant era

Despite the fact that we live in an era of advanced and innovative technologies for elucidating underlying mechanisms of diseases and molecularly designing new drugs, infectious diseases continue to be one of the greatest health challenges worldwide. The main drawbacks for conventional antimicrobial agents are the development of multiple drug resistance and adverse side effects. Drug resistance enforces high dose administration of antibiotics, often generating intolerable toxicity, development of new antibiotics, and requests for significant economic, labor, and time investments. Recently, nontraditional antibiotic agents have been of tremendous interest in overcoming resistance that is developed by several pathogenic microorganisms against most of the commonly used antibiotics. Especially, several classes of antimicrobial nanoparticles (NPs) and nanosized carriers for antibiotics delivery have proven their effectiveness for treating infectious diseases, including antibiotics resistant ones, in vitro as well as in animal models. This review summarizes emerging efforts in combating against infectious diseases, particularly using antimicrobial NPs and antibiotics delivery systems as new tools to tackle the current challenges in treating infectious diseases.

Nanoparticles: Emerging carriers for drug delivery

The core objective of nanoparticles is to control and manipulate biomacromolecular constructs and supramolecular assemblies that are critical to living cells in order to improve the quality of human health. By definition, these constructs and assemblies are nanoscale and include entities such as drugs, proteins, DNA/RNA, viruses, cellular lipid bilayers, cellular receptor sites and antibody variable regions critical for immunology and are involved in events of nanoscale proportions. The emergence of such nanotherapeutics/diagnostics will allow a deeper understanding of human longevity and human ills that include cancer, cardiovascular disease and genetic disorders. A technology platform that provides a wide range of synthetic nanostructures that may be controlled as a function of size, shape and surface chemistry and scale to these nanotechnical dimensions will be a critical first step in developing appropriate tools and a scientific basis for understanding nanoparticles.

Preparation of liposomal vancomycin and intracellular killing of meticillin-resistant Staphylococcus aureus (MRSA)

Meticillin-resistant Staphylococcus aureus (MRSA) can persist in alveolar macrophages and contribute to clinical failure of intravenous vancomycin to cure pneumonia. In this study, it was shown that vancomycin in standard solution is unable to kill intracellular MRSA within macrophages. The intracellular viability of MRSA inside macrophages treated with two different formulations of encapsulated liposomal vancomycin prepared using a hydration-dehydration method was then determined. In contrast to the observations with standard vancomycin, treatment with conventional non-pegylated liposomal vancomycin (lacking any surface modification) resulted in a sufficient concentration of antibiotic inside the intracellular compartment of the macrophages to exert a marked bactericidal effect against MRSA. On the other hand, treatment of infected macrophages with surface-pegylated liposomes resulted in no impact on MRSA survival, and this lack of an inhibitory effect may likely reflect delayed phagocytosis owing to the 'stealth' effect by pegylation. This study indicates the potential for a novel liposomal delivery system that may improve clinical vancomycin treatment outcomes by targeting intracellular MRSA infection.

Rifampicin-loaded liposomes for the passive targeting to alveolar macrophages: in vitro and in vivo evaluation

Mycobacterium avium complex (MAC), the most frequent cause of opportunistic nontuberculous pulmonary infection, is made up of a group of intracellular pathogens that are able to survive and multiply inside lung alveolar macrophages. As nebulized liposomes are reported to be effective to target antibacterial agents to macrophages, in this work we have prepared and characterized re-dispersible freeze-dried rifampicin (RFP)-loaded vesicles by using soy lecithin (SL) and a commercial, enriched mixture of soy phosphatidylcholine (Phospholipon 90, P90) with or without cholesterol. The obtained results showed that RFP could be loaded stably in SL vesicles only when cholesterol was not present in the film preparation, whereas with P90 vesicles, the highest stability was obtained with formulations prepared with P90/cholesterol 7:1 or 4:1 molar ratios. RFP-liposome aerosols were generated using an efficient high-output continuous-flow nebulizer, driven by a compressor. After the experiments, nebulization efficiency (NE%) and nebulization efficiency of the encapsulated drug (NEED%) were evaluated. The results of our study indicated that nebulization properties and viscosity of formulations prepared with the low-transition-temperature phospholipids, SL and P90, are affected by vesicle composition. However, all formulations showed a good stability during nebulization and they were able to retain more than 65% of the incorporated drug. The effect of liposome encapsulation on lung levels of RFP following aerosol inhalation was determined in rats. The in vitro intracellular activity of RFP-loaded liposomes against MAC residing in macrophage-like J774 cells was also evaluated. Results indicated that liposomes are able to inhibit the growth of MAC in infected macrophages and to reach the lower airways in rats.

Use of Liposomes to Deliver Bactericides to Bacterial Biofilms

Methods are described for the preparation of anionic and cationic liposomes and proteoliposomes with covalently linked lectins or antibodies by the extrusion technique (vesicles by extrusion, VETs). The liposomes are prepared from the phospholipid dipalmitoylphosphatidylcholine (DPPC), together with the anionic lipid phosphatidylinositol (PI) or the cationic amphiphile dioctadecyldimethylammonium bromide (DDAB) together with the reactive lipid DPPE-MBS, the m-maleimidobenzoyl-N-hydroxysuccinimide (MBS) derivative of dipalmitoylphosphatidylethanolamine (DPPE). Proteins (lectin or antibody), after derivatization with N-succinimidyl-S-acetylthioacetate (SATA), can be covalently linked to the surface of the liposomes by reaction with the reactive lipid, DPPE-MBS. The physical and chemical characterization of the liposomes and proteoliposomes by photon correlation spectroscopy (PCS) and protein analysis, to determine the number of chemically linked protein molecules (lectin or antibody) per liposome, are described. The liposomes can be used for carrying oil-soluble bactericides (e.g., Triclosan) or water-soluble antibiotics (e.g., vancomycin or benzylpenicillin) and targeted to immobilized bacterial biofilms of oral or skin-associated bacteria adsorbed on microtiter plates. Techniques for the preparation of immobilized bacterial biofilms, applicable to a wide range of bacterial suspensions, and for the analysis of the adsorption (targeting) of the liposomes to the bacterial biofilms are given. The mode of delivery and assessment of antibacterial activity of liposomes encapsulating bactericides and antibiotics, when targeted to the bacterial biofilms, by use of an automated microtiter plate reader, are illustrated, with specific reference to the delivery of the antibiotic benzylpenicillin encapsulated in anionic liposomes to biofilms of Staphylococcus aureus. The methods have potential application for the delivery of oil-soluble or water-soluble bactericidal compounds to a wide range of adsorbed bacteria responsible for infections in implanted devices such as catheters, heart valves, and artificial joints.

Targeted delivery of antibiotics using liposomes and nanoparticles: research and applications

This review examines current technologies for increasing the bioavailability of antibiotics by means of liposomes or nanoparticles. The main focus is on liposomes. These carriers were preferentially developed because their composition is compatible with biological constituents. Biodegradable polymers in the form of colloidal particles have also been used and show promise for future applications in antimicrobial chemotherapy. The in vivo behaviour of both types of carriers and consequently their therapeutic potential, are determined by their route of administration. Conventional carrier strategies permit the mononuclear phagocyte system to be targeted by intravenous injection of antibiotics. Stealthy strategies avoid major uptake by these cells and extend the systemic presence of these carriers. The purpose of this review is to provide background information in antibiotic targeting gathered from papers published over the last twenty years. It seems clear that such drug carriers (liposomes, nanoparticles) allow increased drug concentration at infected sites but reduce drug toxicity.

Intracellular activity of vancomycin and Ly333328, a new semisynthetic glycopeptide, against methicillin-resistant Staphylococcus aureus

The activity of vancomycin and Ly333328, a new semisynthetic glycopeptide, against eight strains of Staphylococcus aureus showing various susceptibilities to methicillin and ciprofloxacin was examined using a colony count method. We compared the growth of strains ingested by polymorphonuclear leucocytes and non-ingested strains. MICs of vancomycin and Ly333328 against staphylococci resistant and susceptible to methicillin were 2 mg/l and 2-4 mg/l, respectively. Against all the tested extracellular staphylococci, vancomycin had only bacteriostatic activity, whereas Ly333328 showed cidal activity at 10 MIC. Against ingested staphylococci, vancomycin had nearly no activity compared with the controls, regardless of the concentration of the drug. Ly333328 at concentrations of 1 MIC and above was highly active against ingested staphylococci regardless of their susceptibility pattern. The results suggest that Ly333328 in contrast to vancomycin is active against intracellular S. aureus.

Antibacterial efficacy against an in vivo Salmonella typhimurium infection model and pharmacokinetics of a liposomal ciprofloxacin formulation

The fluoroquinolone antibiotic ciprofloxacin has been encapsulated into large unilamellar vesicles (LUV) at efficiencies approaching 100%. Drug accumulation proceeded in response to a transmembrane gradient of methylammonium sulfate and occurred concomitantly with the efflux of methylamine. A mechanism for the encapsulation process is described. LUV composed of dipalmitoylphosphatidylcholine-cholesterol (DPPC/chol), distearoylphosphatidylcholine-cholesterol (DSPC/chol), or sphingomyelin-cholesterol (SM/chol) increased the circulation lifetime of ciprofloxacin after intravenous (i.v.) administration by > 15-fold. The retention of ciprofloxacin in liposomes in the circulation decreased in the sequence SM/chol > DSPC/chol > DPPC/chol. Increased circulation lifetimes were associated with enhanced delivery of the drug to the livers, spleens, kidneys, and lungs of mice. Encapsulation of ciprofloxacin also conferred significant increases in the longevity of the drug in the plasma after intraperitoneal administration and in the lungs after intratracheal administration in comparison to free ciprofloxacin. The efficacy of a single i.v. administration of an SM/chol formulation of ciprofloxacin was measured in a Salmonella typhimurium infection model. At 20 mg of ciprofloxacin per kg of body weight, the encapsulated formulation resulted in 10(3)- to 10(4)-fold fewer viable bacteria in the livers and spleens of infected mice than was observed for animals treated with free ciprofloxacin. These results show the utility of liposomal encapsulation of ciprofloxacin in improving the pharmacokinetics, biodistribution, and antibacterial efficacy of the antibiotic. In addition, these formulations are well suited for i.v., intraperitoneal, and intratracheal or aerosol administration.

Reactive liposomes encapsulating a glucose oxidase-peroxidase system with antibacterial activity

Liposomes were prepared from phospholipid mixtures of dipalmitoylphosphatidylcholine (DPPC) and phosphatidylinositol (PI), encapsulating the enzymes glucose oxidase (GO) and GO in combination with horse radish peroxidase (HRP) by both extrusion (VET) and reverse-phase evaporation (REV). The optimum level of PI in DPPC/PI liposomes for targeting to biofilms of the oral bacterium Streptococcus gordonii has been established. The liposomes were characterised in terms of the content and activity of the encapsulated enzymes. The antibacterial activity of these 'reactive' liposomes arising from hydrogen peroxide and oxyacids in the presence of the substrates glucose and iodide ions, after targeting to the biofilms, were measured both as a function of liposome-biofilm incubation time and incubation time with the substrates. Bacterial inhibition increases with both liposome-biofilm and substrate-biofilm incubation time and with the extent of enzyme encapsulation. The reactive liposomes also display antibacterial activity in the presence of saliva. The reactive liposomes have potential value in the context of oral hygiene.

Encapsulation of vancomycin and gentamicin within cationic liposomes for inhibition of growth of Staphylococcus epidermidis

Liposomes have been prepared from dipalmitoylphosphatidylcholine (DPPC), cholesterol (Chol) and dimethyldioctadecylammonium bromide (DDAB). The cationic vesicles adsorb to biofilms of the skin-associated bacteria Staphylococcus epidermidis, which have a negative charge. Encapsulation of the antibacterial drug vancomycin into such liposomes enhanced its activity relative to the free agent. The effectiveness of the preparation was dependent on the fluidity of the liposomal membrane and on the level of drug entrapment within the aqueous core of the vesicles. The aminoglycoside antibiotic gentamicin was also encapsulated within similar liposomes but was less effective, possibly due to its slow passage through the membrane. The liposomal vancomycin preparation has potential medical use in treating bacterial infections of foreign body biomedical devices (e.g. catheters), with either topical or intravenous administration.