Nanocarriers for antibiotics: a promising solution to treat intracellular bacterial infections

Novel Nanotherapeutics as Next-generation Anti-infective Agents: Current Trends and Future Prospectives

With the ever-increasing population and improvement in the healthcare system in the 21st century, the incidence of chronic microbial infections and associated health disorders has also increased at a striking pace. The ability of pathogenic microorganisms to form biofilm matrix aggravates the situation due to antibiotic resistance phenomenon resulting in resistance against conventional antibiotic therapy which has become a public health concern. The canonical Quorum Sensing (QS) signaling system hierarchically regulates the expression of an array of virulence phenotypes and controls the development of biofilm dynamics. It is imperative to develop an alternative, yet effective and non-conventional therapeutic approach, popularly known as "anti-infective therapy" which seems to be interesting. In this regard, targeting microbial QS associated virulence and biofilm development proves to be a quite astonishing approach in counteracting the paucity of traditional antibiotics. A number of synthetic and natural compounds are exploited for their efficacy in combating QS associated microbial infections but the bioavailability and biocompatibility limit their widespread applications. In this context, the nanotechnological intervention offers a new paradigm for widespread biomedical applications starting from targeted drug delivery to diagnostics for the diagnosis and treatment of infectious diseases, particularly to fight against microbial infections and antibiotics resistance in biofilms. A wide range of nanomaterials ranging from metallic nanoparticles to polymeric nanoparticles and recent advances in the development of carbon-based nanomaterials such as Carbon Nanotubes (CNTs), Graphene Oxide (GO) also immensely exhibited intrinsic antiinfective properties when targeted towards microbial infections and associated MDR phenomenon. In addition, the use of nano-based platforms as carriers emphatically increases the efficacy of targeted and sitespecific delivery of potential drug candidates for preventing microbial infections.

Liposomes: From Bangham to Supercritical Fluids

Liposomes are spherical vesicles made up of an aqueous core surrounded by phospholipids. These delivery systems (DS) are largely employed as drug carriers in several industrial fields, such as pharmaceutical and nutraceutical fields. The aim of this short review is to provide a fast overview on the main fundamentals of liposomes, thought as a compact guide for researchers and students that want to approach this topic for the first time. The mini-review will focus on the definitions, production methods and characterization protocols of the liposomes produced, making a critical comparison of the main conventional and supercritical based manufacturing methods available. The literature was analyzed deeply from the first works by Dr. Bangham in 1965 to the most recent supercritical fluid applications. The advantages and disadvantages of conventional and high-pressure processes will be described in terms of solvent elimination, production at the nanometric (50–300 nm) and micrometric level (1–100 μm) and encapsulation efficiency (20–90%). The first proposed methods were characterized by a low encapsulation efficiency (20–40%), resulting in drug loss, a high solvent residue and high operating cost. The repeatability of conventional processes was also low, due to the prevalent batch mode. Supercritical-assisted methods were developed in semi-continuous layouts, resulting in an easy process scale-up, better control of liposome dimensions (polydispersity index, PDI) and also higher encapsulation efficiencies (up to 90%).

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.

A synergistic bactericidal effect of low-frequency and low-intensity ultrasound combined with levofloxacin-loaded PLGA nanoparticles on M. smegmatis in macrophages

Purpose

Tuberculosis (TB) is a highly infectious disease caused by Mycobacterium tuberculosis (Mtb), which often parasites in macrophages. This study is performed to investigate the bactericidal effect and underlying mechanisms of low-frequency and low-intensity ultrasound (LFLIU) combined with levofloxacin-loaded PLGA nanoparticles (LEV-NPs) on M. smegmatis (a surrogate of Mtb) in macrophages.

Methods and results

The LEV-NPs were prepared using a double emulsification method. The average diameter, zeta potential, polydispersity index, morphology, and drug release efficiency in vitro of the LEV-NPs were investigated. M. smegmatis in macrophages was treated using the LEV-NPs combined with 42 kHz ultrasound irradiation at an intensity of 0.13 W/cm² for 10 min. The results showed that ultrasound significantly promoted the phagocytosis of nanoparticles by macrophages (P < 0.05). In addition, further ultrasound combined with the LEV-NPs promoted the production of reactive oxygen species (ROS) in macrophage, and the apoptosis rate of the macrophages was significantly higher than that of the control (P < 0.05). The transmission electronic microscope showed that the cell wall of M. smegmatis was ruptured, the cell structure was incomplete, and the bacteria received severe damage in the ultrasound combined with the LEV-NPs group. Activity assays showed that ultrasound combined with the LEV-NPs exhibited a tenfold higher antibacterial activity against M. smegmatis residing inside macrophages compared with the free drug.

Conclusion

These data demonstrated that ultrasound combined with LEV-NPs has great potential as a therapeutic agent for TB.

Impact of nanosystems in Staphylococcus aureus biofilms treatment

Staphylococcus aureus (S. aureus) is considered by the World Health Organization as a high priority pathogen for which new therapies are needed. This is particularly important for biofilm implant-associated infections once the only available treatment option implies a surgical procedure combined with antibiotic therapy. Consequently, these infections represent an economic burden for Healthcare Systems. A new strategy has emerged to tackle this problem: for small bugs, small particles. Here, we describe how nanotechnology-based systems have been studied to treat S. aureus biofilms. Their features, drawbacks and potentialities to impact the treatment of these infections are highlighted. Furthermore, we also outline biofilm models and assays required for preclinical validation of those nanosystems to smooth the process of clinical translation.

Nucleic Acid Hybrids as Advanced Antibacterial Nanocarriers

Conventional antibiotic therapy is often challenged by poor drug penetration/accumulation at infection sites and poses a significant burden to public health. Effective strategies to enhance the therapeutic efficacy of our existing arsenal include the use of nanoparticulate delivery platforms to improve drug targeting and minimize adverse effects. However, these nanocarriers are often challenged by poor loading efficiency, rapid release and inefficient targeting. Nucleic acid hybrid nanocarriers are nucleic acid nanosystems complexed or functionalized with organic or inorganic materials. Despite their immense potential in antimicrobial therapy, they are seldom utilized against pathogenic bacteria. With the emergence of antimicrobial resistance and the associated complex interplay of factors involved in antibiotic resistance, nucleic acid hybrids represent a unique opportunity to deliver antimicrobials against resistant pathogens and to target specific genes that control virulence or resistance. This review provides an unbiased overview on fabricating strategies for nucleic acid hybrids and addresses the challenges of pristine oligonucleotide nanocarriers. We report recent applications to enhance pathogen targeting, binding and control drug release. As multifunctional next-generational antimicrobials, the challenges and prospect of these nanocarriers are included.

Circumventing antimicrobial-resistance and preventing its development in novel, bacterial infection-control strategies

INTRODUCTION

Development of new antimicrobials with ever 'better' bacterial killing has long been considered the appropriate response to the growing threat of antimicrobial-resistant infections. However, the time-period between the introduction of a new antibiotic and the appearance of resistance amongst bacterial pathogens is getting shorter and shorter. This suggests that alternative pathways than making ever 'better' antimicrobials should be taken.

AREAS COVERED

This review aims to answer the questions (1) whether we have means to circumvent existing antibiotic-resistance mechanisms, (2) whether we can revert existing antibiotic-resistance, (3) how we can prevent the development of antimicrobial-resistance against novel infection-control strategies, including nano-antimicrobials.

EXPERT OPINION

Relying on relieving antibiotic-pressure and natural outcompeting of antimicrobial-resistant bacteria seems an uncertain way out of the antibiotic-crisis facing us. Novel, non-antibiotic, nanotechnology-based infection control-strategies are promising. At the same time, rapid development of new resistance mechanisms once novel strategies is taken into global clinical use, may not be ruled out and must be closely monitored. This suggests focusing research and development on designing suitable combinations of existing antibiotics with new nano-antimicrobials in a way that induction of new antimicrobial-resistance mechanisms is avoided. The latter suggestion, however, requires a change of focus in research and development.

Liposomal delivery of antibiotic loaded nucleic acid nanogels with enhanced drug loading and synergistic anti-inflammatory activity against S. aureus intracellular infections

The persistence of Staphylococcus aureus has been accredited to its ability to escape immune response via host cell invasion. Despite the efficacy of many antibiotics against S. aureus, the high extracellular concentrations of conventional antibiotics required for bactericidal activity is limited by their low cellular accumulation and poor intracellular retention. While nanocarriers have received tremendous attention for antibiotic delivery against persistent pathogens, they suffer daunting challenges such as low drug loading, poor retention and untimely release of hydrophilic cargos. Here, a hybrid system (Van_DNL) is fabricated wherein nucleic acid nanogels are caged within a liposomal vesicle for antibiotic delivery. The central principle of this approach relies on exploiting non-covalent electrostatic interactions between cationic cargos and polyanionic DNA to immobilize antibiotics and enable precise temporal release against intracellular S. aureus. In vitro characterization of Van_DNL revealed a stable homogenous formulation with circular morphology and enhanced vancomycin loading efficiency. The hybrid system significantly sustained the release of vancomycin over 24 h compared to liposomal or nanogel controls. Under enzymatic conditions relevant to S. aureus infections, lipase triggered release of vancomycin was observed from the hybrid. While using Van_DNL to treat S. aureus infected macrophages, a dose dependent reduction in intracellular bacterial load was observed over 24 h and exposure to Van_DNL for 48 h caused negligible cellular toxicity. Pre-treatment of macrophages with the antimicrobial hybrid resulted in a strong anti-inflammatory activity in synergy with vancomycin following endotoxin stimulation. Conceptually, these findings highlight these hybrids as a unique and universal platform for synergistic antimicrobial and anti-inflammatory therapy against persistent infections.

Core-Shell poly-(D,l-Lactide-co-Glycolide)-chitosan Nanospheres with simvastatin-doxycycline for periodontal and osseous repair

This study aimed to evaluated the potential of core-shell poly(D,l-lactide-co-glycolide)-chitosan (PLGA-chitosan) nanospheres encapsulating simvastatin (SIM) and doxycycline (DOX) for promoting periodontal and large-sized osseous defects. SIM, and/or DOX were encapsulated in PLGA-chitosan nanospheres using double emulsion technique and were delivered to sites of experimental periodontitis and large-sized mandibular osseous defects of rats for 1-4 weeks. The resultant nanospheres were ~ 200 nm diameter with distinct core-shell structure and released SIM and DOX sustainably for 28 days. DOX and SIM-DOX nanospheres significantly inhibited P. gingivalis and S. sanguinis. In experimental periodontitis sites, SIM-DOX nanospheres significantly down-regulated IL-1b and MMP-8 and significantly reduced bone loss. In mandibular osseous defects, VEGF was up-regulated, and osteogenesis was significantly augmented with SIM nanospheres treatment. In conclusion, core-shell PLGA-chitosan nanospheres released SIM and DOX sustainably. SIM-DOX and SIM nanospheres could be considered to promote the repair of infected periodontal sites and non-infected osseous defects respectively.

Piperacillin Encapsulation in Nanoliposomes Using Modified Freeze-Drying of a Monophase Solution Method: Preparation, Characterization and In Vitro Antibacterial Activity

Piperacillin (Pip) is a broad spectrum β-lactam against most Gram-positive and Gram-negative aerobic and anaerobic bacteria. However, bacterial resistance restricts its benefits for the treatment of infectious diseases. Recently, nanoliposomal systems have been investigated as encouraging strategies to address this issue owing to their immense potential. We aimed to encapsulate Pip in liposomal nanoparticles and study their antibacterial activities in vitro against Pseudomonas aeruginosa (P. aeruginosa). Different liposomes were prepared based on the freeze-drying of a monophase solution method. Then, they were characterized in terms of size, zeta potential, polydispersity-index, and morphology. For further analysis, spectra of ATR-FTIR and XRD were taken for liposomal Pip. Encapsulation efficiency (EE) was determined via agar diffusion assay. Also, minimum inhibitory concentrations (MICs) were investigated by the standard broth macro-dilution method. The liposomes were from 100.9 to 444.13 nm with z-potential of - 30.70 to - 10.57 mV. EE of the selected formulation was 53.1%. TEM results showed that the liposomes were nanosized and almost spherical. ATR-FTIR results confirmed the full encapsulation of Pip in nanoliposomes. The X-ray pattern indicated that the liposomal Pip was amorphous. The MIC (10.6 µg/ml) of the nanoliposomal Pip against P. aeruginosa was one-half of the MIC (21.25 µg/ml) of free Pip for the same organisms. Considering four aspects (nanosized liposomes, no need for sterilization, suitable EE and enhanced antibacterial effects), this preparation method seems promising and may be used to overcome the bacterial resistance relative to Pip.

Nanomaterials with active targeting as advanced antimicrobials

With a growing health threat of bacterial resistance to antibiotics, the nanomaterials have been extensively studied as an alternative. It is assumed that antimicrobial nanomaterials can affect bacteria by several mechanisms simultaneously and thereby overcome antibiotic resistance. Another promising potential use is employing nanomaterials as nanocarriers for antibiotics in order to overcome bacterial defense mechanisms. The passive targeting of nanomaterials is the often used strategy for bacterial treatment, including intracellular infections of macrophages. Furthermore, the specific targeting enhances the efficacy of antimicrobials and reduces side effects. This review aims to discuss advantages, disadvantages, and challenges of nanomaterials in the context of the targeting strategies for antimicrobials as advanced tools for treatments of bacterial infections. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease.

Novel intracellular antibiotic delivery system against Staphylococcus aureus: cloxacillin-loaded poly(d,l-lactide-co-glycolide) acid nanoparticles

Aim: First, to compare in vitro minimum inhibitory concentrations (MIC) of free cloxacillin and cloxacillin-containing nanoparticles (NP) against methicillin-susceptible (MSSA) and resistant Staphylococcus aureus (MRSA) and second, to assess NP antimicrobial activity against intracellular S. aureus. Methods: Poly(d,l-lactide-co-glycolide) acid (PLGA)-NP were loaded with cloxacillin and physico-chemically characterized. MICs were determined for reference strains Newman-(MSSA) and USA300-(MRSA). Murine alveolar macrophages were infected, and bacterial intracellular survival was assessed after incubating with free-cloxacillin or PLGA-cloxacillin-NP. Results & conclusion: For both isolates, MICs for antibiotic-loaded-NP were lower than those obtained with free cloxacillin, indicating that the drug encapsulation improves antimicrobial activity. A sustained antibiotic release was demonstrated when using the PLGA-cloxacillin-NP. When considering the lowest concentrations, the use of drug-loaded NP enabled a higher reduction of intracellular bacterial load.

Polymyxin Delivery Systems: Recent Advances and Challenges

Polymyxins are vital antibiotics for the treatment of multiresistant Gram-negative ESKAPE pathogen infections. However, their clinical value is limited by their high nephrotoxicity and neurotoxicity, as well as their poor permeability and absorption in the gastrointestinal tract. This review focuses on various polymyxin delivery systems that improve polymyxin bioavailability and reduce drug toxicity through targeted and controlled release. Currently, the most suitable systems for improving oral, inhalation, and parenteral polymyxin delivery are polymer particles, liposomes, and conjugates, while gels, polymer fibers, and membranes are attractive materials for topical administration of polymyxin for the treatment of infected wounds and burns. In general, the application of these systems protects polymyxin molecules from the negative effects of both physiological and pathological factors while achieving higher concentrations at the target site and reducing dosage and toxicity. Improving the properties of polymyxin will be of great interest to researchers who are focused on developing antimicrobial drugs that show increased efficacy and safety.

Oxidative Stress-Generating Antimicrobials, a Novel Strategy to Overcome Antibacterial Resistance

Antimicrobial resistance is becoming one of the most important human health issues. Accordingly, the research focused on finding new antibiotherapeutic strategies is again becoming a priority for governments and major funding bodies. The development of treatments based on the generation of oxidative stress with the aim to disrupt the redox defenses of bacterial pathogens is an important strategy that has gained interest in recent years. This approach is allowing the identification of antimicrobials with repurposing potential that could be part of combinatorial chemotherapies designed to treat infections caused by recalcitrant bacterial pathogens. In addition, there have been important advances in the identification of novel plant and bacterial secondary metabolites that may generate oxidative stress as part of their antibacterial mechanism of action. Here, we revised the current status of this emerging field, focusing in particular on novel oxidative stress-generating compounds with the potential to treat infections caused by intracellular bacterial pathogens.

An alternative penicillin-binding protein involved in Salmonella relapses following ceftriaxone therapy

Background

Salmonella causes intracellular infections in humans. Besides quinolones, third generation cephalosporins are first line drugs used for salmonellosis therapy. An unresolved anomaly of this practice involves high relapse rates associated to quinolone- or cephalosporin-susceptible Salmonella isolates in patients that are discharged clinically following initial recovery. Reduced drug accessibility to intracellular locations has been hypothesized to impair pathogen eradication although supporting evidence is lacking in vivo. Here, we uncover a novel penicillin-binding protein as the first Salmonella factor likely contributing to relapse following beta-lactam, mainly ceftriaxone, therapy.

Methods

We used Salmonella enterica serovar Typhimurium mutants lacking the alternative penicillin-binding proteins PBP2_SAL or PBP3_SAL. Affinity of PBP2_SAL and PBP3_SAL for beta-lactam antibiotics was tested. Relapse after ceftriaxone therapy was analysed in the murine typhoid model.

Findings

S. Typhimurium does not express PBP2_SAL or PBP3_SAL in the Mueller-Hinton medium used for susceptibility testing. The pathogen produces these PBPs in response to acidic pH and nutrient limitation, conditions found in phagosomes of mammalian cells. PBP3_SAL has low affinity for beta-lactams, even at acidic pH. In vitro susceptibility to ceftriaxone at low pH is strongly reduced. S. Typhimurium lacking PBP3_SAL was unable to cause relapse in mice following ceftriaxone therapy.

Interpretation

The reduced capacity of ceftriaxone to clear S. Typhimurium in vivo is favoured by a switch in beta-lactam targets. This switch, involving production of the less-susceptible PBP3_SAL, remains invisible for standard procedures used in clinical therapy. We conclude that eradication of salmonellosis will be possible only upon targeting of PBP3_SAL with novel drugs.

Vancomycin Derivative Inactivates Carbapenem-Resistant Acinetobacter baumannii and Induces Autophagy

Vancomycin is a standard drug for the treatment of multidrug-resistant Gram-positive bacterial infections. Albeit, development of resistance (VRE, VRSA) and its inefficacy against persistent infections is a demerit. It is also intrinsically inactive against Gram-negative bacteria. Herein, we report a vancomycin derivative, VanQAmC₁₀, that addresses these challenges. VanQAmC₁₀ was rapidly bactericidal against carbapenem-resistant A. baumannii (6 log₁₀ CFU/mL reduction in 6 h), disrupted A. baumannii biofilms, and eradicated their stationary phase cells. In MRSA infected macrophages, the compound reduced the bacterial burden by 1.3 log₁₀ CFU/mL while vancomycin exhibited a static effect. Further investigation indicated that the compound, unlike vancomycin, promoted the intracellular degradative mechanism, autophagy, in mammalian cells, which may have contributed to its intracellular activity. The findings of the work provide new perspectives on the field of glycopeptide antibiotics.

Nanomedicine Fight against Antibacterial Resistance: An Overview of the Recent Pharmaceutical Innovations

Based on the recent reports of World Health Organization, increased antibiotic resistance prevalence among bacteria represents the greatest challenge to human health. In addition, the poor solubility, stability, and side effects that lead to inefficiency of the current antibacterial therapy prompted the researchers to explore new innovative strategies to overcome such resilient microbes. Hence, novel antibiotic delivery systems are in high demand. Nanotechnology has attracted considerable interest due to their favored physicochemical properties, drug targeting efficiency, enhanced uptake, and biodistribution. The present review focuses on the recent applications of organic (liposomes, lipid-based nanoparticles, polymeric micelles, and polymeric nanoparticles), and inorganic (silver, silica, magnetic, zinc oxide (ZnO), cobalt, selenium, and cadmium) nanosystems in the domain of antibacterial delivery. We provide a concise description of the characteristics of each system that render it suitable as an antibacterial delivery agent. We also highlight the recent promising innovations used to overcome antibacterial resistance, including the use of lipid polymer nanoparticles, nonlamellar liquid crystalline nanoparticles, anti-microbial oligonucleotides, smart responsive materials, cationic peptides, and natural compounds. We further discuss the applications of antimicrobial photodynamic therapy, combination drug therapy, nano antibiotic strategy, and phage therapy, and their impact on evading antibacterial resistance. Finally, we report on the formulations that made their way towards clinical application.

Zebrafish Embryos Allow Prediction of Nanoparticle Circulation Times in Mice and Facilitate Quantification of Nanoparticle-Cell Interactions

The zebrafish embryo is a vertebrate well suited for visualizing nanoparticles at high resolution in live animals. Its optical transparency and genetic versatility allow noninvasive, real-time observations of vascular flow of nanoparticles and their interactions with cells throughout the body. As a consequence, this system enables the acquisition of quantitative data that are difficult to obtain in rodents. Until now, a few studies using the zebrafish model have only described semiquantitative results on key nanoparticle parameters. Here, a MACRO dedicated to automated quantitative methods is described for analyzing important parameters of nanoparticle behavior, such as circulation time and interactions with key target cells, macrophages, and endothelial cells. Direct comparison of four nanoparticle (NP) formulations in zebrafish embryos and mice reveals that data obtained in zebrafish can be used to predict NPs' behavior in the mouse model. NPs having long or short blood circulation in rodents behave similarly in the zebrafish embryo, with low circulation times being a consequence of NP uptake into macrophages or endothelial cells. It is proposed that the zebrafish embryo has the potential to become an important intermediate screening system for nanoparticle research to bridge the gap between cell culture studies and preclinical rodent models such as the mouse.

A Novel Screening Strategy Reveals ROS-Generating Antimicrobials That Act Synergistically against the Intracellular Veterinary Pathogen Rhodococcus equi

Rhodococcus equi is a facultative intracellular pathogen that causes infections in foals and many other animals such as pigs, cattle, sheep, and goats. Antibiotic resistance is rapidly rising in horse farms, which makes ineffective current antibiotic treatments based on a combination of macrolides and rifampicin. Therefore, new therapeutic strategies are urgently needed to treat R. equi infections caused by antimicrobial resistant strains. Here, we employed a R. equi mycoredoxin-null mutant strain highly susceptible to oxidative stress to screen for novel ROS-generating antibiotics. Then, we used the well-characterized Mrx1-roGFP2 biosensor to confirm the redox stress generated by the most promising antimicrobial agents identified in our screening. Our results suggest that different combinations of antibacterial compounds that elicit oxidative stress are promising anti-infective strategies against R. equi. In particular, the combination of macrolides with ROS-generating antimicrobial compounds such as norfloxacin act synergistically to produce a potent antibacterial effect against R. equi. Therefore, our screening approach could be applied to identify novel ROS-inspired therapeutic strategies against intracellular pathogens.

Lipid oligonucleotides as a new strategy for tackling the antibiotic resistance

Antibiotic resistance has become a major issue in public health especially for one of the most used antibiotics; the third-generation cephalosporins. One of the main resistance mechanisms in Enterobacteriaceae, is the production of Extended-Spectrum β-lactamases. Here, we demonstrated that the oligonucleotide therapy is an efficient approach to reduce the resistance of bacteria to antibiotic treatment. Lipid oligonucleotides (LONs) were proved to be efficient strategies in both delivering the oligonucleotide sequences in the prokaryotic cells and decreasing the Minimum Inhibitory Concentration of resistant bacteria to a third generation cephalosporin, the ceftriaxone. Accordingly, we demonstrated the strong antimicrobial potential of this LON strategy targeting the ß-lactamase activity on both clinical and laboratory strains. Our results support the concept that the self-delivery of oligonucleotide sequences via lipid conjugation may be extended to other antimicrobial drugs, which opens novel ways to struggle against the antibiotic resistance.

Encapsulation of Red Propolis in Polymer Nanoparticles for the Destruction of Pathogenic Biofilms

Microbial biofilms, structured communities of microorganisms, have been often associated to the infection and bacterial multiresistance problem. Conventional treatment of infection involves the use of antibiotics, being an alternative approach is the use of red propolis, a natural product, to prepare polymer nanoparticles. The aim of the present study was to encapsulate red propolis extract in poly(lactic-co-glycolic acid) (PLGA) nanoparticles for destruction in vitro of pathogenic biofilms. Poly(lactic-co-glycolic acid) nanoparticles (PLGA NPs) containing red propolis hydroethanolic extract (2 mg/mL) were produced by emulsification solvent diffusion method. The extract and developed nanoparticles were analyzed for antimicrobial activity and inhibition of bacterial biofilm formation in vitro against Staphylococcus aureus and Pseudomonas aeruginosa. Transmission electron microscopy images confirmed spherical nanoparticles in the range size from 42.4 nm (PLGA NPs) to 69.2 nm (HERP PLGA NPs), with encapsulation efficiencies of 96.99%. The free extract and encapsulated in polymer nanoparticle presented antimicrobial potential, with a minimum inhibitory concentration from 15.6 to 125 μg mL^-1 and from 100 to 1560 μg mL^-1 to inhibit biofilm formation for the Staphylococcus aureus and Pseudomonas aeruginosa, respectively.

An acidity-responsive polyoxometalate with inflammatory retention for NIR-II photothermal-enhanced chemodynamic antibacterial therapy

W/Mo-based polyoxometalate was developed for local photothermal-enhanced chemodynamic antibacterial therapy in the second near-infrared region.

Liposomes with pH responsive 'on and off' switches for targeted and intracellular delivery of antibiotics

pH responsive drug delivery systems are one of the new strategies to address the spread of bacterial resistance to currently used antibiotics. The aim of this study was to formulate liposomes with 'On' and 'Off'' pH responsive switches for infection site targeting. The vancomycin (VCM) loaded liposomes had sizes below 100 nm, at pH 7.4. The QL-liposomes had a negative zeta potential at pH 7.4 that switched to a positive charge at acidic pH. VCM release from the liposome was quicker at pH 6 than pH 7.4. The OA-QL-liposome showed 4-fold lower MIC at pH 7.4 and 8- and 16-fold lower at pH 6.0 against both MSSA and MRSA compared to the bare drug. OA-QL liposome had a 1266.67- and 704.33-fold reduction in the intracellular infection for TPH-1 macrophage and HEK293 cells respectively. In vivo studies showed that the amount of MRSA recovered from mice treated with formulations was 189.67 and 6.33-fold lower than the untreated and bare VCM treated mice respectively. MD simulation of the QL lipid with the phosphatidylcholine membrane (POPC) showed spontaneous binding of the lipid to the bilayer membrane both electrostatic and Van der Waals interactions contributed to the binding. These studies demonstrated that the 'On' and 'Off' pH responsive liposomes enhanced the activity targeted and intracellular delivery VCM.

Recombinant Spider Silk-Silica Hybrid Scaffolds with Drug-Releasing Properties for Tissue Engineering Applications

Fabricating biomaterials with antimicrobial activity to prevent the growth of detrimental microorganisms is of great scientific and practical interest. Here, composite materials comprising recombinant spider silk proteins and mesoporous silica nanoparticles (MSN) loaded with selected antibiotics and antimycotics are fabricated into films and hydrogels. The derived composite materials exhibit excellent antimicrobial properties with sustained release of antibiotics over the course of 15 days. Furthermore, antibiotics/antimycotics inclusion does not impair the cytocompatibility of the composite materials, all of which promote fibroblast cell adhesion and proliferation. Finally, processing of spider silk-MSN composite hydrogels using 3D printing is shown to enable the fabrication of patient-specific antimicrobial implants to prevent infection in the near future.

Carbohydrate-based nanocarriers and their application to target macrophages and deliver antimicrobial agents

Many deadly infections are produced by microorganisms capable of sustained survival in macrophages. This reduces exposure to chemadrotherapy, prevents immune detection, and is akin to criminals hiding in police stations. Therefore, the use of glyco-nanoparticles (GNPs) as carriers of therapeutic agents is a burgeoning field. Such an approach can enhance the penetration of drugs into macrophages with specific carbohydrate targeting molecules on the nanocarrier to interact with macrophage lectins. Carbohydrates are natural biological molecules and the key constituents in a large variety of biological events such as cellular communication, infection, inflammation, enzyme trafficking, cellular migration, cancer metastasis and immune functions. The prominent characteristics of carbohydrates including biodegradability, biocompatibility, hydrophilicity and the highly specific interaction of targeting cell-surface receptors support their potential application to drug delivery systems (DDS). This review presents the 21^st century development of carbohydrate-based nanocarriers for drug targeting of therapeutic agents for diseases localized in macrophages. The significance of natural carbohydrate-derived nanoparticles (GNPs) as anti-microbial drug carriers is highlighted in several areas of treatment including tuberculosis, salmonellosis, leishmaniasis, candidiasis, and HIV/AIDS.

Challenges and strategies in drug delivery systems for treatment of pulmonary infections

Inhalation therapy has been reported as the most effective treatment for respiratory bacterial infections due to the increasing relevance of drug bioavailability. Drug delivery systems (DDS) have the capacity to overcome pulmonary biological barriers limiting the bioavailability of inhaled anti-infectives. This is important to eradicate bacterial infections and to prevent the development of bacterial resistance. Despite substantial efforts in the field, the current state-of-the-art often fails to achieve those goals, and we still observe increasing bacterial resistance. We give a brief insight on benefits and challenges in pulmonary delivery of anti-infectives. In the context of drug delivery development for pulmonary infections, particularly focusing on Pseudomonas aeruginosa (PA) infections, this mini review will critically discuss the main requirements, as well as the recent strategies of drug delivery system synthesis and preparation. Finally, interaction of DDS with crucial pulmonary biological barriers will be of great importance for the success of future applications of the developed DDS.

Bioinspired Liposomes for Oral Delivery of Colistin to Combat Intracellular Infections by Salmonella enterica

Bacterial invasion into eukaryotic cells and the establishment of intracellular infection has proven to be an effective means of resisting antibiotic action, as anti-infective agents commonly exhibit a poor permeability across the host cell membrane. Encapsulation of anti-infectives into nanoscaled delivery systems, such as liposomes, is shown to result in an enhancement of intracellular delivery. The aim of the current work is, therefore, to formulate colistin, a poorly permeable anti-infective, into liposomes suitable for oral delivery, and to functionalize these carriers with a bacteria-derived invasive moiety to enhance their intracellular delivery. Different combinations of phospholipids and cholesterol are explored to optimize liposomal drug encapsulation and stability in biorelevant media. These liposomes are then surface-functionalized with extracellular adherence protein (Eap), derived from Staphylococcus aureus. Treatment of HEp-2 and Caco-2 cells infected with Salmonella enterica using colistin-containing, Eap-functionalized liposomes resulted in a significant reduction of intracellular bacteria, in comparison to treatment with nonfunctionalized liposomes as well as colistin alone. This indicates that such bio-invasive carriers are able to facilitate intracellular delivery of colistin, as necessary for intracellular anti-infective activity. The developed Eap-functionalized liposomes, therefore, present a promising strategy for improving the therapy of intracellular infections.

Azithromycin-liposomes as a novel approach for localized therapy of cervicovaginal bacterial infections

Background

Efficient localized cervicovaginal antibacterial therapy, enabling the delivery of antibiotic to the site of action at lower doses while escaping systemic drug effects and reducing the risk of developing microbial resistance, is attracting considerable attention. Liposomes have been shown to allow sustained drug release into vaginal mucosa and improve delivery of antibiotics to bacterial cells and biofilms. Azithromycin (AZI), a potent broad-spectrum macrolide antibiotic, has not yet been investigated for localized therapy of cervicovaginal infections, although it is administered orally for the treatment of sexually transmitted diseases. Encapsulation of AZI in liposomes could improve its solubility, antibacterial activity, and allow the prolonged drug release in the cervicovaginal tissue, while avoiding systemic side effects.

Purpose

The objective of this study was to develop AZI-liposomes and explore their potentials for treating cervicovaginal infections.

Methods

AZI-liposomes that differed in bilayer elasticity/rigidity and surface charge were prepared and evaluated under simulated cervicovaginal conditions to yield optimized liposomes, which were assessed for antibacterial activity against several planktonic and biofilm-forming Escherichia coli strains and intracellular Chlamydia trachomatis, ex vivo AZI vaginal deposition/penetration, and in vitro cytotoxicity toward cervical cells.

Results

Negatively charged liposomes with rigid bilayers (CL-3), propylene glycol liposomes (PGL-2) and deformable propylene glycol liposomes (DPGL-2) were efficient against planktonic E. coli ATCC 700928 and K-12. CL-3 was superior for preventing the formation of E. coli ATCC 700928 and K-12 biofilms, with IC₅₀ values (concentrations that inhibit biofilm viability by 50%) up to 8-fold lower than those of the control (free AZI). DPGL-2 was the most promising for eradication of already formed E. coli biofilms and for treating C. trachomatis infections. All AZI-liposomes were biocompatible with cervical cells and improved localization of the drug inside vaginal tissue compared with the control.

Conclusion

The performed studies confirm the potentials of AZI-liposomes for localized cervicovaginal therapy.

Cloxacillin benzathine-loaded polymeric nanocapsules: Physicochemical characterization, cell uptake, and intramammary antimicrobial effect

The present work shows the development and evaluation of the veterinary antibiotic cloxacillin benzathine (CLOXB) loaded into poly-ε-caprolactone (PCL) nanocapsules (NC), as a potential new treatment strategy to manage bovine intramammary infections, such as mastitis. Staphylococcus aureus-induced mastitis is often a recurrent disease due to the persistence of bacteria within infected cells. CLOXB-PCL NC were prepared by interfacial deposition of preformed biodegradable polymer followed by solvent displacement method. The mean diameter of NC varied from 241 to 428 nm and from 326 to 375 nm, when determined by dynamic light scattering and by atomic force microscopy, respectively. The zeta potential of NC was negative and varied from -28 to -51 mV. In vitro release studies from the NC were performed in two media under sink conditions: PBS with 1% polyethylene glycol or milk. A reversed-phase HPLC method was developed to determine the NC entrapment efficiency and kinetics of CLOXB release from the NC. Free CLOXB dissolution occurred very fast in both media, while drug release from the NC was slower and incomplete (below 50%) after 9 h. CLOXB release kinetics from polymeric NC was fitted with the Korsmeyer-Peppas model indicating that CLOXB release is governed by diffusion following Fick's law. The fluorescence confocal microscopy images of macrophage-like J774A.1 cells reveal NC uptake and internalization in vitro. In addition, antimicrobial effect of the intramammary administration of CLOXB-PCL NC in cows with mastitis resulted in no clinical signs of toxicity and allowed complete pathogen elimination after treatment. The in vivo results obtained in this work suggest that CLOXB-PCL NC could be a promising formulation for the treatment of intramammary infections in cattle, considering their physicochemical properties, release profiles and effects on bovine mastitis control.

Bioinspired and Biomimetic Nanotherapies for the Treatment of Infectious Diseases

There are still great challenges for the effective treatment of infectious diseases, although considerable achievement has been made by using antiviral and antimicrobial agents varying from small-molecule drugs, peptides/proteins, to nucleic acids. The nanomedicine approach is emerging as a new strategy capable of overcoming disadvantages of molecular therapeutics and amplifying their anti-infective activities, by localized delivery to infection sites, reducing off-target effects, and/or attenuating resistance development. Nanotechnology, in combination with bioinspired and biomimetic approaches, affords additional functions to nanoparticles derived from synthetic materials. Herein, we aim to provide a state-of-the-art review on recent progress in biomimetic and bioengineered nanotherapies for the treatment of infectious disease. Different biomimetic nanoparticles, derived from viruses, bacteria, and mammalian cells, are first described, with respect to their construction and biophysicochemical properties. Then, the applications of diverse biomimetic nanoparticles in anti-infective therapy are introduced, either by their intrinsic activity or by loading and site-specifically delivering various molecular drugs. Bioinspired and biomimetic nanovaccines for prevention and/or therapy of infectious diseases are also highlighted. At the end, major translation issues and future directions of this field are discussed.

The highly efficient elimination of intracellular bacteria via a metal organic framework (MOF)-based three-in-one delivery system

Numerous infectious diseases that cause clinical failures and relapses after antibiotic therapy have been confirmed to be induced by pathogenic intracellular bacteria. The existing therapeutic strategies fail to eliminate intracellular bacteria mainly due to a guard reservoir provided by the cell membrane, which can deactivate antibiotics. Herein, we have reported the design of a pH-responsive metal organic framework (MOF)/antibiotic synergistic system for the targeted highly efficient elimination of intracellular bacteria. The obtained tetracycline (Tet)@ZIF-8@ hyaluronic acid (HA) system (abbreviated to TZH) can be taken up by cells owing to the presence of CD44 receptors on the cell surface via an HA-mediated pathway. Zinc ions and antibiotics, released from TZH under acidic conditions caused by bacteria, have a synergistic antibacterial effect both in vitro and in vivo. The clearance rate of TZH to the intracellular bacteria reached over 98% within the limits of biotoxicity, which indicated that this delivery system can pass the cell membrane "barriers" and restore the efficacy of endangered antibiotics. This synergistic strategy shows potential in optimizing the efficacy-dosage correlation of antibiotics for related infection treatments and constructing versatile controlled release delivery systems for a broad range of applications.

Intracellular Penetration and Effects of Antibiotics on Staphylococcus aureus Inside Human Neutrophils: A Comprehensive Review

Neutrophils are important assets in defense against invading bacteria like staphylococci. However, (dysfunctioning) neutrophils can also serve as reservoir for pathogens that are able to survive inside the cellular environment. Staphylococcus aureus is a notorious facultative intracellular pathogen. Most vulnerable for neutrophil dysfunction and intracellular infection are immune-deficient patients or, as has recently been described, severely injured patients. These dysfunctional neutrophils can become hide-out spots or “Trojan horses” for S. aureus. This location offers protection to bacteria from most antibiotics and allows transportation of bacteria throughout the body inside moving neutrophils. When neutrophils die, these bacteria are released at different locations. In this review, we therefore focus on the capacity of several groups of antibiotics to enter human neutrophils, kill intracellular S. aureus and affect neutrophil function. We provide an overview of intracellular capacity of available antibiotics to aid in clinical decision making. In conclusion, quinolones, rifamycins and sulfamethoxazole-trimethoprim seem very effective against intracellular S. aureus in human neutrophils. Oxazolidinones, macrolides and lincosamides also exert intracellular antibiotic activity. Despite that the reviewed data are predominantly of in vitro origin, these findings should be taken into account when intracellular infection is suspected, as can be the case in severely injured patients.

Biodegradable Antibacterial Polymeric Nanosystems: A New Hope to Cope with Multidrug-Resistant Bacteria

The human society is faced with daunting threats from bacterial infections. Over decades, a variety of antibacterial polymeric nanosystems have exhibited great promise for the eradication of multidrug-resistant bacteria and persistent biofilms by enhancing bacterial recognition and binding capabilities. In this Review, the "state-of-the-art" biodegradable antibacterial polymeric nanosystems, which could respond to bacteria environments (e.g., acidity or bacterial enzymes) for controlled antibiotic release or multimodal antibacterial treatment, are summarized. The current antibacterial polymeric nanosystems can be categorized into antibiotic-containing and intrinsic antibacterial nanosystems. The antibiotic-containing polymeric nanosystems include antibiotic-encapsulated nanocarriers (e.g., polymeric micelles, vesicles, nanogels) and antibiotic-conjugated polymer nanosystems for the delivery of antibiotic drugs. On the other hand, the intrinsic antibacterial polymer nanosystems containing bactericidal moieties such as quaternary ammonium groups, phosphonium groups, polycations, antimicrobial peptides (AMPs), and their synthetic mimics, are also described. The biodegradability of the nanosystems can be rendered by the incorporation of labile chemical linkages, such as carbonate, ester, amide, and phosphoester bonds. The design and synthesis of the degradable polymeric building blocks and their fabrications into nanosystems are also explicated, together with their plausible action mechanisms and potential biomedical applications. The perspectives of the current research in this field are also described.

Rifampicin-Loaded Mesoporous Silica Nanoparticles for the Treatment of Intracellular Infections

Infectious diseases remain a major burden in today’s world, causing high mortality rates and significant economic losses, with >9 million deaths per year predicted by 2030. Invasion of host cells by intracellular bacteria poses treatment challenges due to the poor permeation of antimicrobials into the infected cells. To overcome these limitations, mesoporous silica nanoparticles (MSNP) loaded with the antibiotic rifampicin were investigated as a nanocarrier system for the treatment of intracellular bacterial infection with specific interest in the influence of particle size on treatment efficiency. An intracellular infection model was established using small colony variants (SCV) of S. aureus in macrophages to systemically evaluate the efficacy of rifampicin-loaded MSNP against the pathogen as compared to a rifampicin solution. As hypothesized, the superior uptake of MSNP by macrophages resulted in an enhanced treatment efficacy of the encapsulated rifampicin as compared to free antibiotic. This study provides a potential platform to improve the performance of currently available antibiotics against intracellular infections.

A journey through the emergence of nanomedicines with poly(alkylcyanoacrylate) based nanoparticles

Starting in the late 1970s, the pioneering work of Patrick Couvreur gave birth to the first biodegradable nanoparticles composed of a biodegradable synthetic polymer. These nanoparticles, made of poly(alkylcyanoacrylate) (PACA), were the first synthetic polymer-based nanoparticulate drug carriers undergoing a phase III clinical trial so far. Analyzing the journey from the birth of PACA nanoparticles to their clinical evaluation, this paper highlights their remarkable adaptability to bypass various drug delivery challenges found on the way. At present, PACA nanoparticles include a wide range of nanoparticles that can associate drugs of different chemical nature and can be administered in vivo by different routes. The most recent technologies giving the nanoparticles customised functions could also be implemented on this family of nanoparticles. Through different examples, this paper discusses the seminal role of the PACA nanoparticles' family in the development of nanomedicines.

Nanoparticles: Antimicrobial Applications and Its Prospects

Nowadays, nanomaterials [NPs; size, 1–100 nm] have emerged as unique antimicrobial agents. Specially, several classes of antimicrobial NPs and nanosized carriers for antibiotic delivery have proven their efficacy for handling infectious diseases, including antibiotic-resistant ones, in vitro as well as in animal models, which can offer better therapy than classical drugs due to their high surface area-to-volume ratio, resulting in appearance of new mechanical, chemical, electrical, optical, magnetic, electro-optical, and magneto-optical properties, unlike from their bulk properties. Thus, scientifically NPs have been validated to be fascinating in fighting bacteria. In this chapter, we will discuss precise properties of microorganisms and their modifications among each strain specifically. The toxicity mechanisms vary from one stain to another. Even the NP’s efficacy to treat against bacteria and drug-resistant bacteria and their defense mechanisms change according to strains in particular composition of cell walls, the enzymic composition, and so on. Thus, we provide an outlook on NPs in the microbial world and mechanism to overcome the drug resistance by tagging antibiotics in NPs and its future prospects for the scientific world.

Antibacterial Countermeasures via Metal-Organic Framework-Supported Sustained Therapeutic Release

Long-term antimicrobial therapies are necessary to treat infections caused by virulent intracellular pathogens, including biothreat agents. Current treatment plans include injectable therapeutics given multiple times daily over a period for up to 8 weeks. Here, we present a metal-organic framework (MOF), zeolitic imidazolate framework-8 (ZIF-8), as a robust platform to support the sustained release of ceftazidime, an important antimicrobial agent for many critical bacterial infections. Detailed material characterization confirms the successful encapsulation of ceftazidime within the ZIF-8 matrix, indicating sustained drug release for up to a week. The antibacterial properties of ceftazidime@ZIF-8 particles were confirmed against Escherichia coli, chosen here as a representative of Gram-negative bacteria infection model in a proof-of-concept study. Further, we showed that this material system is compatible with macrophage and lung epithelial cell lines, relevant targets for antibacterial therapy for pulmonary and intracellular infections. A promising methodology to enhance the treatment of intracellular infections is to deliver the antibiotic cargo intracellularly. Importantly, this is the first study to unequivocally demonstrate direct MOF particle internalization using confocal microscopy via 3D reconstructions of z-stacks, taking advantage of the intrinsic emission properties of ZIF-8. This is an important development as it circumvents the need to use any staining dyes and addresses current methodology limitations concerning false impression of cargo uptake in the event of the carrier particle breakdown within biological media.

Promising Recent Strategies with Potential Clinical Translational Value to Combat Antibacterial Resistant Surge

Multiple drug resistance (MDR) for the treatment of bacterial infection has been a significant challenge since the beginning of the 21st century. Many of the small molecule-based antibiotic treatments have failed on numerous occasions due to a surge in MDR, which has claimed millions of lives worldwide. Small particles (SPs) consisting of metal, polymer or carbon nanoparticles (NPs) of different sizes, shapes and forms have shown considerable antibacterial effect over the past two decades. Unlike the classical small-molecule antibiotics, the small particles are less exposed so far to the bacteria to trigger a resistance mechanism, and hence have higher chances of fighting the challenge of the MDR process. Until recently, there has been limited progress of clinical treatments using NPs, despite ample reports of in vitro antibacterial efficacy. In this review, we discuss some recent and unconventional strategies that have explored the antibacterial efficacy of these small particles, alone and in combination with classical small molecules in vivo, and demonstrate possibilities that are favorable for clinical translations in near future.

Optimized Preparation of Levofloxacin Loaded Polymeric Nanoparticles

In this work, poly(lactic-co-glycolic acid) (PLGA) and chitosan (CS) nanoparticles were synthesized with the purpose of encapsulating levofloxacin (LEV). A thorough study has been carried out in order to optimize the preparation of LEV-loaded polymeric nanoparticles (NPs) suitable for parenteral administration. Changes in the preparation method, in the organic solvent nature, in the pH of the aqueous phase, or in the temperature were investigated. To the authors´ knowledge, a systematic study in order to improve the LEV nanocarrier characteristics and the yield of drug encapsulation has not been carried out to date. The physicochemical characterization of the NPs, their encapsulation efficiency (EE), and the in vitro release of LEV revealed that the best formulation was the emulsion-solvent evaporation method using dichloromethane as organic solvent, which renders suitable LEV loaded PLGA NPs. The morphology of these NPs was investigated using TEM. Their antimicrobial activities against several microorganisms were determined in vitro measuring the minimum inhibitory concentration (MIC). The results show that the use of these loaded LEV PLGA nanoparticles has the advantage of the slow release of the antibiotic, which would permit an increase in the time period between administrations as well as to decrease the side effects of the drug.

Recent advances in the treatment of pathogenic infections using antibiotics and nano-drug delivery vehicles

The worldwide misuse of antibiotics and the subsequent rise of multidrug-resistant pathogenic bacteria have prompted a paradigm shift in the established view of antibiotic and bacterial-human relations. The clinical failures of conventional antibiotic therapies are associated with lengthy detection methods, poor penetration at infection sites, disruption of indigenous microflora and high potential for mutational resistance. One of the most promising strategies to improve the efficacy of antibiotics is to complex them with micro or nano delivery materials. Such materials/vehicles can shield antibiotics from enzyme deactivation, increasing the therapeutic effectiveness of the drug. Alternatively, drug-free nanomaterials that do not kill the pathogen but target virulent factors such as adhesins, toxins, or secretory systems can be used to minimize resistance and infection severity. The main objective of this review is to examine the potential of the aforementioned materials in the detection and treatment of antibiotic-resistant pathogenic organisms.