Bioinspired drug delivery strategies for repurposing conventional antibiotics against intracellular infections

Quaternary ammonium chitosan-functionalized mesoporous silica nanoparticles: A promising targeted drug delivery system for the treatment of intracellular MRSA infection

The limited membrane permeability and bacterial resistance pose significant challenges in the management of intracellular drug-resistant bacterial infections. To overcome this issue, we developed a bacterial-targeted drug delivery system based on quaternary ammonium chitosan-modified mesoporous silica nanoparticles (MSN-NH2-CFP@HACC) for the treatment of intracellular Methicillin-resistant Staphylococcus aureus (MRSA) infections. This system utilizes amino-functionalized mesoporous silica nanoparticles to efficiently load cefoperazone (CFP), and the nanoparticles' surface is coated with 2-hydroxypropyltrimethyl ammonium chloride chitosan (HACC) to target bacteria and enhance macrophage uptake. The findings indicate that MSN-NH2-CFP@HACC nanoparticles are efficiently internalized by macrophages, demonstrate accelerated drug release in acidic environments, and exhibit enhanced antibacterial properties, effectively suppressing the proliferation and intracellular escape of MRSA. Moreover, HACC enhances the bacterial capture ability of the nanoparticles and reduces resistance by disrupting bacterial membrane structures and inhibiting bacterial β-lactamase activity. In a murine model of MRSA bacteremia, MSN-NH2-CFP@HACC exhibited remarkable antibacterial efficacy and significantly attenuated severe inflammatory responses. In conclusion, MSN-NH2-CFP@HACC represent a promising antibiotic delivery system with exceptional antibacterial efficacy and favorable biocompatibility, thus presenting a novel strategy for addressing intracellular drug-resistant bacterial infections and demonstrating significant potential for clinical application.

Egg yolk-derived low-density lipoprotein: A potential drug delivery system to eradicate intracellular bacteria

Antibiotics have limited capacities to penetrate and eliminate intracellular bacteria. This study developed a drug delivery system to surmount the cell-membrane barrier and achieve efficient intracellular antibiotic accumulation for intracellular-bacterial eradication. Ceftiofur (CEF) was encapsulated in hen egg-yolk-extracted low-density lipoproteins (heLDLs) to generate CEF-heLDLs. Based on preliminary research, the drug-loading efficiency was approximately 44.48 % ± 2.35 % (encapsulation rate, approximately 99.31 % ± 0.63 %). CEF-heLDLs exhibited smaller particle sizes and higher absolute zeta potentials than heLDLs, indicating improved dispersibility and stability. In-vitro analyses demonstrated receptor-mediated uptake of CEF-heLDL, with lysosome colocalization. In-vivo localization analyses in mice showed multiorgan distribution characteristics. In-vitro and in-vivo antibacterial experiments showed that CEF-heLDLs displayed superior antibacterial effects against intracellular Staphylococcus aureus compared with free CEF, significantly damaging bacterial cell walls and decreasing intracellular-bacterial survival rates (P < 0.001). CEF-heLDLs significantly reduced mortality in methicillin-resistant S. aureus-infected mice (P < 0.001) compared with free CEF and improved bacterial-induced leukocytosis (P < 0.001). The CEF-heLDL synthesized in this study effectively delivers CEF into cells. Compared to free CEF, it has significantly enhanced efficacy in eliminating intracellular S. aureus, offering a promising novel approach for eradication of intracellular bacteria.

Pharmacokinetics of Levofloxacin Entrapped in Non-Ionic Surfactant Vesicles (Niosomes) in Sprague Dawley Rats

Background/Objectives: Bacteria are becoming increasingly resistant to levofloxacin and other fluoroquinolones. Previously, drug loading in colloidal carriers has shown enhanced penetration into and retention in bacterial cells. However, the mechanism of levofloxacin niosomes' bio-disposition in rats has not been reported. This study investigated the pharmacokinetics (PK) of optimized levofloxacin niosomes following intraperitoneal injection into Sprague Dawley rats. Methods: Formulation and processing variables settings were determined using DoE Fusion One software. The resulting data input into the Optimizer module provided niosome formulation for in vivo study in Sprague Dawley rats. Each group of rats (n = 6) was injected intraperitoneally with either conventional levofloxacin or its niosomes at equivalent doses of 7.5 mg/kg/dose. Blood samples were collected via tail snip and analyzed using a validated HPLC method. The plasma-time data were fed into the Gastroplus software (Simulations Plus, CA) and used to model levofloxacin PK. Results: Niosomes for in vivo study had a mean hydrodynamic diameter of 329.16 nm (±18.0), encapsulation efficiency (EE) of 30.74%, Zeta potential of 21.72 (±0.54), and polydispersity index (PDI) of 0.286 (±0.014). Both the Akaike and Schwarz criteria showed levofloxacin niosomes and conventional drug formulation obeying one- and two-compartment PK models, respectively. Thus, formulation in niosomes altered levofloxacin biodistribution by concentrating the drug in the vascular compartment. Conclusions: Niosome encapsulation of levofloxacin altered its biodistribution and pharmacokinetic profile, possibly by protecting i.p. levofloxacin en route into plasma, and significantly enhanced its plasma concentration with enhanced potential for treating intravascular infections.

Engineered Bdellovibrio bacteriovorus enhances antibiotic penetration and biofilm eradication

Biofilms increase bacterial resistance to antibiotics, as conventional antibiotic doses are often ineffective at penetrating the biofilm matrix to eliminate bacteria. Recent research has shown that the Gram-negative predator bacterium Bdellovibrio bacteriovorus can penetrate Gram-positive bacterial biofilms during its predation phase and benefit from them without direct predation. Here, based on the penetration ability of B. bacteriovorus, we constructed antibiotic-loaded liposome-engineered B. bacteriovorus as a drug delivery strategy for biofilm-related diseases. As a "living antibiotic," B. bacteriovorus can prey on Gram-negative bacteria, penetrate biofilms, and disrupt their dense structure. During this process, the rapid movement of B. bacteriovorus enhances the delivery of antibiotic-loaded liposomes into the biofilm, promoting efficient antibiotic release and improving biofilm eradication. Our findings demonstrate that this engineered living antibiotic strategy significantly improves the control and removal of bacterial biofilms, accelerates the elimination of dental plaque, promotes wound healing, and holds promise as a novel platform for treating biofilm-related infections.

Transforming Medicine: Cutting-Edge Applications of Nanoscale Materials in Drug Delivery

Since their inception in the early 1960s, the development and use of nanoscale materials have progressed tremendously, and their roles in diverse fields ranging from human health to energy and electronics are undeniable. The application of nanotechnology inventions has revolutionized many aspects of everyday life including various medical applications and specifically drug delivery systems, maximizing the therapeutic efficacy of the contained drugs by means of bioavailability enhancement or minimization of adverse effects. In this review, we utilize the CAS Content Collection, a vast repository of scientific information extracted from journal and patent publications, to analyze trends in nanoscience research relevant to drug delivery in an effort to provide a comprehensive and detailed picture of the use of nanotechnology in this field. We examine the publication landscape in the area to provide insights into current knowledge advances and developments. We review the major classes of nanosized drug delivery systems, their delivery routes, and targeted diseases. We outline the most discussed concepts and assess the advantages of various nanocarriers. The objective of this review is to provide a broad overview of the evolving landscape of current knowledge regarding nanosized drug delivery systems, to outline challenges, and to evaluate growth opportunities. The merit of the review stems from the extensive, wide-ranging coverage of the most up-to-date scientific information, allowing unmatched breadth of landscape analysis and in-depth insights.

Current developments and prospects of the antibiotic delivery systems

Antibiotics have remained the cornerstone for the treatment of bacterial infections ever since their discovery in the twentieth century. The uproar over antibiotic resistance among bacteria arising from genome plasticity and biofilm development has rendered current antibiotic therapies ineffective, urging the development of innovative therapeutic approaches. The development of antibiotic resistance among bacteria has further heightened the clinical failure of antibiotic therapy, which is often linked to its low bioavailability, side effects, and poor penetration and accumulation at the site of infection. In this review, we highlight the potential use of siderophores, antibodies, cell-penetrating peptides, antimicrobial peptides, bacteriophages, and nanoparticles to smuggle antibiotics across impermeable biological membranes to achieve therapeutically relevant concentrations of antibiotics and combat antimicrobial resistance (AMR). We will discuss the general mechanisms via which each delivery system functions and how it can be tailored to deliver antibiotics against the paradigm of mechanisms underlying antibiotic resistance.

pH-Responsive Protein-Polycation Nanocarriers for Efficient Eradication of Bacterial Biofilms and Intracellular Bacteria

Bacterial biofilms and intracellular pathogens pose significant challenges in eradication, often leading to persistent infections that are difficult to treat. To address this issue, the hydrophobic biofilm dispersant D-tyrosine is encapsulated within protein-polycation nanoparticles, designed using a mannose-terminated cationic polymer and concanavalin through electrostatic interactions. Thermodynamic studies reveal that free mannosyl groups on the nanoparticle surface promote spontaneous binding to receptor molecules mimicking those on bacterial biofilms and host cells. Under mildly acidic conditions, the nanoparticles reduce in size from 550 to ≈48 nm within 2 h, releasing 76% of encapsulated D-tyrosine. The combination of mannose targeting, particle size reduction, and controlled D-tyrosine release enable the nanoparticles to eliminate 70%-80% of the Pseudomonas aeruginosa and Staphylococcus aureus biofilm biomass at minimum bactericidal concentration (MBC) and 2MBC while eradicating 8 log of bacteria embedded within the biofilm. In an intracellular Pseudomonas aeruginosa infection model using RAW 264.7 macrophages, the nanoparticles at 2MBC eliminate over 95% of the intracellular bacteria without inducing an increase in the inflammatory cytokine interleukin-6. These protein-polycation nanoparticles, which activate their antimicrobial properties under acidic conditions, efficiently penetrate bacterial biofilms and host cell barriers via their mannose-rich surface, offering a promising strategy for the treatment of persistent infections.

The modification of conventional liposomes for targeted antimicrobial delivery to treat infectious diseases

Some of the most crucial turning points in the treatment strategies for some major infectious diseases including AIDS, malaria, and TB, have been reached with the introduction of antimicrobials and vaccines. Drug resistance and poor effectiveness are key limitations that need to be overcome. Conventional liposomes have been explored as a delivery system for infectious diseases bioactives to treat infectious diseases to provide an efficient approach to maximize the therapeutic outcomes, drug stability, targetability, to reduce the side-effects of antimicrobials, and enhance vaccine performance where necessary. However, as the pathological understanding of infectious diseases become more known, the need for more advanced liposomal technologies was born to continue having a profound effect on targeted chemotherapy for infectious diseases. This review therefore provides a concise incursion into the most recent and vogue liposomal formulations used to treat infectious diseases. An appraisal of immunological, stimuli-responsive, biomimetic and functionalized liposomes and other novel modifications to conventional liposomes is assimilated in sync with mutations of resistant pathogens.

Maltodextrin-derived nanoparticles resensitize intracellular dormant Staphylococcus aureus to rifampicin

Intracellular bacteria are recognized as a crucial factor in the persistence and recurrence of infections. The efficacy of current antibiotic treatments faces substantial challenges due to the dormant state formation of intracellular bacteria. In this study, we devised a strategy aimed at reverting intracellular dormant bacteria to a metabolically active state, thereby increasing their vulnerability to antibiotics. We found that oligosaccharides, especially maltodextrin (MD), can be absorbed by dormant S. aureus, leading to their revival and restoration of sensitivity to rifampicin (Rif). We then synthesized a reactive oxygen species (ROS)-responsive MD-prodrug by covalently binding MD with 4-(hydroxymethyl) phenylboronic acid pinacol ester (MD-PBAP) and prepared a ROS-responsive nanoparticles (MDNP) using a nanoprecipitation and self-assembly method. Once internalized by host cells, MDNP was degraded to MD, reactivating dormant S. aureus, and enhancing their susceptibility to Rif. More importantly, MDNP treatment restored the sensitivity of intracellular persistent S. aureus to Rif in both a reservoir transfer model and whole-body infection model. Additionally, MDNP have demonstrated excellent biocompatibility in both in vitro and in vivo settings. These results offer a promising therapeutic avenue for managing persistent intracellular bacterial infections by reviving and resensitizing intracellular dormant bacteria to conventional antibiotics.

Clearance of Intracellular Pathogens with Hyaluronic Acid Nanomicelles Responsive to H2S and pH

Hyaluronic acid (HA) is an acidic mucopolysaccharide of animal origin composed of repeating disaccharide units of N-acetylglucosamine and glucuronic acid. Due to its excellent biocompatibility, biodegradability, and selective affinity for CD44 receptors on cell surfaces, HA is widely employed as a drug carrier. In our study, we aimed to target subcellular bacteria by grafting cystamine onto HA scaffolds through an amide reaction, producing a linker responsive to H2S and pH changes. Subsequently, hydrophobic dodecylamine was attached to HA, forming amphiphilic molecules. These amphiphilic entities can self-assemble into nanomicelles in an aqueous solution, thereby encapsulating the antibacterial agent triclosan (TCS). The resulting HA-based system (HASS-TCS) can be internalized via CD44-mediated endocytosis, releasing substantial amounts of streptomycin and TCS in H2S-rich and acidic environments. Additionally, HASS-TCS has demonstrated effectiveness in eradicating biofilms and addressing intracellular infections caused by Salmonella. This study underscores a novel pH-sensitive hyaluronic acid-based drug delivery system with significant potential for the effective treatment of intracellular infections.

Precise Clearance of Intracellular MRSA via Internally and Externally Mediated Bioorthogonal Activation of Micro/Nano Hydrogel Microspheres

Traditional high-dose antibiotic treatments of intracellular methicillin-resistant staphylococcus aureus (MRSA) are highly inefficient and associated with a high rate of infection relapse. As an effective antibacterial technology, sonodynamic therapy (SDT) may be able to break the dilemma. However, indiscriminate reactive oxygen species (ROS) release leads to potential side effects. This study incorporates Staphylococcal Protein A antibody-modified Cu2+/tetracarboxyphenylporphyrin nanoparticles (Cu(II)NS-SPA) into hydrogel microspheres (HAMA@Cu(II)NS-SPA) to achieve precise eradication of intracellular bacteria. This eradication is under bioorthogonal activation mediated by bacillithiol (BSH) (internally) and ultrasound (US) (externally). To specify, the US responsiveness of Cu(II)NS-SPA is restored when it is reduced to Cu(I)NS-SPA by the BSH secreted characteristically by intracellular MRSA, thus forming a bioorthogonal activation with the external US, which confines ROS production within the infected MΦ. Under external US activation at 2 W cm-2, over 95% of intracellular MRSA can be cleared. In vivo, a single injection of HAMA@Cu(II)NS-SPA achieves up to two weeks of antibacterial sonodynamic therapy, reducing pro-inflammatory factor expression by 90%, and peri-implant bone trabeculae numbers exceed the control group by five times. In summary, these micro/nano hydrogel microspheres mediated by internal and external bioorthogonal activation can precisely eliminate intracellular MRSA, effectively treating multi-drug resistant intracellular bacterial infections.

Preparation of ceftiofur-encapsulated hen-egg low-density lipoproteins and their antibacterial effects on intracellular Staphylococcus aureus

Hen egg low-density lipoprotein (heLDL), as alternative of serum-derived LDL, was used as drug delivery system of ceftiofur (CEF). The CEF-loaded hen egg low-density lipoprotein (CEF-heLDL) with complete apolipoprotein structure and high drug loading rate was synthesized, possesses suitable particle size. CEF-heLDL undergoes cellular uptake and colocalizes with lysosomes in vitro. An intracellular infection model of the bovine endometrial epithelial cells and a coeliac-induced inflammation model of mice by Staphylococcus aureus (S. aureus) were established, and significantly lower intracellular S. aureus levels of CEF-heLDL group than CEF-free group (P < 0.001) was observed. The antibacterial efficacy was sustained for 24 h. Up to 400 mg/kg of CEF-heLDL, 20 times the clinical practice, were intraperitoneally administrated, and no significant toxicity signs on mice were observed. HeLDLs is an effective, safe, and cheap drug carrier, and could also be used for transmembrane delivering other antibiotics.

Seeking Cells, Targeting Bacteria: A Cascade-Targeting Bacteria-Responsive Nanosystem for Combating Intracellular Bacterial Infections

Intracellular bacteria pose a great challenge to antimicrobial therapy due to various physiological barriers at both cellular and bacterial levels, which impede drug penetration and intracellular targeting, thereby fostering antibiotic resistance and yielding suboptimal treatment outcomes. Herein, a cascade-target bacterial-responsive drug delivery nanosystem, MM@SPE NPs, comprising a macrophage membrane (MM) shell and a core of SPE NPs. SPE NPs consist of phenylboronic acid-grafted dendritic mesoporous silica nanoparticles (SP NPs) encapsulated with epigallocatechin-3-gallate (EGCG), a non-antibiotic antibacterial component, via pH-sensitive boronic ester bonds are introduced. Upon administration, MM@SPE NPs actively home in on infected macrophages due to the homologous targeting properties of the MM shell, which is subsequently disrupted during cellular endocytosis. Within the cellular environment, SPE NPs expose and spontaneously accumulate around intracellular bacteria through their bacteria-targeting phenylboronic acid groups. The acidic bacterial microenvironment further triggers the breakage of boronic ester bonds between SP NPs and EGCG, allowing the bacterial-responsive release of EGCG for localized intracellular antibacterial effects. The efficacy of MM@SPE NPs in precisely eliminating intracellular bacteria is validated in two rat models of intracellular bacterial infections. This cascade-targeting responsive system offers new solutions for treating intracellular bacterial infections while minimizing the risk of drug resistance.

Antibiotic-loaded nanoparticles for the treatment of intracellular methicillin-resistant Staphylococcus Aureus infections: In vitro and in vivo efficacy of a novel antibiotic

Antimicrobial resistance is considered one of the biggest threats to public health worldwide. Methicillin-resistant S. aureus is the causative agent of a number of infections and lung colonization in people suffering from cystic fibrosis. Moreover, a growing body of evidence links the microbiome to the development of cancer, as well as to the success of the treatment. In this view, the development of novel antibiotics is of critical importance, and SV7, a novel antibiotic active against MRSA at low concentrations, represents a promising candidate. However, the low aqueous solubility of SV7 hampers its therapeutic translation. In this study, SV7 was encapsulated in poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) to improve the solubility profile, to ensure sustained release and eventually support deposition in the airways. Furthermore, PLGA NPs were formulated as dry powder to extend their shelf-life and were shown to efficiently target intracellular infections. After identifying a formulation with suitable physico-chemical characteristics, SV7-loaded NPs were investigated in vitro in terms of inhibitory activity against MRSA, and their safety profile in lung epithelial cells. Subsequently, the activity against MRSA intracellular infections was investigated in a co-culture model of MRSA and macrophages. To test the translatability of our findings, SV7-loaded NPs were tested in vivo in a Galleria mellonella infection model. In conclusion, SV7-loaded NPs showed a safe profile and efficient inhibitory activity against MRSA at low concentrations. Furthermore, their activity against intracellular infections was confirmed, and was retained in vivo, rendering them a promising candidate for treatment of MRSA lung infections.

Unveiling Trends: Nanoscale Materials Shaping Emerging Biomedical Applications

The realm of biomedical materials continues to evolve rapidly, driven by innovative research across interdisciplinary domains. Leveraging big data from the CAS Content Collection, this study employs quantitative analysis through natural language processing (NLP) to identify six emerging areas within nanoscale materials for biomedical applications. These areas encompass self-healing, bioelectronic, programmable, lipid-based, protein-based, and antibacterial materials. Our Nano Focus delves into the multifaceted utilization of nanoscale materials in these domains, spanning from augmenting physical and electronic properties for interfacing with human tissue to facilitating intricate functionalities like programmable drug delivery.

Cellular uptake and in vitro antibacterial activity of lipid-based nanoantibiotics are influenced by protein corona

Bacteria have evolved survival mechanisms that enable them to live within host cells, triggering persistent intracellular infections that present significant clinical challenges due to the inability for conventional antibiotics to permeate cell membranes. In recent years, antibiotic nanocarriers or 'nanoantibiotics' have presented a promising strategy for overcoming intracellular infections by facilitating cellular uptake of antibiotics, thus improving targeting to the bacteria. However, prior to reaching host cells, nanocarriers experience interactions with proteins that form a corona and alter their physiological response. The influence of this protein corona on the cellular uptake, drug release and efficacy of nanoantibiotics for intracellular infections is poorly understood and commonly overlooked in preclinical studies. In this study, protein corona influence on cellular uptake was investigated for two nanoparticles; liposomes and cubosomes in macrophage and epithelial cells that are commonly infected with pathogens. Studies were conducted in presence of fetal bovine serum (FBS) to form a biologically relevant protein corona in an in vitro setting. Protein corona impact on cellular uptake was shown to be nanoparticle-dependent, where reduced internalization was observed for liposomes, the opposite was observed for cubosomes. Subsequently, vancomycin-loaded cubosomes were explored for their drug delivery performance against intracellular small colony variants of Staphylococcus aureus. We demonstrated improved bacterial killing in macrophages, with greater reduction in bacterial viability upon internalization of cubosomes mediated by the protein corona. However, no differences in efficacy were observed in epithelial cells. Thus, this study provides insights and evidence to the role of protein corona in modulating the performance of nanoparticles in a dynamic manner; these findings will facilitate improved understanding and translation of future investigations from in vitro to in vivo.

Antibiotic resistance and tolerance: What can drug delivery do against this global threat?

Antimicrobial resistance and tolerance (AMR&T) are urgent global health concerns, with alarmingly increasing numbers of antimicrobial drugs failing and a corresponding rise in related deaths. Several reasons for this situation can be cited, such as the misuse of traditional antibiotics, the massive use of sanitizing measures, and the overuse of antibiotics in agriculture, fisheries, and cattle. AMR&T management requires a multifaceted approach involving various strategies at different levels, such as increasing the patient's awareness of the situation and measures to reduce new resistances, reduction of current misuse or abuse, and improvement of selectivity of treatments. Also, the identification of new antibiotics, including small molecules and more complex approaches, is a key factor. Among these, novel DNA- or RNA-based approaches, the use of phages, or CRISPR technologies are some potent strategies under development. In this perspective article, emerging and experienced leaders in drug delivery discuss the most important biological barriers for drugs to reach infectious bacteria (bacterial bioavailability). They explore how overcoming these barriers is crucial for producing the desired effects and discuss the ways in which drug delivery systems can facilitate this process.

Intracellular infection-responsive macrophage-targeted nanoparticles for synergistic antibiotic immunotherapy of bacterial infection

Intracellular bacteria are considered to play a key role in the failure of bacterial infection therapy and increase of antibiotic resistance. Nanotechnology-based drug delivery carriers have been receiving increasing attention for improving the intracellular antibacterial activity of antibiotics, but are accompanied by disadvantages such as complex preparation procedures, lack of active targeting, and monotherapy, necessitating further design improvements. Herein, nanoparticles targeting bacteria-infected macrophages are fabricated to eliminate intracellular bacterial infections via antibiotic release and upregulation of intracellular reactive oxygen species (ROS) levels and proinflammatory responses. These nanoparticles were formed through the reaction of the amino group on selenocystamine dihydrochloride and the aldehyde group on oxidized dextran (ox-Dex), which encapsulates vancomycin (Van) through hydrophobic interactions. These nanoparticles could undergo targeted uptake by macrophages via endocytosis and respond to the bacteria-infected intracellular microenvironment (ROS and glutathione (GSH)) for controlled release of antibiotics. Furthermore, these nanoparticles could consume intracellular GSH and promote a significant increase in the level of ROS in macrophages, subsequently up-regulating the proinflammatory response to reinforce antibacterial activity. These nanoparticles can accelerate bacteria-infected wound healing. In this work, nanoparticles were fabricated for bacteria-infected macrophage-targeted and microenvironment-responsive antibiotic delivery, cellular ROS generation, and proinflammatory up-regulation activity to eliminate intracellular bacteria, which opens up a new possibility for multifunctional drug delivery against intracellular infection.

Co-delivery of doxycycline and rifampicin using CdTe-labeled poly (lactic-co-glycolic) acid for treatment of Brucella melitensis infection

Brucellosis poses a significant challenge in the medical field as a systemic infection with a propensity for relapse. This study presented a novel approach to brucellosis treatment, enhancing the efficacy of doxycycline and rifampicin through the use of poly (lactic-co-glycolic) acid coupled with cadmium-telluride quantum dots (Dox-Rif-PLGA@CdTe). The double emulsion solvent evaporation method was employed to prepare Dox-Rif-PLGA@CdTe. The study scrutinized the physicochemical attributes of these nanoparticles. The impact of antibiotic-loaded nanoparticles on Brucella melitensis was evaluated through well diffusion, minimum inhibitory concentration (MIC), and cell culture. The chemical analysis results demonstrated a possibility of chemical reactions occurring among the constituents of nanoparticles. Assessments using the well diffusion and MIC methods indicated that the impact of free drugs and nanoparticles on bacteria was equivalent. However, the drug-loaded nanoparticles significantly decreased the colony-forming units (CFUs) within the cell lines compared to free drugs. In conclusion, the synthesis of nanoparticles adhered to environmentally friendly practices and demonstrated safety. The sustained drug release over 100 h facilitated drug accumulation at the bacterial site, resulting in a heightened therapeutic effect on B. melitensis and improved outcomes in brucellosis treatment. The application of these synthesized nanodrugs exhibited promising therapeutic potential.

Targeting Intracellular Bacteria with Dual Drug-loaded Lactoferrin Nanoparticles

Treatment of microbial infections is becoming daunting because of widespread antimicrobial resistance. The treatment challenge is further exacerbated by the fact that certain infectious bacteria invade and localize within host cells, protecting the bacteria from antimicrobial treatments and the host's immune response. To survive in the intracellular niche, such bacteria deploy surface receptors similar to host cell receptors to sequester iron, an essential nutrient for their virulence, from host iron-binding proteins, in particular lactoferrin and transferrin. In this context, we aimed to target lactoferrin receptors expressed by macrophages and bacteria; as such, we prepared and characterized lactoferrin nanoparticles (Lf-NPs) loaded with a dual drug combination of antimicrobial natural alkaloids, berberine or sanguinarine, with vancomycin or imipenem. We observed increased uptake of drug-loaded Lf-NPs by differentiated THP-1 cells with up to 90% proportion of fluorescent cells, which decreased to about 60% in the presence of free lactoferrin, demonstrating the targeting ability of Lf-NPs. The encapsulated antibiotic drug cocktail efficiently cleared intracellular Staphylococcus aureus (Newman strain) compared to the free drug combinations. However, the encapsulated drugs and the free drugs alike exhibited a bacteriostatic effect against the hard-to-treat Mycobacterium abscessus (smooth variant). In conclusion, the results of this study demonstrate the potential of lactoferrin nanoparticles for the targeted delivery of antibiotic drug cocktails for the treatment of intracellular bacteria.

Freeze-Thaw Microfluidic System Produces "Themis" Nanocomplex for Cleaning Persisters-Infected Macrophages and Enhancing Uninfected Macrophages

Macrophages are the primary effectors against potential pathogen infections. They can be "parasitized" by intracellular bacteria, serving as "accomplices", protecting intracellular bacteria and even switching them to persisters. Here, using a freeze-thaw strategy-based microfluidic chip, a "Themis" nanocomplex (TNC) is created. The TNC consists of Lactobacillus reuteri-derived membrane vesicles, heme, and vancomycin, which cleaned infected macrophages and enhanced uninfected macrophages. In infected macrophages, TNC releases heme that led to the reconstruction of the respiratory chain complexes of intracellular persisters, forcing them to regrow. The revived bacteria produces virulence factors that destroyed host macrophages (accomplices), thereby being externalized and becoming vulnerable to immune responses. In uninfected macrophages, TNC upregulates the TCA cycle and oxidative phosphorylation (OXPHOS), contributing to immunoenhancement. The combined effect of TNC of cleaning the accomplice (infected macrophages) and reinforcing uninfected macrophages provides a promising strategy for intracellular bacterial therapy.

Liposome-siderophore conjugates loaded with moxifloxacin serve as a model for drug delivery against Mycobacterium tuberculosis

Tuberculosis (TB) is an infectious disease that annually affects millions of people, and resistance to available antibiotics has exacerbated this situation. Another notable characteristic of Mycobacterium tuberculosis, the primary causative agent of TB, is its ability to survive inside macrophages, a key component of the immune system. In our quest for an effective and safe treatment that facilitates the targeted delivery of antibiotics to the site of infection, we have proposed a nanotechnology approach based on an iron chelator. Iron chelators are the primary mechanism by which bacteria acquire iron, a metal essential for their metabolism. Four liposomes were synthesized and characterized using the dynamic light scattering technique (DLS), nanoparticle tracking analysis (NTA), and transmission electron microscopy (TEM). All of these methods revealed the presence of spherical particles, approximately 200 nm in size. NTA indicated a concentration of around 1011 particles/mL. We also developed and validated a high-performance liquid chromatography method for quantifying Moxifloxacin to determine encapsulation efficiency (EE) and release profiles (RF). The EE was 51.31 % for LipMox and 45.76 % for LipIchMox. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed the phagocytosis of liposomal vesicles by macrophages. Functionalizing liposomes with iron chelators can offer significant benefits for TB treatment, such as targeted drug delivery to intracellular bacilli through the phagocytosis of liposomal particles by cells like macrophages.

Mechanochemically Reprogrammed Interface Orchestrates Neutrophil Bactericidal Activity and Apoptosis for Preventing Implant-Associated Infection

The onset of implant-associated infection (IAI) triggers a cascade of immune responses, which are initially dominated by neutrophils. Bacterial aggregate formation and hypoxic microenvironment, which occur shortly after implantation, may be two major risk factors that impair neutrophil function and lead to IAI. Here, the implant surface with phytic acid-Zn2+ coordinated TiO2 nanopillar arrays (PA-Zn@TiNPs) and oxygen self-supporting CaO2 nanoparticles, named as CPZTs, is mechanochemically reprogrammed. The engineered CPZTs interface integrates multiple properties to inhibit the formation of nascent biofilm, encompassing antibacterial adhesion, mechanobactericidal effect, and chemobiocidal effect. Meanwhile, continuous oxygenation fuels the neutrophils with reactive oxygen species (ROS) for efficient bacterial elimination on the implant surface and inside the neutrophils. Furthermore, this surface modulation strategy accelerates neutrophil apoptosis and promotes M2 macrophage-mediated osteogenesis both in vitro and in a rat model of IAI. In conclusion, targeting neutrophils for immunomodulation is a practical and effective strategy to prevent IAI and promote bone-implant integration.

Nitroreductase-Responsive Photosensitizers for Selective Imaging and Photo-Inactivation of Intracellular Bacteria

Intracellular Staphylococcus aureus (S. aureus), especially the methicillin resistant staphylococcus aureus (MRSA), are difficult to detect and eradicate due to the protection by the host cells. Antibacterial photodynamic therapy (aPDT) offers promise in treating intracellular bacteria, provided that selective damage to the bacteria ranther than host cells can be realized. According to the different nitroreductase (NTR) levels in mammalian cells and S. aureus, herein NTR-responsive photosensitizers (PSs) (T)CyI-NO2 were designed and synthesized. The emission and 1O2 generation of (T)CyI-NO2 are quenched by the 4-nitrobenzyl group, but can be specifically switched on by bacterial NTR. Therefore, selective imaging and photo-inactivation of intracellular S. aureus and MRSA were achieved. Our findings may pave the way for the development of more efficient and selective aPDT agents to combat intractable intracellular infections.

Minimum Information for Conducting and Reporting In Vitro Intracellular Infection Assays

Bacterial pathogens are constantly evolving to outsmart the host immune system and antibiotics developed to eradicate them. One key strategy involves the ability of bacteria to survive and replicate within host cells, thereby causing intracellular infections. To address this unmet clinical need, researchers are adopting new approaches, such as the development of novel molecules that can penetrate host cells, thus exerting their antimicrobial activity intracellularly, or repurposing existing antibiotics using nanocarriers (i.e., nanoantibiotics) for site-specific delivery. However, inconsistency in information reported across published studies makes it challenging for scientific comparison and judgment of experiments for future direction by researchers. Together with the lack of reproducibility of experiments, these inconsistencies limit the translation of experimental results beyond pre-clinical evaluation. Minimum information guidelines have been instrumental in addressing such challenges in other fields of biomedical research. Guidelines and recommendations provided herein have been designed for researchers as essential parameters to be disclosed when publishing their methodology and results, divided into four main categories: (i) experimental design, (ii) establishing an in vitro model, (iii) assessment of efficacy of novel therapeutics, and (iv) statistical assessment. These guidelines have been designed with the intention to improve the reproducibility and rigor of future studies while enabling quantitative comparisons of published studies, ultimately facilitating translation of emerging antimicrobial technologies into clinically viable therapies that safely and effectively treat intracellular infections.

A macrophage cell membrane-coated cascade-targeting photothermal nanosystem for combating intracellular bacterial infections

Current antibacterial interventions encounter formidable challenges when confronting intracellular bacteria, attributable to their clustering within phagocytes, particularly macrophages, evading host immunity and resisting antibiotics. Herein, we have developed an intelligent cell membrane-based nanosystem, denoted as MM@DAu NPs, which seamlessly integrates cascade-targeting capabilities with controllable antibacterial functions for the precise elimination of intracellular bacteria. MM@DAu NPs feature a core comprising D-alanine-functionalized gold nanoparticles (DAu NPs) enveloped by a macrophage cell membrane (MM) coating. Upon administration, MM@DAu NPs harness the intrinsic homologous targeting ability of their macrophage membrane to infiltrate bacteria-infected macrophages. Upon internalization within these host cells, exposed DAu NPs from MM@DAu NPs selectively bind to intracellular bacteria through the bacteria-targeting agent, D-alanine present on DAu NPs. This intricate process establishes a cascade mechanism that efficiently targets intracellular bacteria. Upon exposure to near-infrared irradiation, the accumulated DAu NPs surrounding intracellular bacteria induce local hyperthermia, enabling precise clearance of intracellular bacteria. Further validation in animal models infected with the typical intracellular bacteria, Staphylococcus aureus, substantiates the exceptional cascade-targeting efficacy and photothermal antibacterial potential of MM@DAu NPs in vivo. Therefore, this integrated cell membrane-based cascade-targeting photothermal nanosystem offers a promising approach for conquering persistent intracellular infections without drug resistance risks. STATEMENT OF SIGNIFICANCE: Intracellular bacterial infections lead to treatment failures and relapses because intracellular bacteria could cluster within phagocytes, especially macrophages, evading the host immune system and resisting antibiotics. Herein, we have developed an intelligent cell membrane-based nanosystem MM@DAu NPs, which is designed to precisely eliminate intracellular bacteria through a controllable cascade-targeting photothermal antibacterial approach. MM@DAu NPs combine D-alanine-functionalized gold nanoparticles with a macrophage cell membrane coating. Upon administration, MM@DAu NPs harness the homologous targeting ability of macrophage membrane to infiltrate bacteria-infected macrophages. Upon internalization, exposed DAu NPs from MM@DAu NPs selectively bind to intracellular bacteria through the bacteria-targeting agent, enabling precise clearance of intracellular bacteria through local hyperthermia. This integrated cell membrane-based cascade-targeting photothermal nanosystem offers a promising avenue for conquering persistent intracellular infections without drug resistance risks.

Metal-based nanoparticles in antibacterial application in biomedical field: Current development and potential mechanisms

The rise in drug resistance in pathogenic bacteria greatly endangers public health in the post-antibiotic era, and drug-resistant bacteria currently pose a great challenge not only to the community but also to clinical procedures, including surgery, stent implantation, organ transplantation, and other medical procedures involving any open wound and compromised human immunity. Biofilm-associated drug failure, as well as rapid resistance to last-resort antibiotics, necessitates the search for novel treatments against bacterial infection. In recent years, the flourishing development of nanotechnology has provided new insights for exploiting promising alternative therapeutics for drug-resistant bacteria. Metallic agents have been applied in antibacterial usage for several centuries, and the functional modification of metal-based biomaterials using nanotechnology has now attracted great interest in the antibacterial field, not only for their intrinsic antibacterial nature but also for their ready on-demand functionalization and enhanced interaction with bacteria, rendering them with good potential in further translation. However, the possible toxicity of MNPs to the host cells and tissue still hinders its application, and current knowledge on their interaction with cellular pathways is not enough. This review will focus on recent advances in developing metallic nanoparticles (MNPs), including silver, gold, copper, and other metallic nanoparticles, for antibacterial applications, and their potential mechanisms of interaction with pathogenic bacteria as well as hosts.

Exploring the Synergy between Nano-Formulated Linezolid and Polymyxin B as a Gram-Negative Effective Antibiotic Delivery System Based on Mesoporous Silica Nanoparticles

Antimicrobial resistance is a current silent pandemic that needs new types of antimicrobial agents different from the classic antibiotics that are known to lose efficiency over time. Encapsulation of antibiotics inside nano-delivery systems could be a promising, effective strategy that is able to delay the capability of pathogens to develop resistance mechanisms against antimicrobials. These systems can be adapted to deliver already discovered antibiotics to specific infection sites in a more successful way. Herein, mesoporous silica nanomaterials are used for an efficient delivery of a linezolid gram-positive antibiotic that acts synergistically with gram-negative antimicrobial polymyxin B. For this purpose, linezolid is encapsulated in the pores of the mesoporous silica, whose outer surface is coated with a polymyxin B membrane disruptor. The nanomaterial showed a good controlled-release performance in the presence of lipopolysaccharide, found in bacteria cell membranes, and the complete bacteria E. coli DH5α. The performed studies demonstrate that when the novel formulation is near bacteria, polymyxin B interacts with the cell membrane, thereby promoting its permeation. After this step, linezolid can easily penetrate the bacteria and act with efficacy to kill the microorganism. The nano-delivery system presents a highly increased antimicrobial efficacy against gram-negative bacteria, where the use of free linezolid is not effective, with a fractional inhibitory concentration index of 0.0063 for E. coli. Moreover, enhanced toxicity against gram-positive bacteria was confirmed thanks to the combination of both antibiotics in the same nanoparticles. Although this new nanomaterial should be further studied to reach clinical practice, the obtained results pave the way to the development of new nanoformulations which could help in the fight against bacterial infections.

Chemical Biology Approach to Reveal the Importance of Precise Subcellular Targeting for Intracellular Staphylococcus aureus Eradication

Intracellular bacterial pathogens, such as Staphylococcus aureus, that may hide in intracellular vacuoles represent the most significant manifestation of bacterial persistence. They are critically associated with chronic infections and antibiotic resistance, as conventional antibiotics are ineffective against such intracellular persisters due to permeability issues and mechanistic reasons. Direct subcellular targeting of S. aureus vacuoles suggests an explicit opportunity for the eradication of these persisters, but a comprehensive understanding of the chemical biology nature and significance of precise S. aureus vacuole targeting remains limited. Here, we report an oligoguanidine-based peptidomimetic that effectively targets and eradicates intracellular S. aureus persisters in the phagolysosome lumen, and this oligomer was utilized to reveal the mechanistic insights linking precise targeting to intracellular antimicrobial efficacy. The oligomer has high cellular uptake via a receptor-mediated endocytosis pathway and colocalizes with S. aureus persisters in phagolysosomes as a result of endosome-lysosome interconversion and lysosome-phagosome fusion. Moreover, the observation of a bacterium's altered susceptibility to the oligomer following a modification in its intracellular localization offers direct evidence of the critical importance of precise intracellular targeting. In addition, eradication of intracellular S. aureus persisters was achieved by the oligomer's membrane/DNA dual-targeting mechanism of action; therefore, its effectiveness is not hampered by the hibernation state of the persisters. Such precise subcellular targeting of S. aureus vacuoles also increases the agent's biocompatibility by minimizing its interaction with other organelles, endowing excellent in vivo bacterial targeting and therapeutic efficacy in animal models.

Inulin-lipid hybrid (ILH) microparticles promote pH-triggered release of rifampicin within infected macrophages

Intracellular bacteria serve as a problematic source of infection due to their ability to evade biological immune responses and the inability for conventional antibiotics to efficiently penetrate cellular membranes. Subsequently, new treatment approaches are urgently required to effectively eradicate intracellular pathogens residing within immune cells (e.g. macrophages). In this study, the poorly soluble and poorly permeable antibiotic, rifampicin, was re-purposed via micro-encapsulation within inulin-lipid hybrid (ILH) particles for the treatment of macrophages infected with small colony variants of Staphylococcus aureus (SCV S. aureus). Rifampicin-encapsulated ILH (Rif-ILH) microparticles were synthesized by spray drying a lipid nano-emulsion, with inulin dissolved throughout the aqueous phase and rifampicin pre-loaded within the lipid phase. Rif-ILH were strategically designed and engineered with pH-responsive properties to promote lysosomal drug release upon cellular internalization, while preventing premature rifampicin release in plasma-simulating media. The pH-responsiveness of Rif-ILH was controlled by the acid-mediated hydrolysis of the inulin coating, where exposure to acidic media simulating the lysosomal environment of macrophages triggered hydrolysis of the oligofructose chain and the subsequent diffusion of rifampicin from Rif-ILH. This pH-provoked release mechanism, as well as the ability for ILH microparticles to be more readily internalized by macrophages, was found to be influential in triggering a 2.9-fold increase in intracellular rifampicin concentration within infected macrophages, compared to the pure drug. The subsequent increase in exposure of intracellular pathogens to rifampicin leads to a ~ 2-log improvement in antibacterial activity for Rif-ILH, at a rifampicin dose of 2.5 µg/mL. Thus, the reduction in viability of intracellular SCV S. aureus, in the absence of cellular toxicity, is indicative of ILH microparticles serving as a unique approach for the safe and efficacious delivery of antibiotics to phagocytic cells for the treatment of intracellular infections.

Cubosome Lipid Nanocarriers As a Drug Delivery Vehicle for Intracellular Mycobacterium tuberculosis Infections

Mycobacterium tuberculosis (MTB) causes the infectious disease tuberculosis (TB), responsible for more deaths than any other single infectious disease in history. Intracellular MTB are slow growing and difficult to target with traditional antitubercular drugs, leading to the emergence of multidrug resistance in TB infection, which is a major global public health issue. Recent advances in innovative lipid nanotechnologies for drug delivery have demonstrated promising outcomes for chronic infectious diseases but have not yet been tested as potential delivery systems for intracellular infections such as TB. The current study evaluates the potential of monoolein (MO)-based cationic cubosomes for the encapsulation and delivery of the first line antitubercular drug rifampicin (RIF) against an MTB-H37Ra in vitro culture model. In particular, we show that the use of cationic cubosomes as delivery vehicles reduced the minimum inhibitory concentration (MIC) of RIF by 2-fold against actively replicating MTB-H37Ra (compared to that of the free drug) and also shortened the lifecycle duration of axenic MTB-H37Ra from 5 to 3 days. The cubosome-mediated delivery was also found to be effective against intracellular MTB-H37Ra within THP-1 human macrophages, with a 2.8 log reduction in viability of the bacilli after 6 days incubation at the MIC. The killing time was also reduced from 8 to 6 days without distressing the host macrophages. Mechanistic studies on the uptake of RIF-loaded cationic cubosomes using total internal reflection fluorescence microscopy (TIRFM) demonstrated the capacity of these lipid particles to effectively target intracellular bacteria. Overall, these results demonstrate that cationic cubosomes are a potent delivery system for the antitubercular drug RIF for therapeutic management of TB.

Advanced delivery systems for peptide antibiotics

Antimicrobial peptides (AMPs) hold promise as alternatives to traditional antibiotics for preventing and treating multidrug-resistant infections. Although they have potent antimicrobial efficacy, AMPs are mainly limited by their susceptibility to proteases and potential off-site cytotoxicity. Designing the right delivery system for peptides can help to overcome such limitations, thus improving the pharmacokinetic and pharmacodynamic profiles of these drugs. The versatility of peptides and their genetically encodable structure make them suitable for both conventional and nucleoside-based formulations. In this review, we describe the main drug delivery procedures developed so far for peptide antibiotics: lipid nanoparticles, polymeric nanoparticles, hydrogels, functionalized surfaces, and DNA- and RNA-based delivery systems.

Liquid crystalline lipid nanoparticles improve the antibacterial activity of tobramycin and vancomycin against intracellular Pseudomonas aeruginosa and Staphylococcus aureus

The intracellular survival of bacteria is a significant challenge in the fight against antimicrobial resistance. Currently available antibiotics suffer from limited penetration across host cell membranes, resulting in suboptimal treatment against the internalised bacteria. Liquid crystalline nanoparticles (LCNP) are gaining significant research interest in promoting the cellular uptake of therapeutics due to their fusogenic properties; however, they have not been reported for targeting intracellular bacteria. Herein, the cellular internalisation of LCNPs in RAW 264.7 macrophages and A549 epithelial cells was investigated and optimized through the incorporation of a cationic lipid, dimethyldioctadecylammonium bromide (DDAB). LCNPs displayed a honeycomb-like structure, while the inclusion of DDAB resulted into an onion-like organisation with larger internal pores. Cationic LCNPs enhanced the cellular uptake in both cells, reaching up to ∼90% uptake in cells. Further, LCNPs were encapsulated with tobramycin or vancomycin to improve their activity against intracellular gram-negative, Pseudomonas aeruginosa (P. aeruginosa) and gram-positive, Staphylococcus aureus (S. aureus) bacteria. The enhanced cellular uptake of cationic LCNP resulted in significant reduction of intracellular bacterial load (up to 90% reduction), compared to antibiotic dosed in its free form; with reduced performance observed for epithelial cells infected with S. aureus. Specifically engineered LCNP can re-sensitise antibiotics against both intracellular Gram positive and negative bacteria in diverse cell lines.

Flourishing Antibacterial Strategies for Osteomyelitis Therapy

Osteomyelitis is a destructive disease of bone tissue caused by infection with pathogenic microorganisms. Because of the complex and long-term abnormal conditions, osteomyelitis is one of the refractory diseases in orthopedics. Currently, anti-infective therapy is the primary modality for osteomyelitis therapy in addition to thorough surgical debridement. However, bacterial resistance has gradually reduced the benefits of traditional antibiotics, and the development of advanced antibacterial agents has received growing attention. This review introduces the main targets of antibacterial agents for treating osteomyelitis, including bacterial cell wall, cell membrane, intracellular macromolecules, and bacterial energy metabolism, focuses on their mechanisms, and predicts prospects for clinical applications.

Functional biomaterials for biomimetic 3D in vitro tumor microenvironment modeling

The translational potential of promising anticancer medications and treatments may be enhanced by the creation of 3D in vitro models that can accurately reproduce native tumor microenvironments. Tumor microenvironments for cancer treatment and research can be built in vitro using biomaterials. Three-dimensional in vitro cancer models have provided new insights into the biology of cancer. Cancer researchers are creating artificial three-dimensional tumor models based on functional biomaterials that mimic the microenvironment of the real tumor. Our understanding of tumor stroma activity over the course of cancer has improved because of the use of scaffold and matrix-based three-dimensional systems intended for regenerative medicine. Scientists have created synthetic tumor models thanks to recent developments in materials engineering. These models enable researchers to investigate the biology of cancer and assess the therapeutic effectiveness of available medications. The emergence of biomaterial engineering technologies with the potential to hasten treatment outcomes is highlighted in this review, which also discusses the influence of creating in vitro biomimetic 3D tumor microenvironments utilizing functional biomaterials. Future cancer treatments will rely much more heavily on biomaterials engineering.

pH-responsive microparticles of rifampicin for augmented intramacrophage uptake and enhanced antitubercular efficacy

In this study we present pH-responsive rifampicin (RIF) microparticles comprising lecithin and a biodegradable hydrophobic polymer, polyethylene sebacate (PES), to achieve high intramacrophage delivery and enhanced antitubercular efficacy. PES and PES-lecithin combination microparticles (PL MPs) prepared by single step precipitation revealed average size of 1.5 to 2.7 µm, entrapment efficiency ∼ 60 %, drug loading 12-15 % and negative zeta potential. Increase in lecithin concentration enhanced hydrophilicity. PES MPs demonstrated faster release in simulated lung fluid pH 7.4, while lecithin MPs facilitated faster and concentration dependent release in acidic artificial lysosomal fluid (ALF) pH 4.5 due to swelling and destabilization confirmed by TEM. PES and PL (1:2) MPs exhibited comparable macrophage uptake which was ∼ 5-fold superior than free RIF, in the RAW 264.7 macrophage cells. Confocal microscopy depicted intensified accumulation of the MPs in the lysosomal compartment, with augmented release of coumarin dye from the PL MPs, confirming pH-triggered increased intracellular release. Although, PES MPs and PL (1:2) MPs displayed comparable and high macrophage uptake, antitubercular efficacy against macrophage internalised M. tuberculosis was significantly higher with PL (1:2) MPs. This suggested great promise of the pH-sensitive PL (1:2) MPs for enhanced antitubercular efficacy.

Mesoporous Organosilica Nanoparticles to Fight Intracellular Staphylococcal Aureus Infections in Macrophages

Intracellular bacteria are inaccessible and highly tolerant to antibiotics, hence are a major contributor to the global challenge of antibiotic resistance and recalcitrant clinical infections. This, in tandem with stagnant antibacterial discovery, highlights an unmet need for new delivery technologies to treat intracellular infections more effectively. Here, we compare the uptake, delivery, and efficacy of rifampicin (Rif)-loaded mesoporous silica nanoparticles (MSN) and organo-modified (ethylene-bridged) MSN (MON) as an antibiotic treatment against small colony variants (SCV) Staphylococcus aureus (SA) in murine macrophages (RAW 264.7). Macrophage uptake of MON was five-fold that of equivalent sized MSN and without significant cytotoxicity on human embryonic kidney cells (HEK 293T) or RAW 264.7 cells. MON also facilitated increased Rif loading with sustained release, and seven-fold increased Rif delivery to infected macrophages. The combined effects of increased uptake and intracellular delivery of Rif by MON reduced the colony forming units of intracellular SCV-SA 28 times and 65 times compared to MSN-Rif and non-encapsulated Rif, respectively (at a dose of 5 µg/mL). Conclusively, the organic framework of MON offers significant advantages and opportunities over MSN for the treatment of intracellular infections.

Tumor-Targeting Nanoassembly for Enhanced Colorectal Cancer Therapy by Eliminating Intratumoral Fusobacterium nucleatum

Fusobacterium nucleatum (Fn) has long been found to be related to colorectal cancer (CRC), which could promote colorectal tumor progression and cause cancer resistance to chemotherapy. Great efforts have been made to understand the relationship between Fn and CRC, but how to efficiently eliminate intratumoral Fn and overcome chemoresistance remains a critical challenge. Here, an active tumor-targeting acidity-responsive nanomaterial toward eliminating intratumoral Fn is developed for enhancing the treatment of cancer. Lauric acid and phenylboric acid are conjugated to oligomethyleneimine to form OLP followed by interacting with oxaliplatin prodrug-modified polyglycidyl ether (PP) to obtain the OLP/PP nanoassembly. The nanoassembly shows good structural stability under the simulated physiological conditions and has a pH-responsive drug release in an acidic tumor microenvironment. More attractively, the nanoassembly can specifically target the tumor cell, guide cellular uptake, and efficiently eliminate tumor-resident extracellular and intracellular Fn. Through the on-site drug delivery, the nanoassembly can overcome chemoresistance and significantly inhibit tumor growth. Both in vitro and vivo studies show that the prepared nanoassembly presents good biocompatibility. Therefore, this biocompatible nanoassembly possessing efficient antibacterial and antitumor activities provides new promise for the therapy of bacterial infected tumors.

Bacterial Membrane Mimetics: From Biosensing to Disease Prevention and Treatment

Plasma membrane mimetics can potentially play a vital role in drug discovery and immunotherapy owing to the versatility to assemble facilely cellular membranes on surfaces and/or nanoparticles, allowing for direct assessment of drug/membrane interactions. Recently, bacterial membranes (BMs) have found widespread applications in biomedical research as antibiotic resistance is on the rise, and bacteria-associated infections have become one of the major causes of death worldwide. Over the last decade, BM research has greatly benefited from parallel advancements in nanotechnology and bioelectronics, resulting in multifaceted systems for a variety of sensing and drug discovery applications. As such, BMs coated on electroactive surfaces are a particularly promising label-free platform to investigate interfacial phenomena, as well as interactions with drugs at the first point of contact: the bacterial membrane. Another common approach suggests the use of lipid-coated nanoparticles as a drug carrier system for therapies for infectious diseases and cancer. Herein, we discuss emerging platforms that make use of BMs for biosensing, bioimaging, drug delivery/discovery, and immunotherapy, focusing on bacterial infections and cancer. Further, we detail the synthesis and characteristics of BMs, followed by various models for utilizing them in biomedical applications. The key research areas required to augment the characteristics of bacterial membranes to facilitate wider applicability are also touched upon. Overall, this review provides an interdisciplinary approach to exploit the potential of BMs and current emerging technologies to generate novel solutions to unmet clinical needs.

Nanocarriers for the delivery of antibiotics into cells against intracellular bacterial infection

The barrier function of host cells enables intracellular bacteria to evade the lethality of the host immune system and antibiotics, thereby causing chronic and recurrent infections that seriously threaten human health. Currently, the main clinical strategy for the treatment of intracellular bacterial infections involves the use of long-term and high-dose antibiotics. However, insufficient intracellular delivery of antibiotics along with various resistance mechanisms not only weakens the efficacy of current therapies but also causes serious adverse drug reactions, further increasing the disease and economic burden. Improving the delivery efficiency, intracellular accumulation, and action time of antibiotics remains the most economical and effective way to treat intracellular bacterial infections. The rapid development of nanotechnology provides a strategy to efficiently deliver antibiotics against intracellular bacterial infections into cells. In this review, we summarize the types of common intracellular pathogens, the difficulties faced by antibiotics in the treatment of intracellular bacterial infections, and the research progress of several types of representative nanocarriers for the delivery of antibiotics against intracellular bacterial infections that have emerged in recent years. This review is expected to provide a reference for further elucidating the intracellular transport mechanism of nanocarrier-drug complexes, designing safer and more effective nanocarriers and establishing new strategies against intracellular bacterial infection.

Targeted Drug Delivery Systems for Eliminating Intracellular Bacteria

The intracellular survival of pathogenic bacteria requires a range of survival strategies and virulence factors. These infections are a significant clinical challenge, wherein treatment frequently fails because of poor antibiotic penetration, stability, and retention in host cells. Drug delivery systems (DDSs) are promising tools to overcome these shortcomings and enhance the efficacy of antibiotic therapy. In this review, the classification and the mechanisms of intracellular bacterial persistence are elaborated. Furthermore, the systematic design strategies applied to DDSs to eliminate intracellular bacteria are also described, and the strategies used for internalization, intracellular activation, bacterial targeting, and immune enhancement are highlighted. Finally, this overview provides guidance for constructing functionalized DDSs to effectively eliminate intracellular bacteria.

Advances in image-guided drug delivery for antibacterial therapy

The emergence of antibiotic-resistant bacterial strains is seriously endangering the global healthcare system. There is an urgent need for combining imaging with therapies to realize the real-time monitoring of pathological condition and treatment progress. It also provides guidance on exploring new medicines and enhance treatment strategies to overcome the antibiotic resistance of existing conventional antibiotics. In this review, we provide a thorough overview of the most advanced image-guided approaches for bacterial diagnosis (e.g., computed tomography imaging, magnetic resonance imaging, photoacoustic imaging, ultrasound imaging, fluorescence imaging, positron emission tomography, single photon emission computed tomography imaging, and multiple imaging), and therapies (e.g., photothermal therapy, photodynamic therapy, chemodynamic therapy, sonodynamic therapy, immunotherapy, and multiple therapies). This review focuses on how to design and fabricate photo-responsive materials for improved image-guided bacterial theranostics applications. We present a potential application of different image-guided modalities for both bacterial diagnosis and therapies with representative examples. Finally, we highlighted the current challenges and future perspectives image-guided approaches for future clinical translation of nano-theranostics in bacterial infections therapies. We envision that this review will provide for future development in image-guided systems for bacterial theranostics applications.

Polymeric nano-system for macrophage reprogramming and intracellular MRSA eradication

Intracellular Methicillin-Resistant Staphylococcus aureus (MRSA) remains a major factor of refractory and recurrent infections, which cannot be well addressed by antibiotic therapy. Here, we design a cellular infectious microenvironment-activatable polymeric nano-system to mediate targeted intracellular drug delivery for macrophage reprogramming and intracellular MRSA eradication. The polymeric nano-system is composed of a ferrocene-decorated polymeric nanovesicle formulated from poly(ferrocenemethyl methacrylate)-block-poly(2-methacryloyloxyethyl phosphorylcholine) (PFMMA-b-PMPC) copolymer with co-encapsulation of clofazimine (CFZ) and interferon-γ (IFN-γ). The cellular-targeting PMPC motifs render specific internalization by macrophages and allow efficient intracellular accumulation. Following the internalization, the ferrocene-derived polymer backbone sequentially undergoes hydrophobic-to-hydrophilic transition, charge reversal and Fe release in response to intracellular hydrogen peroxide over-produced upon infection, eventually triggering endosomal escape and on-site cytosolic drug delivery. The released IFN-γ reverses the immunosuppressive status of infected macrophages by reprogramming anti-inflammatory M2 to pro-inflammatory M1 phenotype. Meanwhile, intracellular Fe²⁺-mediated Fenton reaction together with antibiotic CFZ contributes to increased intracellular hydroxyl radical (•OH) generation. Ultimately, the nano-system achieves robust potency in ablating intracellular MRSA and antibiotic-tolerant persisters by synchronous immune modulation and efficient •OH killing, providing an innovative train of thought for intracellular MRSA control.

Intracellular infection-responsive release of NO and peptides for synergistic bacterial eradication

Bacteria have the ability to invade and survive in host cells to form intracellular bacteria (ICBs), and challenges remain in the intracellular delivery of sufficient antibiotics to remove ICBs. Herein, antimicrobial peptide of epsilon-poly-l-lysine (ePL) and nitric oxide (NO) donors are integrated into nanoparticles (NPs) for ICB treatment without using any antibiotics. ePL was grafted with dodecyl alcohol through ethyl dichlorophosphate to prepare ePL-C₁₂, followed by conjugation of nitrate-functionalized NO donors to obtain ePL-C₁₂NO. PNO/C NPs were prepared from mixtures of ePL-C₁₂NO and ePL-C₁₂ and the optimal ePL-C₁₂NO ratio was 7% in terms of bactericidal effect and macrophage toxicity. Once being engulfed by bacteria-infected macrophages (BIMs), NPs are disintegrated when encountering with ICB-secreted phosphatase, and the NP degradation accelerates intracellular NO release in response to the elevated glutathione levels in BIMs. The selective and abrupt release of NO and ePL with different antimicrobial mechanisms exhibits synergistic eradication of ICBs and no apparent toxicity to macrophages. ICB-infected mice show persistent weight loss and 100% of mortality rate after treatment with ePL-C₁₂ NPs for 7 days, while PNO/C treatment causes entire survival of infected mice and full recovery of body weights to normal values. ICB-infected mice are also accompanied with apparent hepatomegaly and splenomegaly, which are only eliminated by PNO/C treatment without associated any pathological abnormality. PNO/C treatment reduces bacterial burdens in livers (2.45 log), spleens (2.16 log) and kidneys (3.46 log) and restores hepatic and renal function to normal levels. Thus, this study provides a feasible strategy to selectively release NO and cationic peptides in response to intracellular infection-derived signals, achieving synergistic eradication of ICBs and function restoration of the main tissues.

Strategies and progresses for enhancing targeted antibiotic delivery

Antibiotic resistance is a global health issue and a potential risk for society. Antibiotics administered through conventional formulations are devoid of targeting effect and often spread to various undesired body sites, leading to sub-lethal concentrations at the site of action and thus resulting in emergence of resistance, as well as side effects. Moreover, we have a very slim antibiotic pipeline. Drug-delivery systems have been designed to control the rate, time, and site of drug release, and innovative approaches for antibiotic delivery provide a glint of hope for addressing these issues. This review elaborates different delivery strategies and approaches employed to overcome the limitations of conventional antibiotic therapy. These include antibiotic conjugates, prodrugs, and nanocarriers for local and targeted antibiotic release. In addition, a wide range of stimuli-responsive nanocarriers and biological carriers for targeted antibiotic delivery are discussed. The potential advantages and limitations of targeted antibiotic delivery strategies are described along with possible solutions to avoid these limitations. A number of antibiotics successfully delivered through these approaches with attained outcomes and potentials are reviewed.

Multi-Mode Antibacterial Strategies Enabled by Gene-Transfection and Immunomodulatory Nanoparticles in 3D-Printed Scaffolds for Synergistic Exogenous and Endogenous Treatment of Infections

As research on refractory Staphylococcus aureus-related implant infection intensifies, certain challenges remain, including low antibiotic concentrations within infected areas, immune escape achieved by intracellular bacteria, myeloid-derived suppressor cells (MDSCs) inducing regional immunosuppression, and recurrence of residual pathogenic bacteria after drug suspension. Herein, a novel antimicrobial system to simultaneously address these issues is proposed. Specifically, an oxygen-species-responsive 3D-printed scaffold with shell-core nanoparticles is designed, which are loaded with an antimicrobial peptide plasmid (LL37 plasmid) and have LL37 grafted on their surface (LL37@ZIF8-LL37). The surface-grafted LL37 directly kills S. aureus and, following entry into cells, the nanoparticles kill intracellular bacteria. Moreover, in vitro and in vivo, following translation of the LL37 plasmid, cells function as factories of the antimicrobial peptide, thereby generating a continuous, prolonged antibacterial effect at the site of infection. This system significantly reduces the abnormal increase in MDSCs within the infected microenvironment, thus relieving the immunosuppressive state and restoring a protective antimicrobial immune response. Hence, this proposed antimicrobial system provides an antimicrobial immune response and a novel strategy for S. aureus-related infections by offering a combined active antimicrobial and immunotherapeutic strategy, thereby significantly reducing the recurrence rate following recovery from implant-associated infections.

Foscarnet-Type Inorganic-Organic Hybrid Nanoparticles for Effective Antiviral Therapy

[ZrO]²⁺[(FCN)_0.4(OH)_0.8]^2- and Gd³⁺[FCN]^3- inorganic-organic hybrid nanoparticles (IOH-NPs) are novel saline antiviral nanocarriers with foscarnet (FCN) as a drug anion. FCN as a pyrophosphate analogue serves as a prototype of a viral DNA polymerase inhibitor. FCN is used for the treatment of herpesvirus infections, including the drug-resistant cytomegalovirus (CMV) and herpes simplex viruses, HSV-1 and HSV-2. The novel [ZrO]²⁺[(FCN)_0.4(OH)_0.8]^2- and Gd³⁺[FCN]^3- IOH-NPs are characterized by aqueous synthesis, small size (20-30 nm), low material complexity, high biocompatibility, and high drug load (up to 44 wt % FCN per nanoparticle). The antiviral activity of the FCN-type IOH-NPs is probed for the human cytomegalovirus (HCMV). Moreover, the uptake of FCN-type IOH-NPs into vesicles, cytoplasm, and nuclei of nonphagocytic lung epithelial cells is evaluated. As a result, a promising antiviral activity of the FCN-type IOH-NPs that significantly outperforms freely dissolved FCN at the level of clinical formulations is observed, encouraging a future use of FCN-type IOH-NPs for the delivery of antivirals against respiratory viruses.

A Review: Antimicrobial Therapy for Human Pythiosis

Human pythiosis is associated with poor prognosis with significant mortality caused by Pythium insidiosum. Antimicrobials’ in vitro and in vivo results against P. insidiosum are inconsistent. Although antimicrobials are clinically useful, they are not likely to achieve therapeutic success alone without surgery and immunotherapy. New therapeutic options are therefore needed. This non-exhaustive review discusses the rationale antimicrobial therapy, minimum inhibitory concentrations, and efficacy of antibacterial and antifungal agents against P. insidiosum. This review further provides insight into the immunomodulating effects of antimicrobials that can enhance the immune response to infections. Current data support using antimicrobial combination therapy for the pharmacotherapeutic management of human pythiosis. Also, the success or failure of antimicrobial treatment in human pythiosis might depend on the immunomodulatory effects of drugs. The repurposing of existing drugs is a safe strategy for anti-P. insidiosum drug discovery. To improve patient outcomes in pythiosis, we suggest further research and a deeper understanding of P. insidiosum virulence factors, host immune response, and host immune system modification by antimicrobials.