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

Coating based on chitosan/vancomycin nanoparticles: Patterns of formation in a water-carbon dioxide biphase system and in vivo stability

The patterns of formation of chitosan nanoparticles doped with vancomycin and coatings based on them in carbonate solutions have been investigated for the first time in this study. Using a technique of radioactive indicators, it was found that at a CO2 pressure of 30 MPa, the yield of the nanoparticles was ∼85 %, and a maximum antibiotic encapsulation efficiency of ∼30 % was achieved. By spectrophotometric and high-resolution microscopy, it was found that the coating of stabilized xenopericardial tissue of bioprosthetic heart valve, based on chitosan nanoparticles doped with vancomycin with a zeta potential |ζ| ∼20 mV completely covers collagen fibers by depositing about 60 nm nanoparticles onto them under direct deposition from carbonic acid at a pressure of 30 MPa CO2. The coating preserves the mechanical strength characteristics of collagen tissue and completely suppresses the growth of S. aureus pathogenic biofilm. This is consistent with the observed increase in antibiotic release of 15 % when the medium was acidified. Histological study demonstrated that the structure of pericardial tissues was not significantly altered by the deposition nanoparticles from carbonic acid. It was found that the rate of biodegradation of polymers and vancomycin in the coating differs by half (16 weeks for the rat model). A significantly lower degradation rate of antibiotics (∼50 % of vancomycin total remaining mass and ∼25 % of chitosan) was associated with its reliable encapsulation into nanoparticles.

Synergistic antibacterial and wound healing effects of chitosan nanofibers with ZnO nanoparticles and dual antibiotics

One concern that has been considered potentially fatal is bacterial infection. In addition to the development of biocompatible antibacterial dressings, the screening and combination of new antibiotics effective against antibiotic resistance are crucial. In this study, designing hemostasis electrospun composite nanofibers containing chitosan (CS), polyvinyl pyrrolidone (PVP) and Gelatin (G) as the major components of hydrogel and natural nanofibrillated sodium alginate (SA)/polyvinyl alcohol (PVA) and ZnO nanoparticles (ZnONPs) combination as the nanofiller ingredient, has been investigated which demonstrated significant potential for accelerating wound healing. The hydrogels were developed for the delivery of the amikacin and cefepime antibiotics, along with zinc oxide nanoparticles that were applied to an electrospun layer. Amikacin is a highly effective aminoglycoside antibiotic, particularly for hospital-acquired infections, but its use is limited due to its toxicity. By utilizing it in low concentrations in the form of nanofibers and combining it with cefepime, which exhibits synergistic effects, enhanced efficacy against bacterial pathogens is achieved while potentially minimizing cytotoxicity compared to individual antibiotics. This dressing demonstrated efficient drug release, flexibility, and good swelling properties, indicating its suitable mechanical properties for therapeutic applications. After applying the biocompatible hydrogel to wounds, a significant acceleration in wound closure was observed within 14 days compared to the control group. Furthermore, the notable antibiotic and anti-inflammatory properties underscore its effectiveness in wound healing, making it a promising candidate for medical applications.

Biomimetic Metal-Organic Framework Gated Nanoplatform for Sonodynamic Therapy against Extensively Drug Resistant Bacterial Lung Infection

Novel antimicrobial strategies are urgently needed to treat extensively drug-resistant (XDR) bacterial infections due to the high mortality rate and lack of effective therapeutic agents. Herein, nanoengineered human umbilical cord mesenchymal stem cells (hUC-MSCs), named PMZMU, are designed as a sonosensitizer for synergistic sonodynamic-nano-antimicrobial therapy against gram-negative XDR bacteria. PMZMU is composed of a bacterial targeting peptide (UBI29-41) modified hUC-MSCs membrane (MSCm), a sonosensitizer meso-tetra(4-car-boxyphenyl) porphine doped mesoporous organo-silica nanoparticle and an acidity-responsive metal-organic framework ZIF-8. This innovative formulation enables efficient loading of polymyxin B, reduces off-target drug release, increases circulation and targeting efficacy, and generates reactive oxygen species upon ultrasound irradiation. PMZMU exhibits remarkable in vitro inhibitory activity against four XDR bacteria: Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa (PA), and Escherichia coli. Taking advantage of the bacterial targeting ability of UBI29-41 and the inflammatory chemotaxis of hUC-MSC, PMZMU can be precisely delivered to lung infection sites thereby augmenting polymyxin B concentration. PMZMU-mediated sonodynamic therapy significantly reduces bacterial burden, relieves inflammatory damage by promoting the polarization of macrophages toward M2 phenotype, and improves survival rates without introducing adverse events. Overall, this study offers promising strategies for treating deep-tissue XDR bacterial infections, and guides the design and optimization of biomimetic nanomedicine.

Nanotechnology-based approaches for antibacterial therapy

The technique of antimicrobial therapy action is to stop or slow the growth of bacteria that can kill people, animals, and crops. The most widely used antibacterial agents are antibiotics. Even though these antimicrobial medications are quite effective, there are still certain barriers or challenges in using them effectively. To solve these issues, new antimicrobial drug molecules that don't have side effects or resistance are needed. These days, antimicrobial drugs placed in nanosized vehicles, or nanomedicine, made of different metal and metallic oxides as well as of polymer, carbon or lipid-based may be used to address these issues with conventional therapy and delivery techniques. This review focuses on the importance of nanotechnology in antimicrobial therapy, nanoparticles (NPs) used in this therapy, their mode of action, and the recent advancement in nanotechnology for antimicrobial therapy.

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.

Antibiotic-loaded lactoferrin nanoparticles as a platform for enhanced infection therapy through targeted elimination of intracellular bacteria

Intracellular bacteria can multiply inside host cells and manipulate their biology, and the efficacy of traditional antibiotic drug therapy for intracellular bacteria is limited by inadequate drug accumulation. Fighting against these stealthy bacteria has been a long-standing challenge. Here, a system of stimuli-responsive lactoferrin (Lf) nanoparticles is prepared using protein self-assembly technology to deliver broad-spectrum antibiotic rifampicin (Rif) (Rif@Lf NPs) for enhanced infection therapy through targeted elimination of intracellular bacteria. Compared to Rif@BSA NPs, the Rif@Lf NPs can specifically target macrophages infected by bacteria, thus increasing the accumulation of Rif within macrophages. Subsequently, Rif@Lf NPs with positive surface charge further displayed targeted adherence to the bacteria within macrophages and released Rif rapidly in a redox-responsive manner. Combined with the antibacterial activities of Lf and Rif, the Rif@Lf NPs showed broad-spectrum antibiotic abilities to intracellular bacteria and biofilms. As a result, the Rif@Lf NPs with high safety exhibited excellent therapeutic efficacy in the disease models of subcutaneous infection, sepsis, and bacterial keratitis. Taken together, the antibiotic-loaded Lf nanoparticles present a promising platform to combat pathogen infections through targeted elimination of intracellular bacteria.

Engineering dynamic covalent bond-based nanosystems for delivery of antimicrobials against bacterial infections

Nanodrug delivery systems (NDDS) continue to be explored as novel strategies enhance therapy outcomes and combat microbial resistance. The need for the formulation of smart drug delivery systems for targeting infection sites calls for the engineering of responsive chemical designs such as dynamic covalent bonds (DCBs). Stimuli response due to DCBs incorporated into nanosystems are emerging as an alternative way to target infection sites, thus enhancing the delivery of antibacterial agents. This leads to the eradication of bacterial infections and the reduction of antimicrobial resistance. Incorporating DCBs on the backbone of the nanoparticles endows the systems with several properties, including self-healing, controlled disassembly, and stimuli responsiveness, which are beneficial in the delivery and release of the antimicrobial at the infection site. This review provides a comprehensive and current overview of conventional DCBs-based nanosystems, stimuli-responsive DCBs-based nanosystems, and targeted DCBs-based nanosystems that have been reported in the literature for antibacterial delivery. The review emphasizes the DCBs used in their design, the nanomaterials constructed, the drug release-triggering stimuli, and the antibacterial efficacy of the reported DCBs-based nanosystems. Additionally, the review underlines future strategies that can be used to improve the potential of DCBs-based nanosystems to treat bacterial infections and overcome antibacterial resistance.

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.

Deciphering the Drug Delivery Potential of Milk Exosome Nanovesicles for Aminobenzylpenicillin Therapeutic Efficacy against Contagious Staphylococcus Aureus in Bovine Mastitis

The emergence of antimicrobial resistance and failure of antibiotic treatment are challenging tasks for managing bovine mastitis, which is mainly caused by the contagious Staphylococcus aureus (S. aureus).To overcome these difficulties, there is an urgent need for a novel drug system. In the present study, the aim is to develop next-generation therapeutics against S. aureus by harnessing the drug delivery potential of milk nanovesicles called milk exosomes (mENs). In the present work, a drug system is developed by encapsulating aminobenzylpenicillin (AMP) in mENs (mENs-AMP). Electron microscopy and zeta-sizer results indicate that the size of mENs-AMP ranged from 55.79 ± 2.8 to 85.53 ± 7.4 nm. The AMP loading efficiency in mENs is 88.61% with its sustained release. Fluorescence spectroscopy results indicated that mENs are biocompatible with mammary epithelial cells. In vitro studies show that the antibacterial activity and the minimum inhibitory concentrations of mENs-AMP are eleven times greater and four times lower than that of unencapsulated AMP, respectively. The mENs-AMP exhibit significantly higher therapeutic efficacy than AMP at the same dosage and treatment frequency. Validation of this approach is demonstrated in mastitis-affected animals through an observation in the reduction of somatic cell counts and bacterial loads in the milk of treated animals.

Cascade-Targeted Nanoplatforms for Synergetic Antibiotic/ROS/NO/Immunotherapy against Intracellular Bacterial Infection

Intracellular bacteria in dormant states can escape the immune response and tolerate high-dose antibiotic treatment, leading to severe infections. To overcome this challenge, cascade-targeted nanoplatforms that can target macrophages and intracellular bacteria, exhibiting synergetic antibiotic/reactive oxygen species (ROS)/nitric oxide (NO)/immunotherapy, were developed. These nanoplatforms were fabricated by encapsulating trehalose (Tr) and vancomycin (Van) into phosphatidylserine (PS)-coated poly[(4-allylcarbamoylphenylboric acid)-ran-(arginine-methacrylamide)-ran-(N,N'-bisacryloylcystamine)] nanoparticles (PABS), denoted as PTVP. PS on PTVP simulates a signal of "eat me" to macrophages to promote cell uptake (the first-step targeting). After the uptake, the nanoplatform in the acidic phagolysosomes could release Tr, and the exposed phenylboronic acid on the nanoplatform could target bacteria (the second-step targeting). Nanoplatforms can release Van in response to infected intracellular overexpressed glutathione (GSH) and weak acid microenvironment. l-arginine (Arg) on the nanoplatforms could be catalyzed by upregulated inducible nitric oxide synthase (iNOS) in the infected macrophages to generate nitric oxide (NO). N,N'-Bisacryloylcystamine (BAC) on nanoplatforms could deplete GSH, allow the generation of ROS in macrophages, and then upregulate proinflammatory activity, leading to the reinforced antibacterial capacity. This nanoplatform possesses macrophage and bacteria-targeting antibiotic delivery, intracellular ROS, and NO generation, and pro-inflammatory activities (immunotherapy) provides a new strategy for eradicating intracellular bacterial infections.

Ciprofloxacin-Loaded Inhalable Formulations against Lower Respiratory Tract Infections: Challenges, Recent Advances, and Future Perspectives

Inhaled ciprofloxacin (CFX) has been investigated as a treatment for lower respiratory tract infections (LRTIs) associated with cystic fibrosis (CF), chronic obstructive pulmonary disease (COPD), and bronchiectasis. The challenges in CFX effectiveness for LRTI treatment include poor aqueous solubility and therapy resistance. CFX dry powder for inhalation (DPI) formulations were well-tolerated, showing a remarkable decline in overall bacterial burden compared to a placebo in bronchiectasis patients. Recent research using an inhalable powder combining Pseudomonas phage PEV20 with CFX exhibited a substantial reduction in bacterial density in mouse lungs infected with clinical P. aeruginosa strains and reduced inflammation. Currently, studies suggest that elevated biosynthesis of fatty acids could serve as a potential biomarker for detecting CFX resistance in LRTIs. Furthermore, inhaled CFX has successfully addressed various challenges associated with traditional CFX, including the incapacity to eliminate the pathogen, the recurrence of colonization, and the development of resistance. However, further exploration is needed to address three key unresolved issues: identifying the right patient group, determining the optimal treatment duration, and accurately assessing the risk of antibiotic resistance, with additional multicenter randomized controlled trials suggested to tackle these challenges. Importantly, future investigations will focus on the effectiveness of CFX DPI in bronchiectasis and COPD, aiming to differentiate prognoses between these two conditions. This review underscores the importance of CFX inhalable formulations against LRTIs in preclinical and clinical sectors, their challenges, recent advancements, and future perspectives.

Emerging polymeric materials for treatment of oral diseases: design strategy towards a unique oral environment

Oral diseases are prevalent but challenging diseases owing to the highly movable and wet, microbial and inflammatory environment. Polymeric materials are regarded as one of the most promising biomaterials due to their good compatibility, facile preparation, and flexible design to obtain multifunctionality. Therefore, a variety of strategies have been employed to develop materials with improved therapeutic efficacy by overcoming physicobiological barriers in oral diseases. In this review, we summarize the design strategies of polymeric biomaterials for the treatment of oral diseases. First, we present the unique oral environment including highly movable and wet, microbial and inflammatory environment, which hinders the effective treatment of oral diseases. Second, a series of strategies for designing polymeric materials towards such a unique oral environment are highlighted. For example, multifunctional polymeric materials are armed with wet-adhesive, antimicrobial, and anti-inflammatory functions through advanced chemistry and nanotechnology to effectively treat oral diseases. These are achieved by designing wet-adhesive polymers modified with hydroxy, amine, quinone, and aldehyde groups to provide strong wet-adhesion through hydrogen and covalent bonding, and electrostatic and hydrophobic interactions, by developing antimicrobial polymers including cationic polymers, antimicrobial peptides, and antibiotic-conjugated polymers, and by synthesizing anti-inflammatory polymers with phenolic hydroxy and cysteine groups that function as immunomodulators and electron donors to reactive oxygen species to reduce inflammation. Third, various delivery systems with strong wet-adhesion and enhanced mucosa and biofilm penetration capabilities, such as nanoparticles, hydrogels, patches, and microneedles, are constructed for delivery of antibiotics, immunomodulators, and antioxidants to achieve therapeutic efficacy. Finally, we provide insights into challenges and future development of polymeric materials for oral diseases with promise for clinical translation.

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.

Use of Bacteriophages to Target Intracellular Pathogens

Bacteriophages (phages) have shown great potential as natural antimicrobials against extracellular pathogens (eg, Escherichia coli or Klebsiella pneumoniae), but little is known about how they interact with intracellular targets (eg, Shigella spp., Salmonella spp., Mycobacterium spp.) in the mammalian host. Recent research has demonstrated that phages can enter human cells. However, for the design of successful clinical applications, further investigation is required to define their subcellular behavior and to understand the complex biological processes that underlie the interaction with their bacterial targets. In this review, we summarize the molecular evidence of phage internalization in eucaryotic cells, with specific focus on proof of phage activity against their bacterial targets within the eucaryotic host, and the current proposed strategies to overcome poor penetrance issues that may impact therapeutic use against the most clinically relevant intracellular pathogens.

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.

Recent progress in carbon dots for anti-pathogen applications in oral cavity

Background

Oral microbial infections are one of the most common diseases. Their progress not only results in the irreversible destruction of teeth and other oral tissues but also closely links to oral cancers and systemic diseases. However, traditional treatment against oral infections by antibiotics is not effective enough due to microbial resistance and drug blocking by oral biofilms, along with the passive dilution of the drug on the infection site in the oral environment.

Aim of review

Besides the traditional antibiotic treatment, carbon dots (CDs) recently became an emerging antimicrobial and microbial imaging agent because of their excellent (bio)physicochemical performance. Their application in treating oral infections has received widespread attention, as witnessed by increasing publication in this field. However, to date, there is no comprehensive review available yet to analyze their effectiveness and mechanism. Herein, as a step toward addressing the present gap, this review aims to discuss the recent advances in CDs against diverse oral pathogens and thus propose novel strategies in the treatment of oral microbial infections.

Key scientific concepts of review

In this manuscript, the recent progress of CDs against oral pathogens is summarized for the first time. We highlighted the antimicrobial abilities of CDs in terms of oral planktonic bacteria, intracellular bacteria, oral pathogenic biofilms, and fungi. Next, we introduced their microbial imaging and detection capabilities and proposed the prospects of CDs in early diagnosis of oral infection and pathogen microbiological examination. Lastly, we discussed the perspectives on clinical transformation and the current limitations of CDs in the treatment of oral microbial infections.

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

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

SK-03-92 Drug Kills Intracellular Mycobacterium tuberculosis

BACKGROUND

Tuberculosis affects millions of people worldwide. The emergence of drug-resistant Mycobacterium tuberculosis strains has made treatment more difficult. A drug discovery project initiated to screen natural products identified a lead stilbene compound, and structure function analysis of hundreds of analogs led to the discovery of the SK-03-92 stilbene lead compound with activity against several non-tuberculoid mycobacteria.

METHODS

For this study, an MIC analysis and intracellular killing assay were performed to test SK-03-92 against M. tuberculosis grown in vitro as well as within murine macrophage cells.

RESULTS

The MIC analysis showed that SK-03-92 had activity against M. tuberculosis in the range of 0.39 to 6.25 μg/mL, including activity against single-drug-resistant strains. Further, an intracellular kill assay demonstrated that the SK-03-92 lead compound killed M. tuberculosis cells within murine macrophage cells.

CONCLUSION

Together, the data show the SK-03-92 lead compound can kill M. tuberculosis bacteria within mammalian macrophages.

Co-delivery of streptomycin and hydroxychloroquine by labeled solid lipid nanoparticles to treat brucellosis: an animal study

Can brucellosis-related biochemical and immunological parameters be used as diagnostic and treatment indicators? The goal of this project was to look at biochemical parameters, trace elements, and inflammatory factors in the acute and chronic stages of brucellosis after treatment with streptomycin and hydroxychloroquine-loaded solid lipid nanoparticles (STR-HCQ-SLN). The double emulsion method was used for the synthesis of nanoparticles. Serum levels of trace elements, vitamin D, CRP, and biochemical parameters were measured in rats involved in brucellosis. The therapeutic effect of STR-HCQ-SLN was compared with that of free drugs. In both healthy and infected rats, serum concentrations of copper, zinc, iron, magnesium, potassium, and biochemical parameters of the liver were significantly different. By altering the serum levels of the aforementioned factors, treatment with STR-HCQ-SLN had a positive therapeutic effect on chronic brucellosis. Vitamin D levels declined (46.4%) and CRP levels rose (from 7.5 mg to less than 1 mg) throughout the acute and chronic stages of brucellosis. This study showed that by comparing the biochemical parameters and the levels of trace elements in the serum of healthy and diseased mice in the acute and chronic stages of brucellosis, it is possible to get help from other routine methods for diagnosis.

Methylene Blue-Loaded NanoMOFs: Accumulation in Chlamydia trachomatis Inclusions and Light/Dark Antibacterial Effects

Metal-organic framework nanoparticles (nanoMOFs) are promising nanomaterials for biomedical applications. Some of them, including biodegradable porous iron carboxylates are proposed for encapsulation and delivery of antibiotics. Due to the high drug loading capacity and fast internalization kinetics, nanoMOFs are more beneficial for the treatment of intracellular bacterial infections compared to free antibacterial drugs, which poorly accumulate inside the cells because of the inability to cross membrane barriers or have low intracellular retention. However, nanoparticle internalization does not ensure their accumulation in the cell compartment that shelters a pathogen. This study shows the availability of MIL-100(Fe)-based MOF nanoparticles to co-localize with Chlamydia trachomatis, an obligate intracellular bacterium, in the infected RAW264.7 macrophages. Furthermore, nanoMOFs loaded with photosensitizer methylene blue (MB) exhibit complete photodynamic inactivation of C. trachomatis growth. Simultaneous infection and treatment of RAW264.7 cells with empty nanoMOFs resulted in a bacterial load reduction from 100 to 36% that indicates an intrinsic anti-chlamydial effect of this iron-containing nanomaterial. Thus, our findings suggest the use of iron-based nanoMOFs as a promising drug delivery platform, which contributes to antibacterial effect, for the treatment of chlamydial infections.

Multidrug-Resistant Pathogens in Burn Wound, Prevention, Diagnosis, and Therapeutic Approaches (Conventional Antimicrobials and Nanoparticles)

Multidrug-resistant pathogens are one of the common causes of death in burn patients and have a high risk of nosocomial infections, especially pneumonia, urinary tract infections, and cellulitis. The role of prolonged hospitalization and empirical antibiotics administration in developing multidrug-resistant pathogens is undeniable. In the early days of admitting burn patients, Gram-positive bacteria were the dominant isolates with a more sensitive antibiotic pattern. However, the emergence of Gram-negative bacteria that are more resistant later occurs. Trustworthy guideline administration in burn wards is one of the strategies to prevent multidrug-resistant pathogens. Also, a multidisciplinary therapeutic approach is an effective way to avoid antibiotic resistance that involves infectious disease specialists, pharmacists, and burn surgeons. However, the emerging resistance to conventional antimicrobial approaches (such as systemic antibiotic exposure, traditional wound dressing, and topical antibiotic ointments) among burn patients has challenged the treatment of multidrug-resistant infections, and using nanoparticles is a suitable alternative. In this review article, we will discuss different aspects of multidrug-resistant pathogens in burn wounds, emphasizing the full role of these pathogens in burn wounds and discussing the application of nanotechnology in dealing with them. Also, some advances in various types of nanomaterials, including metallic nanoparticles, liposomes, hydrogels, carbon quantum dots, and solid lipid nanoparticles in burn wound healing, will be explained.

Clearance of intracellular bacterial infections by hyaluronic acid-based ROS responsive drug delivery micelles

Pathogenic bacteria residing inside cells could cause disruption of cellular metabolic balance. Therefore, basing on high oxidative stress response of the intracellular bacteria infected micro-environment, a novel amphipathic micelle (HATAD-TCS) was developed consisting of hyaluronic acid-derivative and reactive oxygen species (ROS) - responsive group and antibacterial agent triclosan (TCS). ROS-generating cinnamaldehyde (CA) was incorporated into ROS-cleavable linkages which are future linked to the 1-decylamine to form hydrophobicity. The cinnamaldehyde released did not just killed bacteria however, also maintained intracellular ROS levels. In this study, the HATAD-TCS micelles have been characterized by scanning electron microscopy (SEM) and dynamic light scattering (DLS). The HATAD-TCS micelles could release drug gradually upon exposure to endogenous ROS being caused by infected intracellular bacteria. Furthermore, the more promising therapeutic effect of the HATAD-TCS micelles was observed in a mouse pneumonia model. These results might highlight a ROS-responsive hyaluronic acid-based nanoparticle, which could effectively treat intracellular bacterial infections.

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.

Metal-Organic Framework-Based Nanomedicines for the Treatment of Intracellular Bacterial Infections

Metal-organic frameworks (MOFs) are a highly versatile class of ordered porous materials, which hold great promise for different biomedical applications, including antibacterial therapy. In light of the antibacterial effects, these nanomaterials can be attractive for several reasons. First, MOFs exhibit a high loading capacity for numerous antibacterial drugs, including antibiotics, photosensitizers, and/or photothermal molecules. The inherent micro- or meso-porosity of MOF structures enables their use as nanocarriers for simultaneous encapsulation of multiple drugs resulting in a combined therapeutic effect. In addition to being encapsulated into an MOF's pores, antibacterial agents can sometimes be directly incorporated into an MOF skeleton as organic linkers. Next, MOFs contain coordinated metal ions in their structure. Incorporation of Fe2/3+, Cu2+, Zn2+, Co2+, and Ag+ can significantly increase the innate cytotoxicity of these materials for bacteria and cause a synergistic effect. Finally, abundance of functional groups enables modifying the external surface of MOF particles with stealth coating and ligand moieties for improved drug delivery. To date, there are a number of MOF-based nanomedicines available for the treatment of bacterial infections. This review is focused on biomedical consideration of MOF nano-formulations designed for the therapy of intracellular infections such as Staphylococcus aureus, Mycobacterium tuberculosis, and Chlamydia trachomatis. Increasing knowledge about the ability of MOF nanoparticles to accumulate in a pathogen intracellular niche in the host cells provides an excellent opportunity to use MOF-based nanomedicines for the eradication of persistent infections. Here, we discuss advantages and current limitations of MOFs, their clinical significance, and their prospects for the treatment of the mentioned infections.

Mitigating Lactate-Associated Immunosuppression against Intracellular Bacteria Using Thermoresponsive Nanoparticles for Septic Arthritis Therapy

Intracellular bacteria are the major contributor to the intractability of septic arthritis, which are sequestered in macrophages to undermine the innate immune response and avoid the antibacterial effect of antibiotics due to the obstruction of the cell membrane. Herein, we report a thermoresponsive nanoparticle, which consists of a phase-change material shell (fatty acids) and an oxygen-producing core (CaO₂-vancomycin). Under external thermal stimulation, the shell of the nanoparticle transforms from a solid phase to a liquid phase. Then the CaO₂-Vancomycin core is exposed to the surrounding aqueous solution to release vancomycin and generate Ca(OH)₂ and oxygen, thereby depleting accumulated lactate to mitigate lactate-associated immunosuppression, stabilizing hypoxia-inducible factor-1α (HIF-1α) to enhance M1-like polarization of macrophages, and increasing reactive oxygen species (ROS) and reactive nitrogen species (RNS) production. This combined effect between the controlled release of antibiotics and enhancement of host innate immunity provides a promising strategy to combat intracellular bacteria for septic arthritis therapy.

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.

Rapid Screening and Synthesis of Abiotic Synthetic Receptors for Selective Bacterial Recognition

The major challenges that impede the preparation of abiotic synthetic receptors designed to feature selective bacterial recognition properties are the complexity, nonrobustness, and environmental adaptability of live microbes. Here, we describe a new rapid screening strategy to determine the optimal polymer formulation on 96-well plates and then produce abiotic synthetic receptors by imprinting the surface marker lipopolysaccharide (LPS) of Gram-negative bacteria. The resulting LPS-imprinted nanoparticles reveal remarkable affinity toward LPS with an equilibrium dissociation constant (K_D) value of 10^-12 M and can distinguish and selectively recognize specific bacteria in whole blood at concentrations down to 10 cells/mL. The incorporation of gold nanorods into imprinted nanoparticles allows selective microbial inactivation based on photothermal treatment. We have also demonstrated that the imprinted nanoparticles with high affinity for bacteria could induce bacteria clustering, drive the expression of quorum-sensing-controlled signal molecules, and eventually enhance the productivity of the cell factory.

Type I interferon induced by polyinosinic-polycytidylic acid does not contribute to the efficacy of a formalin-killed cell vaccine against Edwardsiella piscicida in the Japanese flounder (Paralichthys olivaceus)

Polyinosinic-polycytidylic acid (poly I:C) is a type of pathogen-associated molecular pattern that can strongly induce the expression of type I interferon (I-IFN). Our previous study has demonstrated that the combination of poly I:C with a recombinant protein antigen not only stimulated the expression of I-IFN but also conferred protection against Edwardsiella piscicida in the Japanese flounder (Paralichthys olivaceus). In this study, our aim was to develop a better immunogenic and protective fish vaccine, for which we intraperitoneally coinjected P. olivaceus with poly I:C and formalin-killed cells (FKCs) of E. piscicida and compared the efficiency of protection against E. piscicida infection with that of FKC vaccine alone. Results showed that the expression levels of I-IFN, IFN-γ, interleukin (IL)-1β, tumor necrosis factor (TNF)-α, and the interferon-stimulated genes (ISGs) ISG15 and Mx were significantly increased in the spleen of fish inoculated with poly I:C + FKC. The results of ELISA showed that the levels of specific serum antibodies in the FKC and FKC + poly I:C groups were gradually increased until 28 days postvaccination and were significantly higher than those in the PBS and poly I:C groups. At 3 weeks after vaccination in the challenge test, the respective cumulative mortality rates of fish in the PBS, FKC, poly I:C, and poly I:C + FKC groups were 46.7%, 20.0%, 33.3%, and 13.3% under low-concentration challenge and 93.3%, 46.7%, 78.6%, and 53.3% under high-concentration challenge. This study showed that poly I:C may not provide an effective adjuvant effect with FKC vaccine for intracellular bacterial infections.

Photoactivated antibiotics to treat intracellular infection of bacteria

Antibiotic resistance combined with pathogen internalization leads to debilitating infections. Here we test novel superoxide producing, stimuli-activated quantum dots (QDs), to treat an intracellular infection of Salmonella enterica serovar Typhimurium in an osteoblast precursor cell line. These QDs are precisely tuned to reduce dissolved oxygen to superoxide and kill bacteria upon stimulation (e.g., light). We show QDs provide tunable clearance at various multiplicities of infection and limited host cell toxicity by modulating their concentration and stimuli intensity, proving the efficacy of superoxide producing QDs for intracellular infection treatment and establishing a framework for further testing in different infection models.

Colistin- and amikacin-loaded lipid-based drug delivery systems for resistant gram-negative lung and wound bacterial infections

Antimicrobial resistance (AMR) is a global health issue, which needs to be tackled without further delay. The World Health Organization(WHO) has classified three gram-negative bacteria, Pseudomonas aeruginosa, Klebsiella pneumonia and Acinetobacter baumannii, as the principal responsible for AMR, mainly causing difficult to treat nosocomial lung and wound infections. In this regard, the need for colistin and amikacin, the re-emerged antibiotics of choice for resistant gram-negative infections, will be examined as well as their associated toxicity. Thus, current but ineffective clinical strategies designed to prevent toxicity related to colistin and amikacin will be reported, highlighting the importance of lipid-based drug delivery systems (LBDDSs), such as liposomes, solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs), as efficient delivery strategies for reducing antibiotic toxicity. This review reveals that colistin- and amikacin-NLCs are promising carriers with greater potential than liposomes and SLNs to safely tackle AMR, especially for lung and wound infections.

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.

AIEgen-Based Nanomaterials for Bacterial Imaging and Antimicrobial Applications: Recent Advances and Perspectives

Microbial infections have always been a thorny problem. Multi-drug resistant (MDR) bacterial infections rendered the antibiotics commonly used in clinical treatment helpless. Nanomaterials based on aggregation-induced emission luminogens (AIEgens) recently made great progress in the fight against microbial infections. As a family of photosensitive antimicrobial materials, AIEgens enable the fluorescent tracing of microorganisms and the production of reactive oxygen (ROS) and/or heat upon light irradiation for photodynamic and photothermal treatments targeting microorganisms. The novel nanomaterials constructed by combining polymers, antibiotics, metal complexes, peptides, and other materials retain the excellent antimicrobial properties of AIEgens while giving other materials excellent properties, further enhancing the antimicrobial effect of the material. This paper reviews the research progress of AIEgen-based nanomaterials in the field of antimicrobial activity, focusing on the materials' preparation and their related antimicrobial strategies. Finally, it concludes with an outlook on some of the problems and challenges still facing the field.

Dual-targeted poly(amino acid) nanoparticles deliver drug combinations on-site: an intracellular synergistic strategy to eliminate intracellular bacteria

Multi-drug combinations are a common strategy for the treatment of intracellular bacterial infections. However, different internalized pathways and the accumulation of the composite drugs at different subcellular organelles very much reduce their efficacy. Herein, an intracellular synergistic strategy is proposed, which is realized by on-site delivery of a drug combination using a macrophage/intracellular bacterium-dual targeted drug delivery system (DDS). The DDS is fabricated by encapsulating vancomycin (Van) and curcumin (Cur) into poly(α-N-acryloyl-phenylalanine)-block-poly(β-N-acryloyl-D-aminoalanine-co-2-O-acetyl-α-D-mannosyloxy) nanoparticles, denoted by (Van + Cur)@F(AM) NPs. Mannose ligands on (Van + Cur)@F(AM) NPs trigger their specific internalization in macrophages, while aminoalanine moieties subsequently drive the NPs to target intracellular methicillin-resistant Staphylococcus aureus (MRSA). Thereafter, Van and Cur are durably released in a synergistic dose at the residence site of intracellular MRSA. Under this intracellular synergistic effect, (Van + Cur)@F(AM) NPs show superior elimination efficiency in vitro and in vivo compared to the control groups, including free Van, (Van + Cur), the DDS encapsulated Van and the DDSs separately-encapsulated Van and Cur. Furthermore, (Van + Cur)@F(AM) NPs significantly enhance the in vivo antibacterial capacity by modulating the immune response. Therefore, this dual-targeted DDS-assisted intracellular synergistic antibacterial strategy of drug combination is an effective therapeutic against intracellular bacteria.

Chitosan -based nanoniosome for potential wound healing applications: Synergy of controlled drug release and antibacterial activity

This study aims to develop a niosomal platform which can delivery drugs such as tetracycline hydrochloride (TCH) to treat bacterial infections in wounds. To this end, chitosan (CS) was used to obtain a controlled drug release and at the same time antibacterial activity. By design of experiments the niosome encapsulated TCH (TCH-Nio) were optimized for their particle size and encapsulation efficiency, followed by analysis of the release profile of TCH and stability of TCH-Nio and TCH-Nio@CS. The antibacterial activity and cytotoxicity of the fabricated nanoparticles were investigated as well. The release rate of TCH from TCH-Nio@CS in all conditions is less than TCH-Nio. In addition, higher temperature increases the release rate of drug from these formulations. The size, polydispersity index, and encapsulation efficacy of TCH-Nio and TCH-Nio@CS were more stable in 4 °C compared to 25 °C. TCH, TCH-Nio, and TCH-Nio@CS had MIC values of 7.82, 3.91, and 1.95 μg/mL for Escherichia coli, 3.91, 1.95, and 0.98 μg/mL for Pseudomonas aeruginosa, and 1.96, 0.98, and 0.49 μg/mL for Staphylococcus aureus, respectively. Coating of chitosan on niosome encapsulated TCH (TCH-Nio@CS) led to a reduced burst release of TCH from niosome (TCH-Nio), and enabled 2-fold higher antibacterial and anti-biofilm activity against the tested bacterial pathogens E. coli, P. aeruginosa and S. aureus, compared to the uncoated TCH-Nio, and 4-folder higher than the TCH solution, suggesting the synergetic effect of niosome encapsulation and chitosan coating. Moreover, the formulated niosomes displayed no in vitro toxicity toward the human foreskin fibroblast cells (HFF). Both TCH-Nio and TCH-Nio@CS were found to down-regulate the expression of certain biofilm genes, i.e., csgA, ndvB, and icaA in the tested bacteria, which might partially explain the improved antibacterial activity compared to TCH. The obtained results demonstrated that TCH-Nio@CS is capable of controlled drug release, leading to high antibacterial efficacy. The established platform of TCH-Nio@CS enlighten a clinic potential toward the treatment of bacterial infections in skin wounds, dental implants and urinary catheter.

Ocular Drug Delivery: a Comprehensive Review

The human eye is a sophisticated organ with distinctive anatomy and physiology that hinders the passage of drugs into targeted ophthalmic sites. Effective topical administration is an interest of scientists for many decades. Their difficult mission is to prolong drug residence time and guarantee an appropriate ocular permeation. Several ocular obstacles oppose effective drug delivery such as precorneal, corneal, and blood-corneal barriers. Routes for ocular delivery include topical, intravitreal, intraocular, juxtascleral, subconjunctival, intracameral, and retrobulbar. More than 95% of marketed products exists in liquid state. However, other products could be in semi-solid (ointments and gels), solid state (powder, insert and lens), or mixed (in situ gel). Nowadays, attractiveness to nanotechnology-based carries is resulted from their capabilities to entrap both hydrophilic and lipophilic drugs, enhance ocular permeability, sustain residence time, improve drug stability, and augment bioavailability. Different in vitro, ex vivo, and in vivo characterization approaches help to predict the outcomes of the constructed nanocarriers. This review aims to clarify anatomy of the eye, various ocular diseases, and obstacles to ocular delivery. Moreover, it studies the advantages and drawbacks of different ocular routes of administration and dosage forms. This review also discusses different nanostructured platforms and their characterization approaches. Strategies to enhance ocular bioavailability are also explained. Finally, recent advances in ocular delivery are described.

SAR investigation and optimization of benzimidazole-based derivatives as antimicrobial agents against Gram-negative bacteria

Antibiotic-resistant bacteria represent a serious threat to modern medicine and human life. Only a minority of antibacterial agents are active against Gram-negative bacteria. Hence, the development of novel antimicrobial agents will always be a vital need. In an effort to discover new therapeutics against Gram-negative bacteria, we previously reported a structure-activity-relationship (SAR) study on 1,2-disubstituted benzimidazole derivatives. Compound III showed a potent activity against tolC-mutant Escherichia coli with an MIC value of 2 μg/mL, representing a promising lead for further optimization. Building upon this study, herein, 49 novel benzimidazole compounds were synthesized to investigate their antibacterial activity against Gram-negative bacteria. Our design focused on three main goals, to address the low permeability of our compounds and improve their cellular accumulation, to expand the SAR study to the unexplored ring C, and to optimize the lead compound (III) by modification of the methanesulfonamide moiety. Compounds (25a-d, 25f-h, 25k, 25l, 25p, 25r, 25s, and 26b) exhibited potent activity against tolC-mutant E. coli with MIC values ranging from 0.125 to 4 μg/mL, with compound 25d displaying the highest potency among the tested compounds with an MIC value of 0.125 μg/mL. As its predecessor, III, compound 25d exhibited an excellent safety profile without any significant cytotoxicity to mammalian cells. Time-kill kinetics assay indicated that 25d exhibited a bacteriostatic activity and significantly reduced E. coli JW55031 burden as compared to DMSO. Additionally, combination of 25d with colistin partially restored its antibacterial activity against Gram-negative bacterial strains (MIC values ranging from 4 to 16 μg/mL against E. coli BW25113, K. pneumoniae, A. baumannii, and P. aeruginosa). Furthermore, formulation of III and 25d as lipidic nanoparticles (nanocapsules) resulted in moderate enhancement of their antibacterial activity against Gram-negative bacterial strains (A. Baumannii, N. gonorrhoeae) and compound 25d demonstrated superior activity to the lead compound III. These findings establish compound 25d as a promising candidate for treatment of Gram-negative bacterial infections and emphasize the potential of nano-formulations in overcoming poor cellular accumulation in Gram-negative bacteria where further optimization and investigation are warranted to improve the potency and broaden the spectrum of our compounds.

Hydrophobic modification improves the delivery of cell-penetrating peptides to eliminate intracellular pathogens in animals

Infections induced by intracellular pathogens are difficult to eradicate due to poor penetration of antimicrobials into cell membranes. It is of great importance to develop a new generation of antibacterial agents with dual functions of efficient cell penetration and bacterial inhibition. In this study, the association between hydrophobicity and cell-penetrating peptide delivery efficiency was investigated by fragment interception and hydrophobicity modification of natural porcine antimicrobial peptide PR-39 and the combination of cationic cell-penetrating peptide (R6) with antimicrobial peptide fragments modified with hydrophobic residues. The chimeric peptides P3I7 and P3L7, obtained through biofunctional screening, exhibited potent broad-spectrum antibacterial activity and low cytotoxicity. Moreover, P3I7 and P3L7 can effectively penetrate cells to eliminate intracellular pathogens mainly through endocytosis. The membrane destruction mechanism makes the peptides fast sterilizers and less prone to developing drug resistance. Finally, their good biocompatibility and antibacterial infection effects were verified in mice and piglets. To conclude, the chimeric peptides P3I7 and P3L7 show great potential as affordable and effective antimicrobial agents and may serve as ideal candidates for the treatment of intracellular bacterial infections. STATEMENT OF SIGNIFICANCE: The low permeability of antibacterial drugs makes infections induced by intracellular bacteria extremely difficult to treat. To address this issue, we designed chimeric peptides with dual cell-penetrating and antibacterial functions. The active peptides P3I7 and P3L7, acquired through functional screening have strong broad-spectrum antibacterial activity and powerful bactericidal effects against intracellular Staphylococcus aureus. The membrane permeation mechanism of P3I7 and P3L7 against bacteria endows fast bactericidal activity with low drug resistance. The biosafety and antibacterial activity of P3I7 and P3L7 were also validated by in vivo trials. This study provides an ideal drug candidate against intracellular bacterial infections.

Nanomedicine: New Frontiers in Fighting Microbial Infections

Microbes have dominated life on Earth for the past two billion years, despite facing a variety of obstacles. In the 20th century, antibiotics and immunizations brought about these changes. Since then, microorganisms have acquired resistance, and various infectious diseases have been able to avoid being treated with traditionally developed vaccines. Antibiotic resistance and pathogenicity have surpassed antibiotic discovery in terms of importance over the course of the past few decades. These shifts have resulted in tremendous economic and health repercussions across the board for all socioeconomic levels; thus, we require ground-breaking innovations to effectively manage microbial infections and to provide long-term solutions. The pharmaceutical and biotechnology sectors have been radically altered as a result of nanomedicine, and this trend is now spreading to the antibacterial research community. Here, we examine the role that nanomedicine plays in the prevention of microbial infections, including topics such as diagnosis, antimicrobial therapy, pharmaceutical administration, and immunizations, as well as the opportunities and challenges that lie ahead.

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.

Emerging Target-Directed Approaches for the Treatment and Diagnosis of Microbial Infections

With the rising levels of drug resistance, developing efficient antimicrobial therapies has become a priority. A promising strategy is the conjugation of antibiotics with relevant moieties that can potentiate their activity by target-directing. The conjugation of siderophores with antibiotics allows them to act as Trojan horses by hijacking the microorganisms' highly developed iron transport systems and using them to carry the antibiotic into the cell. Through the analysis of relevant examples of the past decade, this Perspective aims to reveal the potential of siderophore-antibiotic Trojan horses for the treatment of infections and the role of siderophores in diagnostic techniques. Other conjugated molecules will be the subject of discussion, namely those involving vitamin B12, carbohydrates, and amino acids, as well as conjugated compounds targeting protein degradation and β-lactamase activated prodrugs.

Tumor resident microbiota and response to therapies: An insight on tissue bacterial microbiota

The role of the intestinal microbiota in the promotion, progression, and response to therapies is gaining importance, but recent studies confirm the presence of microbiota also in the tumor, thus becoming a component of the tumor microenvironment. There is not much knowledge on the characteristics and mechanisms of action of the tumor resident microbiota, but there are already indications of its involvement in conditioning the response to therapies. In this review, we discuss recent publications on the interaction between microbiota and anticancer treatments, mechanisms of resistance and possible strategies for manipulating the microbiota that could improve treatments in a personalized medicine perspective.

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.

Microscopy-based phenotypic profiling of infection by Staphylococcus aureus clinical isolates reveals intracellular lifestyle as a prevalent feature

Staphylococcus aureus is increasingly recognized as a facultative intracellular pathogen, although the significance and pervasiveness of its intracellular lifestyle remain controversial. Here, we applied fluorescence microscopy-based infection assays and automated image analysis to profile the interaction of 191 S. aureus isolates from patients with bone/joint infections, bacteremia, and infective endocarditis, with four host cell types, at five times post-infection. This multiparametric analysis revealed that almost all isolates are internalized and that a large fraction replicate and persist within host cells, presenting distinct infection profiles in non-professional vs. professional phagocytes. Phenotypic clustering highlighted interesting sub-groups, including one comprising isolates exhibiting high intracellular replication and inducing delayed host death in vitro and in vivo. These isolates are deficient for the cysteine protease staphopain A. This study establishes S. aureus intracellular lifestyle as a prevalent feature of infection, with potential implications for the effective treatment of staphylococcal infections.

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.

Can intracellular Staphylococcus aureus in osteomyelitis be treated using current antibiotics? A systematic review and narrative synthesis

Approximately 40% of treatments of chronic and recurrent osteomyelitis fail in part due to bacterial persistence. Staphylococcus aureus, the predominant pathogen in human osteomyelitis, is known to persist by phenotypic adaptation as small-colony variants (SCVs) and by formation of intracellular reservoirs, including those in major bone cell types, reducing susceptibility to antibiotics. Intracellular infections with S. aureus are difficult to treat; however, there are no evidence-based clinical guidelines addressing these infections in osteomyelitis. We conducted a systematic review of the literature to determine the demonstrated efficacy of all antibiotics against intracellular S. aureus relevant to osteomyelitis, including protein biosynthesis inhibitors (lincosamides, streptogramins, macrolides, oxazolidines, tetracyclines, fusidic acid, and aminoglycosides), enzyme inhibitors (fluoroquinolones and ansamycines), and cell wall inhibitors (beta-lactam inhibitors, glycopeptides, fosfomycin, and lipopeptides). The PubMed and Embase databases were screened for articles related to intracellular S. aureus infections that compared the effectiveness of multiple antibiotics or a single antibiotic together with another treatment, which resulted in 34 full-text articles fitting the inclusion criteria. The combined findings of these studies were largely inconclusive, most likely due to the plethora of methodologies utilized. Therefore, the reported findings in the context of the models employed and possible solutions for improved understanding are explored here. While rifampicin, oritavancin, linezolid, moxifloxacin and oxacillin were identified as the most effective potential intracellular treatments, the scientific evidence for these is still relatively weak. We advocate for more standardized research on determining the intracellular effectiveness of antibiotics in S. aureus osteomyelitis to improve treatments and patient outcomes.

Intracellular Bacterial Targeting by a Thiazolyl Benzenesulfonamide and Octaarginine Peptide Complex

A brominated thiazolyl benzenesulfonamide (BTB) derivative is conjugated with the cell-penetrating peptide octaarginine (R8) in an effort to construct innovative antibacterial products. The noncovalent complex of BTB and R8 is characterized by Fourier transform infrared (FTIR) spectroscopy, which indicates hydrogen bonding between the two constituents. Attachment of the peptide moiety renders aqueous solubility to the hydrophobic benzenesulfonamide drug and bestows bactericidal activity. Confocal imaging in conjunction with dye probes shows successful clearance of intracellular Staphylococcus aureus bacteria by the BTB-R8 complex. Scanning electron micrographs and studies with a set of fluorescent dyes suggest active disruption of the bacterial cell membrane by the BTB-R8 complex. In contrast, the complex of BTB with octalysine (K8) fails to cause membrane damage and displays a modest antibacterial effect. A complex of BTB with the water-soluble hydrophilic polymer poly(vinylpyrrolidone) (PVP) does not display any antibacterial effect, indicating the distinctive role of the cell-penetrating peptide (CPP) R8 in the cognate complex. The leakage of the encapsulated dye from giant unilamellar vesicles upon interaction with the BTB-R8 complex further highlights the membrane activity of the complex, which cannot be accomplished by bare sulfonamide alone. This work broadens the scope of use of CPPs with respect to eliciting antibacterial activity and potentially expands the limited arsenal of membrane-targeting antibiotics.

Biological foundations of successful bacteriophage therapy

Bacteriophages (phages) are selective viral predators of bacteria. Abundant and ubiquitous in nature, phages can be used to treat bacterial infections (phage therapy), including refractory infections and those resistant to antibiotics. However, despite an abundance of anecdotal evidence of efficacy, significant hurdles remain before routine implementation of phage therapy into medical practice, including a dearth of robust clinical trial data. Phage-bacterium interactions are complex and diverse, characterized by co-evolution trajectories that are significantly influenced by the environments in which they occur (mammalian body sites, water, soil, etc.). An understanding of the molecular mechanisms underpinning these dynamics is essential for successful clinical translation. This review aims to cover key aspects of bacterium-phage interactions that affect bacterial killing by describing the most relevant published literature and detailing the current knowledge gaps most likely to influence therapeutic success.

Investigating the Antimicrobial Activity of Vancomycin-Loaded Soy Protein Nanoparticles

Developing targeted and slow-release antibiotic delivery systems can effectively reduce drug overdose and side effects. This study aimed to investigate the antimicrobial activity of vancomycin-loaded soy protein nanoparticles (vancomycin-SPNs). For the preparation of SPNs, the desolvation method was applied in different concentrations of vancomycin and soy protein (15:5, 10:15, 6:20, 8:25, and 10:30 of vancomycin:soy protein). Scanning electron microscope (SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS), and FTIR were used for nanoparticle characterization. Antibacterial activity was evaluated by the radial diffusion assay (RDA) and absorbance methods. Proper synthesis was demonstrated by characterization. The best drug loading (% entrapment efficiency = 90.2%), the fastest release rate (% release = 88.2%), and the best antibacterial activity were observed in ratio 10:30 of vancomycin:SPNs. Results showed that SPNs are a potent delivery system for antibiotic loading and slow release to control antibiotic use.