Superenhanced Removal of Fungal Biofilms by Protease‐Functionalized Amphotericin B Nanocarriers

Overcoming Beta-Lactamase-Based Antimicrobial Resistance by Nanocarrier-Loaded Clavulanic Acid and Antibiotic Cotreatments

Antimicrobial resistance (AMR) is one of the major threats to modern healthcare. Many types of bacteria have developed resistance to multiple antibiotic treatments, while additional antibiotics have not been recently brought to market. One approach to counter AMR based on the beta-lactamase enzyme has been to use cotreatments of an antibiotic and an inhibitor, to enhance the antibiotic action. Here, we aimed to enhance this technique by developing nanocarriers of two cationic beta-lactam class antibiotics, amoxicillin, and ticarcillin, combined with a beta-lactamase inhibitor, clavulanic acid, which can potentially overcome this type of AMR. We demonstrate for the first time that beta-lactamase inhibitor-loaded nanocarriers in cotreatments with either free or nanocarrier-loaded beta-lactam antibiotics can enhance their effectiveness further than when used alone. We use surface-functionalized shellac-/Poloxamer 407-stabilized antibiotic nanocarriers on Pseudomonas aeruginosa, which is susceptible to ticarcillin but is resistant to amoxicillin. We show an amplification of the antibiotic effect of amoxicillin and ticarcillin loaded in shellac nanoparticles, both alone and as a cotreatment with free or nanocarrier-loaded clavulanic acid. We also report a significant increase in the antimicrobial effects of clavulanic acid loaded in such nanocarriers as a cotreatment. We explain the increased antimicrobial activity of the cationically functionalized antibiotic-loaded nanoparticles with electrostatic attraction to the bacterial cell wall, which delivers higher local antibiotic and inhibitor concentrations. The effect is due to the accumulation of the clavulanic acid-loaded nanocarriers on the bacterial cell walls that allows a higher proportion of the inhibitor to engage with the produced intracellular beta-lactamases. These nanocarriers were also found to have a very low cytotoxic effect against human keratinocytes, which shows great potential for overcoming enzyme-based AMR.

Nanotechnologies for control of pathogenic microbial biofilms

Biofilms are formed at interfaces by microorganisms, which congregate in microstructured communities embedded in a self-produced extracellular polymeric substance (EPS). Biofilm-related infections are problematic due to the high resistance towards most clinically used antimicrobials, which is associated with high mortality and morbidity, combined with increased hospital stays and overall treatment costs. Several new nanotechnology-based approaches have recently been proposed for targeting resistant bacteria and microbial biofilms. Here we discuss the impacts of biofilms on healthcare, food processing and packaging, and water filtration and distribution systems, and summarize the emerging nanotechnological strategies that are being developed for biofilm prevention, control and eradication. Combination of novel nanomaterials with conventional antimicrobial therapies has shown great potential in producing more effective platforms for controlling biofilms. Recent developments include antimicrobial nanocarriers with enzyme surface functionality that allow passive infection site targeting, degradation of the EPS and delivery of high concentrations of antimicrobials to the residing cells. Several stimuli-responsive antimicrobial formulation strategies have taken advantage of the biofilm microenvironment to enhance interaction and passive delivery into the biofilm sites. Nanoparticles of ultralow size have also been recently employed in formulations to improve the EPS penetration, enhance the carrier efficiency, and improve the cell wall permeability to antimicrobials. We also discuss antimicrobial metal and metal oxide nanoparticle formulations which provide additional mechanical factors through externally induced actuation and generate reactive oxygen species (ROS) within the biofilms. The review helps to bridge microbiology with materials science and nanotechnology, enabling a more comprehensive interdisciplinary approach towards the development of novel antimicrobial treatments and biofilm control strategies.

Emerging nanotechnologies for targeting antimicrobial resistance

Antimicrobial resistance is a leading cause of mortality worldwide. Without newly approved antibiotics and antifungals being brought to the market, resistance is being developed to the ones currently available to clinicians. The reason is the applied evolutionary pressure to bacterial and fungal species due to the wide overuse of common antibiotics and antifungals in clinical practice and agriculture. Biofilms harbour antimicrobial-resistant subpopulations, which make their antimicrobial treatment even more challenging. Nanoparticle-based technologies have recently been shown to successfully overcome antimicrobial resistance in both planktonic and biofilms phenotypes. This results from the combination of novel nanomaterial research and classic antimicrobial therapies which promise to deliver a whole new generation of high-performance active nanocarrier systems. This review discusses the latest developments of promising nanotechnologies with applications against resistant pathogens and evaluates their potential and feasibility for use in novel antimicrobial therapies.

Multiscale Shellac-Based Delivery Systems: From Macro- to Nanoscale

Delivery systems play a crucial role in enhancing the activity of active substances; however, they require complex processing techniques and raw material design to achieve the desired properties. In this regard, raw materials that can be easily processed for different delivery systems are garnering attention. Among these raw materials, shellac, which is the only pharmaceutically used resin of animal origin, has been widely used in the development of various delivery systems owing to its pH responsiveness, biocompatibility, and degradability. Notably, shellac performs better on encapsulating hydrophobic active substances than other natural polymers, such as polysaccharides and proteins. In addition, specially designed shellac-based delivery systems can also be used for the codelivery of hydrophilic and hydrophobic active substances. Shellac is most widely used for oral administration, as shellac-based delivery systems can form a compact structure through hydrophobic interaction, protecting transported active substances from the harsh environment of the stomach to achieve targeted delivery in the small intestine or colon. In this review, the advantages of shellac in delivery systems are discussed in detail. Multiscale shellac-based delivery systems from the macroscale to nanoscale are comprehensively introduced, including matrix tablets, films, enteric coatings, hydrogels, microcapsules, microparticles (beads/spheres), nanoparticles, and nanofibers. Furthermore, the hotspots, deficiencies, and future perspectives of shellac-based delivery system development are also analyzed. We hoped this review will increase the understanding of shellac-based delivery systems and inspire their further development.

Enhanced clearing of Candida biofilms on a 3D urothelial cell in vitro model using lysozyme-functionalized fluconazole-loaded shellac nanoparticles

Candida urinary tract biofilms are increasingly witnessed in nosocomial infections due to reduced immunity of patients and the hospital ecosystem. The indwelling devices utilized to support patients with urethral diseases that connect the unsterilized external environment with the internal environment of the patient are another significant source of urinary tract biofilm infections. Recently, nanoparticle (NP)-associated therapeutics have gained traction in a number of areas, including fighting antibiotic-resistant bacterial biofilm infection. However, most studies on nanotherapeutic delivery have only been carried out in laboratory settings rather than in clinical trials due to the lack of precise in vitro and in vivo models for testing their efficiency. Here we develop a novel biofilm-infected 3D human urothelial cell culture model to test the efficiency of nanoparticle (NP)-based antifungal therapeutics. The NPs were designed based on shellac cores, loaded with fluconazole and coated with the cationic enzyme lysozyme. Our formulation of 0.2 wt% lysozyme-coated 0.02 wt% fluconazole-loaded 0.2 wt% shellac NPs, sterically stabilised by 0.25 wt% poloxamer 407, showed an enhanced efficiency in removing Candida albicans biofilms formed on 3D layer of urothelial cell clusteroids. The NP formulation exhibited low toxicity to urothelial cells. This study provides a reliable in vitro model for Candida urinary tract biofilm infections, which could potentially replace animal models in the testing of such antifungal nanotechnologies. The reproducibility and availability of a well-defined biofilm-infected 3D urothelial cell culture model give valuable insights into the formation and clearing of fungal biofilms and could accelerate the clinical use of antifungal nanotherapeutics.

Enhanced Antimicrobial Action of Chlorhexidine Loaded in Shellac Nanoparticles with Cationic Surface Functionality

We report on an active nanocarrier for chlorhexidine (CHX) based on sterically stabilized shellac nanoparticles (NPs) with dual surface functionalization, which greatly enhances the antimicrobial action of CHX. The fabrication process for the CHX nanocarrier is based on pH-induced co-precipitation of CHX-DG from an aqueous solution of ammonium shellac and Poloxamer 407 (P407), which serves as a steric stabilizing agent. This is followed by further surface modification with octadecyl trimethyl ammonium bromide (ODTAB) through a solvent change to yield cationic surface functionality. In this study, we assessed the encapsulation efficiency and release kinetics of the novel nanocarrier for CHX. We further examined the antimicrobial effects of the CHX nanocarriers and their individual components in order to gain better insight into how they work, to improve their design and to explore the impacts of their dual functionalization. The antimicrobial actions of CHX loaded in shellac NPs were examined on three different proxy microorganisms: a Gram-negative bacterium (E. coli), a yeast (S. cerevisiae) and a microalgae (C. reinhardtii). The antimicrobial actions of free CHX and CHX-loaded shellac NPs were compared over the same CHX concentration range. We found that the non-coated shellac NPs loaded with CHX showed inferior action compared with free CHX due to their negative surface charge; however, the ODTAB-coated, CHX-loaded shellac NPs strongly amplified the antimicrobial action of the CHX for the tested microorganisms. The enhancement of the CHX antimicrobial action was thought to be due to the increased electrostatic adhesion between the cationic surface of the ODTAB-coated, CHX-loaded shellac NPs and the anionic surface of the cell walls of the microorganisms, ensuring direct delivery of CHX with a high concentration locally on the cell membrane. The novel CHX nanocarriers with enhanced antimicrobial action may potentially find applications in dentistry for the development of more efficient formulations against conditions such as gingivitis, periodontitis and other oral infections, as well as enabling formulations to have lower CHX concentrations.

Biofilm-Infected Human Clusteroid Three-Dimensional Coculture Platform to Replace Animal Models in Testing Antimicrobial Nanotechnologies

Microbial biofilms are a major concern in wound care, implant devices, and organ infections. Biofilms allow higher tolerance to antimicrobial drugs, can impair wound healing, and potentially lead to sepsis. There has been a recent focus on developing novel nanocarrier-based delivery vehicles to enhance the biofilm penetration of traditional antibacterial drugs. However, a feasible in vitro human skin model to mimic the biofilm formation and its treatment for clearance have not yet been reported. This study describes the benefits of using an innovative bacterial biofilm-infected keratinocyte clusteroid model for the first time. It paves a new way for testing innovative nanomedicine delivery systems in a rapid and reproducible way on a realistic human cell-based platform, free of any animal testing. Herein, we have developed a novel composite 3D biofilm/human keratinocyte clusteroid coculture platform, which was used to measure biofilm clearance efficiency of nanoparticle (NP)-based therapeutics. We tested this model by treating the biofilm-infected 3D coculture layers by a ciprofloxacin-loaded Carbopol nanogel particles, surface-functionalized by the cationic protease Alcalase. We measured the antibacterial efficiency of the NP treatment on clearing Staphylococcus aureus and Pseudomonas aeruginosa biofilms on the 3D keratinocyte clusteroid/biofilm coculture model. Our experiments showed that these bacteria can infect the 3D layer of keratinocyte clusteroids and produce a stable biofilm. The biofilms were efficiently cleared by treatment with a formulation of 0.0032 wt % ciprofloxacin-loaded in 0.2 wt % Carbopol NPs surface-functionalized with 0.2 wt % Alcalase. Taken together, these promising results demonstrate that our coculture model can be exploited as a novel platform for testing the biofilm-eliminating efficiency of various NP formulations emulating skin and wound infections and could have wider applicability to replace animal models in similar experiments. This 3D cell culture-based platform could help in developing and testing of more effective antibacterial agents for clinical applications of antiplaque dental treatments, implants, infection control, and wound dressings.

Enhanced Antimould Action of Surface Modified Copper Oxide Nanoparticles with Phenylboronic Acid Surface Functionality

Antimould agents are widely used in different applications, such as specialty paints, building materials, wood preservation and crop protection. However, many antimould agents can be toxic to the environment. This work aims to evaluate the application of copper oxide nanoparticles (CuONPs) surface modified with boronic acid (BA) terminal groups as antimould agents. We developed CuONPs grafted with (3-glycidyloxypropyl) trimethoxysilane (GLYMO), coupled with 4-hydroxyphenylboronic acid (4-HPBA), which provided a strong boost of their action as antimould agents. We studied the antimould action of the 4-HPBA-functionalized CuONPs against two mould species: Aspergillus niger (A. niger) and Penicillium chrysogenum (P. chrysogenum). The cis-diol groups of polysaccharides expressed on the mould cell walls can form reversible covalent bonds with the BA groups attached on the CuONPs surface. This allowed them to bind strongly to the mould surface, resulting in a very substantial boost of their antimould activity, which is not based on electrostatic adhesion, as in the case of bare CuONPs. The impact of these BA-surface functionalized nanoparticles was studied by measuring the growth of the mould colonies versus time. The BA-functionalized CuONPs showed significant antimould action, compared to the untreated mould sample at the same conditions and period of time. These results can be applied for the development of more efficient antimould treatments at a lower concentration of active agent with potentially substantial economic and environmental benefits.