The use of nanomaterials for the mitigation of pathogenic biofilm formation

2-D transition metal trichalcophosphogenide FePS3 against multi-drug resistant microbial infections

Antimicrobial resistance (AMR) is a significant concern to society as it threatens the effectiveness of antibiotics and leads to increased morbidity and mortality rates. Innovative approaches are urgently required to address this challenge. Among promising solutions, two dimensional (2-D) nanomaterials with layered crystal structures have emerged as potent antimicrobial agents owing to their unique physicochemical properties. This antimicrobial activity is largely attributed to their high surface area, which allows for efficient interaction with microbial cell membranes, leading to physical disruption or oxidative stress through the generation of reactive oxygen species (ROS). The latter mechanism is particularly noteworthy as it involves the degradation of these nanomaterials under specific conditions, releasing ROS that can effectively kill bacteria and other pathogens without harming human cells. This study explores the antimicrobial properties of a novel biodegradable nanomaterial based on 2-D transition metal trichalcogenides, FePS3, as a potential solution to drug-resistant microbes. Our findings indicate that FePS3 is an exceptionally effective antimicrobial agent with over 99.9% elimination of various bacterial strains. Crucially, it exhibits no cytotoxic effects on mammalian cells, underscoring the potential for safe biomedical application. The primary mechanism driving the antimicrobial efficacy of FePS3 is the release of ROS during biodegradation. ROS has a crucial role in neutralizing bacterial cells, conferring significant antipathogenic properties to this compound. The unique combination of high antimicrobial activity, biocompatibility, and biodegradability makes FePS3 a promising candidate for developing new antimicrobial strategies. This research contributes to the increasing body of evidence supporting the use of 2-D nanomaterials in addressing the global challenge of AMR, offering a potential pathway for the development of advanced, effective, and safe antimicrobial agents.

Microbial Biofilm Inhibition Using Magnetic Cross-Linked Polyphenol Oxidase Aggregates

Microbial biofilm accumulation poses a serious threat to the environment, presents significant challenges to different industries, and exhibits a large impact on public health. Since there has not been a conclusive answer found despite various efforts, the potential green and economical methods are being focused on, particularly the innovative approaches that employ biochemical agents. In the present study, we propose a bio-nanotechnological method using magnetic cross-linked polyphenol oxidase aggregates (PPO m-CLEA) for inhibition of microbial biofilm including multidrug resistant bacteria. Free PPO solution showed only 55-60% biofilm inhibition, whereas m-CLEA showed 70-75% inhibition, as confirmed through microscopic techniques. The carbohydrate and protein contents in biofilm extracellular polymeric substances (EPSs) were reduced significantly. The m-CLEA demonstrated reusability up to 5 cycles with consistent efficiency in biofilm inhibition. Computational work was also done where molecular docking of PPO with microbial proteins associated with biofilm formation was conducted, resulting in favorable binding scores and inter-residual interactions. Overall, both in vitro and in silico results suggest that PPO interferes with microbial cell attachment and EPS formation, thereby preventing biofilm colonization.

Gold nanoparticle adsorption alters the cell stiffness and cell wall bio-chemical landscape of Candida albicans fungal cells

HYPOTHESIS

Nanomaterials have been extensively investigated for a wide range of biomedical applications, including as antimicrobial agents, drug delivery vehicles, and diagnostic devices. The commonality between these biomedical applications is the necessity for the nanoparticle to interact with or pass through the cellular wall and membrane. Cell-nanomaterial interactions/uptake can occur in various ways, including adhering to the cell wall, forming aggregates on the surface, becoming absorbed within the cell wall itself, or transversing into the cell cytoplasm. These interactions are common to mammalian cells, bacteria, and yeast cells. This variety of interactions can cause changes to the integrity of the cell wall and the cell overall, but the precise mechanisms underpinning such interactions remain poorly understood. Here, we investigate the interaction between commonly investigated gold nanoparticles (AuNPs) and the cell wall/membrane of a model fungal cell to explore the general effects of interaction and uptake.

EXPERIMENTS

The interactions between 100 nm citrate-capped AuNPs and the cell wall of Candida albicans fungal cells were studied using a range of advanced microscopy techniques, including atomic force microscopy, confocal laser scanning microscopy, scanning electron microscopy, transmission electron microscopy, and synchrotron-FTIR micro-spectroscopy.

FINDINGS

In most cases, particles adhered on the cell surface, although instances of particles being up-taken into the cell cytoplasm and localised within the cell wall and membrane were also observed. There was a measurable increase in the stiffness of the fungal cell after AuNPs were introduced. Analysis of the synchrotron-FTIR data showed significant changes in spectral features associated with phospholipids and proteins after exposure to AuNPs.

Dual-action silver functionalized nanostructured titanium against drug resistant bacterial and fungal species

HYPOTHESIS

Titanium and its alloys are commonly used implant materials. Once inserted into the body, the interface of the biomaterials is the most likely site for the development of implant-associated infections. Imparting the titanium substrate with high-aspect-ratio nanostructures, which can be uniformly achieved using hydrothermal etching, enables a mechanical contact-killing (mechanoresponsive) mechanism of bacterial and fungal cells. Interaction between cells and the surface shows cellular inactivation via a physical mechanism meaning that careful engineering of the interface is needed to optimse the technology. This mechanism of action is only effective towards surface adsorbed microbes, thus any cells not directly in contact with the substrate will survive and limit the antimicrobial efficacy of the titanium nanostructures. Therefore, we propose that a dual-action mechanoresponsive and chemical-surface approach must be utilised to improve antimicrobial activity. The addition of antimicrobial silver nanoparticles will provide a secondary, chemical mechanism to escalate the microbial response in tandem with the physical puncture of the cells.

EXPERIMENTS

Hydrothermal etching is used as a facile method to impart variant nanostrucutres on the titanium substrate to increase the antimicrobial response. Increasing concentrations (0.25 M, 0.50 M, 1.0 M, 2.0 M) of sodium hydroxide etching solution were used to provide differing degrees of nanostructured morphology on the surface after 3 h of heating at 150 °C. This produced titanium nanospikes, nanoblades, and nanowires, respectively, as a function of etchant concentration. These substrates then provided an interface for the deposition of silver nanoparticles via a reduction pathway. Methicillin-resistant Staphylococcous aureus (MRSA) and Candida auris (C. auris) were used as model bacteria and fungi, respectively, to test the effectiveness of the nanostructured titanium with and without silver nanoparticles, and the bio-interactions at the interface.

FINDINGS

The presence of nanostructure increased the bactericidal response of titanium against MRSA from ∼ 10 % on commercially pure titanium to a maximum of ∼ 60 % and increased the fungicidal response from ∼ 10 % to ∼ 70 % in C. auris. Introducing silver nanoparticles increased the microbiocidal response to ∼ 99 % towards both bacteria and fungi. Importantly, this study highlights that nanostructure alone is not sufficient to develop a highly antimicrobial titanium substrate. A dual-action, physical and chemical antimicrobial approach is better suited to produce highly effective antibacterial and antifungal surface technologies.

Medicinal plants mediated the green synthesis of silver nanoparticles and their biomedical applications

The alarming effect of antibiotic resistance prompted the search for alternative medicine to resolve the microbial resistance conflict. Over the last two decades, scientists have become increasingly interested in metallic nanoparticles to discover their new dimensions. Green nano synthesis is a rapidly expanding field of interest in nanotechnology due to its feasibility, low toxicity, eco‐friendly nature, and long‐term viability. Some plants have long been used in medicine because they contain a variety of bioactive compounds. Silver has long been known for its antibacterial properties. Silver nanoparticles have taken a special place among other metal nanoparticles. Silver nanotechnology has a big impact on medical applications like bio‐coating, novel antimicrobial agents, and drug delivery systems. This review aims to provide a comprehensive understanding of the pharmaceutical qualities of medicinal plants, as well as a convenient guideline for plant‐based silver nanoparticles and their antimicrobial activity.

Cytotoxic Activity and Antibiofilm Efficacy of Biosynthesized Silver Nanoparticles against Methicillin-Resistant Staphylococcus aureus Strains Colonizing Cell Phones

The interest for green synthesis of metallic nanoparticles (NPs) has acquired particular attention due to its low toxicity and economic feasibility compared with chemical or physical process. Here we carried out an extracellular synthesis approach of silver nanoparticles (AgNPs) using dried orange peel extract. Characterization studies revealed the synthesis of 25–30 nm AgNPs with distinct morphology as observed in transmission electron microscopes. Dynamic light scattering spectroscopy and Fourier transform infrared spectroscopy analyses further characterized nanoparticles confirming their stability and the presence of functional groups. The biological properties of biosynthesized AgNPs were subsequently investigated. Our results revealed anticancer activity of biogenic silver NPs against the B16 melanoma cell line with an IC50 value of 25 µg/ml. Additionally, the developed AgNPs displayed a considerable antagonistic activity against methicillin-resistant Staphylococcus aureus (MRSA) strains colonizing cell phones, with inhibition zones between 12 and 14 mm and minimum inhibitory concentration values between 1.56 and 12.5 µg/ml. Furthermore, the AgNPs exhibited potent antibiofilm activity against MRSA strains with the percent biofilm disruption reaching 80%. Our results highlighted the efficacy of biosynthesized AgNPs against bacterial biofilms and pointed to the exploration of orange peels as a natural and cost-effective strategy.

Illuminating the biochemical interaction of antimicrobial few-layer black phosphorus with microbial cells using synchrotron macro-ATR-FTIR

In the fight against drug-resistant pathogenic bacterial and fungal cells, low-dimensional materials are emerging as a promising alternative treatment method. Specifically, few-layer black phosphorus (BP) has demonstrated its effectiveness against a wide range of pathogenic bacterial and fungal cells with studies suggesting low cytotoxicity towards healthy mammalian cells. However, the antimicrobial mechanism of action of BP is not well understood. Before new applications for this material can be realised, further in-depth investigations are required. In this work, the biochemical interaction between BP and a series of microbial cells is investigated using a variety of microscopy and spectroscopy techniques to provide a greater understanding of the antimicrobial mechanism. Synchrotron macro-attenuated total reflection-Fourier transform infrared (ATR-FTIR) micro-spectroscopy is used to elucidate the chemical changes occurring outside and within the cell of interest after exposure to BP nanoflakes. The ATR-FTIR data, coupled with high-resolution microscopy, reveals major physical and bio-chemical changes to the phospholipids and amide I and II proteins, as well as minor chemical changes to the structural polysaccharides and nucleic acids when compared to untreated cells. These changes can be attributed to the physical interaction of the BP nanoflakes with the cell membranes, combined with the oxidative stress induced by the degradation of the BP nanoflakes. This study provides insight into the biochemical interaction of BP nanoflakes with microbial cells, allowing for a better understanding of the antimicrobial mechanism of action that will be important for the next generation of applications such as implant coatings, wound dressings, or medical surfaces.

Potentially Bioactive Fungus Mediated Silver Nanoparticles

Fungal metabolites, proteins, and enzymes have been rich sources of therapeutics so far. Therefore, in this study, the hypha extract of a newly identified noble fungus (Alternaria sp. with NCBI Accession number: MT982648) was used to synthesize silver nanoparticles (F-AgNPs) to utilize against bacteria, fungi, and lung cancer. F-AgNPs were characterized by using physical techniques, including UV–visible spectroscopy, zeta potential, DLS, XRD, TEM, and HR-TEM. The particles were found to be polydispersed and quasi-spherical in shape under TEM. They had an average size of ~15 nm. The well dispersed particles were found to have consistent crystallinity with cubic phase geometry under XRD and HR-TEM. The presence of different functional groups on the surfaces of biosynthesized F-AgNPs was confirmed by FTIR. The particle distribution index was found to be 0.447 with a hydrodynamic diameter of ~47 d.nm, and the high value of zeta potential (−20.3 mV) revealed the stability of the nanoemulsion. These particles were found to be active against Staphylococcus aureus (multidrug resistance-MDR), Klebsiella pneumonia, Salmonella abony, and Escherichia coli (MDR) with MIC₅₀ 10.3, 12.5, 22.69, and 16.25 µg/mL, respectively. Particles also showed inhibition against fungal strains, including A. flavus, A. niger, T. viridens, and F. oxysporium. Their inhibition of biofilm formation by the same panel of bacteria was also found to be very promising and ranged from 16.66 to 64.81%. F-AgNPs also showed anticancer potential (IC₅₀—21.6 µg/mL) with respect to methotrexate (IC₅₀—17.7 µg/mL) against lung cancer cell line A549, and they did not result in any significant inhibition of the normal cell line BEAS-2. The particles were found to alter the mitochondrial membrane potential, thereby disturbing ATP synthesis and leading to high ROS formation, which are responsible for cell membrane damage and release of LDH, intracellular proteins, lipids, and DNA. A high level of ROS also elicits pro-inflammatory signaling cascades that lead to programmed cell death by either apoptosis or necrosis.

Broad-Spectrum Solvent-free Layered Black Phosphorus as a Rapid Action Antimicrobial

Antimicrobial resistance has rendered many conventional therapeutic measures, such as antibiotics, ineffective. This makes the treatment of infections from pathogenic micro-organisms a major growing health, social, and economic challenge. Recently, nanomaterials, including two-dimensional (2D) materials, have attracted scientific interest as potential antimicrobial agents. Many of these studies, however, rely on the input of activation energy and lack real-world utility. In this work, we present the broad-spectrum antimicrobial activity of few-layered black phosphorus (BP) at nanogram concentrations. This property arises from the unique ability of layered BP to produce reactive oxygen species, which we harness to create this unique functionality. BP is shown to be highly antimicrobial toward susceptible and resistant bacteria and fungal species. To establish cytotoxicity with mammalian cells, we showed that both L929 mouse and BJ-5TA human fibroblasts were metabolically unaffected by the presence of BP. Finally, we demonstrate the practical utility of this approach, whereby medically relevant surfaces are imparted with antimicrobial properties via functionalization with few-layer BP. Given the self-degrading properties of BP, this study demonstrates a viable and practical pathway for the deployment of novel low-dimensional materials as antimicrobial agents without compromising the composition or nature of the coated substrate.

A search for enhanced photodynamic activity against Staphylococcus aureus planktonic cells and biofilms: the evaluation of phthalocyanine-detonation nanodiamond-Ag nanoconjugates

The present work reports on the synthesis and characterization of novel zinc (2) and indium (3) 2-amino-4-bromophenoxy substituted phthalocyanines (Pcs) along with the self-assembled nanoconjugates formed viaπ-π stacking interaction onto detonation nanodiamonds (DNDs) to form 2@DNDs and 3@DNDs. 2@DNDs and 3@DNDs were covalently linked to chitosan-silver mediated nanoparticles (CSAg) to form 2@DNDs-CSAg and 3@DNDs-CSAg nanoconjugates. High singlet oxygen quantum yields in DMSO of 0.69 and 0.72 for Pcs alone and 0.90 and 0.92 for 2@DNDs-CSAg and 3@DNDs-CSAg, respectively, were obtained. The photodynamic antimicrobial chemotherapy (PACT) activity of both phthalocyanines and nanoconjugates was tested against planktonic cells and biofilms of S. aureus. 2@DNDs-CSAg and 3@DNDs-CSAg caused effective killing with a log reduction of 9.74. In addition, PACT studies on single-species S. aureus biofilms were carried out with log reduction values of 5.12 and 5.27 at 200 μg mL^-1 for 2@DNDs-CSAg and 3@DNDs-CSAg, respectively.

Conformationally tuned antibacterial oligomers target the peptidoglycan of Gram-positive bacteria

The recent rise of antibiotic resistance amongst Staphylococcus aureus (S. aureus) populations has made treating Staph-based infections a global medical challenge. Therapies that specifically target the peptidoglycan layer of S. aureus have emerged as new treatment avenues, towards which bacteria are less likely to develop resistance. While the majority of antibacterial polymers/oligomers have the ability to disrupt bacterial membranes, the design parameters for the enhanced disruption of peptidoglycan outer layer of Gram-positive bacteria remain unclear. Here, the design of oligomeric structures with favorable conformational characteristics for improved disruption of the peptidoglycan outer layer of Gram-positive bacteria is reported. Molecular dynamics simulations were employed to inform the structure design and composition of cationic oligomers displaying collapsed and expanded conformations. The most promising diblock and triblock cationic oligomers were synthesized by photo-induced atom transfer radical polymerization (photo ATRP). Following synthesis, the diblock and triblock oligomers displayed average antibacterial activity of ~99% and ~98% for S. aureus and methicillin-resistant S. aureus (MRSA), respectively, at the highest concentrations tested. Importantly, triblock oligomers with extended conformations showed significantly higher disruption of the peptidoglycan outer layer of S. aureus compared to diblock oligomers with more collapsed conformation, as evidenced by a number of characterization techniques including scanning electron, confocal and atomic force microscopy. This work provides new insight into the structure/property relationship of antibacterial materials and advances the design of functional materials for combating the rise of drug-resistant bacteria.

Anti-biofilm and Antibacterial Activities of Silver Nanoparticles Synthesized by the Reducing Activity of Phytoconstituents Present in the Indian Medicinal Plants

Biofilm forming from a variety of microbial pathogens can pose a serious health hazard that is difficult to combat. Nanotechnology, however, represents a new approach to fighting and eradicating biofilm-forming microorganisms. In the present study, the sustainable synthesis and characterization of biocompatible silver nanoparticles (AgNPs) from leaf extracts of Semecarpus anacardium, Glochidion lanceolarium, and Bridelia retusa was explored. Continuous synthesis was observed in a UV–vis spectroscopic analysis and the participating phytoconstituents, flavonoids, phenolic compounds, phytosterols, and glycosides, were characterized by Attenuated total reflectance-Fourier transform infrared spectroscopy. The size and surface charge of the particles were also measured by dynamic light scattering spectroscopy. Scanning electron microscopy study was employed to examine the morphology of the nanoparticles. The spectroscopic and microscopic study confirmed the successful synthesis of AgNPs by plant extracts acting as strong reducing agents. The synthesized AgNPs were screened for antibacterial and anti-biofilm activity against human pathogens Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus. Results of the study demonstrate the potential of phyto-synthesized AgNPs to act as anti-biofilm agents and for other biomedical applications.

Antibacterial Liquid Metals: Biofilm Treatment via Magnetic Activation

Antibiotic resistance has made the treatment of biofilm-related infections challenging. As such, the quest for next-generation antimicrobial technologies must focus on targeted therapies to which pathogenic bacteria cannot develop resistance. Stimuli-responsive therapies represent an alternative technological focus due to their capability of delivering targeted treatment. This study provides a proof-of-concept investigation into the use of magneto-responsive gallium-based liquid metal (LM) droplets as antibacterial materials, which can physically damage, disintegrate, and kill pathogens within a mature biofilm. Once exposed to a low-intensity rotating magnetic field, the LM droplets become physically actuated and transform their shape, developing sharp edges. When placed in contact with a bacterial biofilm, the movement of the particles resulting from the magnetic field, coupled with the presence of nanosharp edges, physically ruptures the bacterial cells and the dense biofilm matrix is broken down. The antibacterial efficacy of the magnetically activated LM particles was assessed against both Gram-positive and Gram-negative bacterial biofilms. After 90 min over 99% of both bacterial species became nonviable, and the destruction of the biofilms was observed. These results will impact the design of next-generation, LM-based biofilm treatments.

Facile Route of Fabricating Long-Term Microbicidal Silver Nanoparticle Clusters against Shiga Toxin-Producing Escherichia coli O157:H7 and Candida auris

Microbial contamination remains a significant issue for many industrial, commercial, and medical applications. For instance, microbial surface contamination is detrimental to numerous aspects of food production, infection transfer, and even marine applications. As such, intense scientific interest has focused on improving the antimicrobial properties of surface coatings via both chemical and physical routes. However, there is a lack of synthetic coatings that possess long-term microbiocidal performance. In this study, silver nanoparticle cluster coatings were developed on copper surfaces via an ion-exchange and reduction reaction, followed by a silanization step. The durability of the microbiocidal activity for these develped surfaces was tested against pathogenic bacterial and fungal species, specifically Escherichia coli O157:H7 and Candida auris, over periods of 1- and 7-days. It was observed that more than 90% of E. coli and C. auris were found to be non-viable following the extended exposure times. This facile material fabrication presents as a new surface design for the production of durable microbicidal coatings which can be applied to numerous applications.

Polymerization-Induced Phase Segregation and Self-Assembly of Siloxane Additives to Provide Thermoset Coatings with a Defined Surface Topology and Biocidal and Self-Cleaning Properties

In this work, we report on the incorporation of a siloxane copolymer additive, poly((2-phenylethyl) methylsiloxane)-co(1-phenylethyl) methylsiloxane)-co-dimethylsiloxane), which is fully soluble at room temperature, in a rapid-cure thermoset polyester coating formulation. The additive undergoes polymerization-induced phase segregation (PIPS) to self-assemble on the coating surface as discrete discoid nanofeatures during the resin cure process. Moreover, the copolymer facilitates surface co-segregation of titanium dioxide pigment microparticulate present in the coating. Depending on the composition, the coatings can display persistent superhydrophobicity and self-cleaning properties and, surprisingly, the titanium dioxide pigmented coatings that include the siloxane copolymer additive display high levels of antibacterial performance against Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa) bacteria. This antibacterial performance is believed to be associated with the unique surface topology of these coatings, which comprise stimuli-responsive discoid nanofeatures. This paper provides details of the surface morphology of the coatings and how these relates to the antimicrobial properties of the coating.