Effect of magnetic hyperthermia on the structure of biofilm and cellular viability of a food spoilage bacterium

An integrated preventive and therapeutic magnetic nanoparticle loaded with rhamnolipid and vancomycin for combating subgingival biofilms

OBJECTIVES

Mechanical debridement supplemented with antibacterial agents effectively eradicates subgingival biofilms formed in the periodontal pockets of severe periodontitis patients. However, the available antimicrobial agents have limited penetrating ability to kill the bacteria encased in the deep layers of biofilms. This study aimed to fabricate a novel magnetic nanoparticle (MNP) loaded with rhamnolipid (RL) and vancomycin (Vanc, Vanc/RL-Ag@Fe3O4) to combat subgingival biofilms.

METHODS

The multispecies subgingival biofilm was formed by periodontal pathogens, including Streptococcus oralis (S. oralis), Streptococcus sanguinis (S. sanguinis), Actinomyces naeslundii (A. naeslundii), Porphyromonas gingivalis (P. gingivalis) and Fusobacterium nucleatum (F. nucleatum). Scanning electron microscope (SEM), confocal laser scanning microscopy (CLSM), and quantitative real-time polymerase chain reaction (qRT-PCR) were used to determine the anti-biofilm efficacy of Vanc/RL-Ag@Fe3O4 with or without a magnetic field on multispecies subgingival biofilms.

RESULTS

The minimal inhibitory concentration (MIC) values of Vanc/RL-Ag@Fe3O4 on S. oralis, S. sanguinis, A. naeslundii, P. gingivalis, and F. nucleatum were 25, 50, 100, 50, and 25 μg/mL, respectively. Vanc/RL-Ag@Fe3O4 (200 μg/mL) reduced the 7-d biofilm thickness from 22 to 13 µm by degrading extracellular polymeric substance (EPS) and killing most bacteria except for tolerant F. nucleatum. A magnetic field enhanced the anti-biofilm effect of Vanc/RL-Ag@Fe3O4 by facilitating its penetration into the bottom layers of biofilms and killing tolerant F. nucleatum.

SIGNIFICANCE

Vanc/RL-Ag@Fe3O4 MNPs can release RL, Vanc, and Ag and eradicate subgingival biofilms by disrupting EPS and killing bacteria. Vanc/RL-Ag@Fe3O4 combined with a magnetic force is a promising approach for combating periodontal infection.

Magnetic Iron Oxide Nanoparticles Coated by Coumarin-Bound Copolymer for Enhanced Magneto- and Photothermal Heating and Luminescent Thermometry

In this work, we report on the synthesis and investigation of new hybrid multifunctional iron oxide nanoparticles (IONPs) coated by coumarin-bound copolymer, which combine magneto- or photothermal heating with luminescent thermometry. A series of amphiphilic block copolymers, including Coum-C11-PPhOx27-PMOx59 and Coum-C11-PButOx8-PMOx42 bearing luminescent and photodimerizable coumarin moiety, as well as coumarin-free PPhOx27-PMOx57, were evaluated for their utility as luminescent thermometers and for encapsulating spherical 26 nm IONPs. The obtained IONP@Coum-C11-PPhOx27-PMOx59 nano-objects are perfectly dispersible in water and able to provide macroscopic heating remotely triggered by an alternating current magnetic field (AMF) with a specific absorption rate (SAR) value of 240 W.g-1 or laser irradiation with a photothermal conversion efficiency of η = 68%. On the other hand, they exhibit temperature-dependent emission of coumarin offering the function of luminescent thermometer, which operates in the visible region between 20 °C and 60 °C in water displaying a maximal relative thermal sensitivity (Sr) of 1.53%·°C-1 at 60 °C.

Nano-Bio Interactions: Biofilm-Targeted Antibacterial Nanomaterials

Biofilm is a spatially organized community formed by the accumulation of both microorganisms and their secretions, leading to persistent and chronic infections because of high resistance toward conventional antibiotics. In view of the tunable physicochemical properties and the related unique biological behavior (e.g., size-, shape-, and surface charge-dependent penetration, protein corona endowed targeting, catalytic- and electronic-related oxidative stress, optical- and magnetic-associated hyperthermia, etc.), nanomaterials-based therapeutics are widely used for the treatment of biofilm-associated infections. In this review, the biological characteristics of biofilm are introduced. And the nanomaterials-based antibacterial strategies are further discussed via biofilm targeting, including preventing biofilm formation, enhancing biofilm penetration, disrupting the mature biofilm, and acting as drug delivery systems. In which, the interactions between biofilm and nanomaterials include mechanical disruption, electron transfer, enzymatic degradation, oxidative stress, and hyperthermia. Additionally, the current advances of nanomaterials for antibacterial nanomaterials by biofilm targeting are summarized. This review aims to present a complete vision of antibacterial nanomaterials-biofilm (nano-bio) interactions, paving the way for the future development and clinical translation of effective antibacterial nanomedicines.

A review of mechanism analysis methods in multi-species biofilm of foodborne pathogens

Biofilms are an aggregation of microorganisms that have high resistance to antimicrobial agents. In the food industry, it has been widely studied that foodborne pathogens on both food surfaces and food-contact surfaces can form biofilms thereby threatening the safety of the food. In the natural environment, multi-species biofilms formed by more than two different microorganisms are abundant. In addition, the resistance of multi-species biofilms to antimicrobial agents is higher than that of mono-species biofilms. Therefore, studies to elucidate the mechanisms of multi-species biofilms formed by foodborne pathogens are still required in the food industry. In this review paper, we summarized the novel analytical methods studied to evaluate the mechanisms of multi-species biofilms formed by foodborne pathogens by dividing them into four categories: spatial distribution, bacterial interaction, extracellular polymeric substance production and quorum sensing analytical methods.

The Determination, Monitoring, Molecular Mechanisms and Formation of Biofilm in E. coli

Biofilms are cell assemblies embedded in an exopolysaccharide matrix formed by microorganisms of a single or many different species. This matrix in which they are embedded protects the bacteria from external influences and antimicrobial effects. The biofilm structure that microorganisms form to protect themselves from harsh environmental conditions and survive is found in nature in many different environments. These environments where biofilm formation occurs have in common that they are in contact with fluids. The gene expression of bacteria in complex biofilm differs from that of bacteria in the planktonic state. The differences in biofilm cell expression are one of the effects of community life. Means of quorum sensing, bacteria can act in coordination with each other. At the same time, while biofilm formation provides many benefits to bacteria, it has positive and negative effects in many different areas. Depending on where they occur, biofilms can cause serious health problems, contamination risks, corrosion, and heat and efficiency losses. However, they can also be used in water treatment plants, bioremediation, and energy production with microbial fuel cells. In this review, the basic steps of biofilm formation and biofilm regulation in the model organism Escherichia coli were discussed. Finally, the methods by which biofilm formation can be detected and monitored were briefly discussed.

Application of Iron Nanoparticle-Based Materials in the Food Industry

Due to their different properties compared to other materials, nanoparticles of iron and iron oxides are increasingly used in the food industry. Food technologists have especially paid attention to their ease of separation by magnetic fields and biocompatibility. Unfortunately, the consumption of increasing amounts of nanoparticles has raised concerns about their biotoxicity. Hence, knowledge about the applicability of iron nanoparticle-based materials in the food industry is needed not only among scientists, but also among all individuals who are involved in food production. The first part of this article describes typical methods of obtaining iron nanoparticles using chemical synthesis and so-called green chemistry. The second part of this article describes the use of iron nanoparticles and iron nanoparticle-based materials for active packaging, including the ability to eliminate oxygen and antimicrobial activity. Then, the possibilities of using the magnetic properties of iron nano-oxides for enzyme immobilization, food analysis, protein purification and mycotoxin and histamine removal from food are described. Other described applications of materials based on iron nanoparticles are the production of artificial enzymes, process control, food fortification and preserving food in a supercooled state. The third part of the article analyzes the biocompatibility of iron nanoparticles, their impact on the human body and the safety of their use.

A PEDOT nano-composite for hyperthermia and elimination of urological bacteria

Novel modalities for overcoming recurrent urinary tract infections associated with indwelling urinary catheters are needed, and rapidly induced hyperthermia is one potential solution. PEDOT nanotubes are a class of photothermal particles that can easily be incorporated into silicone to produce thin, uniform coating on medical grade silicone catheters; subsequent laser stimulation therein imparts temperature elevations that can eliminate bacteria and biofilms. PEDOT silicone coatings are stable following thermal sterilization and repeated heating and cooling cycles. Laser stimulation can induce temperature increases of up to 55 °C in 300 s, but only 45 s was needed for ablation of UTI inducing E. coli biofilms in vitro. This work also demonstrates that mild hyperthermia of 50 °C, applied for only 31 s in the presence of antibiotics could eliminate E. coli biofilm as effectively as high temperatures. This work culminates in the evaluation of the PEDOT NTs for photothermal elimination of E. coli in an in vivo model to demonstrate the safety and effectiveness of a photothermal nanocomposite (16 s treatment time) for rapid clearance of E. coli.

Applications of Antimicrobial Photodynamic Therapy against Bacterial Biofilms

Antimicrobial photodynamic therapy and allied photodynamic antimicrobial chemotherapy have shown remarkable activity against bacterial pathogens in both planktonic and biofilm forms. There has been little or no resistance development against antimicrobial photodynamic therapy. Furthermore, recent developments in therapies that involve antimicrobial photodynamic therapy in combination with photothermal hyperthermia therapy, magnetic hyperthermia therapy, antibiotic chemotherapy and cold atmospheric pressure plasma therapy have shown additive and synergistic enhancement of its efficacy. This paper reviews applications of antimicrobial photodynamic therapy and non-invasive combination therapies often used with it, including sonodynamic therapy and nanozyme enhanced photodynamic therapy. The antimicrobial and antibiofilm mechanisms are discussed. This review proposes that these technologies have a great potential to overcome the bacterial resistance associated with bacterial biofilm formation.

A drug-free strategy to combat bacterial infections with magnetic nanoparticles biosynthesized in bacterial pathogens

The extensive and indiscriminate use of antibiotics in the ongoing COVID-19 pandemic might significantly contribute to the growing number of multiple drug resistant (MDR) bacteria. With the dwindling pipeline of new and effective antibiotics, we might soon end up in a post-antibiotic era, in which even common bacterial infections would be a challenge to control. To prevent this, an antibiotic-free strategy would be highly desirable. Magnetic nanoparticle (MNP)-mediated hyperthermia-induced antimicrobial therapy is an attractive option as it is considered safe for human use. Given that iron and zinc are critical for bacterial virulence, we evaluated the response of multiple pathogenic bacteria to these elements. Treatment with 1 mM iron and zinc precursors resulted in the intracellular biosynthesis of MNPs in multiple Gram-positive and Gram-negative disease-causing bacteria. The superparamagnetic nanoparticles in the treated bacteria/biofilms, generated heat upon exposure to an alternating magnetic field (AMF), which resulted in an increase in the temperature (5-6 °C) of the milieu with a subsequent decrease in bacterial viability. Furthermore, we observed for the first time that virulent bacteria derived from infected samples harbour MNPs, suggesting that the bacteria had biosynthesised the MNPs using the metal ions acquired from the host. AMF treatment of the bacterial isolates from the infected specimens resulted in a strong reduction in viability (3-4 logs) as compared to vancomycin/ciprofloxacin treatment. The therapeutic efficacy of the MNPs to induce bacterial death with AMF alone was confirmed ex vivo using infected tissues. Our proposed antibiotic-free approach for killing bacteria using intracellular MNPs is likely to evolve as a promising strategy to combat a wide range of bacterial infections.

Superparamagnetic Iron Oxide Nanoparticles Decorated Mesoporous Silica Nanosystem for Combined Antibiofilm Therapy

A crucial challenge to face in the treatment of biofilm-associated infection is the ability of bacteria to develop resistance to traditional antimicrobial therapies based on the administration of antibiotics alone. This study aims to apply magnetic hyperthermia together with controlled antibiotic delivery from a unique magnetic-responsive nanocarrier for a combination therapy against biofilm. The design of the nanosystem is based on antibiotic-loaded mesoporous silica nanoparticles (MSNs) externally functionalized with a thermo-responsive polymer capping layer, and decorated in the outermost surface with superparamagnetic iron oxide nanoparticles (SPIONs). The SPIONs are able to generate heat upon application of an alternating magnetic field (AMF), reaching the temperature needed to induce a change in the polymer conformation from linear to globular, therefore triggering pore uncapping and the antibiotic cargo release. The microbiological assays indicated that exposure of E. coli biofilms to 200 µg/mL of the nanosystem and the application of an AMF (202 kHz, 30 mT) decreased the number of viable bacteria by 4 log10 units compared with the control. The results of the present study show that combined hyperthermia and antibiotic treatment is a promising approach for the effective management of biofilm-associated infections.

Microscopy Methods for Biofilm Imaging: Focus on SEM and VP-SEM Pros and Cons

Simple Summary

Bacterial biofilms cause infections that are often resistant to antibiotic treatments. Research about the formation and elimination of biofilms cannot be undertaken without detailed imaging techniques. In this review, traditional and cutting-edge microscopy methods to study biofilm structure, ultrastructure, and 3-D architecture, with particular emphasis on conventional scanning electron microscopy and variable pressure scanning electron microscopy, are addressed, with the respective advantages and disadvantages. When ultrastructural characterization of biofilm matrix and its embedded bacterial cells is needed, as in studies on the effects of drug treatments on biofilm, scanning electron microscopy with customized protocols such as the osmium tetroxide (OsO₄), ruthenium red (RR), tannic acid (TA), and ionic liquid (IL) must be preferred over other methods for the following: unparalleled image quality, magnification and resolution, minimal sample loss, and actual sample structure preservation. The first step to make a morphological assessment of the effect of the various pharmacological treatments on clinical biofilms is the production of images that faithfully reflect the structure of the sample. The extraction of quantitative parameters from images, possible using specific software, will allow for the scanning electron microscopy morphological evaluation to no longer be considered as an accessory technique, but a quantitative method to all effects.

Abstract

Several imaging methodologies have been used in biofilm studies, contributing to deepening the knowledge on their structure. This review illustrates the most widely used microscopy techniques in biofilm investigations, focusing on traditional and innovative scanning electron microscopy techniques such as scanning electron microscopy (SEM), variable pressure SEM (VP-SEM), environmental SEM (ESEM), and the more recent ambiental SEM (ASEM), ending with the cutting edge Cryo-SEM and focused ion beam SEM (FIB SEM), highlighting the pros and cons of several methods with particular emphasis on conventional SEM and VP-SEM. As each technique has its own advantages and disadvantages, the choice of the most appropriate method must be done carefully, based on the specific aim of the study. The evaluation of the drug effects on biofilm requires imaging methods that show the most detailed ultrastructural features of the biofilm. In this kind of research, the use of scanning electron microscopy with customized protocols such as osmium tetroxide (OsO₄), ruthenium red (RR), tannic acid (TA) staining, and ionic liquid (IL) treatment is unrivalled for its image quality, magnification, resolution, minimal sample loss, and actual sample structure preservation. The combined use of innovative SEM protocols and 3-D image analysis software will allow for quantitative data from SEM images to be extracted; in this way, data from images of samples that have undergone different antibiofilm treatments can be compared.

Effective production of multifunctional magnetic-sensitive biomaterial by an extrusion-based additive manufacturing technique

A calcium phosphate (CaP)-based scaffold used as synthetic bone grafts, which smartly combines precise dimensions, controlled porosity and therapeutic functions, presents benefits beyond those offered by conventional practices, although its fabrication is still a challenge. The sintering step normally required to improve the strength of the ceramic scaffolds precludes the addition of any biomolecules or functional particles before this stage. This study presents a proof of concept of multifunctional CaP-based scaffolds, fabricated by additive manufacturing from an innovative ink composition, with potential for bone regeneration, cancer treatment by local magnetic hyperthermia and drug delivery platforms. Highly loaded inks comprising iron-doped hydroxyapatite and β-tricalcium phosphate powders suspended in a chitosan-based solution, in the presence of levofloxacin (LEV) as model drug and magnetic nanoparticles (MNP), were developed. The sintering step was removed from the production process, and the integrity of the printed scaffolds was assured by the polymerization capacity of the ink composite, using genipin as a crosslinking agent. The effects of MNP and LEV on the inks' rheological properties, as well as on the mechanical and structural behaviour of non-doped and iron-doped scaffolds, were evaluated. Magnetic and magneto-thermal response, drug delivery and biological performance, such as cell proliferation in the absence and presence of an applied magnetic field, were also assessed. The addition of a constant amount of MNP in the iron-doped and non-doped CaP-based inks enhances their magnetic response and induction heating, with these effects more pronounced for the iron-doped CaP-based ink. These results suggest a synergistic effect between the iron-doped CaP-based powders and the MNP due to ferro/ferrimagnetic interactions. Furthermore, the iron presence enhances human mesenchymal stem cell metabolic activity and proliferation.

Preparation of AAEK-functionalized cellulose film with antibacterial and anti-adhesion activities

Bacterial adhesion infection caused by medical materials in clinical application has become a serious threat, and it urgently needs new strategies to deal with these clinical challenges. The purpose of this study is to explore the effectiveness of surface-decorated aryl (β-amino) ethyl ketones (AAEK), a promising sorting enzyme A (SrtA) inhibitor of Staphylococcus aureus, to improve the anti-adhesion ability of biomaterials. AAEK was covalently grafted onto cellulose films (CF) via copper-catalyzed azide-alkyne 1, 3-dipolar cycloaddition click reaction. The data of contact angle measurements, ATR-FTIR and XPS proved the successful covalent attachment of AAEK-CF, and the antimicrobial efficacy of AAEK coating was assessed by CFUs, crystal violet staining, scanning electron microscopy and Living/Dead bacteria staining assay. The results illustrated that AAEK-CF exhibited excellent anti-adhesion ability to Staphylococcus aureus, and significantly reduced the number of bacteria adhering to the film. More importantly, AAEK-CF could hinder the formation of bacterial biofilm. Furthermore, AAEK-CF indicated no cytotoxicity to mammalian cells, and the cells could grow normally on the modified surface. Hence, our present work demonstrated that the grafting of the SrtA inhibitor-AAEK onto cellulose films enabled to combat bacterial biofilm formation in biomedical applications.

Mild magnetic nanoparticle hyperthermia enhances the susceptibility of Staphylococcus aureus biofilm to antibiotics

Objective:

A critical challenge in the treatment of biofilm infection is the capacity of biofilm-grown bacteria to develop resistance to traditional antimicrobial therapies. The objective of this study was to validate the therapeutic potential of magnetic nanoparticle/alternating magnetic field (MNP/AMF) hyperthermia in combination with conventional antibiotics against biofilm infection.

Materials and methods:

The impact of MNP/AMF hyperthermia on the viability of S. aureus biofilm in the absence and presence of antibiotics as well as on the bactericidal activity of macrophages were evaluated at varying conditions of MNPs concentration and AMF intensity using in vitro cell culture models.

Results:

The application of MNP/AMF alone at a CEM43 thermal dose below the threshold for skin tissue exhibited a modest efficacy in the eradication of Staphylococcus aureus (S. aureus) biofilm (<1-log reduction). The treatment of antibiotics (ciprofloxacin, vancomycin) alone at a bactericidal concentration for planktonic S. aureus had no significant effect on the eradication of biofilm phase of S. aureus. However, when the biofilm was pre-exposed to mild MNP/AMF hyperthermia, the treatment of antibiotics could exhibit bactericidal effects against S. aureus biofilm, which was associated with increased uptake of antibiotics to the bacterial cells. Importantly, the application of MNP/AMF could promote the bactericidal activity of macrophages against intracellular bacteria via MNP-dependent generation of reactive oxygen species (ROS).

Conclusion:

Our results validate that the application of mild MNP/AMF hyperthermia within a safe thermal dose threshold is synergistic with conventional antibiotics as well as aids host innate immune response of macrophages for the clearance of intracellular bacteria.

Applications of Iron Oxide-Based Magnetic Nanoparticles in the Diagnosis and Treatment of Bacterial Infections

Diseases caused by bacterial infections, especially drug-resistant bacteria have seriously threatened human health throughout the world. It has been predicted that antimicrobial resistance alone will cause 10 million deaths per year and that early diagnosis and therapy will efficiently decrease the mortality rate caused by bacterial infections. Considering this severity, it is urgent to develop effective methods for the early detection, prevention and treatment of these infections. Until now, numerous efforts based on nanoparticles have been made to detect and kill pathogenic bacteria. Iron oxide-based magnetic nanoparticles (MNPs), as potential platforms for bacteria detection and therapy, have drawn great attention owing to their magnetic property. These MNPs have also been broadly used as bioimaging contrast agents and drug delivery and magnetic hyperthermia agents to diagnose and treat bacterial infections. This review therefore overviews the recent progress on MNPs for bacterial detection and therapy, including bacterial separation and enrichment in vitro, bacterial infection imaging in vivo, and their therapeutic activities on pathogenic bacteria. Furthermore, some bacterial-specific targeting agents, used to selectively target the pathogenic bacteria, are also introduced. In addition, the challenges and future perspective of MNPs for bacterial diagnosis and therapy are given at the end of this review. It is expected that this review will provide a better understanding toward the applications of MNPs in the detection and therapy of bacterial infections.

Recent Advances in Non-Conventional Antimicrobial Approaches for Chronic Wound Biofilms: Have We Found the 'Chink in the Armor'?

Chronic wounds are a major healthcare burden, with huge public health and economic impact. Microbial infections are the single most important cause of chronic, non-healing wounds. Chronic wound infections typically form biofilms, which are notoriously recalcitrant to conventional antibiotics. This prompts the need for alternative or adjunct ‘anti-biofilm’ approaches, notably those that account for the unique chronic wound biofilm microenvironment. In this review, we discuss the recent advances in non-conventional antimicrobial approaches for chronic wound biofilms, looking beyond standard antibiotic therapies. These non-conventional strategies are discussed under three groups. The first group focuses on treatment approaches that directly kill or inhibit microbes in chronic wound biofilms, using mechanisms or delivery strategies distinct from antibiotics. The second group discusses antimicrobial approaches that modify the biological, chemical or biophysical parameters in the chronic wound microenvironment, which in turn enables the disruption and removal of biofilms. Finally, therapeutic approaches that affect both, biofilm bacteria and microenvironment factors, are discussed. Understanding the advantages and limitations of these recent approaches, their stage of development and role in biofilm management, could lead to new treatment paradigms for chronic wound infections. Towards this end, we discuss the possibility that non-conventional antimicrobial therapeutics and targets could expose the ‘chink in the armor’ of chronic wound biofilms, thereby providing much-needed alternative or adjunct strategies for wound infection management.

A new tool to attack biofilms: driving magnetic iron-oxide nanoparticles to disrupt the matrix

A main feature of biofilms is the self-produced extracellular polymeric substances (EPSs) that act as a protective shield, preventing biocide penetration. We use magnetic iron oxide nanoparticles (MNPs) in combination with magnetic fields to damage the biofilm matrix and cause detachment. A Methicillin-resistant Staphylococcus aureus (MRSA) biofilm strain is used to demonstrate the efficacy of the methodology with different sizes and concentrations of MNPs under AC and DC applied field conditions. We achieve up to a nearly 5 log10 reduction in biofilm bacteria after treatment with 30 mg mL-1 of 11 nm MNPs using a magnetic field. The MNPs cause significant mechanical disruption to the matrix and lead to biofilm dispersal. In addition, using magnetic hyperthermia further affects biofilm damage.

Evolution of Magnetic Hyperthermia for Glioblastoma Multiforme Therapy

Glioblastoma multiforme (GBM) is the most common and aggressive type of glial tumor, and despite many recent advances, its prognosis remains dismal. Hence, new therapeutic approaches for successful GBM treatment are urgently required. Magnetic hyperthermia-mediated cancer therapy (MHCT), which is based on heating the tumor tissues using magnetic nanoparticles on exposure to an alternating magnetic field (AMF), has shown promising results in the preclinical studies conducted so far. The aim of this Review is to evaluate the progression of MHCT for GBM treatment and to determine its effectiveness on the treatment either alone or in combination with other adjuvant therapies. The preclinical studies presented MHCT as an effective treatment module for the reduction of tumor cell growth and increase in survival of the tumor models used. Over the years, much research has been done to prove MHCT alone as the missing notch for successful GBM therapy. However, very few combinatorial studies have been reported. Some of the clinical studies carried out so far depicted that MHCT could be applied safely while possessing minimal side effects. Finally, we believe that, in the future, advancements in magnetic nanosystems might contribute toward establishing MHCT as a potential treatment tool for glioma therapy.

Magnetic Glycol Chitin-Based Hydrogel Nanocomposite for Combined Thermal and d-Amino-Acid-Assisted Biofilm Disruption

Bacterial biofilms are highly antibiotic resistant microbial cell associations that lead to chronic infections. Unlike free-floating planktonic bacterial cells, the biofilms are encapsulated in a hardly penetrable extracellular polymeric matrix and, thus, demand innovative approaches for treatment. Recent advancements on the development of gel-nanocomposite systems with tailored therapeutic properties provide promising routes to develop novel antimicrobial agents that can be designed to disrupt and completely eradicate preformed biofilms. In our study, we developed a unique thermoresponsive magnetic glycol chitin-based nanocomposite containing d-amino acids and iron oxide nanoparticles, which can be delivered and undergoes transformation from a solution to a gel state at physiological temperature for sustained release of d-amino acids and magnetic field actuated thermal treatment of targeted infection sites. The d-amino acids in the hydrogel nanocomposite have been previously reported to inhibit biofilm formation and also disrupt existing biofilms. In addition, loading the hydrogel nanocomposite with magnetic nanoparticles allows for combination thermal treatment following magnetic field (magnetic hyperthermia) stimulation. Using this novel two-step approach to utilize an externally actuated gel-nanocomposite system for thermal treatment, following initial disruption with d-amino acids, we were able to demonstrate in vitro the total eradication of Staphylococcus aureus biofilms, which were resistant to conventional antibiotics and were not completely eradicated by separate d-amino acid or magnetic hyperthermia treatments.

Advances in Magnetic Nanoparticles for Biomedical Applications

Magnetic nanoparticles (NPs) are emerging as an important class of biomedical functional nanomaterials in areas such as hyperthermia, drug release, tissue engineering, theranostic, and lab-on-a-chip, due to their exclusive chemical and physical properties. Although some works can be found reviewing the main application of magnetic NPs in the area of biomedical engineering, recent and intense progress on magnetic nanoparticle research, from synthesis to surface functionalization strategies, demands for a work that includes, summarizes, and debates current directions and ongoing advancements in this research field. Thus, the present work addresses the structure, synthesis, properties, and the incorporation of magnetic NPs in nanocomposites, highlighting the most relevant effects of the synthesis on the magnetic and structural properties of the magnetic NPs and how these effects limit their utilization in the biomedical area. Furthermore, this review next focuses on the application of magnetic NPs on the biomedical field. Finally, a discussion of the main challenges and an outlook of the future developments in the use of magnetic NPs for advanced biomedical applications are critically provided.

Critical review on biofilm methods

Biofilms are widespread in nature and constitute an important strategy implemented by microorganisms to survive in sometimes harsh environmental conditions. They can be beneficial or have a negative impact particularly when formed in industrial settings or on medical devices. As such, research into the formation and elimination of biofilms is important for many disciplines. Several new methodologies have been recently developed for, or adapted to, biofilm studies that have contributed to deeper knowledge on biofilm physiology, structure and composition. In this review, traditional and cutting-edge methods to study biofilm biomass, viability, structure, composition and physiology are addressed. Moreover, as there is a lack of consensus among the diversity of techniques used to grow and study biofilms. This review intends to remedy this, by giving a critical perspective, highlighting the advantages and limitations of several methods. Accordingly, this review aims at helping scientists in finding the most appropriate and up-to-date methods to study their biofilms.

Magnetically-induced elimination of Staphylococcus aureus by magnetotactic bacteria under a swing magnetic field

This study aims to explore a therapeutic tool that kills pathogens by using mechanical force other than temperature. We fabricated a device that generates a swing magnetic field (sMF) with low-heat production and then evaluated the killing effect of magnetotactic bacteria MO-1 on Staphylococcus aureus (S. aureus) under the sMF. S. aureus was only killed under the sMF when attached to MO-1 cells. The killing efficiency increased with increasing attachment ratio of MO-1 cells to S. aureus. Treatment with antibody-coated MO-1 cells under the sMF improved the healing of S. aureus-infected wound. The theoretical analysis demonstrated that MO-1 cells generated a mechanical force of approximately 8kPa under the sMF, thereby exerting on S. aureus and inducing cell death. The proposed platform, which uses magnetotactic bacteria under the sMF to generate mechanical force, provides a basis for development of therapeutic tools to treat infectious diseases.

Analytical protocols for separation and electron microscopy of nanoparticles interacting with bacterial cells

An important step toward understanding interactions between nanoparticles (NPs) and bacteria is the ability to directly observe NPs interacting with bacterial cells. NP-bacteria mixtures typical in nanomedicine, however, are not yet amendable for direct imaging in solution. Instead, evidence of NP-cell interactions must be preserved in derivative (usually dried) samples to be subsequently revealed in high-resolution images, for example, via scanning electron microscopy (SEM). Here, this concept is realized for a mixed suspension of model NPs and Staphylococcus aureus bacteria. First, protocols for analyzing the relative colloidal stabilities of NPs and bacteria are developed and validated based on systematic centrifugation and comparison of colony forming unit (CFU) counting and optical density (OD) measurements. Rate-dependence of centrifugation efficiency for each component suggests differential sedimentation at a specific predicted rate as an effective method for removing free NPs after co-incubation; the remaining fraction comprises bacteria with any associated NPs and can be examined, for example, by SEM, for evidence of NP-bacteria interactions. These analytical protocols, validated by systematic control experiments and high-resolution SEM imaging, should be generally applicable for investigating NP-bacteria interactions.