Harnessing ultrasound-stimulated phase change contrast agents to improve antibiotic efficacy against methicillin-resistant Staphylococcus aureus biofilms

Nanoparticle-Based Strategies for Managing Biofilm Infections in Wounds: A Comprehensive Review

Chronic wounds containing opportunistic bacterial pathogens are a growing problem, as they are the primary cause of morbidity and mortality in developing and developed nations. Bacteria can adhere to almost every surface, forming architecturally complex communities called biofilms that are tolerant to an individual's immune response and traditional treatments. Wound dressings are a primary source and potential treatment avenue for biofilm infections, and research has recently focused on using nanoparticles with antimicrobial activity for infection control. This Review categorizes nanoparticle-based approaches into four main types, each leveraging unique mechanisms against biofilms. Metallic nanoparticles, such as silver and copper, show promising data due to their ability to disrupt bacterial cell membranes and induce oxidative stress, although their effectiveness can vary based on particle size and composition. Phototherapy-based nanoparticles, utilizing either photodynamic or photothermal therapy, offer targeted microbial destruction by generating reactive oxygen species or localized heat, respectively. However, their efficacy depends on the presence of light and oxygen, potentially limiting their use in deeper or more shielded biofilms. Nanoparticles designed to disrupt extracellular polymeric substances directly target the biofilm structure, enhancing the penetration and efficacy of antimicrobial agents. Lastly, nanoparticles that induce biofilm dispersion represent a novel strategy, aiming to weaken the biofilm's defense and restore susceptibility to antimicrobials. While each method has its advantages, the selection of an appropriate nanoparticle-based treatment depends on the specific requirements of the wound environment and the type of biofilm involved. The integration of these nanoparticles into wound dressings not only promises enhanced treatment outcomes but also offers a reduction in the overall use of antibiotics, aligning with the urgent need for innovative solutions in the fight against antibiotic-tolerant infections. The overarching objective of employing these diverse nanoparticle strategies is to replace antibiotics or substantially reduce their required dosages, providing promising avenues for biofilm infection management.

Fighting fibrin with fibrin: Vancomycin delivery into coagulase-mediated Staphylococcus aureus biofilms via fibrin-based nanoparticle binding

Staphylococcus aureus skin and soft tissue infection is a common ailment placing a large burden upon global healthcare infrastructure. These bacteria are growing increasingly recalcitrant to frontline antimicrobial therapeutics like vancomycin due to the prevalence of variant populations such as methicillin-resistant and vancomycin-resistant strains, and there is currently a dearth of novel antibiotics in production. Additionally, S. aureus has the capacity to hijack the host clotting machinery to generate fibrin-based biofilms that confer protection from host antimicrobial mechanisms and antibiotic-based therapies, enabling immune system evasion and significantly reducing antimicrobial efficacy. Emphasis is being placed on improving the effectiveness of therapeutics that are already commercially available through various means. Fibrin-based nanoparticles (FBNs) were developed and found to interact with S. aureus through the clumping factor A (ClfA) fibrinogen receptor and directly integrate into the biofilm matrix. FBNs loaded with antimicrobials such as vancomycin enabled a targeted and sustained release of antibiotic that increased drug contact time and reduced the therapeutic dose required for eradicating the bacteria, both in vitro and in vivo. Collectively, these findings suggest that FBN-antibiotic delivery may be a novel and potent therapeutic tool for the treatment of S. aureus biofilm infections.

Life at the interface: Engineering bio-nanomaterials through interfacial molecular self-assembly

Interfacial self-assembly describes the directed organization of molecules and colloids at phase boundaries. Believed to be fundamental to the inception of primordial life, interfacial assembly is exploited by a myriad of eukaryotic and prokaryotic organisms to execute physiologic activities and maintain homeostasis. Inspired by these natural systems, chemists, engineers, and materials scientists have sought to harness the thermodynamic equilibria at phase boundaries to create multi-dimensional, highly ordered, and functional nanomaterials. Recent advances in our understanding of the biophysical principles guiding molecular assembly at gas-solid, gas-liquid, solid-liquid, and liquid-liquid interphases have enhanced the rational design of functional bio-nanomaterials, particularly in the fields of biosensing, bioimaging and biotherapy. Continued development of non-canonical building blocks, paired with deeper mechanistic insights into interphase self-assembly, holds promise to yield next generation interfacial bio-nanomaterials with unique, and perhaps yet unrealized, properties. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Emerging Technologies.

pH-responsive polymeric nanomaterials for the treatment of oral biofilm infections

Bacterial and fungal pathogens forming oral biofilms present significant public health challenges due to the failure of antimicrobial drugs. The ability of biofilms to lower pH levels results in dental plaque, leading to gingivitis and cavities. Nanoparticles (NPs) have attracted considerable interest for drug delivery and, thus, as a solution to biofilm-related microbial infections. A novel strategy in this regard involves using pH-responsive polymeric NPs within the acidic microenvironment of oral biofilms. The acidity of the oral biofilm microenvironment is governed by carbohydrate metabolism, accumulation of lactic acid, and extracellular DNA of extracellular polymeric substances by oral biofilm-forming microbial pathogens. This acidity also provides an opportunity to enhance antibacterial activity against biofilm cells using pH-responsive drug delivery approaches. Thus, various polymeric NPs loaded with poorly soluble drugs and responsive to the acidic pH of oral biofilms have been developed. This review focuses on various forms of such polymeric NPs loaded with drugs. The fundamental mechanisms of action of pH-responsive polymeric NPs, their cytological toxicity, and in vivo efficacy testing are thoroughly discussed.

Biofilm modifiers: The disparity in paradigm of oral biofilm ecosystem

A biofilm is a population of sessile microorganisms that has a distinct organized structure and characteristics like channels and projections. Good oral hygiene and reduction in the prevalence of periodontal diseases arise from minimal biofilm accumulation in the mouth, however, studies focusing on modifying the ecology of oral biofilms have not yet been consistently effective. The self-produced matrix of extracellular polymeric substances and greater antibiotic resistance make it difficult to target and eliminate biofilm infections, which lead to serious clinical consequences that are often lethal. Therefore, a better understanding is required to target and modify the ecology of biofilms in order to eradicate the infection, not only in instances of oral disorders but also in terms of nosocomial infections. The review focuses on several biofilm ecology modifiers to prevent biofilm infections, as well as the involvement of biofilm in antibiotic resistance, implants or in-dwelling device contamination, dental caries, and other periodontal disorders. It also discusses recent advances in nanotechnology that may lead to novel strategies for preventing and treating infections caused by biofilms as well as a novel outlook to infection control.

Durable and rechargeable antimicrobial cotton driven by enhanced UV stability and real-time detection of biocidal factors

In this study, graphene oxide/N-halamine nanocomposite was synthesized through Pickering miniemulsion polymerization, which was then coated on cotton surface. The modified cotton exhibited excellent superhydrophobicity, which could effectively prevent microbial infestation and reduce the probability of hydrolysis of active chlorine, with virtually no active chlorine released in water after 72 h. Deposition of reduced graphene oxide nanosheets endowed cotton with ultraviolet-blocking properties, attributing to enhanced UV adsorption and long UV paths. Moreover, encapsulation of polymeric N-halamine resulted in improved UV stability, thus extending the life of N-halamine-based agents. After 24 h of irradiation, 85 % of original biocidal component (active chlorine content) was retained, and approximately 97 % of initial chlorine could be regenerated. Modified cotton has been proven to be an effective oxidizing material against organic pollutants and a potential antimicrobial substance. Inoculated bacteria were completely killed after 1 and 10 min of contact time, respectively. An innovative and simple scheme for determination of active chlorine content was also devised, and real-time inspection of bactericidal activity could be achieved to assure antimicrobial sustainability. Moreover, this method could be utilized to evaluate hazard classification of microbial contamination in different locations, thus broadening the application scope of N-halamine-based cotton fabrics.

Overcoming biological barriers to improve treatment of a Staphylococcus aureus wound infection

Chronic wounds frequently become infected with bacterial biofilms which respond poorly to antibiotic therapy. Aminoglycoside antibiotics are ineffective at treating deep-seated wound infections due to poor drug penetration, poor drug uptake into persister cells, and widespread antibiotic resistance. In this study, we combat the two major barriers to successful aminoglycoside treatment against a biofilm-infected wound: limited antibiotic uptake and limited biofilm penetration. To combat the limited antibiotic uptake, we employ palmitoleic acid, a host-produced monounsaturated fatty acid that perturbs the membrane of gram-positive pathogens and induces gentamicin uptake. This novel drug combination overcomes gentamicin tolerance and resistance in multiple gram-positive wound pathogens. To combat biofilm penetration, we examined the ability of sonobactericide, a non-invasive ultrasound-mediated-drug delivery technology to improve antibiotic efficacy using an in vivo biofilm model. This dual approach dramatically improved antibiotic efficacy against a methicillin-resistant Staphylococcus aureus (MRSA) wound infection in diabetic mice.

Microbubble cavitation restores Staphylococcus aureus antibiotic susceptibility in vitro and in a septic arthritis model

Treatment failure in joint infections is associated with fibrinous, antibiotic-resistant, floating and tissue-associated Staphylococcus aureus aggregates formed in synovial fluid (SynF). We explore whether antibiotic activity could be increased against Staphylococcus aureus aggregates using ultrasound-triggered microbubble destruction (UTMD), in vitro and in a porcine model of septic arthritis. In vitro, when bacterially laden SynF is diluted, akin to the dilution achieved clinically with lavage and local injection of antibiotics, amikacin and ultrasound application result in increased bacterial metabolism, aggregate permeabilization, and a 4-5 log decrease in colony forming units, independent of microbubble destruction. Without SynF dilution, amikacin + UTMD does not increase antibiotic activity. Importantly, in the porcine model of septic arthritis, no bacteria are recovered from the SynF after treatment with amikacin and UTMD-ultrasound without UTMD is insufficient. Our data suggest that UTMD + antibiotics may serve as an important adjunct for the treatment of septic arthritis.

Interactions between Macrophages and Biofilm during Staphylococcus aureus-Associated Implant Infection: Difficulties and Solutions

Staphylococcus aureus (S. aureus) biofilm is the major cause of failure of implant infection treatment that results in heavy social and economic burden on individuals, families, and communities. Planktonic S. aureus attaches to medical implant surfaces where it proliferates and is wrapped by extracellular polymeric substances, forming a solid and complex biofilm. This provides a stable environment for bacterial growth, infection maintenance, and diffusion and protects the bacteria from antimicrobial agents and the immune system of the host. Macrophages are an important component of the innate immune system and resist pathogen invasion and infection through phagocytosis, antigen presentation, and cytokine secretion. The persistence, spread, or clearance of infection is determined by interplay between macrophages and S. aureus in the implant infection microenvironment. In this review, we discuss the interactions between S. aureus biofilm and macrophages, including the effects of biofilm-related bacteria on the macrophage immune response, roles of myeloid-derived suppressor cells during biofilm infection, regulation of immune cell metabolic patterns by the biofilm environment, and immune evasion strategies adopted by the biofilm against macrophages. Finally, we summarize the current methods that support macrophage-mediated removal of biofilms and emphasize the importance of considering multi-dimensions and factors related to implant-associated infection such as immunity, metabolism, the host, and the pathogen when developing new treatments.

Realizing Both Antibacterial Activity and Cytocompatibility in Silicocarnotite Bioceramic via Germanium Incorporation

The treatment of infective or potentially infectious bone defects is a critical problem in the orthopedic clinic. Since bacterial activity and cytocompatibility are always contrary factors, it is hard to have them both in one material. The development of bioactive materials with a good bacterial character and without sacrificing biocompatibility and osteogenic activity, is an interesting and valuable research topic. In the present work, the antimicrobial characteristic of germanium, GeO2 was used to enhance the antibacterial properties of silicocarnotite (Ca5(PO4)2SiO4, CPS). In addition, its cytocompatibility was also investigated. The results demonstrated that Ge–CPS can effectively inhibit the proliferation of both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), and it showed no cytotoxicity to rat bone marrow-derived mesenchymal stem cells (rBMSCs). In addition, as the bioceramic degraded, a sustainable release of germanium could be achieved, ensuring long-term antibacterial activity. The results indicated that Ge–CPS has excellent antibacterial activity compared with pure CPS, while no obvious cytotoxicity was observed, which could make it a promising candidate for the bone repair of infected bone defects.

Regulation of Staphylococcus aureus Virulence and Application of Nanotherapeutics to Eradicate S. aureus Infection

Staphylococcus aureus is a versatile pathogen known to cause hospital- and community-acquired, foodborne, and zoonotic infections. The clinical infections by S. aureus cause an increase in morbidity and mortality rates and treatment costs, aggravated by the emergence of drug-resistant strains. As a multi-faceted pathogen, it is imperative to consolidate the knowledge on its pathogenesis, including the mechanisms of virulence regulation, development of antimicrobial resistance, and biofilm formation, to make it amenable to different treatment strategies. Nanomaterials provide a suitable platform to address this challenge, with the potential to control intracellular parasitism and multidrug resistance where conventional therapies show limited efficacy. In a nutshell, the first part of this review focuses on the impact of S. aureus on human health and the role of virulence factors and biofilms during pathogenesis. The second part discusses the large diversity of nanoparticles and their applications in controlling S. aureus infections, including combination with antibiotics and phytochemicals and the incorporation of antimicrobial coatings for biomaterials. Finally, the limitations and prospects using nanomaterials are highlighted, aiming to foster the development of novel nanotechnology-driven therapies against multidrug-resistant S. aureus.

Ultrasound-Activatable Phase-Shift Nanoparticle as a Targeting Antibacterial Agent for Efficient Eradication of Pseudomonas aeruginosa Biofilms

Biofilms are physical barriers composed of extracellular polymeric substances (EPS) that enable planktonic bacteria to resist host responses and antibacterial treatments, complicating efforts to clear bacteria such as Pseudomonas aeruginosa (P. aeruginosa) and thereby contributing to persistently chronic infections. As such, it is critical to develop a robust antimicrobial strategy capable of effectively eradicating P. aeruginosa biofilms and to further address aggressive clinical infection. In this study, ultrasound-activatable targeted nanoparticles were designed by using poly(lactic-co-glycolic acid) (PLGA) nanoparticles to encapsulate phase-transformable perfluoropentane (PFP) and the antibiotic meropenem via a double emulsion approach, followed by conjugation with anti-P. aeruginosa antibodies. In this strategy, ultrasound exposure can trigger PFP to produce microbubbles, inducing ultrasonic cavitation effects that can disrupt EPS components and allow nanoparticles to release meropenem to kill P. aeruginosa directly and accelerate the associated wound healing. These nanoparticles eradicated biofilms effectively and cleared bacteria in vitro as well as exhibited potent anti-infective activity in vivo. In summary, this study demonstrates the efficacy of a sonobactericidal strategy as a means of effectively and reliably eliminating biofilms.

Shockwaves Increase In Vitro Resilience of Rhizopus oryzae Biofilm under Amphotericin B Treatment

Acoustical biophysical therapies, including ultrasound, radial pressure waves, and shockwaves, have been shown to harbor both a destructive and regenerative potential depending on physical treatment parameters. Despite the clinical relevance of fungal biofilms, little work exits comparing the efficacy of these modalities on the destruction of fungal biofilms. This study evaluates the impact of acoustical low-frequency ultrasound, radial pressure waves, and shockwaves on the viability and proliferation of in vitro Rhizopus oryzae biofilm under Amphotericin B induced apoptosis. In addition, the impact of a fibrin substrate in comparison with a traditional polystyrene well-plate one is explored. We found consistent, mechanically promoted increased Amphotericin B efficacy when treating the biofilm in conjunction with low frequency ultrasound and radial pressure waves. In contrast, shockwave induced effects of mechanotransduction results in a stronger resilience of the biofilm, which was evident by a marked increase in cellular viability, and was not observed in the other types of acoustical pressure waves. Our findings suggest that fungal biofilms not only provide another model for mechanistical investigations of the regenerative properties of shockwave therapies, but warrant future investigations into the clinical viability of the therapy.

Dispersing and Sonoporating Biofilm-Associated Bacteria with Sonobactericide

Bacteria encased in a biofilm poses significant challenges to successful treatment, since both the immune system and antibiotics are ineffective. Sonobactericide, which uses ultrasound and microbubbles, is a potential new strategy for increasing antimicrobial effectiveness or directly killing bacteria. Several studies suggest that sonobactericide can lead to bacterial dispersion or sonoporation (i.e., cell membrane permeabilization); however, real-time observations distinguishing individual bacteria during and directly after insonification are missing. Therefore, in this study, we investigated, in real-time and at high-resolution, the effects of ultrasound-induced microbubble oscillation on Staphylococcus aureus biofilms, without or with an antibiotic (oxacillin, 1 μg/mL). Biofilms were exposed to ultrasound (2 MHz, 100–400 kPa, 100–1000 cycles, every second for 30 s) during time-lapse confocal microscopy recordings of 10 min. Bacterial responses were quantified using post hoc image analysis with particle counting. Bacterial dispersion was observed as the dominant effect over sonoporation, resulting from oscillating microbubbles. Increasing pressure and cycles both led to significantly more dispersion, with the highest pressure leading to the most biofilm removal (up to 83.7%). Antibiotic presence led to more variable treatment responses, yet did not significantly impact the therapeutic efficacy of sonobactericide, suggesting synergism is not an immediate effect. These findings elucidate the direct effects induced by sonobactericide to best utilize its potential as a biofilm treatment strategy.

Ultrasound-Activated Nanodroplet Disruption of the Enterococcus faecalis Biofilm in Dental Root Canal

Conventional methods used to control bacterial biofilm infection in root canals have poor efficacy, causing repeated and chronic infections, which pose a great challenge to clinical treatment. Microbubbles, due to their small size and ultrasound (US)-enhanced cavitation effects, have attracted considerable clinical attention. They possess the potential for therapeutic application in restricted spaces. We address the above problem with a strategy for the restricted space of root canals. Herein, phase-change nanodroplets (P-NDs) exposed to US are combined with common antibacterial drugs to disrupt a 7 day Enterococcus faecalis biofilm in an in vitro human tooth model. Specifically, the preparation of P-NDs is based on secondary cavitation. Their average particle size is ∼144 nm, and the stability is favorable. The clearance effect for the biofilm is notable (the disruption rate of P-NDs + US is 63.1%, P < 0.01), while the effect of an antibacterial in conjunction with 2% chlorhexidine (Chx) is significant (the antibiofilm rate of P-NDs@2% Chx + US is 96.2%, P < 0.001). Furthermore, biocompatibility testing on human periodontal ligament fibroblasts demonstrated that P-NDs are safe. In summary, the strategy that we have proposed is suitable for the removal of biofilms in root canals. Notably, it also has great potential for application in the treatment of bacterial infections in restricted spaces.

Making waves: how ultrasound-targeted drug delivery is changing pharmaceutical approaches

Administration of drugs through oral and intravenous routes is a mainstay of modern medicine, but this approach suffers from limitations associated with off-target side effects and narrow therapeutic windows. It is often apparent that a controlled delivery of drugs, either localized to a specific site or during a specific time, can increase efficacy and bypass problems with systemic toxicity and insufficient local availability. To overcome some of these issues, local delivery systems have been devised, but most are still restricted in terms of elution kinetics, duration, and temporal control. Ultrasound-targeted drug delivery offers a powerful approach to increase delivery, therapeutic efficacy, and temporal release of drugs ranging from chemotherapeutics to antibiotics. The use of ultrasound can focus on increasing tissue sensitivity to the drug or actually be a critical component of the drug delivery. The high spatial and temporal resolution of ultrasound enables precise location, targeting, and timing of drug delivery and tissue sensitization. Thus, this noninvasive, non-ionizing, and relatively inexpensive modality makes the implementation of ultrasound-mediated drug delivery a powerful method that can be readily translated into the clinical arena. This review covers key concepts and areas applied in the design of different ultrasound-mediated drug delivery systems across a variety of clinical applications.

Biofilms in Surgical Site Infections: Recent Advances and Novel Prevention and Eradication Strategies

Surgical site infections (SSIs) are common postoperative occurrences due to contamination of the surgical wound or implanted medical devices with community or hospital-acquired microorganisms, as well as other endogenous opportunistic microbes. Despite numerous rules and guidelines applied to prevent these infections, SSI rates are considerably high, constituting a threat to the healthcare system in terms of morbidity, prolonged hospitalization, and death. Approximately 80% of human SSIs, including chronic wound infections, are related to biofilm-forming bacteria. Biofilm-associated SSIs are extremely difficult to treat with conventional antibiotics due to several tolerance mechanisms provided by the multidrug-resistant bacteria, usually arranged as polymicrobial communities. In this review, novel strategies to control, i.e., prevent and eradicate, biofilms in SSIs are presented and discussed, focusing mainly on two attractive approaches: the use of nanotechnology-based composites and natural plant-based products. An overview of new therapeutic agents and strategic approaches to control epidemic multidrug-resistant pathogenic microorganisms, particularly when biofilms are present, is provided alongside other combinatorial approaches as attempts to obtain synergistic effects with conventional antibiotics and restore their efficacy to treat biofilm-mediated SSIs. Some detection and real-time monitoring systems to improve biofilm control strategies and diagnosis of human infections are also discussed.