Nitric oxide-releasing polyacrylonitrile disperses biofilms formed by wound-relevant pathogenic bacteria

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.

Enhanced antibacterial efficacy against antibiotic-resistant bacteria via nitric oxide-releasing ampicillin polymer substrates

The emergence of antibiotic-resistant bacteria poses a pressing threat to global health and is a leading cause of healthcare-related morbidity and mortality. Herein, we report the fabrication of medical-grade polymers incorporated with a dual-action S-nitroso-N-acetylpenicillamine-functionalized ampicillin (SNAPicillin) conjugated molecule through a solvent evaporation process. The resulting SNAPicillin-incorporated polymer materials act as broad-spectrum antibacterial surfaces that improve the administration efficacy of conventional antibiotics through the targeted release of both nitric oxide and ampicillin. The polymer surfaces were characterized by scanning electron microscopy and static contact angle measurements. The nitric oxide (NO) release profile and diffusion of SNAPicillin from polymers were quantified using a chemiluminescence-based nitric oxide analyzer (NOA) and ultraviolet-visible (UV-vis) spectroscopy. As a result, the films had up to 2.96 × 10-7 mol cm-2 of total NO released within 24 hr. In addition, >79 % of the SNAPicillin reservoir was preserved in the polymers after 24 hr of incubation in the physiological environment, indicating their longer-term NO release ability and therapeutic window for antibacterial effects. The SNAPicillin-incorporated polymers reduced the viability of adhered bacteria in culture, with >95 % reduction found against clinically relevant strains of Staphylococcus aureus (S. aureus). Furthermore, SNAPicillin-modified surfaces did not elicit a cytotoxic effect toward 3T3 mouse fibroblast cells, supporting the material's biocompatibility in vitro. These results indicate that the complementary effects of NO-release and ampicillin in SNAPicillin-eluting polymers can enhance the properties of commonly infected medical device surfaces for antibacterial purposes.

Synthesis and Characterization of Nitric Oxide-Releasing Ampicillin as a Potential Strategy for Combatting Bacterial Biofilm Formation

Biofilm formation on biomaterial interfaces and the development of antibiotic-resistant bacteria have decreased the effectiveness of traditional antibiotic treatment of infections. In this project, ampicillin, a commonly used antibiotic, was conjugated with S-nitroso-N-acetylpenicillamine (SNAP), an S-nitrosothiol compound (RSNO) used for controlled nitric oxide (NO) release. This novel multifunctional molecule is the first of its kind to provide combined antibiotic and NO treatment of infectious pathogens. Characterization of the molecule included NMR, FTIR, and mass spectrometry. NO release behavior was also measured and compared to pure, unmodified SNAP. When evaluating the antimicrobial efficacy, the synthesized SNAPicillin molecule showed the lowest MIC value against Gram-negative Pseudomonas aeruginosa and Gram-positive methicillin-resistant Staphylococcus aureus compared to ampicillin and SNAP alone. SNAPicillin also displayed enhanced biofilm dispersal and killing of both bacterial strains when treating a 48 h biofilm preformed on a polymer surface. The antibacterial results combined with the biocompatibility of the molecule show great promise for infection prevention and treatment of polymeric interfaces to reduce medical device-related infections.

Recent Developments in Nitric Oxide Donors and Delivery for Antimicrobial and Anti-Biofilm Applications

The use of nitric oxide (NO) is emerging as a promising, novel approach for the treatment of antibiotic resistant bacteria and biofilm infections. Depending on the concentration, NO can induce biofilm dispersal, increase bacteria susceptibility to antibiotic treatment, and induce cell damage or cell death via the formation of reactive oxygen or reactive nitrogen species. The use of NO is, however, limited by its reactivity, which can affect NO delivery to its target site and result in off-target effects. To overcome these issues, and enable spatial or temporal control over NO release, various strategies for the design of NO-releasing materials, including the incorporation of photo-activable, charge-switchable, or bacteria-targeting groups, have been developed. Other strategies have focused on increased NO storage and delivery by encapsulation or conjugation of NO donors within a single polymeric framework. This review compiles recent developments in NO drugs and NO-releasing materials designed for applications in antimicrobial or anti-biofilm treatment and discusses limitations and variability in biological responses in response to the use of NO for bacterial eradiation.

Inhibitory Effect of Cold Atmospheric Plasma on Chronic Wound-Related Multispecies Biofilms

The presence of microbial biofilms in the wounds affects negatively the healing process and can contribute to therapeutic failures. This study aimed to establish the effective parameters of cold atmospheric plasma (CAP) against wound-related multispecies and monospecies biofilms, and to evaluate the cytotoxicity and genotoxicity of the protocol. Monospecies and multispecies biofilms were formed by methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa and Enterococcus faecalis. The monospecies biofilms were grown in 96 wells plates and multispecies biofilm were formed on collagen membranes. The biofilms were exposed to helium CAP for 1, 3, 5 and 7 min. In monospecies biofilms, the inhibitory effect was detected after 1 min of exposure for E. faecalis and after 3 min for MRSA. A reduction in P. aeruginosa biofilm’s viability was detected after 7 min of exposure. For the multispecies biofilms, the reduction in the overall viability was detected after 5 min of exposure to CAP. Additionally, cytotoxicity and genotoxicity were evaluated by MTT assay and static cytometry, respectively. CAP showed low cytotoxicity and no genotoxicity to mouse fibroblastic cell line (3T3). It could be concluded that He-CAP showed inhibitory effect on wound-related multispecies biofilms, with low cytotoxicity and genotoxicity to mammalian cells. These findings point out the potential application of CAP in wound care.

Nitrite-enhanced copper-based Fenton reactions for biofilm removal

Unwanted biofilms present challenges for many industries. Herein an innovative biofilm removal technology was developed based on nitrite-accelerated Fenton chemistry, where both dissolved Cu ions and nano-CuO surfaces efficiently generate reactive nitrogen species as disinfectants. This simple, efficient, and cost-effective approach for biofilm removal generates important insights into Fenton chemistry, a fundamental mechanism in nature, considering the ubiquity of copper, hydrogen peroxide, and nitrite in the environment, biological systems, and various industrial processes.

Chronic wounds and novel therapeutic approaches

In the past decade, the frequency of chronic wounds in older population has increased, and their impact on quality of life is substantial. Chronic wounds are a public health problem associated with very high economic and psychosocial costs. These wounds result from various pathologies and comorbidities, such arterial and venous insufficiency, diabetes mellitus and continuous skin pressure. Recently, the role of infection and biofilms in the healing of chronic wounds has been the subject of considerable research. This paper presents an overview of various methods and products used to manage chronic wounds and discusses recent advances in wound care. To decide on the best treatment for any wound, it is crucial to holistically assess the patient and the wound. Additionally, multiple strategies could be used to prevent or treat chronic wounds.

Free radical-releasing systems for targeting biofilms

The recent rise in antibiotic drug resistance and biofilm formation by microorganisms has driven scientists from different fields to develop newer strategies to target microorganisms responsible for infectious diseases. There is a growing interest in free radicals as therapeutic agents for antimicrobial applications. However, limitations such as short half-life has hindered their usage. Currently, several research groups are exploring various biomaterials that can prolong the half-life, increase storage duration and control the release of the therapeutic ranges of free radicals required for different applications, including biofilm eradication. This review paper initially provides a background to, and theoretical knowledge on, free radicals; and then proceeds to review studies that have employed various free radical-incorporated drug delivery systems as an approach to target biofilm formation and eradication. Some of the free radical releasing systems highlighted include polymers, nanoparticles and hydrogels, with a focus on biofilm eradication, where they impact significantly. The various challenges associated with their application are also discussed. Further, the review identifies future research and strategies that can potentiate the application of free radical-incorporated drug delivery systems for inhibiting biofilm formation and eradicating formed biofilms.

Hard-to-heal wounds, biofilm and wound healing: an intricate interrelationship

Hard-to-heal wounds are a major public health problem that incur high economic costs. A major source of morbidity, they can have an overwhelming impact on patients, caregivers and society. In contrast to acute wound healing, which follows an 'orderly and timely reparative process', the healing of hard-to-heal wounds is delayed because the usual biological progression is interrupted. This article discusses hard-to-heal wounds, the impact they have on patients and healthcare systems, and how biofilms and other factors affect the wound-healing process. Controlling and preventing infection is of utmost importance for normal wound healing. Rational use of anti-infectious agents is crucial and is particularly relevant in the context of rising healthcare costs. Knowledge of the complex relationship between hard-to-heal wounds, biofilm formation and wound healing is vital for efficient management of hard-to-heal wounds.

Surface Charge Switchable Supramolecular Nanocarriers for Nitric Oxide Synergistic Photodynamic Eradication of Biofilms

Biofilm has resulted in numerous obstinate clinical infections, posing severe threats to public health. It is urgent to develop original antibacterial strategies for eradicating biofilms. Herein, we develop a surface charge switchable supramolecular nanocarrier exhibiting pH-responsive penetration into an acidic biofilm for nitric oxide (NO) synergistic photodynamic eradication of the methicillin-resistant Staphylococcus aureus (MRSA) biofilm with negligible damage to healthy tissues under laser irradiation. Originally, by integrating the glutathione (GSH)-sensitive α-cyclodextrin (α-CD) conjugated nitric oxide (NO) prodrug (α-CD-NO) and chlorin e6 (Ce6) prodrug (α-CD-Ce6) into the pH-sensitive poly(ethylene glycol) (PEG) block polypeptide copolymer (PEG-(KLAKLAK)₂-DA) via host-guest interaction, the supramolecular nanocarrier α-CD-Ce6-NO-DA was finely prepared. The supramolecular nanocarrier shows complete surface charge reversal from negative charge at physiological pH (7.4) to positive charge at acidic biofilm pH (5.5), promoting efficient penetration into the biofilm. Once infiltrated into the biofilm, the nanocarrier exhibits rapid NO release triggered by the overexpressed GSH in the biofilm, which not only produces abundant NO for killing bacteria but also reduces the biofilm GSH level to improve photodynamic therapy (PDT) efficiency. On the other hand, NO can react with reactive oxygen species (ROS) to produce reactive nitrogen species (RNS), further improving the PDT efficiency. Due to the effective penetration into the biofilm and depletion of biofilm GSH, the surface charge switchable GSH-sensitive NO nanocarrier can greatly improve the PDT efficiency at a low photosensitizer dose and laser intensity and cause negligible side effect to healthy tissues. Considering the above advantages, the strategy developed in this work may offer great possibilities to fight against biofilm infections.

Current Status of In Vitro Models and Assays for Susceptibility Testing for Wound Biofilm Infections

Biofilm infections have gained recognition as an important therapeutic challenge in the last several decades due to their relationship with the chronicity of infectious diseases. Studies of novel therapeutic treatments targeting infections require the development and use of models to mimic the formation and characteristics of biofilms within host tissues. Due to the diversity of reported in vitro models and lack of consensus, this review aims to provide a summary of in vitro models currently used in research. In particular, we review the various reported in vitro models of Pseudomonas aeruginosa biofilms due to its high clinical impact in chronic wounds and in other chronic infections. We assess advances in in vitro models that incorporate relevant multispecies biofilms found in infected wounds, such as P. aeruginosa with Staphylococcus aureus, and additional elements such as mammalian cells, simulating fluids, and tissue explants in an attempt to better represent the physiological conditions found at an infection site. It is hoped this review will aid researchers in the field to make appropriate choices in their proposed studies with regards to in vitro models and methods.

Nitric Oxide-Releasing Macromolecular Scaffolds for Antibacterial Applications

Exogenous nitric oxide (NO) represents an attractive antibacterial agent because of its ability to both disperse and directly kill bacterial biofilms while avoiding resistance. Due to the challenges associated with administering gaseous NO, NO-releasing macromolecular scaffolds are developed to facilitate NO delivery. This progress report describes the rational design and application of NO-releasing macromolecular scaffolds as antibacterial therapeutics. Special consideration is given to the role of the physicochemical properties of the NO storage vehicles on antibacterial or anti-biofilm activity.

Recent advances in nitric oxide delivery for antimicrobial applications using polymer-based systems

The nitric oxide (NO) molecule has gained increasing attention in biological applications to combat biofilm-associated bacterial infections. However, limited NO loading, relatively short half-lives of low molecular weight NO donor compounds, and difficulties in targeted delivery of NO have hindered their practical clinical administration. To overcome these drawbacks, the combination of NO and scaffolds based on biocompatible polymers is an effective way towards realizing the practical utility of NO in biomedical applications. In this regard, the present overview highlights the recent developments in NO-releasing polymeric biomaterials for antimicrobial applications, focusing on antibiofilm treatments and the challenges that need to be overcome.

Facile solvent-free fabrication of nitric oxide (NO)-releasing coatings for prevention of biofilm formation

We describe a simple and solvent-free method to generate nitric oxide (NO)-releasing coatings by incorporating diazeniumdiolate (NONOate) into allylamine or diallylamine plasma polymer coatings. The resulting coatings demonstrate continuous release of NO for over 48 hours and are effective at reducing the adhesion and biofilm formation of medically-relevant Gram-negative and Gram-positive opportunistic pathogens.

Strategies to design antimicrobial contact lenses and contact lens cases

Contact lens wear is a primary risk factor for developing ocular complications, such as contact lens acute red eye (CLARE), contact lens-induced peripheral ulcer (CLPU) and microbial keratitis (MK). Infections occur due to microbial contamination of contact lenses, lens cases and lens care solution, which are exacerbated by extended lens wear and unsanitary lens care practices. The development of microbial biofilms inside lens cases is an additional complication, as the developed biofilms are resistant to conventional lens cleaning solutions. Ocular infections, particularly in the case of MK, can lead to visual impairment or even blindness, so there is a pressing need for the development of antimicrobial contact lenses and cases. Additionally, with the increasing use of bandage contact lenses and contact lenses as drug depots and with the development of smart contact lenses, contact lens hygiene becomes a therapeutically important issue. In this review, we attempt to compile and summarize various chemical strategies for developing antimicrobial contact lenses and lens cases by using silver, free-radical producing agents, antimicrobial peptides or by employing passive surface modification approaches. We also evaluated the advantages and disadvantages of each system and tried to provide input to future directions. Finally, we summarize the developing technologies of therapeutic contact lenses to shed light on the future of contact lens applications.

Mechanistic studies of the antibiofilm activity and synergy with antibiotics of isosorbide mononitrate

The use of nitric oxide (NO), a naturally occurring antimicrobial agent, as an alternative strategy to combat bacterial biofilms has recently gained considerable momentum in light of the global threat of emerging antibiotic resistance. While previous NO-based anti-biofilm approaches were aimed at killing bacterial cells within biofilms, NO has also been recently identified as a key mediator of biofilm dispersal, causing the release of cells from the biofilm community. This is of great interest towards the design of more effective anti-biofilm strategies but further studies are warranted to validate this concept. Therefore, in the present study we investigated whether a NO precursor, isosorbide mononitrate (ISMN) or its analogue D-isosorbide can induce bacteria cell dispersal from Staphylococcus aureus (S. aureus) biofilms and explored the potential synergy of ISMN and the antimicrobial compounds mupirocin and ciprofloxacin in biofilm eradication. This study demonstrate that ISMN causes dispersal of S. aureus biofilm bacteria, particularly when exposed to high levels of drug. ISMN at 60mg/mL increased the number of colony forming units (CFU) (~3log₁₀ and ~5log₁₀) of planktonic bacteria after 6 and 24-h exposure respectively, compared to control biofilms. This suggests that ISMN induces the transition of sessile biofilm cells to free-swimming planktonic cells. In addition, ISMN exhibits synergistic effects against S. aureus biofilms with ciprofloxacin when tested above its minimum inhibitory concentration (MIC). Specifically, exposure to ISMN significantly enhanced the efficacy of ciprofloxacin by reducing the number of CFU (~3log₁₀ or ~2log₁₀) of biofilm-associated and planktonic bacteria respectively, compared to drug alone. Combined exposure to both ISMN and certain antimicrobial agents may therefore offer an innovative approach to control persistent biofilm and biofilm-associated infections.

Central venous catheters and biofilms: where do we stand in 2017?

The use of central venous catheters (CVC) is associated with a risk of microbial colonization and subsequent potentially severe infection. Microbial contamination of the catheter leads to the development of a microbial consortia associated with the CVC surface and embedded in an extracellular matrix, named biofilm. This biofilm provides bacterial cells the ability to survive antimicrobial agents and the host immune system and to disseminate to other sites of the body. The best preventive strategy is to avoid any unnecessary catheterization or to reduce indwelling duration when a CVC is required. Beside aseptic care and antibiotic-impregnated catheters (like minocycline/rifampin), preventive locks can be proposed in some cases, whereas non-biocidal approaches are under active research like anti-adhesive or competitive interactions strategies. When the diagnosis of catheter-related bloodstream infection (CRBSI) is suspected on clinical symptoms, it requires a microbiological confirmation by paired blood cultures in order to avoid unnecessary catheter removal. The treatment of CRBSI relies on catheter removal and systemic antimicrobials. However, antibiotic lock technique (ALT) can be used as an attempt to eradicate biofilm formed on the inside lumen of the catheter in case of uncomplicated long-term catheter-related BSI caused by coagulase-negative staphylococci (CoNS) or Enterobacteriaceae. Recently, promising strategies have been developed to improve biofilm eradication; they rely on matrix degradation or destabilization or the development of anti-persister compounds, targeting the most tolerant bacterial cells inside the biofilm. Understanding biofilm formation at the molecular level may help us to develop new approaches to prevent or treat these frequent infections.

Iron Complex Facilitated Copper Redox Cycling for Nitric Oxide Generation as Nontoxic Nitrifying Biofilm Inhibitor

In this study, we developed poly(vinyl chloride) (PVC)-solvent casted mixed metal copper and iron complexes capable of catalytic generation of the antibiofilm nitric oxide (NO) from endogenous nitrite. In the absence of additional reducing agent, we demonstrated that the presence of iron complex facilitates a redox cycling, converting the copper(II) complex to active copper(I) species, which catalyzes the generation of NO from nitrite. Assessed by protein assay and surface coverage analyses, the presence of the mixed metal complexes in systems containing water industry-relevant nitrite-producing nitrifying biofilms was shown to result in a "nontoxic mode" of biofilm suppression, while confining the bacterial growth to the free-floating planktonic phase. Addition of an NO scavenger into the mixed metal system eliminated the antibiofilm effects, therefore validating first, the capability of the mixed metal complexes to catalytically generate NO from the endogenously produced nitrite and second, the antibiofilm effects of the generated NO. The work highlights the development of self-sustained antibiofilm materials that features potential for industrial applications. The novel NO-generating antibiofilm technology diverts from the unfavorable requirement of adding a reducing agent and importantly, the less tendency for development of bacterial resistance.