Contact killing and antimicrobial properties of copper

Photocatalytic TiO2 nanomaterials as potential antimicrobial and antiviral agents: Scope against blocking the SARS-COV-2 spread

The whole world is struggling with current coronavirus pandemic that shows urgent need to develop novel technologies, medical innovations or innovative materials for controlling SARS-CoV-2 infection. The mode of infection of SARS-CoV-2 is still not well known and seems to spread through surface, air, and water. Therefore, the whole surrounding environment needs to be disinfected with continuous function. For that purpose, materials with excellent antiviral properties, cost effective, environmental friendly and practically applicable should be researched. Titanium dioxide (TiO₂) under ultraviolet light produces strong oxidative effect and is utilized as photocatalytic disinfectant in biomedical field. TiO₂ based photocatalysts are effective antimicrobial/antiviral agents under ambient conditions with potential to be used even in indoor environment for inactivation of bacteria/viruses. Interestingly, recent studies highlight the effective disinfection of SARS-CoV-2 using TiO₂ photocatalysts. Here, scope of TiO₂ photocatalysts as emerging disinfectant against SARS-CoV-2 infection has been discussed in view of their excellent antibacterial and antiviral activities against various bacteria and viruses (e.g. H1N1, MNV, HSV, NDV, HCoV etc.). The current state of development of TiO₂ based nano-photocatalysts as disinfectant shows their potential to combat with SARS-CoV-2 viral infection and are promising for any other such variants or viruses, bacteria in future studies.

Development and characterization of cannabidiol-loaded alginate copper hydrogel for repairing open bone defects in vitro

The clinical treatment of open bone defects caused by accidental bone trauma, bone tumors, bone diseases and bone infections is challenging. In this study, we designed and fabricated a multifunctional alginate-based hydrogel that contains cannabidiol (CBD), SA@Cu/CBD hydrogel, for repairing open bone defects. The results of physicochemical characterization showed that the SA@Cu/CBD hydrogel was successfully prepared and showed a suitable swelling ratio, high thermal stability, and stable mechanical properties. In vitro evaluation of antibacterial activity indicated that more than 90% of S. aureus and E. coli were inhibited compared to the control group. The ALP activity assay showed that the ALP expression level of MC3T3-E1cells in SA@Cu/CBD hydrogel was approximately 2-fold higher than that in the control group on day 7 and 14. Additionally, compared to the control group, the level of mineralized deposits in SA@Cu/CBD hydrogel was also improved by about 2 times on day 14. The PCR results indicated the mRNA expression levels of osteogenic markers (ALP, Col1α1, OCN, and RUNX2 genes) and angiogenic markers (EGFL6 and VEGF genes) in SA@Cu/CBD hydrogel were significantly upregulated compared to that in the control group, and the mRNA expression levels of critical inflammatory cytokines (TNF-α and IL-1β) in the SA@Cu/CBD hydrogel were significantly down-regulated compared to that in SA@Cu hydrogel. Taken together, these results demonstrated that the SA@Cu/CBD hydrogel showed significantly anti-bacterial, anti-inflammation, angiogenic and osteogenic activities in vitro studies. Thus, SA@Cu/CBD hydrogels may be a promising candidate in repairing open bone defects.

Synthesis of Metal-Loaded Carboxylated Biopolymers with Antibacterial Activity through Metal Subnanoparticle Incorporation

Carboxymethyl starch (CMS) and carboxymethyl cellulose (CMC) loaded by highly dispersed metal subnanoparticles (MSNPs) showed antibacterial activity against E. coli and B. subtilis strains. Copper and silver were found to act in both cationic and zero-valence forms. The antibacterial activity depends on the metal species content but only up to a certain level. Silver cation (Ag⁺) showed higher antibacterial activity as compared to Ag⁰, which was, however, more effective than Cu⁰, due to weaker retention. The number of carboxyl groups of the biopolymers was found to govern the material dispersion in aqueous media, the metal retention strength and dispersion in the host-matrices. Cation and metal retention in both biopolymers was found to involve interactions with the oxygen atoms of both hydroxyl and carboxyl groups. There exists a ternary interdependence between the Zeta potential (ZP), pH induced by the biocidal agent and its particle size (PS). This interdependence is a key factor in the exchange processes with the surrounding species, including bacteria. Clay mineral incorporation was found to mitigate material dispersion, due to detrimental competitive clay:polymer interaction. This knowledge advancement opens promising prospects for manufacturing metal-loaded materials for biomedical applications.

The Biodegradability and in Vitro Cytological Study on the Composite of PLGA Combined With Magnesium Metal

The main goal of this study was to develop a novel poly (lactic-co-glycolic acid) (PLGA) composite biodegradable material with magnesium (Mg) metal to overcome the acidic degradation of PLGA and to investigate the cytocompatibility and osteogenesis of the novel material. PLGA composites with 5 and 10 wt% Mg were prepared. The samples were initially cut into 10 mm × 10 mm films, which were used to detect the pH value to evaluate the self-neutralized ability. Murine embryo osteoblast precursor (MC3T3-E1) cells were used for in vitro experiments to evaluate the cytotoxicity, apoptosis, adhesion, and osteogenic differentiation effect of the composite biodegradable material. pH monitoring showed that the average value of PLGA with 10 wt% Mg group was closer to the normal physiological environment than that of other groups. Cell proliferation and adhesion assays indicated no significant difference between the groups, and all the samples showed no toxicity to cells. As for cell apoptosis detection, the rate of early apoptotic cells was proportional to the ratio of Mg. However, the ratios of the experimental groups were lower than those of the control group. Alkaline phosphatase activity staining demonstrated that PLGA with 10 wt% Mg could effectively improve the osteogenic differentiation of MC3T3-E1 cells. In summary, PLGA with 10 wt% Mg possessed effective osteogenic properties and cytocompatibility and therefore could provide a wide range of applications in bone defect repair and scaffold-based tissue engineering in clinical practice.

Sustainable Antibacterial and Antiviral High-Performance Copper-Coated Filter Produced via Ion Beam Treatment

With the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), disease prevention has become incredibly important. Consequently, mask and air-purifier use has increased. The filter is the core component of these items. However, most filter materials lack antimicrobial properties. Copper is a sustainable antimicrobial material. When copper is deposited onto the filter’s surface, the microorganisms that come into contact with it can be effectively inactivated. In this study, we used an oxygen ion beam with a controlled process temperature to treat filter surfaces with copper. This enabled a strong adhesion of at least 4 N/cm between the copper and the filter fibers without damaging them. Upon exposing the filter to bacteria (Staphylococcus aureus ATCC 6538, Klebsiella pneumoniae ATCC 4352, Escherichia coli ATCC 25922, and Pseudomonas aeruginosa ATCC 27853) for one hour, a >99.99% removal rate was attained; when the filter was exposed to SARS-CoV-2 virus for one hour, it inactivated more than 99%. These beneficial properties minimize the risk of secondary infections, which are significantly more likely to occur when a conventional filter is replaced or removed.

Antimicrobial and antifungal properties of NiCu-PANI/PVA quaternary nanocomposite synthesized by chemical oxidative polymerization of polyaniline

Increasing antimicrobial resistance has led to use of novel technologies such as nanomaterials and nanocomposites that have shown effective antimicrobial and/or antifungal activities against several gram-positive and gram-negative bacteria. There have been limited studies on antimicrobial properties of the combined polymer nanocomposites with transitional bimetallic nanoparticles such as nickel (Ni) and copper (Cu). Thus, the main objective of this study was to synthesis, characterize and investigate the antibacterial and antifungal properties of NiCu-PANI/PVA nanocomposite. The nanocomposite films with different amount of Ni and Cu salts were synthesized by chemical oxidative polymerization of polyaniline using HCl as oxidant and PVA as a stabilizer. Optical, chemical composition, and morphological characteristics as well as thermal stability were evaluated using UV-Visible, FTIR, SEM-EDX, and TGA analyses. Antimicrobial properties were then determined using the disc diffusion assay against gram-negative bacteria (i.e., Escherichia coli ATCC 25922, Klebsiella pneumonia ATCC 700603, Proteus sp.,) and gram-positive bacteria (i.e., Staphylococcus aureus ATCC 2593). Fungal plant pathogens including Aspergillus niger and Fusarium oxysporum f. sp. pisi were also evaluated for determination of antifungal activity of NiCu-PANI/PVA films. Among the synthesized films, Ni₆₅Cu₃₅-PANI/PVA showed excellent antibacterial activity against all the bacteria strains examined in this study. The diameters of inhibition zones for Escherichia coli ATCC 25922, Klebsiella pneumoniae ATCC 700603, Proteus sp., and Staphylococcus aureus ATCC 2593 were 23, 23, 17, and 18 mm, respectively indicating good antibacterial activities. Additionally, NiCu-PANI/PVA, particularly the films with higher Cu intake, showed better antifungal activity against Fusarium oxysporum f. sp. pisi. However, NiCu-PANI/PVA was ineffective against Aspergillus niger.

Application of Copper Nanoparticles in Dentistry

Nanoparticles based on metal and metallic oxides have become a novel trend for dental applications. Metal nanoparticles are commonly used in dentistry for their exclusive shape-dependent properties, including their variable nano-sizes and forms, unique distribution, and large surface-area-to-volume ratio. These properties enhance the bio-physio-chemical functionalization, antimicrobial activity, and biocompatibility of the nanoparticles. Copper is an earth-abundant inexpensive metal, and its nanoparticle synthesis is cost effective. Copper nanoparticles readily intermix and bind with other metals, ceramics, and polymers, and they exhibit physiochemical stability in the compounds. Hence, copper nanoparticles are among the commonly used metal nanoparticles in dentistry. Copper nanoparticles have been used to enhance the physical and chemical properties of various dental materials, such as dental amalgam, restorative cements, adhesives, resins, endodontic-irrigation solutions, obturation materials, dental implants, and orthodontic archwires and brackets. The objective of this review is to provide an overview of copper nanoparticles and their applications in dentistry.

Bone Regeneration and Oxidative Stress: An Updated Overview

Bone tissue engineering is a complex domain that requires further investigation and benefits from data obtained over past decades. The models are increasing in complexity as they reveal new data from co-culturing and microfluidics applications. The in vitro models now focus on the 3D medium co-culturing of osteoblasts, osteoclasts, and osteocytes utilizing collagen for separation; this type of research allows for controlled medium and in-depth data analysis. Oxidative stress takes a toll on the domain, being beneficial as well as destructive. Reactive oxygen species (ROS) are molecules that influence the differentiation of osteoclasts, but over time their increasing presence can affect patients and aid the appearance of diseases such as osteoporosis. Oxidative stress can be limited by using antioxidants such as vitamin K and N-acetyl cysteine (NAC). Scaffolds and biocompatible coatings such as hydroxyapatite and bioactive glass are required to isolate the implant, protect the zone from the metallic, ionic exchange, and enhance the bone regeneration by mimicking the composition and structure of the body, thus enhancing cell proliferation. The materials can be further functionalized with growth factors that create a better response and higher chances of success for clinical use. This review highlights the vast majority of newly obtained information regarding bone tissue engineering, such as new co-culturing models, implant coatings, scaffolds, biomolecules, and the techniques utilized to obtain them.

From Copper Tolerance to Resistance in Pseudomonas aeruginosa towards Patho-Adaptation and Hospital Success

The hospital environment constitutes a reservoir of opportunistic pathogens responsible for healthcare-associated infections (HCAI) such as Pseudomonas aeruginosa (Pa). Pa persistence within technological niches, the increasing emergence of epidemic high-risk clones in HCAI, the epidemiological link between plumbing strains and clinical strains, make it a major nosocomial pathogen. Therefore, understanding the mechanisms of Pa adaptation to hospital water systems would be useful in preventing HCAI. This review deciphers how copper resistance contributes to Pa adaptation and persistence in a hospital environment, especially within copper water systems, and ultimately to its success as a causative agent of HCAI. Numerous factors are involved in copper homeostasis in Pa, among which active efflux conferring copper tolerance, and copper-binding proteins regulating the copper compartmentalization between periplasm and cytoplasm. The functional harmony of copper homeostasis is regulated by several transcriptional regulators. The genomic island GI-7 appeared as especially responsible for the copper resistance in Pa. Mechanisms of copper and antibiotic cross-resistance and co-resistance are also identified, with potential co-regulation processes between them. Finally, copper resistance of Pa confers selective advantages in colonizing and persisting in hospital environments but also appears as an asset at the host/pathogen interface that helps in HCAI occurrence.

Selective strategies for antibacterial regulation of nanomaterials

Recalcitrant bacterial infection, as a worldwide challenge, causes large problems for human health and is attracting great attention. The excessive antibiotic-dependent treatment of infections is prone to induce antibiotic resistance. A variety of unique nanomaterials provide an excellent toolkit for killing bacteria and preventing drug resistance. It is of great importance to summarize the design rules of nanomaterials for inhibiting the growth of pathogenic bacteria. We completed a review involving the strategies for regulating antibacterial nanomaterials. First, we discuss the antibacterial manipulation of nanomaterials, including the interaction between the nanomaterial and the bacteria, the damage of the bacterial structure, and the inactivation of biomolecules. Next, we identify six main factors for controlling the antibacterial activity of nanomaterials, including their element composition, size dimensions, surface charge, surface topography, shape selection and modification density. Every factor possesses a preferable standard for maximizing antibacterial activity, providing universal rules for antibacterial regulation of nanomaterials. We hope this comprehensive review will help researchers to precisely design and synthesize nanomaterials, developing intelligent antibacterial agents to address bacterial infections.

Recent Advances in Metal-Based Antimicrobial Coatings for High-Touch Surfaces

International interest in metal-based antimicrobial coatings to control the spread of bacteria, fungi, and viruses via high contact human touch surfaces are growing at an exponential rate. This interest recently reached an all-time high with the outbreak of the deadly COVID-19 disease, which has already claimed the lives of more than 5 million people worldwide. This global pandemic has highlighted the major role that antimicrobial coatings can play in controlling the spread of deadly viruses such as SARS-CoV-2 and scientists and engineers are now working harder than ever to develop the next generation of antimicrobial materials. This article begins with a review of three discrete microorganism-killing phenomena of contact-killing surfaces, nanoprotrusions, and superhydrophobic surfaces. The antimicrobial properties of metals such as copper (Cu), silver (Ag), and zinc (Zn) are reviewed along with the effects of combining them with titanium dioxide (TiO2) to create a binary or ternary contact-killing surface coatings. The self-cleaning and bacterial resistance of purely structural superhydrophobic surfaces and the potential of physical surface nanoprotrusions to damage microbial cells are then considered. The article then gives a detailed discussion on recent advances in attempting to combine these individual phenomena to create super-antimicrobial metal-based coatings with binary or ternary killing potential against a broad range of microorganisms, including SARS-CoV-2, for high-touch surface applications such as hand rails, door plates, and water fittings on public transport and in healthcare, care home and leisure settings as well as personal protective equipment commonly used in hospitals and in the current COVID-19 pandemic.

Antiviral Activities of High Energy E-Beam Induced Copper Nanoparticles against H1N1 Influenza Virus

The pandemic outbreak of COVID-19 in the year of 2020 that drastically changed everyone's life has raised the urgent and intense need for the development of more efficacious antiviral material. This study was designed to develop copper nanoparticles (Cu NPs) as an antiviral agent and to validate the antiviral activities of developed copper NP. The Cu NPs were synthesized using a high energy electron beam, and the characteristic morphologies and antiviral activities of Cu NPs were evaluated. We found that Cu NPs are of spherical shape and uniformly distributed, with a diameter of around 100 nm, as opposed to the irregular shape of commercially available copper microparticles (Cu MPs). An X-ray diffraction analysis showed the presence of Cu and no copper oxide II and I in the Cu NPs. A virus inactivation assay revealed no visible viral DNA after 10- and 30-min treatment of H1N1 virus with the Cu NPs. The infectivity of the Cu NPs-treated H1N1 virus significantly decreased compared with that of the Cu MPs-treated H1N1 virus. The viability of A549 bronchial and Madin-Darby Canine Kidney (MDCK) cells infected with Cu NPs-treated H1N1 was significantly higher than those infected with Cu MPs-treated H1N1 virus. We also found cells infected with Cu NPs-treated H1N1 virus exhibited a markedly decreased presence of virus nucleoprotein (NuP), an influenza virus-specific structural protein, compared with cells infected with Cu MPs-treated H1N1 virus. Taken together, our study shows that Cu NPs are a more effective and efficacious antiviral agent compared with Cu MPs and offer promising opportunities for the prevention of devastatingly infectious diseases.

Associations of Nutritional Behavior and Gut Microbiota with the Risk of COVID-19 in Healthy Young Adults in Poland

The numerous consequences of the coronavirus disease 2019 (COVID-19) pandemic in healthy young people and the lack of clarity as to the long-term disease outcomes have spurred the search for risk factors for SARS-CoV-2 infection. We aimed to evaluate the associations of nutritional behaviors, gut microbiota, and physical activity with the risk of COVID-19 in healthy young nonobese people. Data on body composition, anthropometric measurements, physical activity, dietary intake, and gut microbiota were obtained from 95 adults (mean age, 34.66 ± 5.76 years). A balanced diet rich in vegetables and fruit, including nuts, wholegrain cereal products, and legumes, covers the need for vitamins and minerals. Such a diet can be an effective measure to reduce the risk of COVID-19 in nonobese healthy physically active young people with normal immune function. People with balanced diet and an average daily consumption of >500 g of vegetables and fruit and >10 g of nuts had an 86% lower risk of COVID-19 compared with those whose diet was not balanced and who consumed lower amounts of these products. It is well documented that proper nutrition, physical activity, and maintenance of normal weight facilitate good health by ensuring optimal immune function. The beneficial effects of these interventions should be strongly emphasized during the COVID-19 pandemic.

Biofilm Inhibition and Antiviral Response of Cold Sprayed and Shot Peened Copper Surfaces: Effect of Surface Morphology and Microstructure

Antibacterial properties of copper against planktonic bacteria population are affected by surface microstructure and topography. However, copper interactions with bacteria in a biofilm state are less studied. This work aims at better understanding the difference in biofilm inhibition of bulk, cold-sprayed, and shot-peened copper surfaces and gaining further insights on the underlying mechanisms using optical and scanning electron microscopy to investigate the topography and microstructure of the surfaces. The biofilm inhibition ability is reported for all surfaces. Results show that the biofilm inhibition performance of cold sprayed copper, while initially better, decreases with time and results in an almost identical performance than as-received copper after 18h incubation time. The shot-peened samples with a rough and ultrafine microstructure demonstrated an enhanced biofilm control, especially at 18 hr. The biofilm control mechanisms were explained by the diffusion rates and concentration of copper ions and the interaction between these ions and the biofilm, while surface topography plays a role in the bacteria attachment at the early planktonic state. Furthermore, the data suggest that surface topography plays a key role in antiviral activity of the materials tested, with a smooth surface being the most efficient.

Graphical Abstract

Colloidal dispersion of poly(ionic liquid)/Cu composite particles for protective surface coating against SAR-CoV-2

Herein, we report a waterproof anti-SARS-CoV-2 protective film prepared by spray-coating of an aqueous colloidal dispersion of poly(ionic liquid)/copper (PIL/Cu) composite nanoparticles onto a substrate. The PIL dispersion was prepared by suspension polymerization of 3-dodecyl-1-vinylimdiazolium bromide in water at 70°C. The copper acetate salt was added into the PIL nanoparticle dispersion and in situ reduced into copper nanoparticles anchoring onto the PIL nanoparticles. Despite being waterborne, the PIL in bulk is intrinsically insoluble in water and the formed coating is stable in water. The formed surface coating by PIL/copper composite nanoparticles was able to deactivate SARS-CoV-2 virions by 90.0% in 30 minutes and thus may effectively prevent the spread of SARS-CoV-2 through surface contact. This method may provide waterborne dispersions for a broad range of antivirus protective surface coatings for both outdoor and indoor applications.

Enhancement of Antiviral Effect of Plastic Film against SARS-CoV-2: Combining Nanomaterials and Nanopatterns with Scalability for Mass Manufacturing

Direct contact with contaminated surfaces in frequently accessed areas is a confirmed transmission mode of SARS-CoV-2. To address this challenge, we have developed novel plastic films with enhanced effectiveness for deactivating the SARS-CoV-2 by means of nanomaterials combined with nanopatterns. Results prove that these functionalized films are able to deactivate SARS-CoV-2 by up to 2 orders of magnitude within the first hour compared to untreated films, thus reducing the likelihood of transmission. Nanopatterns can enhance the antiviral effectiveness by increasing the contact area between nanoparticles and virus. Significantly, the established process also considers the issue of scalability for mass manufacturing. A low-cost process for nanostructured antiviral films integrating ultrasonic atomization spray coating and thermal nanoimprinting lithography is proposed. A further in-depth investigation should consider the size, spacing, and shape of nanopillars, the type and concentration of nanoparticles, and the scale-up and integration of these processes with manufacturing for optimal antiviral effectiveness.

Copper Homeostatic Mechanisms and Their Role in the Virulence of Escherichia coli and Salmonella enterica

Copper is an essential micronutrient that also exerts toxic effects at high concentrations. This review summarizes the current state of knowledge on copper handling and homeostasis systems in Escherichia coli and Salmonella enterica. We describe the mechanisms by which transcriptional regulators, efflux pumps, detoxification enzymes, metallochaperones, and ancillary copper response systems orchestrate cellular response to copper stress. E. coli and S. enterica are important pathogens of humans and animals. We discuss the critical role of copper during killing of these pathogens by macrophages and in nutritional immunity at the bacterial-pathogen-host interface. In closing, we identify opportunities to advance our understanding of the biological roles of copper in these model enteric bacterial pathogens.

Recent Advances in the Evaluation of Antimicrobial Materials for Resolution of Orthopedic Implant-Associated Infections In Vivo

While orthopedic implant-associated infections are rare, revision surgeries resulting from infections incur considerable healthcare costs and represent a substantial research area clinically, in academia, and in industry. In recent years, there have been numerous advances in the development of antimicrobial strategies for the prevention and treatment of orthopedic implant-associated infections which offer promise to improve the limitations of existing delivery systems through local and controlled release of antimicrobial agents. Prior to translation to in vivo orthopedic implant-associated infection models, the properties (e.g., degradation, antimicrobial activity, biocompatibility) of the antimicrobial materials can be evaluated in subcutaneous implant in vivo models. The antimicrobial materials are then incorporated into in vivo implant models to evaluate the efficacy of using the material to prevent or treat implant-associated infections. Recent technological advances such as 3D-printing, bacterial genomic sequencing, and real-time in vivo imaging of infection and inflammation have contributed to the development of preclinical implant-associated infection models that more effectively recapitulate the clinical presentation of infections and improve the evaluation of antimicrobial materials. This Review highlights the advantages and limitations of antimicrobial materials used in conjunction with orthopedic implants for the prevention and treatment of orthopedic implant-associated infections and discusses how these materials are evaluated in preclinical in vivo models. This analysis serves as a resource for biomaterial researchers in the selection of an appropriate orthopedic implant-associated infection preclinical model to evaluate novel antimicrobial materials.

Robust bulk micro-nano hierarchical copper structures possessing exceptional bactericidal efficacy

Conventional copper (Cu) metal surfaces are well recognized for their bactericidal properties. However, their slow bacteria-killing potency has historically excluded them as a rapid bactericidal material. We report the development of a robust bulk superhydrophilic micro-nano hierarchical Cu structure that possesses exceptional bactericidal efficacy. It resulted in a 4.41 log₁₀ reduction (>99.99%) of the deadly Staphylococcus aureus (S. aureus) bacteria within 2 min vs. a 1.49 log₁₀ reduction (96.75%) after 240 min on common Cu surfaces. The adhered cells exhibited extensive blebbing, loss of structural integrity and leakage of vital intracellular material, demonstrating the rapid efficacy of the micro-nano Cu structure in destructing bacteria membrane integrity. The mechanism was attributed to the synergistic degradation of the cell envelope through enhanced release and therefore uptake of the cytotoxic Cu ions and the adhesion-driven mechanical strain due to its rapid ultimate superhydrophilicity (contact angle drops to 0° in 0.18 s). The scalable fabrication of this micro-nano Cu structure was enabled by integrating bespoke precursor alloy design with microstructure preconditioning for dealloying and demonstrated on 2000 mm² Cu surfaces. This development paves the way to the practical exploitation of Cu as a low-cost antibiotic-free fast bactericidal material.

Evaluation of in vitro activity of copper gluconate against SARS-CoV-2 using confocal microscopy-based high content screening

CONTEXT

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) that emerged late in 2019 is the etiologic agent of coronavirus disease 2019 (Covid-19). There is an urgent need to develop curative and preventive therapeutics to limit the current pandemic and to prevent the re-emergence of Covid-19. This study aimed to assess the in vitro activity of copper gluconate against SARS-CoV-2.

METHODS

Vero E6 cells were cultured with or without copper gluconate 18-24 hours before infection. Cells were infected with a recombinant GFP expressing SARS-CoV-2. Cells were infected with a recombinant GFP expressing SARS-CoV-2. Infected cells were incubated in fresh medium containing varying concentration of copper gluconate (supplemented with bovine serum albumin or not) for an additional 48 -h period. The infection level was measured by the confocal microscopy-based high content screening method. The cell viability in presence of copper gluconate was assessed by XTT and propidium iodide assays.

RESULTS

The viability of Vero E6 cells exposed to copper gluconate up to 200 μM was found to be similar to that of unexposed cells, but it dropped below 70 % with 400 μM of this agent after 72 h of continuous exposure. The infection rate was 23.8 %, 18.9 %, 20.6 %, 6.9 %, 5.3 % and 5.2 % in cells treated prior infection with 0, 2, 10, 25, 50 and 100 μM of copper gluconate respectively. As compared to untreated cells, the number of infected cells was reduced by 71 %, 77 %, and 78 % with 25, 50, and 100 μM of copper gluconate respectively (p < 0.05). In cells treated only post-infection, the rate of infection dropped by 73 % with 100 μM of copper gluconate (p < 0.05). However, the antiviral activity of copper gluconate was abolished by the addition of bovine serum albumin.

CONCLUSION

Copper gluconate was found to mitigate SARS-CoV-2 infection in Vero E6 cells but this effect was abolished by albumin, which suggests that copper will not retain its activity in serum. Furthers studies are needed to investigate whether copper gluconate could be of benefit in mucosal administration such as mouthwash, nasal spray or aerosols.

Antiviral properties of copper and its alloys to inactivate covid-19 virus: a review

Copper (Cu) and its alloys are prospective materials in fighting covid-19 virus and several microbial pandemics, due to its excellent antiviral as well as antimicrobial properties. Even though many studies have proved that copper and its alloys exhibit antiviral properties, this research arena requires further research attention. Several studies conducted on copper and its alloys have proven that copper-based alloys possess excellent potential in controlling the spread of infectious diseases. Moreover, recent studies indicate that these alloys can effectively inactivate the covid-19 virus. In view of this, the present article reviews the importance of copper and its alloys in reducing the spread and infection of covid-19, which is a global pandemic. The electronic databases such as ScienceDirect, Web of Science and PubMed were searched for identifying relevant studies in the present review article. The review starts with a brief description on the history of copper usage in medicine followed by the effect of copper content in human body and antiviral mechanisms of copper against covid-19. The subsequent sections describe the distinctive copper based material systems such as alloys, nanomaterials and coating technologies in combating the spread of covid-19. Overall, copper based materials can be propitiously used as part of preventive and therapeutic strategies in the fight against covid-19 virus.

Molecular Engineering of Laser-Induced Graphene for Potential-Driven Broad-Spectrum Antimicrobial and Antiviral Applications

Worldwide, countless deaths have been caused by the coronavirus disease 2019. In addition to the virus variants, an increasing number of fatal fungal infections have been reported, which further exacerbates the scenario. Therefore, the development of porous surfaces with both antiviral and antimicrobial capacities is of urgent need. Here, a cost-effective, nontoxic, and metal-free strategy is reported for the surface engineering of laser-induced graphene (LIG). The authors covalently engineer the surface potential of the LIG from -14 to ≈+35 mV (LIG⁺ ), enabling both high-efficiency antimicrobial and antiviral performance under mild conditions. Specifically, several candidate microorganisms of different types, including Escherichia coli, Streptomyces tenebrarius, and Candida albicans, are almost completely inactivated after 10-min solar irradiation. LIG⁺ also exhibits a strong antiviral effect against human coronaviruses: 99% HCoV-OC43 and 100% HCoV-229E inactivation are achieved after 20-min treatment. Such enhancement may also be observed against other types of pathogens that are heat-sensitive and oppositely charged. Besides, the covalent modification strategy alleviates the leaching problem, and the low cytotoxicity of LIG⁺ makes it advantageous. This study highlights the synergy of surface potential and photothermal effect in the inactivation of pathogens and it provides a direction for designing porous materials for airborne disease removal and water disinfection.

Antibacterial approaches in tissue engineering using metal ions and nanoparticles: From mechanisms to applications

Bacterial infection of implanted scaffolds may have fatal consequences and, in combination with the emergence of multidrug bacterial resistance, the development of advanced antibacterial biomaterials and constructs is of great interest. Since decades ago, metals and their ions had been used to minimize bacterial infection risk and, more recently, metal-based nanomaterials, with improved antimicrobial properties, have been advocated as a novel and tunable alternative. A comprehensive review is provided on how metal ions and ion nanoparticles have the potential to decrease or eliminate unwanted bacteria. Antibacterial mechanisms such as oxidative stress induction, ion release and disruption of biomolecules are currently well accepted. However, the exact antimicrobial mechanisms of the discussed metal compounds remain poorly understood. The combination of different metal ions and surface decorations of nanoparticles will lead to synergistic effects and improved microbial killing, and allow to mitigate potential side effects to the host. Starting with a general overview of antibacterial mechanisms, we subsequently focus on specific metal ions such as silver, zinc, copper, iron and gold, and outline their distinct modes of action. Finally, we discuss the use of these metal ions and nanoparticles in tissue engineering to prevent implant failure.

Graphene-based nanomaterials as antimicrobial surface coatings: A parallel approach to restrain the expansion of COVID-19

The recently emerged severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has become a significant and topmost global health challenge of today. SARS-CoV-2 can propagate through several direct or indirect means resulting in its exponential spread in short times. Consequently, finding new research based real-world and feasible solutions to interrupt the spread of pathogenic microorganisms is indispensable. It has been established that this virus can survive on a variety of available surfaces ranging from a few hours to a few days, which has increased the risk of COVID-19 spread to large populations. Currently, available surface disinfectant chemicals provide only a temporary solution and are not recommended to be used in the long run due to their toxicity and irritation. Apart from the urgent development of vaccine and antiviral drugs, there is also a need to design and develop surface disinfectant antiviral coatings for long-term applications even for new variants. The unique physicochemical properties of graphene-based nanomaterials (GBNs) have been widely investigated for antimicrobial applications. However, the research work for their use in antimicrobial surface coatings is minimal. This perspective enlightens the scope of using GBNs as antimicrobial/antiviral surface coatings to reduce the spread of transmittable microorganisms, precisely, SARS-CoV-2. This study attempts to demonstrate the synergistic effect of GBNs and metallic nanoparticles (MNPs), for their potential antiviral applications in the development of surface disinfectant coatings. Some proposed mechanisms for the antiviral activity of the graphene family against SARS-CoV-2 has also been explained. It is anticipated that this study will potentially lead to new insights and future trends to develop a framework for further investigation on this research area of pivotal importance to minimize the transmission of current and any future viral outbreaks.

Transcriptomic Response of Huanglongbing-Infected Citrus sinensis Following Field Application of a Microbial Fermentation Product

Huanglongbing (HLB) is considered the most destructive disease in Citrus production and threatens the future of the industry. Microbial-derived defense elicitors have gained recognition for their role in plant defense priming. This work assessed a 5% (V/V) microbial fermentation application (MFA) and its role in the elicitation of defense responses in HLB-infected Citrus sinensis trees following a foliar application with a pump sprayer. Using a PCR detection method, HLB infection levels were monitored in healthy and infected trees for 20months. Nutrient analysis assessed N, P, K, Ca, Mg, Mn, Zn, Fe, B, and Cu concentrations in the trees. MFA significantly increased Cu concentrations in treated trees and resulted in the stabilization of disease index (DI) in infected trees. Initial real-time qPCR analysis of defense-associated genes showed a significant increase in pathogenesis-related protein 2 (PR2) and phenylalanine ammonia lyase (PAL) gene expression in healthy and HLB-infected trees in response to MFA. Gene expression of PR2 and PAL peaked 6h post-microbial fermentation application during an 8-h sampling period. A transcriptomic assessment using GeneChip microarray of the hour 6 samples revealed differential expression of 565 genes when MFA was applied to healthy trees and 909 genes when applied infected citrus trees when compared to their respective controls. There were 403 uniquely differentially expressed genes in response to MFA following an intersectional analysis of both healthy and infected citrus trees. The transcriptomic analysis revealed that several genes associated with plant development, growth, and defense were upregulated in response to MFA, including multiple PR genes, lignin formation genes, ROS-related genes, hormone synthases, and hormone regulators. This study provides further evidence that MFA may play an important role as a plant elicitor in an integrated pest management strategy in citrus and other agronomically important crops.

Fabrication of Antibacterial Metal Surfaces Using Magnetron-Sputtering Method

One-hundred-nanometer films consisting of silver, copper, and gold nanocrystallites were prepared, and their antibacterial properties were quantitatively measured. The magnetron-sputtering method was used for the preparation of the metallic films over the glass plate. Single- and double-layer films were manufactured. The films were thoroughly characterized with the XRD, SEM, EDS, and XPS methods. The antibacterial activity of the samples was investigated. Gram-negative Escherichia coli, strain K12 ATCC 25922 (E. coli), and Gram-positive Staphylococcus epidermidis, ATCC 49461 (S. epidermidis), were used in the microbial tests. The crystallite size was about 30 nm in the cases of silver and gold and a few nanometers in the case of copper. Significant oxidation of the copper films was proven. The antibacterial efficacy of the tested samples followed the order: Ag/Cu > Au/Cu > Cu. It was concluded that such metallic surfaces may be applied as contact-killing materials for a more effective fight against bacteria and viruses.

What We Are Learning from COVID-19 for Respiratory Protection: Contemporary and Emerging Issues

Infectious respiratory diseases such as the current COVID-19 have caused public health crises and interfered with social activity. Given the complexity of these novel infectious diseases, their dynamic nature, along with rapid changes in social and occupational environments, technology, and means of interpersonal interaction, respiratory protective devices (RPDs) play a crucial role in controlling infection, particularly for viruses like SARS-CoV-2 that have a high transmission rate, strong viability, multiple infection routes and mechanisms, and emerging new variants that could reduce the efficacy of existing vaccines. Evidence of asymptomatic and pre-symptomatic transmissions further highlights the importance of a universal adoption of RPDs. RPDs have substantially improved over the past 100 years due to advances in technology, materials, and medical knowledge. However, several issues still need to be addressed such as engineering performance, comfort, testing standards, compliance monitoring, and regulations, especially considering the recent emergence of pathogens with novel transmission characteristics. In this review, we summarize existing knowledge and understanding on respiratory infectious diseases and their protection, discuss the emerging issues that influence the resulting protective and comfort performance of the RPDs, and provide insights in the identified knowledge gaps and future directions with diverse perspectives.

Application of Copper Iodide Nanoparticle-Doped Film and Fabric To Inactivate SARS-CoV-2 via the Virucidal Activity of Cuprous Ions (Cu+)

As a result of the novel coronavirus disease 2019 pandemic, strengthening control measures against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become an urgent global issue. In addition to antiviral therapy and vaccination strategies, applying available virucidal substances for SARS-CoV-2 inactivation is also a target of research to prevent the spread of infection. Here, we evaluated the SARS-CoV-2 inactivation activity of a copper iodide (CuI) nanoparticle dispersion, which provides Cu+ ions having high virucidal activity, and its mode of actions. In addition, the utility of CuI-doped film and fabric for SARS-CoV-2 inactivation was evaluated. The CuI dispersion exhibited time-dependent rapid virucidal activity. Analyses of the modes of action of CuI performed by Western blotting and real-time reverse transcription-PCR targeting viral proteins and the genome revealed that CuI treatment induced the destruction of these viral components. In this setting, the indirect action of CuI-derived reactive oxygen species contributed to the destruction of viral protein. Moreover, the CuI-doped film and fabric demonstrated rapid inactivation of the SARS-CoV-2 solution in which the viral titer was high. These findings indicated the utility of the CuI-doped film and fabric as anti-SARS-CoV-2 materials for the protection of high-touch environmental surfaces and surgical masks/protective clothes. Throughout this study, we demonstrated the effectiveness of CuI nanoparticles for inactivating SARS-CoV-2 and revealed a part of its virucidal mechanism of action. IMPORTANCE The COVID-19 pandemic has caused an unprecedented number of infections and deaths. As the spread of the disease is rapid and the risk of infection is severe, hand and environmental hygiene may contribute to suppressing contact transmission of SARS-CoV-2. Here, we evaluated the SARS-CoV-2 inactivation activity of CuI nanoparticles, which provide the Cu+ ion as an antiviral agent, and we provided advanced findings of the virucidal mechanisms of action of Cu+. Our results showed that the CuI dispersion, as well as CuI-doped film and fabric, rapidly inactivated SARS-CoV-2 with a high viral titer. We also demonstrated the CuI's virucidal mechanisms of action, specifically the destruction of viral proteins and the genome by CuI treatment. Protein destruction largely depended on CuI-derived reactive oxygen species. This study provides novel information about the utility and mechanisms of action of promising virucidal material against SARS-CoV-2.

Antibacterial Efficacy of Cold-Sprayed Copper Coatings against Gram-Positive Staphylococcus aureus and Gram-Negative Escherichia coli

Contact surfaces have been identified as one of the main routes for pathogen transmission. The efficacy to kill both viruses and bacteria on touch surfaces is critical to reducing the rampant spread of harmful pathogens. Copper is one such material that has been traditionally used for its antimicrobial properties. However, most contact/touch surfaces are made up of steel or aluminum due to their structural properties. Therefore, coating high-touch components with copper is one possible solution to improve antibacterial efficacy. In this study, copper was coated on both stainless steel and aluminum substrates using a cold spray process which is a fast and economic coating technique. The coated samples in both as-deposited and heat-treated states were exposed to Escherichia coli and Staphylococcus aureus bacteria, and their efficacy was compared with bulk copper plate. It was found that both bacterial cells responded differently to the different coating properties such as coating thickness, porosity, hardness, surface roughness, oxide content, and galvanic coupling effect. These correlations were elucidated in light of various results obtained from antibacterial and bacterial attachment tests, and materials characterizations of the coatings. It is possible to tailor copper coating characteristics to render them more effective against targeted bacteria.

A Liquid Metal Mediated Metallic Coating for Antimicrobial and Antiviral Fabrics

Fabrics are widely used in hospitals and many other settings for bedding, clothing, and face masks; however, microbial pathogens can survive on surfaces for a long time, leading to microbial transmission. Coatings of metallic particles on fabrics have been widely used to eradicate pathogens. However, current metal particle coating technologies encounter numerous issues such as nonuniformity, processing complexity, and poor adhesion. To overcome these issues, an easy-to-control and straightforward method is reported to coat a wide range of fabrics by using gallium liquid metal (LM) particles to facilitate the deposition of liquid metal copper alloy (LMCu) particles. Gallium particles coated on the fabric provide nucleation sites for forming LMCu particles at room temperature via galvanic replacement of Cu²⁺ ions. The LM helps promote strong adhesion of the particles to the fabric. The presence of the LMCu particles can eradicate over 99% of pathogens (including bacteria, fungi, and viruses) within 5 min, which is significantly more effective than control samples coated with only Cu. The coating remains effective over multiple usages and against contaminated droplets and aerosols, such as those encountered in facemasks. This facile coating method is promising for generating robust antibacterial, antifungal, and antiviral fabrics and surfaces.

Functionalized Antimicrobial Nanofibers: Design Criteria and Recent Advances

The rise of antibiotic resistance has become a major threat to human health and it is spreading globally. It can cause common infectious diseases to be difficult to treat and leads to higher medical costs and increased mortality. Hence, multifunctional polymeric nanofibers with distinctive structures and unique physiochemical properties have emerged as a neo-tool to target biofilm and overcome deadly bacterial infections. This review emphasizes electrospun nanofibers' design criteria and properties that can be utilized to enhance their therapeutic activity for antimicrobial therapy. Also, we present recent progress in designing the surface functionalization of antimicrobial nanofibers with non-antibiotic agents for effective antibacterial therapy. Lastly, we discuss the future trends and remaining challenges for polymeric nanofibers.

High-Resolution Microscopical Studies of Contact Killing Mechanisms on Copper-Based Surfaces

The mechanisms of bacterial contact killing induced by Cu surfaces were explored through high-resolution studies based on combinations of the focused ion beam (FIB), scanning transmission electron microscopy (STEM), high-resolution TEM, and nanoscale Fourier transform infrared spectroscopy (nano-FTIR) microscopy of individual bacterial cells of Gram-positive Bacillus subtilis in direct contact with Cu metal and Cu5Zn5Al1Sn surfaces after high-touch corrosion conditions. This approach permitted subcellular information to be extracted from the bioinorganic interface between a single bacterium and Cu/Cu5Zn5Al1Sn surfaces after complete contact killing. Early stages of interaction between individual bacteria and the metal/alloy surfaces include cell leakage of extracellular polymeric substances (EPSs) from the bacterium and changes in the metal/alloy surface composition upon adherence of bacteria. Three key observations responsible for Cu-induced contact killing include cell membrane damage, formation of nanosized copper-containing particles within the bacteria cell, and intracellular copper redox reactions. Direct evidence of cell membrane damage was observed upon contact with both Cu metal and Cu5Zn5Al1Sn surfaces. Cell membrane damage permits copper to enter into the cell interior through two possible routes, as small fragmentized Cu₂O particles from the corrosion product layer and/or as released copper ions. This results in the presence of intracellular copper oxide nanoparticles inside the cell. The nanosized particles consist primarily of CuO with smaller amounts of Cu₂O. The existence of two oxidation states of copper suggests that intracellular redox reactions play an important role. The nanoparticle formation can be regarded as a detoxification process of copper, which immobilizes copper ions via transformation processes within the bacteria into poorly soluble or even insoluble nanosized Cu structures. Similarly, the formation of primarily Cu(II) oxide nanoparticles could be a possible way for the bacteria to deactivate the toxic effects induced by copper ions via conversion of Cu(I) to Cu(II).

In situ microwave heating fabrication of copper nanoparticles inside cotton fiber using pressurization in immiscible liquids with raw material solutions

We developed a method for in situ fabrication of copper nanoparticles inside cotton fibers. Copper nanoparticles can be fabricated mainly in the central part of the fiber by absorbing a raw material solution and by applying microwave heating in a state where the raw material solution is pressed with immiscible liquids. Surface SEM images and cross-sectional EDS mapping for the fabricated fibers clarified that copper nanoparticles fabricated on the cotton surface were suppressed considerably more by the hydrophobic raw material solution than by the hydrophilic raw material solution. These cotton fibers containing copper nanoparticles were found to have antiviral properties against the influenza A virus.

Antibacterial and cell-friendly copper-substituted tricalcium phosphate ceramics for biomedical implant applications

The development of new materials with antibacterial properties and the scope to decrease or eliminate the excessive antibiotic use is an urgent priority due to the growing antibiotic resistance-related mortalities. New bone substitute materials with intrinsic antibacterial characteristics are highly requested for various clinical applications. In this study, the choice of copper ions as substitutes for calcium in tricalcium phosphate (TCP) has been justified by their pronounced broad-spectrum antibacterial properties. Copper-substituted TCP (Cu-TCP) ceramics with the copper content of 1.4 and 0.1 wt% were synthesized by mechano-chemical activation. X-ray diffraction (XRD) analyses established that both pure and copper-containing compounds adopted the structure of whitlockite (β-TCP). XRD and electron paramagnetic resonance (EPR) spectroscopy revealed the partial isovalent substitution of calcium ions with copper ions in the β-TCP lattice. With the use of infrared and EPR spectroscopies, it was detected that carbonate ions got incorporated into the β-TCP structure during the synthesis procedure. By releasing the tension in the M(5)O6 octahedron consequential to the lower CaO bond length than the corresponding sum of ionic radii, the substitution of calcium with smaller copper ions stabilizes the structure of β-TCP. As concluded form the thermal analyses, the introduction of Cu prevented the polymorphic transformation of β- to α-TCP. At the same time, the introduction of Cu to the β-TCP structure enhanced the crystal growth and porosity of the ceramics, which had a positive effect on the cytocompatibility of the material. The MTT colorimetric assay showed that the metabolic activity of the mouse fibroblast NCTC L929 cell line during 24 h of incubation with 3-day extracts from Cu-TCP (1.4 wt%) and β-TCP pellets in the cell culture medium was similar to the negative control, indicating the absence of any inhibitory effects on cells. The seeding and the growth of human dental pulp stem cells on the surface of Cu-TCP (1.4 wt%) and β-TCP ceramics also showed the absence of any signs of cytotoxicity. Finally, microbiological assays demonstrated the antibacterial activity of Cu-TCP ceramics against Escherichia coli and Salmonella enteritidis, whereas β-TCP did not exhibit such an activity. Overall, the addition of Cu ions to β-TCP improves its antibacterial properties without diminishing the biocompatibility of the material, thus making it more attractive than pure β-TCP for clinical applications such as synthetic bone grafts and orthopaedic implant coatings.

Membrane Transporters Involved in the Antimicrobial Activities of Pyrithione in Escherichia coli

Pyrithione (2-mercaptopyridine-N-oxide) is a metal binding modified pyridine, the antibacterial activity of which was described over 60 years ago. The formulation of zinc-pyrithione is commonly used in the topical treatment of certain dermatological conditions. However, the characterisation of the cellular uptake of pyrithione has not been elucidated, although an unsubstantiated assumption has persisted that pyrithione and/or its metal complexes undergo a passive diffusion through cell membranes. Here, we have profiled specific membrane transporters from an unbiased interrogation of 532 E. coli strains of knockouts of genes encoding membrane proteins from the Keio collection. Two membrane transporters, FepC and MetQ, seemed involved in the uptake of pyrithione and its cognate metal complexes with copper, iron, and zinc. Additionally, the phenotypes displayed by CopA and ZntA knockouts suggested that these two metal effluxers drive the extrusion from the bacterial cell of potentially toxic levels of copper, and perhaps zinc, which hyperaccumulate as a function of pyrithione. The involvement of these distinct membrane transporters contributes to the understanding of the mechanisms of action of pyrithione specifically and highlights, more generally, the important role that membrane transporters play in facilitating the uptake of drugs, including metal-drug compounds.

Effect of Ca2+ Replacement with Cu2+ Ions in Brushite on the Phase Composition and Crystal Structure

The gradual replacement of Ca2+ with Cu2+ ions in brushite (CaHPO4·2H2O) has been extensively studied and discussed. The approach adopted in this work has not been systematically explored in previous studies. This novel approach may prove beneficial for the production of Ca1−xCuxHPO4·nH2O materials with desired properties suitable for medical applications. Solutions of sodium dihydrogen orthophosphate dihydrate, NaH2PO4·2H2O, calcium nitrate tetrahydrate, Ca(NO3)2·4H2O, copper nitrate trihydrate, Cu(NO3)2·3H2O, ammonium hydroxide solution, and diluted HCl were used for the preparation of these materials. At low Cu/Ca molar ratios (up to 0.25) in the starting solution, biphasic phosphate minerals were formed: brushite and sampleite. When the Cu/Ca molar ratio increases gradually from 0.67 to 1.5, sampleite-like mineral precipitates. Powdered XRD (X-ray diffraction), thermogravimetric (TG) analysis, and SEM (scanning electron microscopy) techniques were employed for the study of the microstructure of the produced materials for different degrees of Ca replacement with Mg. It is found that the Cu/Ca ratio in the starting solution can be adjusted to obtain materials with tailored composition. Thus, a new method of sampleite-like synthesis as a rare mineral is introduced in this study. Both phosphate minerals brushite and sampleite-like minerals are attractive as precursors of bioceramics and biocements. The search for such products that may decrease the possibility of post prosthetic or implant infection can be crucial in preventing devastating post-surgical complications.

The In Vitro Anti-Pseudomonal Activity of Cu2+, Strawberry Furanone, Gentamicin, and Lytic Phages Alone and in Combination: Pros and Cons

In this study, we investigated the anti-pseudomonal activity of cupric ions (Cu²⁺), strawberry furanone (HDMF), gentamicin (GE), and three lytic Pseudomonas aeruginosa bacteriophages (KT28, KTN4, LUZ19), separately and in combination. HDMF showed an anti-virulent effect but only when applied with Cu²⁺ or GE. GE, at a sub-minimal inhibitory concentration, slowed down phage progeny production due to protein synthesis inhibition. Cu²⁺ significantly reduced both the bacterial cell count and the number of infective phage particles, likely due to its genotoxicity or protein inactivation and cell membrane disruption effects. Furthermore, Cu²⁺‘s probable sequestration by phage particles led to the reduction of free toxic metal ions available in the solution. An additive antibacterial effect was only observed for the combination of GE and Cu²⁺, potentially due to enhanced ROS production or to outer membrane permeabilization. This study indicates that possible interference between antibacterial agents needs to be carefully investigated for the preparation of effective therapeutic cocktails.

Proteomic Analysis of Copper Toxicity in Human Fungal Pathogen Cryptococcus neoformans

Cryptococcus neoformans is an invasive human fungal pathogen that causes more than 181,000 deaths each year. Studies have demonstrated that pulmonary C. neoformans infection induces innate immune responses involving copper, and copper detoxification in C. neoformans improves its fitness and pathogenicity during pulmonary C. neoformans infection. However, the molecular mechanism by which copper inhibits C. neoformans proliferation is unclear. We used a metallothionein double-knockout C. neoformans mutant that was highly sensitive to copper to demonstrate that exogenous copper ions inhibit fungal cell growth by inducing reactive oxygen species generation. Using liquid chromatography-tandem mass spectrometry, we found that copper down-regulated factors involved in protein translation, but up-regulated proteins involved in ubiquitin-mediated protein degradation. We propose that the down-regulation of protein synthesis and the up-regulation of protein degradation are the main effects of copper toxicity. The ubiquitin modification of total protein and proteasome activity were promoted under copper stress, and inhibition of the proteasome pathway alleviated copper toxicity. Our proteomic analysis sheds new light on the antifungal mechanisms of copper.

A genome-wide screen reveals the involvement of enterobactin-mediated iron acquisition in Escherichia coli survival during copper stress

Copper (Cu) is a key transition metal that is involved in many important biological processes in a cell. Cu is also utilized by the immune system to hamper pathogen growth during infection. However, genome-level knowledge on the mechanisms involved in adaptation to Cu stress is limited. Here, we report the results of a genome-wide reverse genetic screen for Cu-responsive phenotypes in Escherichia coli. Our screen has identified novel genes involved in adaptation to Cu stress in E. coli. We detected multiple genes involved in the biosynthesis and uptake of enterobactin, a siderophore utilized for high-affinity TonB-dependent acquisition of iron (Fe), as critical players in survival under Cu intoxication. We demonstrated the specificity of Cu-dependent killing by chelation of Cu and by genetic complementation of tonB. Notably, TonB is involved in protection from Cu in both laboratory and uropathogenic strains of E. coli. Cu stress leads to increased expression of the genes involved in Fe uptake, indicating that Fur regulon is derepressed during exposure to excess Cu. Trace element analyses revealed that Fe homeostasis is dysregulated during Cu stress. Taken together, our data supports a model in which lack of enterobactin-dependent Fe uptake leads to exacerbation of Cu toxicity, and elucidates the intricate connection between the homeostasis of Cu and Fe in a bacterial cell.

Endogenous nitric oxide-generating surfaces via polydopamine-copper coatings for preventing biofilm dispersal and promoting microbial killing

INTRODUCTION

Peri-implantitis is a bacterially induced inflammatory disease which affects the hard and soft tissues around a dental implant. Microbial biofilm formation is an important causative factor in peri-implantitis. The aim of this study is to develop an effective multifunctional surface coating for antimicrobial property and to counteract oral biofilm-associated infections via a single polydopamine copper coating (PDAM@Cu) on titanium implant surface to regulate endogenous nitric oxide (NO) generation.

METHODS

PDAM@Cu coatings were made with different concentrations of CuCl₂ on titanium surfaces with a simple dip coating technique. Coatings were characterised to evaluate Cu concentrations as well as NO release rates from the coatings. Further, salivary biofilms were made on the coatings using Brain Heart Infusion (BHI) media in an anaerobic chamber. Biofilms were prepared with three different mixtures, one of which was saliva only, the second had an addition of sheep's blood, and the third was prepared with NO donors S-nitrosoglutathione (GSNO) and L-glutathione (GSH) in the mixture of saliva and blood to evaluate the effects of endogenously produced NO on biofilms. The effectiveness of coated surfaces on biofilms were assessed using four different methods, namely, crystal violet assay, scanning electron microscopy imaging, 2,3-bis (2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino) carbonyl]-2H-tetrazolium hydroxide (XTT) metabolic assay, and live/dead staining.

RESULTS

NO release rates could be controlled with different Cu concentration in PDAM@Cu coatings. NO generated from the PDAM@Cu coatings effectively induced dispersal of biofilms shown by the reduction in biofilm biomass as well as reduced biofilm attachment in samples prepared with blood and NO donors. Cu ions released from the PDAM@Cu coatings resulted in killing of the dispersed bacteria, which was evidenced by the live/dead cell staining and reduced metabolic activity noted from the XTT assay. In contrast, samples prepared with saliva showed no significant reduction in biofilms, indicating the important effect of endogenously generated NO on biofilm dispersal.

CONCLUSION

In conclusion, PDAM@Cu coatings with NO generating surfaces have a dual anti-biofilm function, with a synergistic effect on biofilm dispersal from regulated NO generation and bactericidal effects from Cu ions from the coatings.

How Do We Determine the Efficacy of an Antibacterial Surface? A Review of Standardised Antibacterial Material Testing Methods

Materials that confer antimicrobial activity, be that by innate property, leaching of biocides or design features (e.g., non-adhesive materials) continue to gain popularity to combat the increasing and varied threats from microorganisms, e.g., replacing inert surfaces in hospitals with copper. To understand how efficacious these materials are at controlling microorganisms, data is usually collected via a standardised test method. However, standardised test methods vary, and often the characteristics and methodological choices can make it difficult to infer that any perceived antimicrobial activity demonstrated in the laboratory can be confidently assumed to an end-use setting. This review provides a critical analysis of standardised methodology used in academia and industry, and demonstrates how many key methodological choices (e.g., temperature, humidity/moisture, airflow, surface topography) may impact efficacy assessment, highlighting the need to carefully consider intended antimicrobial end-use of any product.

A review of recent and emerging antimicrobial nanomaterials in wastewater treatment applications

In this paper, we present a critical review on antimicrobial nanomaterials with demonstrated potential for application as a disinfection technology in wastewater treatment. Studies involving fabrication and testing of antimicrobial nanomaterials for wastewater treatment were gathered, critically reviewed, and analyzed. Our review shows that there are only a few eligible candidate nanoparticles (NPs) (metal and metal oxide) that can adequately serve as an antimicrobial agent. Nanosilver (nAg) was the most studied and moderately understood metal NPs with proven antimicrobial activity followed by ZnO (among antimicrobial metal oxide NPs) which outperformed titania (in the absence of light) in efficacy due to its better solubility in aqueous condition. The direction of future work was found to be in the development of antimicrobial nanocomposites, since they provide more stability for antimicrobial metal and metal oxides NPs in water, thereby increasing their activity. This review will serve as an updated survey, yet touching also the fundamentals of the antimicrobial activity, with vital information for researchers planning to embark on the development of superior antimicrobial nanomaterials for wastewater treatment applications.

Nanostructured Copper Surface Kills ESKAPE Pathogens and Viruses in Minutes

In the search for a fast contact-killing antimicrobial surface to break the transmission pathway of lethal pathogens, nanostructured copper surfaces were found to exhibit the desired antimicrobial properties. Compared with plain copper, these nanostructured copper surfaces with Cu(OH)₂ nano-sword or CuO nano-foam were found to completely eliminate pathogens at a fast rate, including clinically isolated drug resistant species. Additionally these nanostructured copper surfaces demonstrated potential antiviral properties when assessed against bacteriophages, as a viral surrogate, and murine hepatitis virus, a surrogate for SARS-CoV-2. The multiple modes of killing, physical killing and copper ion mediated killing contribute to the superior and fast kinetics of antimicrobial action against common microbes, and ESKAPE pathogens. Prototypes for air and water cleaning with current nanostructured copper surface have also been demonstrated.

Recent Advances in the Treatment of Bone Metastases and Primary Bone Tumors: An Up-to-Date Review

In the last decades, the treatment of primary and secondary bone tumors has faced a slow-down in its development, being mainly based on chemotherapy, radiotherapy, and surgical interventions. However, these conventional therapeutic strategies present a series of disadvantages (e.g., multidrug resistance, tumor recurrence, severe side effects, formation of large bone defects), which limit their application and efficacy. In recent years, these procedures were combined with several adjuvant therapies, with different degrees of success. To overcome the drawbacks of current therapies and improve treatment outcomes, other strategies started being investigated, like carrier-mediated drug delivery, bone substitutes for repairing bone defects, and multifunctional scaffolds with bone tissue regeneration and antitumor properties. Thus, this paper aims to present the types of bone tumors and their current treatment approaches, further focusing on the recent advances in new therapeutic alternatives.

Antimicrobial Activity of Metals and Metalloids

Competition shapes evolution. Toxic metals and metalloids have exerted selective pressure on life since the rise of the first organisms on the Earth, which has led to the evolution and acquisition of resistance mechanisms against them, as well as mechanisms to weaponize them. Microorganisms exploit antimicrobial metals and metalloids to gain competitive advantage over other members of microbial communities. This exerts a strong selective pressure that drives evolution of resistance. This review describes, with a focus on arsenic and copper, how microorganisms exploit metals and metalloids for predation and how metal- and metalloid-dependent predation may have been a driving force for evolution of microbial resistance against metals and metalloids. Expected final online publication date for the Annual Review of Microbiology, Volume 75 is October 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Radiation-induced synthesis of copper sulfide nanotubes with improved catalytic and antibacterial activities

In the current paper, copper sulfide nanotubes have been successfully synthesized via the green, simple, and effective gamma-radiolysis method without adding any capping or reducing agents. The structural and morphological characteristics of the as-prepared CuS nanotubes were investigated by X-ray diffraction (XRD), N₂ adsorption-desorption measurements at 77 K, transmission electron microscopy (TEM), and ultraviolet-visible (UV-vis) spectroscopy, which all demonstrated the formation of pure CuS covellite phase with tubular morphology. The synthesized CuS nanotubes possessed not only high activity towards the reduction of both cationic (methylene blue) and anionic (Congo red) dyes in the presence of NaBH₄ but also exhibited excellent reusability. In addition, the pseudo-first-order kinetic model represented the reduction of MB very well, and the value of the normalized rate constant (2.4 × 10^-2 s^-1 mg^-1) was higher than those of other solid catalysts reported in the literature. Ultimately, CuS nanotubes were found to have a broad-spectrum microbicidal action against the common microbiota, such as Gram-positive (exemplified by Bacillus subtilis and Staphylococcus aureus), Gram-negative bacteria (exemplified by Pseudomonas aeruginosa and Escherichia coli), yeast (exemplified by Candida albicans), and plant pathogenic fungi (exemplified by Aspergillus niger).

A case study of SARS-CoV-2 transmission behavior in a severely air-polluted city (Delhi, India) and the potential usage of graphene based materials for filtering air-pollutants and controlling/monitoring the COVID-19 pandemic

Globally, humanity is facing its most significant challenge in 100 years due to the novel coronavirus, SARS-CoV-2, which is responsible for COVID-19. Under the enormous pressure created by the pandemic, scientists are studying virus transmission mechanisms in order to develop effective mitigation strategies. However, no established methods have been developed to control the spread of this deadly virus. In addition, the ease in lockdown has escalated air pollution which may affect SARS-CoV-2 transmission through attachment to particulates. The present review summarizes the role of graphene nanomaterials, which show antimicrobial behavior and have antiviral efficacy, in reducing the spread of COVID-19. Graphene and its derivatives have excellent antimicrobial efficacy, providing both physical and chemical mechanisms of damage. Coupled with their lightness, optimal properties, and ease of functionalization, they are optimal nanomaterials for coating onto fabrics such as personal protection equipment, face masks and gloves to control the transmission of SARS-CoV-2 effectively. Biosensors using graphene can effectively detect the virus with high accuracy and sensitivity, providing rapid quantification. It is envisioned that the present work will boost the development of graphene-based highly sensitive, accurate and cost-effective diagnostic tools for efficiently monitoring and controlling the spread of COVID-19 and other air-borne viruses.