Effects of temperature and humidity on the efficacy of methicillin-resistant Staphylococcus aureus challenged antimicrobial materials containing silver and copper

Evaluation of antibacterial activity and influencing factors of normal and nanostructured copper-based materials

Background

Copper-based materials have garnered extensive recognition for their effective nature against microorganisms and their minimal toxicity. However, the evaluation for their antibacterial activity is still in its nascent stages, and the evaluation results based on existing criteria are not representative of real-world application.

Aim

To evaluate the antibacterial activity and primary determinants of influence of copper-based materials in order to investigate their practical antibacterial activity and potential mechanisms of such materials.

Methods

Staphylococcus aureus and Escherichia coli bacterial suspensions were applied via inoculation onto the surfaces of normal and nanostructured copper foil. Following incubation of the inoculated surfaces under diverse experimental conditions-including varying compositions of the bacterial suspension, the use of chemical neutralizers, the existence of organic interferents, and low temperature and humidity-surviving bacteria were enumerated. Using the scanning electron microscopy and X-ray photoelectron spectroscopy, the surface changes of copper-based materials were examined.

Findings

Following 1 h of exposure to 37 °C and 90% relative humidity, Staphylococcus aureus was reduced by 4.45 log10 on normal copper foil, while all of the bacteria were eradicated on nanostructured copper foil. In addition, it was discovered that preparing a bacterial suspension with PBS results in a significant number of Escherichia coli fatalities during the test, whereas using TPS promotes the bacteria's normal growth. Furthermore, the outcomes of the antibacterial activity test were diminished when chemical neutralization was employed, and the presence of organic interferents had distinct impacts on normal copper foil and nanostructured copper foil. Additionally, low temperatures and humidity diminished the antibacterial activity of copper foil, whereas normal copper foil produced significantly better results.

Conclusion

While copper-based materials exhibit robust antibacterial activity as determined by standard assays, their efficacy in real-world applications is subject to various influencing mechanisms. In order to objectively evaluate the antibacterial activity of copper-based materials and provide precise guidance for their development and practical application, it is essential to regulate test conditions with targeted.

Micro-Addition of Silver to Copper: One Small Step in Composition, a Change for a Giant Leap in Biocidal Activity

The use of copper as an antimicrobial agent has a long history and has gained renewed interest in the context of the COVID-19 pandemic. In this study, the authors investigated the antimicrobial properties of an alloy composed of copper with a small percentage of silver (Cu-0.03% wt.Ag). The alloy was tested against various pathogens, including Escherichia coli, Staphylococcus aureus, Candida albicans, Pseudomonas aeruginosa, and the H1N1 virus, using contact exposure tests. Results showed that the alloy was capable of inactivating these pathogens in two hours or less, indicating its strong antimicrobial activity. Electrochemical measurements were also performed, revealing that the small addition of silver to copper promoted a higher resistance to corrosion and shifted the formation of copper ions to higher potentials. This shift led to a slow but continuous release of Cu2+ ions, which have high biocidal activity. These findings show that the addition of small amounts of silver to copper can enhance its biocidal properties and improve its effectiveness as an antimicrobial material.

Assessing Antimicrobial Efficacy on Plastics and Other Non-Porous Surfaces: A Closer Look at Studies Using the ISO 22196:2011 Standard

The survival and spread of foodborne and nosocomial-associated bacteria through high-touch surfaces or contamination-prone sites, in either healthcare, domestic or food industry settings, are not always prevented by the employment of sanitary hygiene protocols. Antimicrobial surface coatings have emerged as a solution to eradicate pathogenic bacteria and prevent future infections and even outbreaks. Standardised antimicrobial testing methods play a crucial role in validating the effectiveness of these materials and enabling their application in real-life settings, providing reliable results that allow for comparison between antimicrobial surfaces while assuring end-use product safety. This review provides an insight into the studies using ISO 22196, which is considered the gold standard for antimicrobial surface coatings and examines the current state of the art in antimicrobial testing methods. It primarily focuses on identifying pitfalls and how even small variations in methods can lead to different results, affecting the assessment of the antimicrobial activity of a particular product.

Characteristics and Key Features of Antimicrobial Materials and Associated Mechanisms for Diverse Applications

Since the Fourth Industrial Revolution, three-dimensional (3D) printing has become a game changer in manufacturing, particularly in bioengineering, integrating complex medical devices and tools with high precision, short operation times, and low cost. Antimicrobial materials are a promising alternative for combating the emergence of unforeseen illnesses and device-related infections. Natural antimicrobial materials, surface-treated biomaterials, and biomaterials incorporated with antimicrobial materials are extensively used to develop 3D-printed products. This review discusses the antimicrobial mechanisms of different materials by providing examples of the most commonly used antimicrobial materials in bioengineering and brief descriptions of their properties and biomedical applications. This review will help researchers to choose suitable antimicrobial agents for developing high-efficiency biomaterials for potential applications in medical devices, packaging materials, biomedical applications, and many more.

Antibacterial activity of solid surfaces is critically dependent on relative humidity, inoculum volume, and organic soiling

Antimicrobial surface materials potentially prevent pathogen transfer from contaminated surfaces. Efficacy of such surfaces is assessed by standard methods using wet exposure conditions known to overestimate antimicrobial activity compared to dry exposure. Some dry test formats have been proposed but semi-dry exposure scenarios e.g. oral spray or water droplets exposed to ambient environment, are less studied. We aimed to determine the impact of environmental test conditions on antibacterial activity against the model species Escherichia coli and Staphylococcus aureus. Surfaces based on copper, silver, and quaternary ammonium with known or claimed antimicrobial properties were tested in conditions mimicking microdroplet spray or larger water droplets exposed to variable relative air humidity in the presence or absence of organic soiling. All the environmental parameters critically affected antibacterial activity of the tested surfaces from no effect in high-organic dry conditions to higher effect in low-organic humid conditions but not reaching the effect size demonstrated in the ISO 22169 wet format. Copper was the most efficient antibacterial surface followed by silver and quaternary ammonium based coating. Antimicrobial testing of surfaces using small droplet contamination in application-relevant conditions could therefore be considered as one of the worst-case exposure scenarios relevant to dry use surfaces.

Enhancing Biocidal Capability in Cuprite Coatings

The SARS-CoV-2 global pandemic has reinvigorated interest in the creation and widespread deployment of durable, cost-effective, and environmentally benign antipathogenic coatings for high-touch public surfaces. While the contact-kill capability and mechanism of metallic copper and its alloys are well established, the biocidal activity of the refractory oxide forms remains poorly understood. In this study, commercial cuprous oxide (Cu2O, cuprite) powder was rapidly nanostructured using high-energy cryomechanical processing. Coatings made from these processed powders demonstrated a passive "contact-kill" response to Escherichia coli (E. coli) bacteria that was 4× (400%) faster than coatings made from unprocessed powder. No viable bacteria (>99.999% (5-log10) reduction) were detected in bioassays performed after two hours of exposure of E. coli to coatings of processed cuprous oxide, while a greater than 99% bacterial reduction was achieved within 30 min of exposure. Further, these coatings were hydrophobic and no external energy input was required to activate their contact-kill capability. The upregulated antibacterial response of the processed powders is positively correlated with extensive induced crystallographic disorder and microstrain in the Cu2O lattice accompanied by color changes that are consistent with an increased semiconducting bandgap energy. It is deduced that cryomilling creates well-crystallized nanoscale regions enmeshed within the highly lattice-defective particle matrix. Increasing the relative proportion of lattice-defective cuprous oxide exposed to the environment at the coating surface is anticipated to further enhance the antipathogenic capability of this abundant, inexpensive, robust, and easily handled material for wider application in contact-kill surfaces.

Demonstrating the In Vitro and In Situ Antimicrobial Activity of Oxide Mineral Microspheres: An Innovative Technology to Be Incorporated into Porous and Nonporous Materials

The antimicrobial activity of surfaces treated with zinc and/or magnesium mineral oxide microspheres is a patented technology that has been demonstrated in vitro against bacteria and viruses. This study aims to evaluate the efficiency and sustainability of the technology in vitro, under simulation-of-use conditions, and in situ. The tests were undertaken in vitro according to the ISO 22196:2011, ISO 20473:2013, and NF S90-700:2019 standards with adapted parameters. Simulation-of-use tests evaluated the robustness of the activity under worst-case scenarios. The in situ tests were conducted on high-touch surfaces. The in vitro results show efficient antimicrobial activity against referenced strains with a log reduction of >2. The sustainability of this effect was time-dependent and detected at lower temperatures (20 ± 2.5 °C) and humidity (46%) conditions for variable inoculum concentrations and contact times. The simulation of use proved the microsphere's efficiency under harsh mechanical and chemical tests. The in situ studies showed a higher than 90% reduction in CFU/25 cm² per treated surface versus the untreated surfaces, reaching a targeted value of <50 CFU/cm². Mineral oxide microspheres can be incorporated into unlimited surface types, including medical devices, to efficiently and sustainably prevent microbial contamination.

Antiviral and Antibacterial Cold Spray Coating Application on Rubber Substrate, Disruption in Disease Transmission Chain

The objective of this study was to prepare a copper-coated rubber surface using cold spray technology with improved virucidal and antimicrobial properties to fight against highly transmissible viruses and bacteria. A successful cold spray coating was produced using irregular-shaped pure Cu powder on an escalator handrail rubber. The powder particles and the deposited coatings (single and double pass) were characterized in terms of particle morphology and size distribution, coating surface and coat/substrate cross-section properties. The bonding between powder and rubber surfaces was purely mechanical interlocking. The Cu powder penetration depth within the rubber surface increases with a number of depositions pass. The virucidal properties of the coated surface were tested utilizing surrogates for SARS-CoV-2: HCoV-229E, a seasonal human coronavirus, and baculovirus, a high-titer enveloped insect cell virus. A double-pass coated surface showed significant baculovirus inactivation relative to a bare rubber control surface after 2-h (approximately 1.7-log) and 4-h (approximately 6.2-log), while a 4-h exposure reduced HCoV-229E titer to below the limit of detection. A similar microbial test was performed using E. coli, showing a 4-log microbial reduction after 2-h exposure relative to the bare rubber. These promising results open a new application for cold spray in the health sector.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11666-023-01553-x.

Interlaboratory reproducibility of a touch-transfer assay for the assessment of antimicrobial surfaces

BACKGROUND

Various assay methods have been developed to study antimicrobial activity based on contamination of surfaces with different amounts of liquid bacterial suspensions. Since surfaces with frequent hand contact are typically touched in a dry state in clinical settings, these tests may be inappropriate at assessing effectiveness to reduce pathogen transmission.

AIM

To investigate a surface previously confirmed to display antimicrobial activity even after drying of small volumes of bacterial suspension (Egger antimicrobial surfaces: EAS) under conditions modelling dry contamination using a touch-transfer method.

METHODS

EAS, an antimicrobial copper alloy, as well as a negative control were examined to assess interlaboratory test reproducibility.

FINDINGS

Significantly fewer bacteria on EAS after touch transfer and some differences in the touch transmission were detected between the two laboratories. However, an identical assessment of effectiveness for EAS came from both laboratories. Interestingly, despite previously detected antimicrobial efficacy of EAS and the antimicrobial copper alloy after liquid contamination, insufficient activity was observed under dry conditions during a contact time of 4 h by both laboratories. Experiments under standardized air humidity in one laboratory revealed at least for copper a strong influence of humidity on antimicrobial activity. These data indicate that procedures involving contamination of surfaces with organisms suspended in liquids are not directly comparable to dry contamination.

CONCLUSION

Since, in the real world of a hospital, organisms are typically transferred between dry surfaces, further standardization of the touch-transfer method is worthwhile for a better understanding of the efficacy of such surfaces.

Significance of additive manufacturing amidst the pandemic

In the light of COVID-19 pandemic, a global shortage for Personnel Protective Equipment (PPE) led to the search for an alternative to fill the gap where additive manufacturing made necessary development of rapid design and adaptive filtering masks for local manufacturing using 3D printing to help the frontline workers. The review focuses on the utilization of antimicrobial materials in additive manufacturing with the use of bespoke design to facilitate and respond to the disruptions in the medical supply chain. Previous studies confirmed the age-old theory of copper as an antimicrobial material with contact killing properties. The antimicrobial properties of copper have been registered at the U.S. Environmental Protection Agency as the first solid antimicrobial material. Combining the properties of copper in a PLA (Polylactic Acid) filament as a nano composite, Copper-3D facilitates the antimicrobial properties to any 3D printed object. Provided this flexibility of 3D printing, the use of masks designed distinctively based on the 3D scan of an individual's facial structures as an efficient Personnel Protective Equipment is also addressed. Additive manufacturing as a support to the shortage of medical devices and a responsive method to the disruption in the supply chain is discussed.

Antimicrobial Photodynamic Coatings Reduce the Microbial Burden on Environmental Surfaces in Public Transportation—A Field Study in Buses

Millions of people use public transportation daily worldwide and frequently touch surfaces, thereby producing a reservoir of microorganisms on surfaces increasing the risk of transmission. Constant occupation makes sufficient cleaning difficult to achieve. Thus, an autonomous, permanent, antimicrobial coating (AMC) could keep down the microbial burden on such surfaces. A photodynamic AMC was applied to frequently touched surfaces in buses. The microbial burden (colony forming units, cfu) was determined weekly and compared to equivalent surfaces in buses without AMC (references). The microbial burden ranged from 0–209 cfu/cm² on references and from 0–54 cfu/cm² on AMC. The means were 13.4 ± 29.6 cfu/cm² on references and 4.5 ± 8.4 cfu/cm² on AMC (p < 0.001). The difference in microbial burden on AMC and references was almost constant throughout the study. Considering a hygiene benchmark of 5 cfu/cm², the data yield an absolute risk reduction of 22.6% and a relative risk reduction of 50.7%. In conclusion, photodynamic AMC kept down the microbial burden, reducing the risk of transmission of microorganisms. AMC permanently and autonomously contributes to hygienic conditions on surfaces in public transportation. Photodynamic AMC therefore are suitable for reducing the microbial load and closing hygiene gaps in public transportation.

Advances in Copper-Based Biomaterials With Antibacterial and Osteogenic Properties for Bone Tissue Engineering

Treating bone defects coupled with pathogen infections poses a formidable challenge to clinical medicine. Thus, there is an urgent need to develop orthopedic implants that provide excellent antibacterial and osteogenic properties. Of the various types, copper-based biomaterials capable of both regenerating bone and fighting infections are an effective therapeutic strategy for bone tissue engineering and therefore have attracted significant research interest. This review examines the advantages of copper-based biomaterials for biological functions and introduces these materials’ antibacterial mechanisms. We summarize current knowledge about the application of copper-based biomaterials with antimicrobial and osteogenic properties in the prevention and treatment of bone infection and discuss their potential uses in the field of orthopedics. By examining both broad and in-depth research, this review functions as a practical guide to developing copper-based biomaterials and offers directions for possible future work.

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

Preparation and Characterization of Photocatalytically Active Antibacterial Surfaces Covered with Acrylic Matrix Embedded Nano-ZnO and Nano-ZnO/Ag

In the context of healthcare-acquired infections, microbial cross-contamination and the spread of antibiotic resistance, additional passive measures to prevent pathogen carryover are urgently needed. Antimicrobial high-touch surfaces that kill microbes on contact or prevent their adhesion could be considered to mitigate the spread. Here, we demonstrate that photocatalytic nano-ZnO- and nano-ZnO/Ag-based antibacterial surfaces with efficacy of at least a 2.7-log reduction in Escherichia coli and Staphylococcus aureus viability in 2 h can be produced by simple measures using a commercial acrylic topcoat for wood surfaces. We characterize the surfaces taking into account cyclic wear and variable environmental conditions. The light-induced antibacterial and photocatalytic activities of the surfaces are enhanced by short-term cyclic wear, indicating their potential for prolonged effectivity in long-term use. As the produced surfaces are generally more effective at higher relative air humidity and silver-containing surfaces lost their contact-killing properties in dry conditions, it is important to critically evaluate the end-use conditions of materials and surfaces to be tested and select application-appropriate methods for their efficacy assessment.

Nanotechnology as a Novel Approach in Combating Microbes Providing an Alternative to Antibiotics

The emergence of infectious diseases promises to be one of the leading mortality factors in the healthcare sector. Although several drugs are available on the market, newly found microorganisms carrying multidrug resistance (MDR) against which existing drugs cannot function effectively, giving rise to escalated antibiotic dosage therapies and the need to develop novel drugs, which require time, money, and manpower. Thus, the exploitation of antimicrobials has led to the production of MDR bacteria, and their prevalence and growth are a major concern. Novel approaches to prevent antimicrobial drug resistance are in practice. Nanotechnology-based innovation provides physicians and patients the opportunity to overcome the crisis of drug resistance. Nanoparticles have promising potential in the healthcare sector. Recently, nanoparticles have been designed to address pathogenic microorganisms. A multitude of processes that can vary with various traits, including size, morphology, electrical charge, and surface coatings, allow researchers to develop novel composite antimicrobial substances for use in different applications performing antimicrobial activities. The antimicrobial activity of inorganic and carbon-based nanoparticles can be applied to various research, medical, and industrial uses in the future and offer a solution to the crisis of antimicrobial resistance to traditional approaches. Metal-based nanoparticles have also been extensively studied for many biomedical applications. In addition to reduced size and selectivity for bacteria, metal-based nanoparticles have proven effective against pathogens listed as a priority, according to the World Health Organization (WHO). Moreover, antimicrobial studies of nanoparticles were carried out not only in vitro but in vivo as well in order to investigate their efficacy. In addition, nanomaterials provide numerous opportunities for infection prevention, diagnosis, treatment, and biofilm control. This study emphasizes the antimicrobial effects of nanoparticles and contrasts nanoparticles' with antibiotics' role in the fight against pathogenic microorganisms. Future prospects revolve around developing new strategies and products to prevent, control, and treat microbial infections in humans and other animals, including viral infections seen in the current pandemic scenarios.

Antimicrobial Activity of a Novel Cu(NO3)2-Containing Sol-Gel Surface under Different Testing Conditions

In this study, assessment of the antimicrobial activity of a novel, plasma-cured 2.5% (w/v) Cu(NO₃)₂-containing sol–gel surface was performed. In contrast to state-of-the-art sol–gel coatings, the plasma curing led to a gradient in cross-linking with the highest values at the top of the coating. As a result, the coating behaved simultaneously hard, scratch-resistant, and tough, the latter due to the more flexible bulk of the coating toward the substrate. Further, the diffusion and permeation through the coating also increased toward the substrate. In our study, tests according to ISO 22196 showed antibacterial activity of the 2.5% (w/v) Cu(NO₃)₂-containing sol–gel surface against all bacterial strains tested, and we expanded the testing further using a “dry” evaluation without an aqueous contact phase, which confirmed the antimicrobial efficacy of the 2.5% (w/v) Cu(NO₃)₂-containing sol–gel surface. However, further investigation under exposure to soiling with the addition of 0.3% albumin, used to simulate organic load, led to a significant impairment in the antibacterial effect under both tested conditions. Furthermore, re-testing of the surface after disinfection with 70% ethanol led to a total loss of antibacterial activity. Our results showed that besides the mere application of an antimicrobial agent to a surface coating, it is also necessary to consider the future use of these surfaces in the experimental phase combining industry and science. Therefore, a number of tests corresponding to the utilization of the surface should be obligative on the basis of this assessment.

Antimicrobial coatings for environmental surfaces in hospitals: a potential new pillar for prevention strategies in hygiene

Recent reports provide evidence that contaminated healthcare environments represent major sources for the acquisition and transmission of pathogens. Antimicrobial coatings (AMC) may permanently and autonomously reduce the contamination of such environmental surfaces complementing standard hygiene procedures. This review provides an overview of the current status of AMC and the demands to enable a rational application of AMC in health care settings. Firstly, a suitable laboratory test norm is required that adequately quantifies the efficacy of AMC. In particular, the frequently used wet testing (e.g. ISO 22196) must be replaced by testing under realistic, dry surface conditions. Secondly, field studies should be mandatory to provide evidence for antimicrobial efficacy under real-life conditions. The antimicrobial efficacy should be correlated to the rate of nosocomial transmission at least. Thirdly, the respective AMC technology should not add additional bacterial resistance development induced by the biocidal agents and co- or cross-resistance with antibiotic substances. Lastly, the biocidal substances used in AMC should be safe for humans and the environment. These measures should help to achieve a broader acceptance for AMC in healthcare settings and beyond. Technologies like the photodynamic approach already fulfil most of these AMC requirements.

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.

Can Copper Products and Surfaces Reduce the Spread of Infectious Microorganisms and Hospital-Acquired Infections?

Pathogen transfer and infection in the built environment are globally significant events, leading to the spread of disease and an increase in subsequent morbidity and mortality rates. There are numerous strategies followed in healthcare facilities to minimize pathogen transfer, but complete infection control has not, as yet, been achieved. However, based on traditional use in many cultures, the introduction of copper products and surfaces to significantly and positively retard pathogen transmission invites further investigation. For example, many microbes are rendered unviable upon contact exposure to copper or copper alloys, either immediately or within a short time. In addition, many disease-causing bacteria such as E. coli O157:H7, hospital superbugs, and several viruses (including SARS-CoV-2) are also susceptible to exposure to copper surfaces. It is thus suggested that replacing common touch surfaces in healthcare facilities, food industries, and public places (including public transport) with copper or alloys of copper may substantially contribute to limiting transmission. Subsequent hospital admissions and mortality rates will consequently be lowered, with a concomitant saving of lives and considerable levels of resources. This consideration is very significant in times of the COVID-19 pandemic and the upcoming epidemics, as it is becoming clear that all forms of possible infection control measures should be practiced in order to protect community well-being and promote healthy outcomes.

Copper as an antimicrobial agent: recent advances

From its uses in ancient civilisations, copper has an established history as an antimicrobial agent. Extensive research has determined the efficacy and mechanism of copper's antimicrobial activity against microorganisms. The process is multifaceted with the main mechanism of bactericidal activity being the generation of reactive oxygen species (ROS), which irreversibly damages membranes. Copper ions released from surfaces lead to RNA degradation and membrane disruption of enveloped viruses. For fungi, the mechanism involves the physical deterioration of the membrane and copper ion influx. Due to variations in the experimental parameters, it is difficult to compare studies directly. In this review article, we outline the importance of the experimental conditions currently employed and how they bear little resemblance to real-world conditions. We endorse previous recommendations calling for an update to industrial standard tests.

The causes of death for each microorganism by CuNPs and metallic copper is summarised.

Coating Technologies for Copper Based Antimicrobial Active Surfaces: A Perspective Review

Microbial contamination of medical devices and treatment rooms leads to several detrimental hospital and device-associated infections. Antimicrobial copper coatings are a new approach to control healthcare-associated infections (HAI’s). This review paper focuses on the efficient methods for depositing highly adherent copper-based antimicrobial coatings onto a variety of metal surfaces. Antimicrobial properties of the copper coatings produced by various deposition methods including thermal spray technique, electrodeposition, electroless plating, chemical vapor deposition (CVD), physical vapor deposition (PVD), and sputtering techniques are compared. The coating produced using different processes did not produce similar properties. Also, process parameters often could be varied for any given coating process to impart a change in structure, topography, wettability, hardness, surface roughness, and adhesion strength. In turn, all of them affect antimicrobial activity. Fundamental concepts of the coating process are described in detail by highlighting the influence of process parameters to increase antimicrobial activity. The strategies for developing antimicrobial surfaces could help in understanding the mechanism of killing the microbes.

Antibacterial activity testing methods for hydrophobic patterned surfaces

One strategy to decrease the incidence of hospital-acquired infections is to avoid the survival of pathogens in the environment by the development of surfaces with antimicrobial activity. To study the antibacterial behaviour of active surfaces, different approaches have been developed of which ISO 22916 is the standard. To assess the performance of different testing methodologies to analyse the antibacterial activity of hydrophobic surface patterned plastics as part of a Horizon 2020 European research project. Four different testing methods were used to study the antibacterial activity of a patterned film, including the ISO 22916 standard, the immersion method, the touch-transfer inoculation method, and the swab inoculation method, this latter developed specifically for this project. The non-realistic test conditions of the ISO 22916 standard showed this method to be non-appropriate in the study of hydrophobic patterned surfaces. The immersion method also showed no differences between patterned films and smooth controls due to the lack of attachment of testing bacteria on both surfaces. The antibacterial activity of films could be demonstrated by the touch-transfer and the swab inoculation methods, that more precisely mimicked the way of high-touch surfaces contamination, and showed to be the best methodologies to test the antibacterial activity of patterned hydrophobic surfaces. A new ISO standard would be desirable as the reference method to study the antibacterial behaviour of patterned surfaces.

Effective Antibacterial Activity of Degradable Copper-Doped Phosphate-Based Glass Nanozymes

Copper-containing antimicrobials are highly valuable in the field of medical disinfectants owing to their well-known high antimicrobial efficacy. Artificially synthesized nanozymes which can increase the level of reactive oxygen species (ROS) in the bacterial system have become research hotspots. Herein, we describe the design and fabrication of degradable Cu-doped phosphate-based glass (Cu-PBG) nanozyme, which can achieve excellent antibacterial effects against Gram-positive and Gram-negative bacteria. The antibacterial mechanism is based on the generation of ROS storm and the release of copper. It behaves like a peroxidase in wounds which are acidic and exerts lethal oxidative stress on bacteria via catalyzing the decomposition of H₂O₂ into hydroxyl radicals (^•OH). Quite different from any other reported nanozymes, the Cu-PBG is intrinsically degradable due to its phosphate glass nature. It gradually degrades and releases copper ions in a physiological environment, which further enhances the inhibition efficiency. Satisfactory antibacterial effects are verified both in vitro and in vivo. Being biodegradable, the prepared Cu-PBG exhibits excellent in vivo biocompatibility and does not cause any adverse effects caused by its long-time residence time in living organisms. Collectively, these results indicate that the Cu-PBG nanozyme could be used as an efficient copper-containing antimicrobial with great potential for clinical translation.

Fomite Transmission, Physicochemical Origin of Virus-Surface Interactions, and Disinfection Strategies for Enveloped Viruses with Applications to SARS-CoV-2

Inanimate objects or surfaces contaminated with infectious agents, referred to as fomites, play an important role in the spread of viruses, including SARS-CoV-2, the virus responsible for the COVID-19 pandemic. The long persistence of viruses (hours to days) on surfaces calls for an urgent need for effective surface disinfection strategies to intercept virus transmission and the spread of diseases. Elucidating the physicochemical processes and surface science underlying the adsorption and transfer of virus between surfaces, as well as their inactivation, is important for understanding how diseases are transmitted and for developing effective intervention strategies. This review summarizes the current knowledge and underlying physicochemical processes of virus transmission, in particular via fomites, and common disinfection approaches. Gaps in knowledge and the areas in need of further research are also identified. The review focuses on SARS-CoV-2, but discussion of related viruses is included to provide a more comprehensive review given that much remains unknown about SARS-CoV-2. Our aim is that this review will provide a broad survey of the issues involved in fomite transmission and intervention to a wide range of readers to better enable them to take on the open research challenges.

Brass Alloys: Copper-Bottomed Solutions against Hospital-Acquired Infections?

Copper has been used for its antimicrobial properties since Antiquity. Nowadays, touch surfaces made of copper-based alloys such as brasses are used in healthcare settings in an attempt to reduce the bioburden and limit environmental transmission of nosocomial pathogens. After a brief history of brass uses, the various mechanisms that are thought to be at the basis of brass antimicrobial action will be described. Evidence shows that direct contact with the surface as well as cupric and cuprous ions arising from brass surfaces are instrumental in the antimicrobial effectiveness. These copper ions can lead to oxidative stress, membrane alterations, protein malfunctions, and/or DNA damages. Laboratory studies back up a broad spectrum of activity of brass surfaces on bacteria with the possible exception of bacteria in their sporulated form. Various parameters influencing the antimicrobial activity such as relative humidity, temperature, wet/dry inoculation or wear have been identified, making it mandatory to standardize antibacterial testing. Field trials using brass and copper surfaces consistently report reductions in the bacterial bioburden but, evidence is still sparse as to a significant impact on hospital acquired infections. Further work is also needed to assess the long-term effects of chemical/physical wear on their antimicrobial effectiveness.

Antibacterial and Antiviral Functional Materials: Chemistry and Biological Activity toward Tackling COVID-19-like Pandemics

The ongoing worldwide pandemic due to COVID-19 has created awareness toward ensuring best practices to avoid the spread of microorganisms. In this regard, the research on creating a surface which destroys or inhibits the adherence of microbial/viral entities has gained renewed interest. Although many research reports are available on the antibacterial materials or coatings, there is a relatively small amount of data available on the use of antiviral materials. However, with more research geared toward this area, new information is being added to the literature every day. The combination of antibacterial and antiviral chemical entities represents a potentially path-breaking intervention to mitigate the spread of disease-causing agents. In this review, we have surveyed antibacterial and antiviral materials of various classes such as small-molecule organics, synthetic and biodegradable polymers, silver, TiO2, and copper-derived chemicals. The surface protection mechanisms of the materials against the pathogen colonies are discussed in detail, which highlights the key differences that could determine the parameters that would govern the future development of advanced antibacterial and antiviral materials and surfaces.

Micro-structured copper and nickel metal foams for wastewater disinfection: proof-of-concept and scale-up

It is necessary to disinfect treated wastewater prior to discharge to reduce exposure risks to humans and the environment. The currently practiced wastewater disinfection technologies are challenged by toxic by-products, chemicals and energy demand, a range of effectiveness limitations, among other concerns. An effective, eco-friendly, and energy-efficient alternative disinfection technique is desirable to modernize and enhance wastewater treatment operations. Copper and nickel micro-structured metal foams, and a conventional copper mesh, were evaluated as disinfecting surfaces for treating secondary-treated wastewater contaminated with coliform bacteria. The micro-structured copper foam was adopted for scale-up study, due to its stable and satisfactory bactericidal performance obtained over a wide range of bacterial concentrations and metal-to-liquid ratios. Three scales of experiments, using two types of reactor designs, were performed using municipal wastewater to determine the optimal scale-up factors: small lab-scale batch reactor, intermediate lab-scale batch reactor, and pilot-scale continuous tubular reactor experiments. The performance was evaluated with the aim of minimizing metal material requirement with respect to bactericidal efficiency and leaching risks at all scales. Copper foam, at or above optimal conditions, consistently inactivated over 95 % of total coliforms, fecal coliforms and E.coli in wastewater at various scales, and leachate copper concentrations were determined to be below Canadian guideline values for outfall. This study successfully implemented the "structure" strategy of process intensification, and opens up the possibility to apply micro-structured copper foam in a range of other water disinfection systems, from pre-treatment to point-of-use, and should thus become a topic of further research.

A critical evaluation of current protocols for self-sterilizing surfaces designed to reduce viral nosocomial infections

BACKGROUND

Biocidal high-touch surfaces contact surfaces can be used to help reduce healthcare-acquired infections (HAIs). While the bactericidal protocols are well developed, there remains high variability in the methods used to evaluate the virucidal properties of such surfaces. This paper seeks to identify the most commonly used methods and critically evaluate the strengths of each method by comparing tests from standard testing organisations and related bactericidal protocols.

METHODS

Three databases and grey literature were queried using a key-word search for relevant articles. Articles were selected if they met the criteria of virucidal properties of self-sterilizing surfaces designed to prevent HAIs. Of the resulting 177 articles, 38 met the inclusion criteria.

RESULTS

The resulting papers varied greatly in their testing methods and recommendations. Further, no standard test adequately meets the needs for specifically testing virucidal properties of self-sterilizing surfaces.

CONCLUSIONS

Studies have shown that temperature and humidity can affect the performance of virucidal touch-surfaces, but no standard protocols were found to test these factors.

Investigating alternative materials to EPDM for automatic taps in the context of Pseudomonas aeruginosa and biofilm control

BACKGROUND

Automatic taps use solenoid valves (SVs) which incorporate a rubber (typically EPDM) diaphragm to control water flow. Contaminated SVs can be reservoirs of opportunistic pathogens such as Pseudomonas aeruginosa; an important cause of healthcare-associated infection.

AIMS

To investigate the attachment and biofilm formation of P. aeruginosa on EPDM and relevant alternative rubbers to assess the impact on water hygiene in a laboratory model.

METHODS

Biofilm formation on EPDM, silicone and nitrile rubber coupons was investigated using a CDC biofilm reactor. SVs incorporating EPDM or nitrile rubber diaphragms were installed on to an experimental water distribution system (EWDS) and inoculated with P. aeruginosa. P. aeruginosa water levels were monitored for 12-weeks. SVs incorporating diaphragms (EPDM, silicone or silver ion-impregnated silicone rubber), pre-colonized with P. aeruginosa, were installed and the effect of flushing as a control measure was investigated. The concentration of P. aeruginosa in the water was assessed by culture and biofilm assessed by culture and microscopy.

FINDINGS

Bacterial attachment was significantly higher on nitrile (6.2 × 10⁵ cfu/coupon) and silicone (5.4 × 10⁵ cfu/coupon) rubber than on EPDM (2.9 ×10⁵ cfu/coupon) (P<0.05, N = 17). Results obtained in vitro did not translate to the EWDS where, after 12-weeks in situ, there was no significant difference in P. aeruginosa water levels or biofilm levels. Flushing caused a superficial reduction in bacterial counts after <5 min of stagnation.

CONCLUSION

This study did not provide evidence to support replacement of EPDM with (currently available) alternative rubbers and indicated the first sample of water dispensed from a tap should be avoided for use in healthcare settings.

Robust rapid-setting antibacterial liquid bandages

Bandaging is a steadfast but time-consuming component of wound care with limited technical advancements to date. Bandages must be changed and infection risk managed. Rapid-set liquid bandages are efficient alternatives but lack durability or inherent infection control. We show here that antibacterial zinc (Zn) and copper (Cu) species greatly enhance the barrier properties of the natural, waterproof, bio-adhesive polymer, shellac. The material demonstrated marked antibacterial contact properties and, in ex-vivo studies, effectively locked-in pre-applied therapeutics. When challenged in vivo with the polybacterial bovine wound infection 'digital dermatitis', Zn/Cu-shellac adhered rapidly and robustly over pre-applied antibiotic. The bandage self-degraded, appropriately, over 7 days despite extreme conditions (faecal slurry). Treatment was well-tolerated and clinical improvement was observed in animal mobility. This new class of bandage has promise for challenging topical situations in humans and other animals, especially away from controlled, sterile clinical settings where wounds urgently require protection from environmental and bacterial contamination.

Impact of a dry inoculum deposition on the efficacy of copper-based antimicrobial surfaces

BACKGROUND

The introduction of antimicrobial surfaces into healthcare environments is believed to impact positively on the rate of healthcare-associated infections by significantly decreasing pathogen presence on surfaces.

AIM

To report on a novel efficacy test that uses a dry bacterial inoculum to measure the microbicidal efficacy of antimicrobial surfaces.

METHODS

An aerosolized dry inoculum of Staphylococcus aureus or Acinetobacter baumannii was deposited on copper alloy surfaces or a hospital-grade stainless-steel surface. Surviving bacteria were enumerated following incubation of the inoculated surfaces at an environmentally relevant temperature and relative humidity. Damage caused to bacteria by the aerosolization process and by the different surfaces was investigated.

FINDINGS

Dry inoculum testing showed a <2-log₁₀ reduction in S. aureus or A. baumannii on the copper alloy surfaces tested after 24 h at 20°C and 40% relative humidity. Potential mechanisms of action included membrane damage, DNA damage and arrested cellular respiration. The aerosolization process caused some damage to bacterial cells. Once this effect was taken into account, the antimicrobial activity of copper surfaces was evident.

CONCLUSIONS

Our test provided a realistic deposition of a bacterial inoculum to a surface and, as such, a realistic protocol to assess the efficacy of dry antimicrobial environmental surfaces in vitro.

Copper Kills Escherichia coli Persister Cells

Due to their reduced metabolism, persister cells can survive most antimicrobial treatments, which usually rely on corrupting active biochemical pathways. Therefore, molecules that kill bacterial persisters should function in a metabolism-independent manner. Some anti-persister compounds have been found previously, such as the DNA-crosslinkers mitomycin C and cisplatin, but more effective and lower cost alternatives are needed. Copper alloys have been used since ancient times due to their antimicrobial properties, and they are still used in agriculture to control plant bacterial diseases. By stopping transcription with rifampicin and by treating with ampicillin to remove non-persister cells, we created a population that consists solely of Escherichia coli persister cells. Using this population of persister cells, we demonstrate that cupric compounds kill E. coli persister cells. Hence, copper ions may be used in controlling the spread of important bacterial strains that withstand treatment with conventional antimicrobials by forming persister cells.

Selection of resistance by antimicrobial coatings in the healthcare setting

Antimicrobial touch surfaces have been introduced in healthcare settings with the aim of supporting existing hygiene procedures, and to help combat the increasing threat of antimicrobial resistance. However, concerns have been raised over the potential selection pressure exerted by such surfaces, which may drive the evolution and spread of antimicrobial resistance. This review highlights studies that indicate risks associated with resistance on antimicrobial surfaces by different processes, including evolution by de-novo mutation and horizontal gene transfer, and species sorting of inherently resistant bacteria dispersed on to antimicrobial surfaces. The review focuses on antimicrobial surfaces made of copper, silver and antimicrobial peptides because of the practical application of copper and silver, and the promising characteristics of antimicrobial peptides. The available data point to a potential for resistance selection and a subsequent increase in resistant strains via cross-resistance and co-resistance conferred by metal and antibiotic resistance traits. However, translational studies describing the development of resistance to antimicrobial touch surfaces in healthcare-related environments are rare, and will be needed to assess whether and how antimicrobial surfaces lead to resistance selection in these settings. Such studies will need to consider numerous variables, including the antimicrobial concentrations present in coatings, the occurrence of biofilms on surfaces, and the humidity relevant to dry-surface environments. On-site tests on the efficacy of antimicrobial coatings should routinely evaluate the risk of selection associated with their use.

Copper Resistance Mediates Long-Term Survival of Cupriavidus metallidurans in Wet Contact With Metallic Copper

Metallic copper to combat bacterial proliferation in drinking water systems is being investigated as an attractive alternative to existing strategies. A potential obstacle to this approach is the induction of metal resistance mechanisms in contaminating bacteria, that could severely impact inactivation efficacy. Thus far, the role of these resistance mechanisms has not been studied in conditions relevant to drinking water systems. Therefore, we evaluated the inactivation kinetics of Cupriavidus metallidurans CH34 in contact with metallic copper in drinking water. Viability and membrane permeability were examined for 9 days through viable counts and flow cytometry. After an initial drop in viable count, a significant recovery was observed starting after 48 h. This behavior could be explained by either a recovery from an injured/viable-but-non-culturable state or regrowth of surviving cells metabolizing lysed cells. Either hypothesis would necessitate an induction of copper resistance mechanisms, since no recovery was seen in a CH34 mutant strain lacking metal resistance mechanisms, while being more pronounced when copper resistance mechanisms were pre-induced. Interestingly, no biofilms were formed on the copper surface, while extensive biofilm formation was observed on the stainless steel control plates. When CH34 cells in water were supplied with CuSO4, a similar initial decrease in viable counts was observed, but cells recovered fully after 7 days. In conclusion, we have shown that long-term bacterial survival in the presence of a copper surface is possible upon the induction of metal resistance mechanisms. This observation may have important consequences in the context of the increasing use of copper as an antimicrobial surface, especially in light of potential co-selection for metal and antimicrobial resistance.

Antimicrobial Copper-Based Materials and Coatings: Potential Multifaceted Biomedical Applications

Surface contamination by microbes leads to several detrimental consequences like hospital- and device-associated infections. One measure to inhibit surface contamination is to confer the surfaces with antimicrobial properties. Copper's antimicrobial properties have been known since ancient times, and the recent resurgence in exploiting copper for application as antimicrobial materials or coatings is motivated by the growing concern about antibiotic resistance and the pressure to reduce antibiotic use. Copper, unlike silver, demonstrates rapid and high microbicidal efficacy against pathogens that are in close contact under ambient indoor conditions, which enhances its range of applicability. This review highlights the mechanisms behind copper's potent antimicrobial property, the design and fabrication of different copper-based antimicrobial materials and coatings comprising metallic copper/copper alloys, copper nanoparticles or ions, and their potential for practical applications. Finally, as the antimicrobial coatings market is expected to grow, we offer our perspectives on the implications of increased copper release into the environment and the potential ecotoxicity effects and possibility of development of resistant genes in pathogens.

A biodegradable Zn-1Cu-0.1Ti alloy with antibacterial properties for orthopedic applications

Zinc (Zn) alloys are receiving increasing attention in the field of biodegradable implant materials due to their unique combination of suitable biodegradability and good biological functionalities. However, the currently existing industrial Zn alloys are not necessarily biocompatible, nor sufficiently mechanically strong and wear-resistant. In this study, a Zn-1Cu-0.1Ti alloy is developed with enhanced mechanical strength, corrosion wear property, biocompatibility, and antibacterial ability for biodegradable implant material applications. HR and HR + CR were performed on the as-cast alloy and its microstructure, mechanical properties, frictional and wear behaviors, corrosion resistance, in vitro cytocompatibility, and antibacterial ability were systematically assessed. The microstructures of the Zn-1Cu-0.1Ti alloy after different deformation conditions included a η-Zn phase, a ε-CuZn₅ phase, and an intermetallic phase of TiZn₁₆. The HR+CR sample of Zn-1Cu-0.1Ti exhibited a yield strength of 204.2 MPa, an ultimate tensile strength of 249.9 MPa, and an elongation of 75.2%; significantly higher than those of the HR alloy and the AC alloy. The degradation rate in Hanks' solution was 0.029 mm/y for the AC alloy, 0.032 mm/y for the HR+CR alloy, and 0.034 mm/y for the HR alloy. The HR Zn-1Cu-0.1Ti alloy showed the best wear resistance, followed by the AC alloy and the alloy after HR + CR. The extract of the AC Zn-1Cu-0.1Ti alloy showed over 80% cell viability with MC3T3-E1 pre-osteoblast and MG-63 osteosarcoma cells at a concentration of ≤ 25%. The as-cast Zn-1Cu-0.1Ti alloy showed good blood compatibility and antibacterial ability. STATEMENT OF SIGNIFICANCE: This work repots a Zn-1Cu-0.1Ti alloy with enhanced mechanical strength, corrosion wear property, biocompatibility, and antibacterial ability for biodegradable implant applications. Our findings showed that Zn-1Cu-0.1Ti after hot-rolling plus cold-rolling exhibited a yield strength of 204.2 MPa, an ultimate tensile strength of 249.9 MPa, an elongation of 75.2%, and a degradation rate of 0.032 mm/y in Hanks' Solution. The hot-rolled Zn-1Cu-0.1Ti showed the best wear resistance. The extract of the as-cast alloy at a concentration of ≤ 25% showed over 80% cell viability with MC3T3-E1 and MG-63 cells. The Zn-1Cu-0.1Ti alloy showed good hemocompatibility and antibacterial ability.

Enhanced bactericidal activity of brucite through partial copper substitution

Copper substituted Mg(OH)₂nanoplatelets exhibit high bactericidal activity towardsS. aureusandE. coliwith fast kinetics.

Factors Enhancing the Antibacterial Effect of Monovalent Copper Ions

This study continues the series of experiments that demonstrate the high antibacterial properties of monovalent copper ions (Cu⁺). While in previous study we examined different metals (copper and silver) and their metal states (mono- and divalent), showing that monovalent copper is best for controlling bacterial growth, the current study focuses on finding conditions which further enhance the antibacterial effect of monovalent copper. This approach may also shed light on mechanisms of Cu⁺ ions which still remain unknown. To this end, the influence of Cu⁺ ions on model gram-negative Escherichia coli bacteria at different pH levels with a variety of carbon sources and elevated temperatures was examined. It was found that in both aerobic and anaerobic conditions in a poor growth medium, Cu²⁺ ions barely suppress any growth of E. coli, whereas Cu⁺ ions even at very low concentrations dramatically deplete bacterial populations in a time scale of minutes at room temperature, and less than one minute at elevated temperatures. Acidic pH, unfavorable carbon sources, and elevated temperatures boost the antibacterial action of Cu⁺ ions. On the whole, the study confirms that monovalent copper ions are strongly superior to divalent copper ions in their antibacterial action across a wide range of tested conditions.

Self-Disinfecting Copper Beds Sustain Terminal Cleaning and Disinfection Effects throughout Patient Care

Microbial burden associated with near-patient touch surfaces results in a greater risk of health care-associated infections (HAIs). Acute care beds may be a critical fomite, as traditional plastic surfaces harbor the highest concentrations of bacteria associated with high-touch surfaces in a hospital room's patient zone. Five high-touch intensive care unit (ICU) bed surfaces encountered by patients, health care workers, and visitors were monitored by routine culture to assess the effect U.S. Environmental Protection Agency (U.S. EPA)-registered antimicrobial copper materials have on the microbial burden. Despite both daily and discharge cleaning and disinfection, each control bed's plastic surfaces exceeded bacterial concentrations recommended subsequent to terminal cleaning and disinfection (TC&D) of 2.5 aerobic CFU/cm² Beds with self-disinfecting (copper) surfaces harbored significantly fewer bacteria throughout the patient stay than control beds, at levels below those considered to increase the likelihood of HAIs. With adherence to routine daily and terminal cleaning regimes throughout the study, the copper alloy surfaces neither tarnished nor required additional cleaning or special maintenance. Beds encapsulated with U.S. EPA-registered antimicrobial copper materials were found to sustain the microbial burden below the TC&D risk threshold levels throughout the patient stay, suggesting that outfitting acute care beds with such materials may be an important supplement to controlling the concentration of infectious agents and thereby potentially reducing the overall HAI risk.IMPORTANCE Despite cleaning efforts of environmental service teams and substantial compliance with hand hygiene best practices, the microbial burden in patient care settings often exceeds concentrations at which transfer to patients represents a substantial acquisition risk for health care-associated infections (HAIs). Approaches to limit HAI risk have relied on designing health care equipment and furnishings that are easier to clean and/or the use of no-touch disinfection interventions such as germicidal UV irradiation or vapor deposition of hydrogen peroxide. In a clinical trial evaluating the largest fomite in the patient care setting, the bed, a bed was encapsulated with continuously disinfecting antimicrobial copper surfaces, which reduced the bacteria on surfaces by 94% and sustained the microbial burden below the terminal cleaning and disinfection risk threshold throughout the patient's stay. Such an intervention, which continuously limits microbes on high-touch surfaces, should be studied in a broader range of health care settings to determine its potential long-range efficacy for reducing HAI.

Development of Antibacterial Ti-Cux Alloys for Dental Applications: Effects of Ageing for Alloys with Up to 10 wt% Cu

Peri-implantitis, a disease caused by bacteria, affects dental implants in patients. It is widely treated with antibiotics, however, with growing antibiotic resistance new strategies are required. Titanium-copper alloys are prospective antibacterial biomaterials, with the potential to be a remedy against peri-implantitis and antibiotic resistance. The aim of this study was to investigate Ti-Cu_x alloys, exploring how Cu content (up to 10 wt%) and ageing affect the material properties. Electron microscopy, X-ray diffraction, hardness testing, bacteriological culture, and electrochemical testing were employed to characterize the materials. It was found that alloys with above 3 wt% Cu had two phases and ageing increased the volume fraction of Ti₂Cu. An un-aged alloy of 5 wt% Cu showed what could be Ti₃Cu, in addition to the α-Ti phase. The hardness gradually increased with increased Cu additions, while ageing only affected the alloy with 10 wt% Cu (due to changes in microstructure). Ageing resulted in faster passivation of the alloys. After two hours the aged 10 wt% Cu alloy was the only material with an antibacterial effect, while after six hours, bacteria killing occurred in all alloys with above 5 wt% Cu. In conclusion, it was possible to tune the material and antibacterial properties of Ti-Cu_x alloys by changing the Cu concentration and ageing, which makes further optimization towards an antibacterial material promising.

The Use of Copper as an Antimicrobial Agent in Health Care, Including Obstetrics and Gynecology

Health care-associated infections (HAIs) are a global problem associated with significant morbidity and mortality. Controlling the spread of antimicrobial-resistant bacteria is a major public health challenge, and antimicrobial resistance has become one of the most important global problems in current times. The antimicrobial effect of copper has been known for centuries, and ongoing research is being conducted on the use of copper-coated hard and soft surfaces for reduction of microbial contamination and, subsequently, reduction of HAIs. This review provides an overview of the historical and current evidence of the antimicrobial and wound-healing properties of copper and explores its possible utility in obstetrics and gynecology.

Impacts of indoor surface finishes on bacterial viability

Microbes in indoor environments are constantly being exposed to antimicrobial surface finishes. Many are rendered non-viable after spending extended periods of time under low-moisture, low-nutrient surface conditions, regardless of whether those surfaces have been amended with antimicrobial chemicals. However, some microorganisms remain viable even after prolonged exposure to these hostile conditions. Work with specific model pathogens makes it difficult to draw general conclusions about how chemical and physical properties of surfaces affect microbes. Here, we explore the survival of a synthetic community of non-model microorganisms isolated from built environments following exposure to three chemically and physically distinct surface finishes. Our findings demonstrated the differences in bacterial survival associated with three chemically and physically distinct materials. Alkaline clay surfaces select for an alkaliphilic bacterium, Kocuria rosea, whereas acidic mold-resistant paint favors Bacillus timonensis, a Gram-negative spore-forming bacterium that also survives on antimicrobial surfaces after 24 hours of exposure. Additionally, antibiotic-resistant Pantoea allii did not exhibit prolonged retention on antimicrobial surfaces. Our controlled microcosm experiment integrates measurement of indoor chemistry and microbiology to elucidate the complex biochemical interactions that influence the indoor microbiome.

Copper-containing glass ceramic with high antimicrobial efficacy

Hospital acquired infections (HAIs) and the emergence of antibiotic resistant strains are major threats to human health. Copper is well known for its high antimicrobial efficacy, including the ability to kill superbugs and the notorious ESKAPE group of pathogens. We sought a material that maintains the antimicrobial efficacy of copper while minimizing the downsides – cost, appearance and metallic properties – that limit application. Here we describe a copper-glass ceramic powder as an additive for antimicrobial surfaces; its mechanism is based on the controlled release of copper (I) ions (Cu¹⁺) from cuprite nanocrystals that form in situ in the water labile phase of the biphasic glass ceramic. Latex paints containing copper-glass ceramic powder exhibit ≥99.9% reduction in S. aureus, P. aeruginosa, K. aerogenes and E. Coli colony counts when evaluated by the US EPA test method for efficacy of copper-alloy surfaces as sanitizer, approaching that of benchmark metallic copper.

Copper is well known for its high antimicrobial efficacy; however, cost, appearance and metallic properties limit application. Here the authors describe a stable, water dispersible copper-glass ceramic powder with long-term antimicrobial activity as an additive for antimicrobial surfaces.

Transparent Copper-Based Antibacterial Coatings with Enhanced Efficacy against Pseudomonas aeruginosa

Bacterial surface contamination is a major cause of hospital-associated infections. Antibacterial coatings can play an important role in reducing bacterial transmission via inanimate surfaces in healthcare settings. In this work, transparent copper-based antibacterial coatings were fabricated on commercial poly(vinyl fluoride) and stainless steel. Acrylated quaternized chitosan and ethylenediaminetetraacetic acid were covalently grafted on the substrate for complexation with copper ions. The number of viable Staphylococcus aureus in a droplet [containing ∼10⁴ colony forming units (CFU)], deposited on the copper-containing coating decreased by ∼96% within 60 min at 25 °C. With Pseudomonas aeruginosa, one of the most virulent and hardest to kill bacteria, no CFU could be observed within the same time span (killing efficacy >99.8% based on the detection limit). An increase in copper release from the coating was observed in the presence of P. aeruginosa, which was postulated to be due to the proteolytic activity of P. aeruginosa. The higher efficacy of the coating against P. aeruginosa compared to S. aureus is thus attributed to this increased copper release from the coating, which resulted in extensive bacterial membrane damage and death. The copper-containing coating on poly(vinyl fluoride) retained its antibacterial efficacy after 100 wipes with a water-wetted cloth or isopropanol wipes, demonstrating its durability and long-term efficacy. The coating did not exhibit significant cytotoxicity toward mammalian fibroblasts, further demonstrating its potential for mitigating bacterial transmission in a clinical setting.

Rapid in situ assessment of Cu-ion mediated effects and antibacterial efficacy of copper surfaces

Release of metal ions from metal-based surfaces has been considered one of the main drivers of their antimicrobial activity. Here we describe a method that enables parallel assessment of metal ion release from solid metallic surfaces and antimicrobial efficacy of these surfaces in a short time period. The protocol involves placement of a small volume of bioluminescent bacteria onto the tested surface and direct measurement of bioluminescence at various time points. In this study, two recombinant Escherichia coli strains, one expressing bioluminescence constitutively and applicable for general antimicrobial testing, and the other induced by Cu ions, were selected. Decrease in bioluminescence of constitutive E. coli on the surfaces showed a good correlation with the decrease in bacterial viability. Response of Cu-inducible E. coli showed a correlation with Cu content in the tested surfaces but not with Cu dissolution suggesting the role of direct bacteria-surface contact in Cu ion-driven antibacterial effects. In summary, the presented protocol enables the analysis of microbial toxicity and bioavailability of surface-released metal ions directly on solid surfaces within 30-60 min. Although optimized for copper and copper alloy surfaces and E. coli, the method can be extended to other types of metallic surfaces and bacterial strains.

New insights on antimicrobial efficacy of copper surfaces in the healthcare environment: a systematic review

OBJECTIVES

Hospital-acquired infections (HAIs) are a major public health issue. The potential of antimicrobial copper surfaces in reducing HAIs' rates is of interest but remains unclear. We conducted a systematic review of studies assessing the activity of copper surfaces (colony-forming unit (CFU)/surface, both in vitro and in situ) as well as clinical studies. In vitro study protocols were analysed through a tailored checklist developed specifically for this review, in situ studies and non-randomized clinical studies were assessed using the ORION (Outbreak Reports and Intervention studies Of Nosocomial infection) checklist and randomized clinical studies using the CONSORT guidelines.

METHODS

The search was conducted using PubMed database with the keywords 'copper' and 'surfaces' and 'healthcare associated infections' or 'antimicrobial'. References from relevant articles, including reviews, were assessed and added when appropriate. Articles were added until 30 August 2016. Overall, 20 articles were selected for review including 10 in vitro, eight in situ and two clinical studies.

RESULTS

Copper surfaces were found to have variable antimicrobial activity both in vitro and in situ, although the heterogeneity in the designs and the reporting of the results prevented conclusions from being drawn regarding their spectrum and activity/time compared to controls. Copper effect on HAIs incidence remains unclear because of the limited published data and the lack of robust designs. Most studies have potential conflicts of interest with copper industries.

CONCLUSIONS

Copper surfaces have demonstrated an antimicrobial activity but the implications of this activity in healthcare settings are still unclear. No clear effect on healthcare associated infections has been demonstrated yet.