Antimicrobial coating innovations to prevent infectious disease: a consensus view from the AMiCl COST Action

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.

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.

Effectiveness and Durability of a Quaternary Ammonium Compounds-Based Surface Coating to Reduce Surface Contamination

Foodborne diseases are of major concern as they have a significant impact on public health, both socially and economically. The occurrence of cross-contamination of food in household kitchens is a serious threat and the adoption of safe food practices is of paramount importance. This work aimed to study the effectiveness and durability of a commercial quaternary ammonium compound-based surface coating which, according to the manufacturer, retains its antimicrobial activity for 30 days, and is suitable for all types of hard surfaces for the prevention and/or control of cross-contamination. For that, its antimicrobial efficacy, killing contact time and durability on three different surfaces-polyvinyl chloride, glass, and stainless-steel-against three pathogens-Escherichia coli ATCC 25922, Acinetobacter baumannii ESB260 and Listeria monocytogenes Scott A-were tested according to the current antimicrobial treated surfaces efficacy test (ISO22196:2011). The results showed that the antimicrobial coating was effective against all pathogens with a reduction of >5.0 log CFU/cm² in less than one minute for the three surfaces, but its durability was less than one week on all surfaces cleaned in the usual manner. Additionally, trace amounts (≤0.2 mg/kg) of the antimicrobial coating, which may migrate into food when contacting the surface, did not show cytotoxicity to human colorectal adenocarcinoma cells. The suggested antimicrobial coating has the potential to significantly reduce surface contamination, ensure surface disinfection and reduce the likelihood of cross-contamination in domestic kitchens, although it is less durable than suggested. The use of this technology in household settings is an attractive complement to the existing cleaning protocols and solutions that are already in place.

Weathering and Antimicrobial Properties of Laminate and Powder Coatings Containing Silver Phosphate Glass Used as High-Touch Surfaces

Increasing the use of hygienic high-touch surfaces with antimicrobial properties in health care and public spaces is one way to hinder the spread of bacteria and infections. This study investigates the antimicrobial efficacy and surface reactivity of commercial laminate and powder coated surfaces treated with silver-doped phosphate glass as antimicrobial additive towards two model bacterial strains, Escherichia coli and Bacillus subtilis, in relation to surface weathering and repeated cleaning. High-touch conditions in indoor environments were simulated by different extents of pre-weathering (repeated daily cycles in relative humidity at constant temperature) and simplified fingerprint contact by depositing small droplets of artificial sweat. The results elucidate that the antimicrobial efficacy was highly bacteria dependent (Gram-positive or Gram-negative), not hampered by differences in surface weathering but influenced by the amount of silver-doped additive. No detectable amounts of silver were observed at the top surfaces, though silver was released into artificial sweat in concentrations a thousand times lower than regulatory threshold values stipulated for materials and polymers in food contact. Surface cleaning with an oxidizing chemical agent was more efficient in killing bacteria compared with an agent composed of biologically degradable constituents. Cleaning with the oxidizing agent resulted further in increased wettability and presence of residues on the surfaces, effects that were beneficial from an antimicrobial efficacy perspective.

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.

Joining European Scientific Forces to Face Pandemics

Despite the international guidelines on the containment of the coronavirus disease 2019 (COVID-19) pandemic, the European scientific community was not sufficiently prepared to coordinate scientific efforts. To improve preparedness for future pandemics, we have initiated a network of nine European-funded Cooperation in Science and Technology (COST) Actions that can help facilitate inter-, multi-, and trans-disciplinary communication and collaboration.

Does copper treatment of commonly touched surfaces reduce healthcare-acquired infections? A systematic review and meta-analysis

BACKGROUND

Healthcare-acquired infections (HAIs) cause substantial morbidity and mortality. Copper appears to have strong antimicrobial properties under laboratory conditions.

AIM

To examine the potential effect of copper treatment of commonly touched surfaces in healthcare facilities.

METHODS

Controlled trials comparing the effect of copper-treated surfaces (furniture or bed linens) in hospital rooms compared with standard rooms on HAIs were included in this systematic review. Two reviewers independently screened retrieved articles, extracted data, and assessed the risk of bias of included studies. The primary outcome was the occurrence of HAIs.

FINDINGS

In total, 638 records were screened, and seven studies comprising 12,362 patients were included. All included studies were judged to be at high risk of bias in two or more of the seven domains. All seven studies reported the effect of various copper-treated surfaces on HAIs. Overall, this review found low-quality evidence of potential clinical importance that copper-treated hard surfaces and/or bed linens and clothes reduced HAIs by 27% (risk ratio 0.73, 95% confidence interval 0.57-0.94; I² = 44%, P=0.01).

CONCLUSION

Given the clinical and economic costs of HAIs, the potentially protective effect of copper treatment appears to be important. The current evidence is insufficient to make a strong positive recommendation. However, it would appear worthwhile and urgent to conduct larger publicly funded clinical trials into the impact of copper treatment.

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.