Biocidal Surfaces Research Articles

Fighting nosocomial infections with biocidal non-intrusive hard and soft surfaces

Approximately 7 million people worldwide acquire a healthcare associated infection each year. Despite aggressive monitoring, hand washing campaigns and other infection control measures, nosocomial infections (NI) rates, especially those caused by antibiotic resistant pathogens, are unacceptably high worldwide. Additional ways to fight these infections need to be de veloped. A potential overlooked and neglected source of nosocomial pathogens are those found in non-intrusive soft and hard surfaces located in clinical settings. Soft surfaces, such as patient pyjamas and beddings, can be an excellent substrate for bacterial and fungal growth under appropriate temperature and humidity conditions as those present between patients and the bed. Bed making in hospitals releases large quantities of microorganisms into the air, which contaminate the immediate and non-immediate surroundings. Microbes can survive on hard surfaces, such as metal trays, bed rails and door knobs, for very prolonged periods of time. Thus soft and hard surfaces that are in direct or indirect contact with the patients can serve as a source of nosocomial pathogens. Recently it has been demonstrated that copper surfaces and copper oxide containing textiles have potent intrinsic biocidal properties. This manuscript reviews the recent laboratory and clinical studies, which demonstrate that biocidal surfaces made of copper or containing copper can reduce the microbiological burden and the NI rates.

Mode of Action of Cationic Antimicrobial Peptides Defines the Tethering Position and the Efficacy of Biocidal Surfaces

Covalent immobilization of cationic antimicrobial peptides (CAPs) at sufficient density and distance from the solid matrix has been suggested as a successful strategy for the generation of biocidal surfaces. To test the hypothesis that the mode of peptide action is decisive for the selection of an appropriate tethering position on solid surfaces, melittin (MEL), a channel-forming peptide, buforin 2 (BUF2), a peptide able to translocate bacterial membranes without permeabilization and targeting nucleic acids, and tritrpticin (TP), described to be membrane-lytic and to have intracellular targets, were C- and N-terminally immobilized on TentaGel S NH(2) resin beads as model surface. The peptide termini were modified with aminooxyacetic acid (AOA) and coupled via oxime-forming ligation. The comparison of the activities of the three peptides and their AOA-modified analogues with a KLAL model peptide which permeabilizes membranes by a so-called "carpet-like" mode provided the following results: The peptides in solution state were active against Bacillus subtilis and Escherichia coli at micromolar concentrations. MEL and TP but not BUF2-derived peptides permeabilized the inner and outer membrane of E. coli and enhanced the permeability of lipid bilayers at concentrations around their antimicrobial values (MICs). Immobilization reduced peptide activity to millimolar MICs. The activity reduction for KLAL was independent of the tethering position and comparably low, as reflected by a low ratio of MIC(tethered)/MIC(free). In contrary, the pore-forming MEL was much less active when immobilized at the N-terminus compared with the C-terminally tethered peptide. C- and N-terminal TP tethering caused an identical but much pronounced activity decrease. The tethered BUF2 peptides were inactive at the tested concentrations suggesting that the peptides could not reach the intracellular targets. In conclusion, membrane active peptides seem to be most suitable for the generation of antimicrobial surfaces, but knowledge about their mode of membrane insertion and positioning is required to identify optimal tethering positions. The relationship between the mechanism of action and position of immobilization is highly relevant for the establishment of a general approach to obtain efficient biocidal solid matrices loaded with CAPs.

Mechanism of copper surface toxicity in Escherichia coli O157:H7 and Salmonella involves immediate membrane depolarization followed by slower rate of DNA destruction which differs from that observed for Gram‐positive bacteria

We have reported previously that copper I and II ionic species, and superoxide but not Fenton reaction generated hydroxyl radicals, are important in the killing mechanism of pathogenic enterococci on copper surfaces. In this new work we determined if the mechanism was the same in non-pathogenic ancestral (K12) and laboratory (DH5α) strains, and a pathogenic strain (O157), of Escherichia coli. The pathogenic strain exhibited prolonged survival on stainless steel surfaces compared with the other E. coli strains but all died within 10 min on copper surfaces using a 'dry' inoculum protocol (with approximately 10(7) cfu cm(-2) ) to mimic dry touch contamination. We observed immediate cytoplasmic membrane depolarization, not seen with enterococci or methicillin resistant Staphylococcus aureus, and loss of outer membrane integrity, inhibition of respiration and in situ generation of reactive oxygen species on copper and copper alloy surfaces that did not occur on stainless steel. Chelation of copper (I) and (II) ionic species still had the most significant impact on bacterial survival but protection by d-mannitol suggests hydroxyl radicals are involved in the killing mechanism. We also observed a much slower rate of DNA destruction on copper surfaces compared with previous results for enterococci. This may be due to protection of the nucleic acid by the periplasm and the extensive cell aggregation that we observed on copper surfaces. Similar results were obtained for Salmonella species but partial quenching by d-mannitol suggests radicals other than hydroxyl may be involved. The results indicate that copper biocidal surfaces are effective for Gram-positive and Gram-negative bacteria but bacterial morphology affects the mechanism of toxicity. These surfaces could not only help to prevent infection spread but also prevent horizontal gene transmission which is responsible for the evolution of virulent toxin producing and antibiotic resistant bacteria.

Durability of Silver Nanoparticulate Films Within a Silica Matrix by Flame Assisted Chemical Vapour Deposition for Biocidal Applications

Healthcare acquired infection (HCAI) rates have come under increasing scrutiny in recent years and been a major priority for health professionals in the UK and elsewhere. Of particular concern is the rise of so called 'superbugs', or those resistant to conventional antibiotics, such as Escherichia coli, Clostridium difficile and methicillin resistant Staphylococcus aureus (MRSA). The reasons for this rise are many and complex, but one important factor is bacterial survival rates on wards and other hospital areas. In this respect, nanostructured biocidal surfaces offer a potentially powerful weapon in the fight against HCAI. In addition to providing a toxic environment to a range of infectious disease-causing bacteria (while remaining harmless to human health), any potential bioactive coated surface is required to be durable enough to withstand regular hospital cleaning methods without a reduction in biocidal activity over time and be economically viable to mass produce. The flame assisted chemical vapour deposition (FACVD) of silver and silver/silica films offer a means of producing such surfaces. In this work, we report investigations into a wide range of experimental factors and parameters affecting film durability, including burner head design and relative water vapour content in the flame environment. The produced films were assessed in terms of durability (by scratch testing) and relative silver content using glow discharge optical emission spectroscopy (GDOES).

Mechanism of Copper Surface Toxicity in Vancomycin-Resistant Enterococci following Wet or Dry Surface Contact

Contaminated touch surfaces have been implicated in the spread of hospital-acquired infections, and the use of biocidal surfaces could help to reduce this cross-contamination. In a previous study we reported the death of aqueous inocula of pathogenic Enterococcus faecalis or Enterococcus faecium isolates, simulating fomite surface contamination, in 1 h on copper alloys, compared to survival for months on stainless steel. In our current study we observed an even faster kill of over a 6-log reduction of viable enterococci in less than 10 min on copper alloys with a "dry" inoculum equivalent to touch contamination. We investigated the effect of copper(I) and copper(II) chelation and the quenching of reactive oxygen species on cell viability assessed by culture and their effects on genomic DNA, membrane potential, and respiration in situ on metal surfaces. We propose that copper surface toxicity for enterococci involves the direct or indirect action of released copper ionic species and the generation of superoxide, resulting in arrested respiration and DNA breakdown as the first stages of cell death. The generation of hydroxyl radicals by the Fenton reaction does not appear to be the dominant instrument of DNA damage. The bacterial membrane potential is unaffected in the early stages of wet and dry surface contact, suggesting that the membrane is not compromised until after cell death. These results also highlight the importance of correct surface cleaning protocols to perpetuate copper ion release and prevent the chelation of ions by contaminants, which could reduce the efficacy of the surface.

New insights into the antimicrobial mechanisms of copper touch surfaces

Survival of pathogens on touch surfaces contributes to increasing incidence and spread of antibiotic resistance and infection in hospitals. One way to address this could be to use biocidal surfaces in conjunction with improved cleaning regimes. Exposure to moist copper alloy surfaces, to simulate fomite contamination, resulted in a rapid kill of significant bacterial, viral and fungal pathogens. We now report studies on dry surfaces with a range of pathogens to elucidate the antimicrobial mechanism.

Surface Characterization of Biocidal Polyurethane Modifiers Having Poly(3,3-substituted)oxetane Soft Blocks with Alkylammonium Side Chains

This paper focuses on surface characterization of P[ AB] copolyoxetane soft block polyurethanes having either fluorous (3FOx, -CH2OCH 2CF3) or PEG-like (ME2Ox, -CH2(OCH2CH2) 2OCH3), A side chains and alkylammonium, B side chains. Physical surface characterization data were analyzed in light of the previously observed order of antimicrobial effectiveness for a set of four surface modifiers. Ample physical evidence for surface concentration of fluorous 2 wt % P[ AB]-polyurethane modifiers was obtained from XPS, contact angles, ATR-IR spectroscopy, and TM-AFM. In TM-AFM phase imaging, the most effective biocidal surface modifier, 2 wt % HMDI-BD(30)/P[(3FOx)(C12)-0.89:0.11]-PU, showed a nanoscale phase-separated structure consisting of 200 nm domains with background features about 10 times smaller. Despite similar surface characterization data, the 2 wt % fluorous C6 analog ranked third in contact biocidal effectiveness. Physical evidence for surface concentration of 2 wt % P[(ME2Ox)(C12)-0.86:0.14]-PU was modest, considering that antimicrobial effectiveness was second only to 2 wt % HMDI-BD(30)/P[(3FOx)(C12)-0.89:0.11]-PU. In this set of surface modifiers, nanoscale morphology is largely driven by the fluorous component, whereas antimicrobial effectiveness is more strongly influenced by alkylammonium chain length. The effect of alkylammonium side chain length on surface concentration and antimicrobial behavior is more pronounced for ME2Ox polyurethanes compared to the 3FOx analogs.

Controlled Nanostructured Silver Coated Surfaces by Atmospheric Pressure Chemical Vapour Deposition

AbstractThin film silver has been widely reported for its interesting properties. In this paper we describe a route to produce controlled nanostructured silver layers. A combination of Flame Assisted Chemical Vapour Deposition at atmospheric pressure, with low cost and a low toxicity silver precursor, was used to generate coatings of structured silver surfaces on glass. This approach gives a high degree of control of surface structure, density and topography.These layers have potential applications in areas such as catalysis, photo‐activity and for biocidal surfaces. Our results indicate very high biocidal activity where the nano‐structure is proposed as playing a significant role.

Biocidal Silver and Silver/Titania Composite Films Grown by Chemical Vapour Deposition

This paper describes the growth and testing of highly active biocidal films based on photocatalytically active films of TiO2, grown by thermal CVD, functionally and structurally modified by deposition of nanostructured silver via a novel flame assisted combination CVD process. The resulting composite films are shown to be highly durable, highly photocatalytically active and are also shown to possess strong antibacterial behaviour. The deposition control, arising from the described approach, offers the potential to control the film nanostructure, which is proposed to be crucial in determining the photo and bioactivity of the combined film structure, and the transparency of the composite films. Furthermore, we show that the resultant films are active to a range of organisms, including Gram‐negative and Gram‐positive bacteria, and viruses. The very high‐biocidal activity is above that expected from the concentrations of silver present, and this is discussed in terms of nanostructure of the titania/silver surface. These properties are especially significant when combined with the well‐known durability of CVD deposited thin films, offering new opportunities for enhanced application in areas where biocidal surface functionality is sought.

Permanent, non-leaching antibacterial surfaces—2: How high density cationic surfaces kill bacterial cells

Rational controlled synthesis of poly(quaternary ammonium) compounds has been used to prepare antimicrobial polymer brushes on inorganic surfaces. The systematic variation of several structural parameters of the polymeric brushes allowed us to elicit the minimum surface requirements and a probable mechanism of action for Escherichia coli cell kill. Polymeric brushes were prepared by surface-initiated atom transfer radical polymerization of 2-(dimethylamino)ethyl methacrylate (DMAEMA), a method that allows the molecular weight of the polymer chains to be precisely controlled as they grow from the target surface. The tertiary amino groups of the polyDMAEMA were then quaternized with alkyl bromides to provide a surface with antimicrobial activity. Dry layer thickness of the polymer brushes was controlled by polymerization time and/or initiator density on the surface. This tunability of surface structure allows the antimicrobial polymer brushes to be tailored rationally. A combinatorial screening tool was developed to elucidate the role of chain length and chain density on cell kill in a single experiment. The results indicate that surface charge density, is a critical element in designing a surface for maximum kill efficiency. The most biocidal surfaces had charge densities of greater than 1–5×10 15 accessible quaternary amine units/cm 2. The relevance of this finding to the mechanism of action is discussed.

Novel N-halamine siloxane monomers and polymers for preparing biocidal coatings

Precursor N-halamine siloxane monomers and polymers have been prepared for the purpose of functionalising the surfaces of materials in order to render them biocidal upon exposure to oxidative halogen solutions. The biocidal function can be imparted to the N-halamine moiety either before or after siloxane bonding or adhesion to the surface or material. The biocidal surfaces and materials can then be used to inactivate pathogenic micro-organisms such as bacteria, fungi and yeasts, as well as virus particles, which can cause infectious diseases, and those micro-organisms which cause noxious odours and unpleasant colouring such as mildew. Examples of surfaces and materials which can be rendered biocidal with the N-halamine siloxanes include cellulose, synthetic fibres, ceramics, plastics, polyurethanes and metals. Preparation procedures and some biocidal efficacy data on paper, cotton and polyurethane paint are discussed.

Antimicrobial properties of novel n-halamine siloxane coatings

Antimicrobial coatings on a wide variety of hard and soft substrates were prepared by exposing surfaces treated with novel N-halamine siloxane precursor monomers and macro-monomers to oxidative halogen solutions. Suspensions of a range of bacterial, viral, fungal and yeast micro-organisms were applied to the halogen-charged coatings for defined intervals, before recovery and quantification of surviving microbes using appropriate neutralisation and culture techniques. The biocidal surfaces exhibited powerful, broad-spectrum antimicrobial properties, inactivating most challenge microbes in contact times measured in minutes to hours, rather than the extended contact incubation periods usually associated with substrate-bound antimicrobial agents. Antimicrobial effects were also demonstrated to prevent odour caused by bacterial generation of ammonia in an experimental simulation of a urine-soaked nappy pad. Contact times for efficacy were related to bound halogen concentrations per unit of surface area. Potential benefits of these novel rechargeable biocidal surfaces cover a range, from limiting contamination of environmental surfaces with disease agents in healthcare or food service facilities, to controlling odour and mildew in bathrooms, and preventing odour formation in incontinence pads. They also confer antimicrobial protective functions on textiles and non-woven filter media for air and water.