Polymeric materials with antimicrobial activity

Modification of the surfaces of medical devices to prevent microbial adhesion and biofilm formation

BACKGROUND

The development of devices with surfaces that have an effect against microbial adhesion or viability is a promising approach to the prevention of device-related infections.

AIM

To review the strategies used to design devices with surfaces able to limit microbial adhesion and/or growth.

METHODS

A PubMed search of the published literature.

FINDINGS

One strategy is to design medical devices with a biocidal agent. Biocides can be incorporated into the materials or coated or covalently bonded, resulting either in release of the biocide or in contact killing without release of the biocide. The use of biocides in medical devices is debated because of the risk of bacterial resistance and potential toxicity. Another strategy is to modify the chemical or physical surface properties of the materials to prevent microbial adhesion, a complex phenomenon that also depends directly on microbial biological structure and the environment. Anti-adhesive chemical surface modifications mostly target the hydrophobicity features of the materials. Topographical modifications are focused on roughness and nanostructures, whose size and spatial organization are controlled. The most effective physical parameters to reduce bacterial adhesion remain to be determined and could depend on shape and other bacterial characteristics.

CONCLUSIONS

A prevention strategy based on reducing microbial attachment rather than on releasing a biocide is promising. Evidence of the clinical efficacy of these surface-modified devices is lacking. Additional studies are needed to determine which physical features have the greatest potential for reducing adhesion and to assess the usefulness of antimicrobial coatings other than antibiotics.

Development and characterization of essential oil component-based polymer films: a potential approach to reduce bacterial biofilm

The development of new polymeric materials aimed to control the bacterial biofilm appears to be an important practical approach. The goal of the present study was to prepare and characterize poly(ethylene-co-vinyl acetate) copolymer (EVA) films containing citronellol, eugenol, and linalool and evaluate their efficiency on growth and biofilm formation of Listeria monocytogenes, Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, and Pseudomonas aeruginosa in monospecies and dual species. The results showed that the addition of oil components influenced the elastic modulus (15 % decrease), the tensile stress (30 % decrease), the elongation at break (10 % increase), and the contact angle values (10-20° decrease) while leaving the homogeneity of the surface unaltered. Among the polymeric films, EVA + citronellol and EVA + eugenol at 7 wt% had the best inhibitory effect. After 24-48 h of incubation, EVA + citronellol was more effective against the growth (30-60 % reduction) than EVA + eugenol (15-30 % inhibition). However, this inhibition decreased after 240 h of incubation. On the contrary, the biofilm evaluation revealed a strong inhibition trend also after prolonged incubation time: the amount of biomass per square centimeter formed on copolymer with oil components was significantly less (40-70 % decrease) than that on pure copolymer control for L. monocytogenes, S. aureus, and E. coli. When polymeric materials were simultaneously inoculated with combinations of S. aureus and E. coli, the biomass accumulated was higher for EVA + citronellol and lower for EVA + eugenol than that in monoculture biofilm. The findings were similar to the results obtained by 2,3-bis[2-methyloxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide assay that measures the metabolic activity of viable cells.

Antibacterial high-genus polymer vesicle as an "armed" drug carrier

Presented in this paper is an "armed" high-genus block copolymer vesicle (g = 18) which has excellent blood compatibility and more internal barriers than simple polymer vesicles (g = 0) for controlled anti-cancer drug delivery. The high-genus vesicle also shows better antibacterial activity against both Gram-positive and Gram-negative bacteria without quaternary ammonium moieties or the loading of any external antibiotics compared to the non-self-assembled individual polymer chains, or a conventional simple vesicle. This high-genus polymer vesicle was prepared by the self-assembly of PMEO₂MA₂₀-b-PTA₂₀ diblock copolymers in DMF-water, where PMEO₂MA is thermo-responsive poly[2-(2-methoxyethoxy)ethyl methacrylate] and PTA is pH-responsive and antibacterial poly[2-(tert-butylaminoethyl) methacrylate]. Doxorubicin (DOX) loading/release experiments revealed a retarded release rate of DOX in high-genus block copolymer vesicles than conventional simple vesicles, which could be used as an efficient drug delivery carrier with more internal barriers for drug molecules than conventional simple vesicles. Moreover, this "armed" drug delivery vehicle makes antibacterial and anti-cancer therapeutic processes proceed spontaneously, representing a safer and more efficient drug delivery system in nanomedicine.

Deep eutectic solvent-assisted synthesis of biodegradable polyesters with antibacterial properties

Bacterial infection related to the implantation of medical devices represents a serious clinical complication, with dramatic consequences for many patients. In past decades, numerous attempts have been made to develop materials with antibacterial and/or antifouling properties by the incorporation of antibiotic and/or antiseptic compounds. In this context, deep eutectic solvents (DESs) are acquiring increasing interest not only as efficient carriers of active principle ingredients (APIs) but also as assistant platforms for the synthesis of a wide repertoire of polymer-related materials. Herein, we have successfully prepared biodegradable poly(octanediol-co-citrate) polyesters with acquired antibacterial properties by the DES-assisted incorporation of quaternary ammonium or phosphonium salts into the polymer network. In the resulting polymers, the presence of these salts (i.e., choline chloride, tetraethylammonium bromide, hexadecyltrimethylammonium bromide, and methyltriphenylphosphonium bromide) inhibits bacterial growth in the early postimplantation steps, as tested in cultures of Escherichia coli on solid agar plates. Later, positive polymer cytocompatibility is expected to support cell colonization, as anticipated from in vitro preliminary studies with L929 fibroblasts. Finally, the attractive elastic properties of these polyesters permit matching those of soft tissues such as skin. For all of these reasons, we envisage the utility of some of these antibacterial, biocompatible, and biodegradable polyesters as potential candidates for the preparation of antimicrobial wound dressings. These results further emphasize the enormous versatility of DES-assisted synthesis for the incorporation, in the synthesis step, of a wide palette of APIs into polymeric networks suitable for biomedical applications.

The effect of a silver nanoparticle polysaccharide system on streptococcal and saliva-derived biofilms

In this work, we studied the antimicrobial properties of a nanocomposite system based on a lactose-substituted chitosan and silver nanoparticles: Chitlac-nAg. Twofold serial dilutions of the colloidal Chitlac-nAg solution were both tested on Streptococcus mitis, Streptococcus mutans, and Streptococcus oralis planktonic phase and biofilm growth mode as well as on saliva samples. The minimum inhibitory and bactericidal concentrations of Chitlac-nAg were evaluated together with its effect on sessile cell viability, as well as both on biofilm formation and on preformed biofilm. In respect to the planktonic bacteria, Chitlac-nAg showed an inhibitory/bactericidal effect against all streptococcal strains at 0.1% (v/v), except for S. mitis ATCC 6249 that was inhibited at one step less. On preformed biofilm, Chitlac-nAg at a value of 0.2%, was able to inhibit the bacterial growth on the supernatant phase as well as on the mature biofilm. For S. mitis ATCC 6249, the biofilm inhibitory concentration of Chitlac-nAg was 0.1%. At sub-inhibitory concentrations, the Streptococcal strains adhesion capability on a polystyrene surface showed a general reduction following a concentration-dependent-way; a similar effect was obtained for the metabolic biofilm activity. From these results, Chitlac-nAg seems to be a promising antibacterial and antibiofilm agent able to hinder plaque formation.

Candida infections, causes, targets, and resistance mechanisms: traditional and alternative antifungal agents

The genus Candida includes about 200 different species, but only a few species are human opportunistic pathogens and cause infections when the host becomes debilitated or immunocompromised. Candida infections can be superficial or invasive. Superficial infections often affect the skin or mucous membranes and can be treated successfully with topical antifungal drugs. However, invasive fungal infections are often life-threatening, probably due to inefficient diagnostic methods and inappropriate initial antifungal therapies. Here, we briefly review our current knowledge of pathogenic species of the genus Candida and yeast infection causes and then focus on current antifungal drugs and resistance mechanisms. An overview of new therapeutic alternatives for the treatment of Candida infections is also provided.

Comprehensive review in current developments of imidazole-based medicinal chemistry

Imidazole ring is an important five-membered aromatic heterocycle widely present in natural products and synthetic molecules. The unique structural feature of imidazole ring with desirable electron-rich characteristic is beneficial for imidazole derivatives to readily bind with a variety of enzymes and receptors in biological systems through diverse weak interactions, thereby exhibiting broad bioactivities. The related research and developments of imidazole-based medicinal chemistry have become a rapidly developing and increasingly active topic. Particularly, numerous imidazole-based compounds as clinical drugs have been extensively used in the clinic to treat various types of diseases with high therapeutic potency, which have shown the enormous development value. This work systematically gives a comprehensive review in current developments of imidazole-based compounds in the whole range of medicinal chemistry as anticancer, antifungal, antibacterial, antitubercular, anti-inflammatory, antineuropathic, antihypertensive, antihistaminic, antiparasitic, antiobesity, antiviral, and other medicinal agents, together with their potential applications in diagnostics and pathology. It is hoped that this review will be helpful for new thoughts in the quest for rational designs of more active and less toxic imidazole-based medicinal drugs, as well as more effective diagnostic agents and pathologic probes.

Cationic antimicrobial polymers and their assemblies

Cationic compounds are promising candidates for development of antimicrobial agents. Positive charges attached to surfaces, particles, polymers, peptides or bilayers have been used as antimicrobial agents by themselves or in sophisticated formulations. The main positively charged moieties in these natural or synthetic structures are quaternary ammonium groups, resulting in quaternary ammonium compounds (QACs). The advantage of amphiphilic cationic polymers when compared to small amphiphilic molecules is their enhanced microbicidal activity. Besides, many of these polymeric structures also show low toxicity to human cells; a major requirement for biomedical applications. Determination of the specific elements in polymers, which affect their antimicrobial activity, has been previously difficult due to broad molecular weight distributions and random sequences characteristic of radical polymerization. With the advances in polymerization control, selection of well defined polymers and structures are allowing greater insight into their structure-antimicrobial activity relationship. On the other hand, antimicrobial polymers grafted or self-assembled to inert or non inert vehicles can yield hybrid antimicrobial nanostructures or films, which can act as antimicrobials by themselves or deliver bioactive molecules for a variety of applications, such as wound dressing, photodynamic antimicrobial therapy, food packing and preservation and antifouling applications.

Molecular interaction of a new antibacterial polymer with a supported lipid bilayer measured by an in situ label-free optical technique

The interaction of the antibacterial polymer-branched poly(ethylene imine) substituted with quaternary ammonium groups, PEO and alkyl chains, PEI25QI5J5A815-with a solid supported lipid bilayer was investigated using surface sensitive optical waveguide spectroscopy. The analysis of the optogeometrical parameters was extended developing a new composite layer model in which the structural and optical anisotropy of the molecular layers was taken into consideration. Following in situ the change of optical birefringence we were able to determine the composition of the lipid/polymer surface layer as well as the displacement of lipid bilayer by the antibacterial polymer without using additional labeling. Comparative assessment of the data of layer thickness and optical anisotropy helps to reveal the molecular mechanism of antibacterial effect of the polymer investigated.

Cold processed oil-in-water emulsions for dermatological purpose: formulation design and structure analysis

The aim of this work is to develop, optimize and characterize cold process emulsions that are stable at acidic pH. The main surfactant was selected according to the hydrophilic lipophilic balance (HLB) concept and surface tension, whereas polymers were selected by viscoelastic measurements and analytical centrifugation. It was showed that the inclusion of methyl vinyl ether/maleic anhydride copolymer crosslinked with decadiene (PVM/MA) increased the storage modulus (G') of the gels (23.9-42.1 Pa) two-fold and the droplet migration decreased from 3.66% to 0.95%/h. Cetrimide was selected as a preservative based on its microbiological results and additional contribution to the stability of the emulsions. Four emulsions were developed that differed by the co-emulsifier used (PEG-20 glyceril laurate and polyglyceryl-4-isostearate) and the glycol (2-methyl-2,4-pentanediol and ethoxydiglycol). Viscoelastic measurements and droplet size/microscopic analysis showed that the structure of PEG-20 glyceril laurate emulsion (η' = 76.0 Pa.s at 0.01 Hz and 32.9 ± 3.7 µm, respectively) was stronger compared to polyglyceryl-4-isostearate (η' = 37.4 Pa.s at 0.01 Hz and 37.8 ± 15.7 µm, respectively). Differential scanning calorimetry (DSC) results were in accordance with the latter and showed that PEG-20 glyceril laurate with 2-methyl-2,4-pentanediol corresponded to the strongest structure (|224.4| W °C g(-1)). This cold process allowed a total production savings of more than 17% when compared to the traditional hot process.

Drug/Medical Device Combination Products with Stimuli-responsive Eluting Surface

Drug-eluting medical devices are designed to improve the primary function of the device and at the same time offer local release of drugs which otherwise might find it difficult to reach the insertion/implantation site. The incorporation of the drug enables the tuning of the host/microbial responses to the device and the management of device-related complications. On the other hand, the medical device acts as platform for the delivery of the drug for a prolonged period of time just at the site where it is needed and, consequently, the efficacy and the safety of the treatment, as well as its cost-effectiveness are improved. This chapter begins with an introduction to the combination products and then focuses on the techniques available (compounding, impregnation, coating, grafting of the drug or of polymers that interact with it) to endow medical devices with the ability to host drugs/biological products and to regulate their release. Furthermore, the methods for surface modification with stimuli-responsive polymers or networks are analyzed in detail and the performance of the modified materials as drug-delivery systems is discussed. A wide range of chemical-, irradiation- and plasma-based techniques for grafting of brushes and networks that are sensitive to changes in temperature, pH, light, ionic strength or concentration of certain biomarkers, from a variety of substrate materials, is currently available. Although in vivo tests are still limited, such a surface functionalization of medical devices has already been shown useful for the release on-demand of drugs and biological products, being switchable on/off as a function of the progression of certain physiological or pathological events (e.g. healing, body integration, biofouling or biofilm formation). Improved knowledge of the interactions among the medical device, the functionalized surface, the drug and the body are expected to pave the way to the design of drug-eluting medical devices with optimized and novel performances.

Preparation and self-sterilizing properties of Ag@TiO2-styrene-acrylic complex coatings

In this study, we report a simple and cost-effective method for self-sterilized complex coatings obtained by Ag@TiO2 particle incorporation into styrene-acrylic latex. The Ag@TiO2 particles were prepared via a coupling agent modification process. The composite latices characterized by transmission electron microscopy (TEM) study were highly homogeneous at the nanometric scale, and the Ag@TiO2 particles were well dispersed and exhibited an intimate contact between both the organic and inorganic components. The Ag@TiO2 nanoparticles significantly enhanced the absorption in the visible region and engendered a good heat-insulating effect of the complex coatings. Moreover, the Ag@TiO2 nanoparticle incorporation into this polymer matrix renders self-sterilized nanocomposite materials upon light excitation, which are tested against Escherichia coli and Staphylococcus aureus. The complex coatings display an impressive performance in the killing of all micro-organisms with a maximum for a Ag@TiO2 loading concentration of 2-5 wt.%. The weathering endurance of the complex coating was also measured.

Understanding the dark and light-enhanced bactericidal action of cationic conjugated polyelectrolytes and oligomers

A multiscale investigation was carried out to study the dark and light-enhanced bactericidal mechanisms of poly(phenylene ethynylene) (PPE)-based cationic conjugated polyelectrolytes (CPEs) and oligo-phenylene ethynylenes (OPEs). On the morphological scale, Gram-negative E. coli cells exposed to CPE and OPE compounds in the dark show damage to the cell envelope, plasma membrane, and in some cases the cytoplasm, while with UV-irradiation, E. coli sustained catastrophic damages to both the cell envelope and cytoplasm. In contrast, the Gram-positive S. epi bacteria appeared intact when exposed to CPE and OPE compounds in the dark but showed damages to the cell envelope with UV-irradiation. To better understand the molecular basis of CPE- and OPE-induced morphological changes and damages to bacteria, we investigated the effect of these compounds on model bacterial plasma membrane and bacterial proteins and plasmid DNA. Measurements of dark membrane perturbation activity of the CPEs and OPEs using model lipid membranes support a carpet or detergent-like mechanism by which the antimicrobial compounds induce membrane collapse and phase transitions. Under UV-irradiation, E. coli bacteria exposed to CPEs and OPEs showed covalent modifications and damages to both cellular protein and plasmid DNA, likely through oxidative pathways mediated by singlet oxygen and subsequent reactive oxygen species sensitized by the CPE and OPE compounds. Our finding thus show that the antimicrobial polymers and oligomers exert toxicity toward Gram-negative bacteria by disrupting the morphology and structures of cell envelope and cytoplasm, including cellular components such as proteins and DNA, while exert toxicity toward Gram-positive bacteria by binding to and disrupting just the cell wall.

Novel polymeric inhibitors of HCoV-NL63

The human coronavirus NL63 is generally classified as a common cold pathogen, though the infection may also result in severe lower respiratory tract diseases, especially in children, patients with underlying disease, and elderly. It has been previously shown that HCoV-NL63 is also one of the most important causes of croup in children. In the current manuscript we developed a set of polymer-based compounds showing prominent anticoronaviral activity. Polymers have been recently considered as promising alternatives to small molecule inhibitors, due to their intrinsic antimicrobial properties and ability to serve as matrices for antimicrobial compounds. Most of the antimicrobial polymers show antibacterial properties, while those with antiviral activity are much less frequent. A cationically modified chitosan derivative, N-(2-hydroxypropyl)-3-trimethylammonium chitosan chloride (HTCC), and hydrophobically-modified HTCC were shown to be potent inhibitors of HCoV-NL63 replication. Furthermore, both compounds showed prominent activity against murine hepatitis virus, suggesting broader anticoronaviral activity.

In vitro biocompatibility and antimicrobial activity of poly(ε-caprolactone)/montmorillonite nanocomposites

A triblock copolymer based on poly(ε-caprolactone) (PCL) and 2-(N,N-diethylamino)ethyl methacrylate (DEAEMA)/2-(methyl-7-nitrobenzofurazan)amino ethyl acrylate (NBD-NAcri), was synthesized via atom transfer radical polymerization (ATRP). The corresponding chlorohydrated copolymer, named as PCL-b-DEAEMA, was prepared and anchored via cationic exchange on montmorillonite (MMT) surface. (PCL)/layered silicate nanocomposites were prepared through melt intercalation, and XRD and TEM analysis showed an exfoliated/intercalated morphology for organomodified clay. The surface characterization of the nanocomposites was undertaken by using contact angle and AFM. An increase in the contact angle was observed in the PCL/MMT(PCL-b-DEAEMA) nanocomposites with respect to PCL. The AFM analysis showed that the surface of the nanocomposites became rougher with respect to the PCL when MMTk10 or MMT(PCL-b-DEAEMA) was incorporated, and the value increased with the clay content. The antimicrobial activity of the nanocomposites against B. subtilis and P. putida was tested. It is remarkable that the biodegradation of PCL/MMT(PCL-b-DEAEMA) nanocomposites, monitored by the production of carbon dioxide and by chemiluminescence emission, was inhibited or retarded with respect to the PCL and PCL/1-MMTk10. It would indicate that nature of organomodifier in the clay play an important role in B. subtilis and P. putida adhesion processes. Biocompatibility studies demonstrate that both PCL and PCL/MMT materials allow the culture of murine L929 fibroblasts on its surface with high viability, very low apoptosis, and without plasma membrane damage, making these materials very adequate for tissue engineering.

Antibacterial soybean-oil-based cationic polyurethane coatings prepared from different amino polyols

Antibacterial soybean-oil-based cationic polyurethane (PU) coatings have been successfully prepared from five different amino polyols. The structure and hydroxyl functionality of these amino polyols affects the particle morphology, mechanical properties, thermal stability, and antibacterial properties of the resulting coatings. An increase in the hydroxyl functionality of the amino polyols increases the cross-link density, resulting in an increased glass transition temperature and improved mechanical properties. Both the cross-link density and the amount of ammonium cations incorporated into the PU backbone affect the thermal stability of PU films. PUs with the lowest ammonium cation content and highest cross-link density exhibit the best thermal stability. With some strain-specific exceptions, these PUs show good antibacterial properties toward a panel of bacterial pathogens comprised of Listeria monocytogenes NADC 2045, Salmonella typhimurium ATCC 13311 and Salmonella minnesota (S. minnesota) R613. S. minnesota R613 is a "deep rough" mutant lacking a full outer membrane (OM) layer, an important barrier structure in gram-negative bacteria. With wild-type strains, the PU coatings exhibit better antibacterial properties toward the gram-positive Listeria monocytogenes than the gram-negative S. minnesota. However, the coatings have excellent activity against S. minnesota R613, suggesting a protective role for an intact OM against the action of these PUs.

Modification of the surfaces of silicon wafers with temperature-responsive cross-linkable poly[oligo(ethylene oxide) methacrylate]-based star polymers

Temperature-responsive photo-cross-linkable poly[oligo(ethylene oxide) monomethyl ether methacrylate] (POEOMA)-based star polymers were synthesized by atom transfer radical polymerization (ATRP), for the modification of silicon (Si) wafer surfaces. The polymers showed a lower critical solution temperature (LCST) behavior in aqueous media. The polymers were modified with benzophenone (Bzp) functional groups that were utilized in UV-triggered (λ = 365 nm) cross-linking reactions for the preparation of polymer networks. The star polymers were deposited onto the surfaces of Si wafers by spin coating, and stable polymer films were formed by simple UV irradiation. The stability of thermoresponsive cross-linked polymer films deposited on the Si wafer was confirmed by changing their hydrophilicity by changing the temperature of the environment. In addition, the POEOMA-based star polymers could be utilized for the preparation of photolithography-patterned surfaces. The successful formation of uniform stable polymeric films indicates that Bzp-functionalized POEOMA star polymers can be used for a simple Si surface modification.

Antimicrobial polymers as synthetic mimics of host-defense peptides

Antibiotic-resistant bacteria 'superbugs' are an emerging threat to public health due to the decrease in effective antibiotics as well as the slowed pace of development of new antibiotics to replace those that become ineffective. The need for new antimicrobial agents is a well-documented issue relating to world health. Tremendous efforts have been given to developing compounds that not only show high efficacy, but also those that are less susceptible to resistance development in the bacteria. However, the development of newer, stronger antibiotics which can overcome these acquired resistances is still a scientific challenge because a new mode of antimicrobial action is likely required. To that end, amphiphilic, cationic polymers have emerged as a promising candidate for further development as an antimicrobial agent with decreased potential for resistance development. These polymers are designed to mimic naturally occurring host-defense antimicrobial peptides which act on bacterial cell walls or membranes. Antimicrobial-peptide mimetic polymers display antibacterial activity against a broad spectrum of bacteria including drug-resistant strains and are less susceptible to resistance development in bacteria. These polymers also showed selective activity to bacteria over mammalian cells. Antimicrobial polymers provide a new molecular framework for chemical modification and adaptation to tune their biological functions. The peptide-mimetic design of antimicrobial polymers will be versatile, generating a new generation of antibiotics toward implementation of polymers in biomedical applications.

Biocidal polymers: synthesis and antimicrobial properties of benzaldehyde derivatives immobilized onto amine-terminated polyacrylonitrile

BACKGROUND

The design and applications of antimicrobial polymers is a growing field. Antimicrobial polymers can help to solve the problems associated with the use of conventional antimicrobial agents. Polymers with active functional groups can act as a carrier system for antimicrobial agents. In our study, we aim to prepare and develop some antimicrobial polymers for biomedical applications and water treatment.

RESULTS

The antimicrobial polymers based on polyacrylonitrile (PAN) were prepared. Functional groups were created onto polyacrylonitrile via amination using different types of diamines such as ethylenediamine (EDA) and hexamethylenediamine (HMDA) to yield amine-terminated polymers. Antimicrobial polymers were obtained by immobilization of benzaldehyde and its derivatives which include, 4-hydroxybenzaldehyde and 2,4-dihydroxybenzaldehyde onto amine-terminated polymers. The antimicrobial activity of the prepared polymers against different types of microorganisms including Gram-positive bacteria (Staphylococcus aureus), Gram-negative bacteria (Pseudomonas aeruginosa; Escherichia coli; and Salmonella typhi) as well as fungi (Aspergillus flavus, Aspergillus niger, Candida albicans, Cryptpcoccus neoformans) were explored by the cut plug method and viable cell counting methods.

CONCLUSIONS

Amine-terminated polyacrylonitrile were used as a novel polymeric carrier for benzaldehyde derivatives as antimicrobial agents. The prepared polymers can inhibit the growth of the microorganisms. The activity was varied according to the tested microorganism as well as the polymer microstructure. It was found that the activity increased with increasing the number phenolic hydroxyl group of the bioactive group. Finally, it is anticipated that the prepared antimicrobial polymers would be of great help in the field of biomedical applications and biological water treatment.

Attachment of Salmonella serovars and Listeria monocytogenes to stainless steel and plastic conveyor belts

In poultry industry, cross-contamination due to processing equipment and contact surfaces is very common. This study examined the extent of bacterial attachment to 6 different types and design of conveyor belts: stainless steel-single loop, stainless steel-balance weave, polyurethane with mono-polyester fabric, acetal, polypropylene mesh top, and polypropylene. Clean conveyor belts were immersed separately in either a cocktail of Salmonella serovars (Salmonella Typhimurium and Salmonella Enteritidis) or Listeria monocytogenes strains (Scott A, Brie 1, ATCC 6744) for 1 h at room temperature. Soiled conveyor chips were dipped in poultry rinses contaminated with Salmonella or Listeria cocktail and incubated at 10°C for 48 h. The polyurethane with mono-polyester fabric conveyor belt and chip exhibited a higher (P<0.05) mean number of attached Salmonella serovars (clean: 1.6 to 3.6 cfu/cm2; soiled: 0.8 to 2.4 cfu/cm2) and L. monocytogenes (clean: 4.0 to 4.3 cfu/cm2; soiled: 0.3 to 2.1 cfu/cm2) in both clean and soiled conditions. The stainless steel conveyor belt attached a lower (P<0.05) number of Salmonella serovars (clean: 0 to 2.6 cfu/cm2; soiled: 0.4 to 1.3 cfu/cm2) and L. monocytogenes (clean: 0.4 to 2.9 cfu/cm2; soiled: 0 to 0.7 cfu/cm2) than the polymeric materials, indicating weaker adhesion properties. Plastic conveyor belts exhibited stronger bacterial adhesion compared with stainless steel. The result suggests the importance of selecting the design and finishes of conveyor belt materials that are most resistant to bacterial attachment.

Preparation of poly(vinyl chloride)/copper nanocomposite films with reduced bacterial adhesion

Films of poly(vinyl chloride)/copper (Cu) nanocomposites exhibiting reduced bacterial adhesion were prepared by film-casting method. Cu nanoparticles (NPs) synthesized using polyol method and stabilized with poly( N-vinyl-2-pyrrolidone) (PVP) at different Cu/PVP molar ratio were previously characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD) and ultraviolet–visible spectroscopy. Zero valent Cu NPs with average diameter of 4 nm were obtained. The nanocomposite films with low and high Cu content were prepared with Cu NPs obtained from Cu/PVP molar ratio of 7.2, 45 and 270. XRD patterns of PVC/Cu nanocomposite films did not show peaks associated at copper oxide and other impurities. Scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy Cu-mapping revealed a homogenous distribution of Cu NPs agglomerates in nanocomposite films prepared with Cu NPs obtained from Cu/PVP ratio of 7.2 and high Cu content, while TEM images of this nanocomposite film with low Cu content showed well-dispersed and distributed Cu NPs in PVC matrix. The films prepared with Cu NPs obtained from Cu/PVP ratio of 270 showed a vertical phase separation, where PVP was segregated to the free surface. SEM images revealed a reduced Escherichia coli adhesion to PVC/Cu nanocomposite films after 4 days of incubation with respect to plasticized PVC.

Direct visualization of bactericidal action of cationic conjugated polyelectrolytes and oligomers

The bactericidal mechanisms of poly(phenylene ethynylene) (PPE)-based cationic conjugated polyelectrolytes (CPE) and oligo-phenylene ethynylenes (OPE) were investigated using electron/optical microscopy and small-angle X-ray scattering (SAXS). The ultrastructural analysis shows that polymeric PPE-Th can significantly remodel the bacterial outer membrane and/or the peptidoglycan layer, followed by the possible collapse of the bacterial cytoplasm membrane. In contrast, oligomeric end-only OPE (EO-OPE) possesses potent bacteriolysis activity, which efficiently disintegrates the bacterial cytoplasm membrane and induces the release of bacterial cell content. Using single giant vesicles and SAXS, we demonstrated that the membrane perturbation mechanism of EO-OPE against model bacterial membranes results from a 3D membrane phase transition or perturbation.