Copper as an antibacterial agent for human pathogenic multidrug resistant Burkholderia cepacia complex bacteria

Investigations on the Degradation Behavior of Processed FeMnSi-xCu Shape Memory Alloys

A new functional Fe-30Mn-5Si-xCu (x = 1.5 and 2 wt%) biomaterial was obtained from the levitation induction melting process and evaluated as a biodegradable material. The degradation characteristics were assessed in vitro using immersion tests in simulated body fluid (SBF) at 37 ± 1 °C, evaluating mass loss, pH variation that occurred in the solution, open circuit potential (OCP), linear and cyclic potentiometry (LP and CP), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and nano-FTIR. To obtain plates as samples, the cast materials were thermo-mechanically processed by hot rolling. Dynamic mechanical analysis (DMA) was employed to evaluate the thermal properties of the smart material. Atomic force microscopy (AFM) was used to show the nanometric and microstructural changes during the hot rolling process and DMA solicitations. The type of corrosion identified was generalized corrosion, and over the first 3-5 days, an increase in mass was observed, caused by the compounds formed at the metal-solution interface. The formed compounds were identified mainly as oxides that passed into the immersion liquid. The degradation rate (DR) was obtained as a function of mass loss, sample surface area and immersion duration. The dynamic mechanical behavior and dimensions of the sample were evaluated after 14 days of immersion. The nanocompounds found on the surface after atmospheric corrosion and immersion in SBF were investigated with the Neaspec system using the nano-FTIR technique.

Inhibitory role of copper and silver nanocomposite on important bacterial and fungal pathogens in rice (Oryza sativa)

Rice (Oryza sativa) being among the most important food crops in the world is also susceptible to various bacterial and fungal diseases that are the major stumbling blocks in the way of increased production and productivity. The bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae and the sheath blight disease caused by Rhizoctonia solani are among the most devastating diseases of the rice crop. In spite of the availability of array of chemical control, there are chances of development of resistance. Thus, there is a need for the nanotechnological intervention for management of disease in the form of copper and silver nano-composites. The copper (CuNPs) and silver nanoparticles (AgNPs) were synthesized using green route and characterized using different high throughput techniques, i.e., UV-Vis, FT-IR, DLS, XRD, FE-SEM, TEM. The particle size and zeta potential of synthesized CuNPs and AgNPs were found 273 nm and - 24.2 mV; 95.19 nm and - 25.5 mV respectively. The nanocomposite of CuNPs and AgNPs were prepared having particle size in the range of 375-306 nm with improved stability (zeta potential - 54.7 to - 39.4 mV). The copper and silver nanoparticle composites evaluated against Xanthomonas oryzae pv. oryzae and Rhizoctonia solani were found to have higher antibacterial (inhibition zone 13 mm) and antifungal activities (77%) compared to only the copper nanoparticle (8 mm; 62% respectively). Net house trials of nano-composite formulations against the bacterial blight of rice also corroborated the potential of nanocomposite formulation. In silico studies were carried out selecting two disease-causing proteins, peptide deformylase (Xanthomonas oryzae) and pectate lyase (Rhizoctonia solani) to perform the molecular docking. Interaction studies indicatedthat both of these proteins generated better complex with CuNPs than AgNPs. The study suggested that the copper and silver nano-composites could be used for developing formulations to control these devastating rice diseases.

Stability of SARS-CoV-2 on inanimate surfaces: A review

The stability of SARS-CoV-2 for varying periods on a wide range of inanimate surfaces has raised concerns about surface transmission; however, there is still no evidence to confirm this route. In the present review, three variables affecting virus stability, namely temperature, relative humidity (RH), and initial virus titer, were considered from different experimental studies. The stability of SARS-CoV-2 on the surfaces of six different contact materials, namely plastic, metal, glass, protective equipment, paper, and fabric, and the factors affecting half-life period was systematically reviewed. The results showed that the half-life of SARS-CoV-2 on different contact materials was generally 2-10 h, up to 5 d, and as short as 30 min at 22 °C, whereas the half-life of SARS-CoV-2 on non-porous surfaces was generally 5-9 h d, up to 3 d, and as short as 4 min at 22 ℃. The half-life on porous surfaces was generally 1-5 h, up to 2 d, and as short as 13 min at 22 °C. Therefore, the half-life period of SARS-CoV-2 on non-porous surfaces is longer than that on porous surfaces, and thehalf-life of the virus decreases with increasing temperature, whereas RH produces a stable negative inhibitory effect only in a specific humidity range. Various disinfection precautions can be implemented in daily life depending on the stability of SARS-CoV-2 on different surfaces to interrupt virus transmission, prevent COVID-19 infections, and avoid over-disinfection. Owing to the more stringent control of conditions in laboratory studies and the lack of evidence of transmission through surfaces in the real world, it is difficult to provide strong evidence for the efficiency of transmission of the contaminant from the surface to the human body. Therefore, we suggest that future research should focus on exploring the systematic study of the entire transmission process of the virus, which will provide a theoretical basis for optimizing global outbreak prevention and control measures.

Antibacterial property, corrosion and discoloration resistance of pure copper containing Zn or Ni

This study focused on the effects of Zn and Ni addition on the antibacterial properties and corrosion resistance of copper alloys. The antimicrobial properties of copper and copper alloys were evaluated using Escherichia coli ATCC 8739 bacterial strain by employing the overlay and plate counting methods. X-ray photoelectron spectroscopy (XPS) was used to analyze the surface composition of the alloy after contact with bacteria. A salt spray method was used to simulate an artificial sweat contact environment to test the discoloration and corrosion resistance of the alloy, and scanning electron microscopy (SEM) was used to analyze the film layer and surface material composition of the corroded samples. The addition of Ni reduced the antibacterial performance of pure copper; however, the antibacterial performance of the alloy remained fast and efficient after the addition of Zn. Moreover, the addition of Zn and Ni significantly improved the corrosion resistance and surface discoloration of copper alloys in artificial sweat environments. This study provided support for the future application of copper alloys as antimicrobial surface-contact materials with safer public and medical environments in the face of diseases spread by large populations.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12598-022-02098-8.

Diversity and abundance of antibiotic resistance genes in rhizosphere soil and endophytes of leafy vegetables: Focusing on the effect of the vegetable species

Antibiotic resistance genes (ARGs) in the endophytes of vegetables represent a potential route of human exposure to the soil resistome. However, the effect of vegetable species on the endophytic ARG profiles is unclear, hampering our understanding of how ARGs migrate into the soil-vegetable system and their potential health risks. Here, we planted four leafy vegetables (cilantro, endive, lettuce, and pak choi), which are commonly eaten raw, and analyzed the resistomes and microbiomes in three sample types (rhizosphere soil, root, and leaf endophytes). A total of 150 ARG subtypes were detected using high-throughput quantitative PCR. Vegetable species had a significant effect on ARG diversity and abundance, and pak choi accumulated more ARGs in its associated microbiome than the other three vegetables. The bacterial community was the primary factor shaping ARG profiles and was significantly correlated with ARG subtypes. We identified aadE, tet(34), and vanSB as shared ARGs among leaves of the four vegetables; the bacterial families correlated with tet(34) and vanSB were also shared across the vegetables and belonged to Proteobacteria. This study deepens our understanding of how endophytic ARG profiles vary among different vegetables and highlights the potential health risk associated with consuming these vegetables raw.

Antibacterial Efficiency of Stainless-Steel Grids Coated with Cu-Ag by Thermionic Vacuum Arc Method

Autonomous smart natural ventilation systems (SVS) attached to the glass façade of living quarters and office buildings can help reducing the carbon footprint of city buildings in the future, especially during warm seasons and can represent an alternative to the conventional mechanical ventilation systems. The work performed in this manuscript focuses on the investigation of bacteria trapping and killing efficiency of stainless steel grids coated with a mixed layer of Cu-Ag. These grids are to be employed as decontamination filters for a smart natural ventilation prototype that we are currently building in our laboratory. The tested grids were coated with a mixed Cu-Ag layer using thermionic vacuum arc plasma processing technology. The fixed deposition geometry allowed the variation of Cu and Ag atomic concentration in coated layers as a function of substrate position in relation to plasma sources. The test conducted with air contaminated with a pathogen strain of staphylococcus aureus indicated that the filtering efficiency is influenced by two parameters: the pore size dimension and the coating layer composition. The results show that the highest filtering efficiency of 100% was obtained for fine pore (0.5 × 0.5 mm) grids coated with a mixed metallic layer composed of 65 at% Cu and 35 at% Ag. The second test performed only on reference grids and Cu-Ag (65–35 at%) under working conditions, confirm a similar filtering efficiency for the relevant microbiological markers. This particular sample was investigated from morphological, structural, and compositional point of view. The results show that the layer has a high surface roughness with good wear resistance and adhesion to the substrate. The depth profiles presented a uniform composition of Cu and Ag in the layer with small variations caused by changes in deposition rates during the coating process. Identification of the two metallic phases of the Cu and Ag in the layers evidences their crystalline nature. The calculated grain size of the nanocrystalline was in the range 14–21 nm.

Integrated proteomics and metabolomics analysis reveals the antifungal mechanism of the C-coordinated O-carboxymethyl chitosan Cu(II) complex

With wide application in agriculture, copper fungicides have undergone three stages of development: inorganic copper, synthetic organic copper, and natural organic copper. Using chitin/chitosan (CS) as a substrate, the natural organic copper fungicide C-coordinated O-carboxymethyl chitosan Cu(II) complex (O-CSLn-Cu) was developed in the laboratory. Taking Phytophthora capsici Leonian as an example, we explored the antifungal mechanism of O-CSLn-Cu by combining tandem mass tag (TMT)-based proteomics with non-targeted liquid chromatography-mass spectrometry (LC-MS)-based metabolomics. A total of 1172 differentially expressed proteins were identified by proteomics analysis. According to the metabolomics analysis, 93 differentially metabolites were identified. Acetyl-CoA-related and membrane localized proteins showed significant differences in the proteomics analysis. Most of the differential expressed metabolites were distributed in the cytoplasm, followed by mitochondria. The integrated analysis revealed that O-CSLn-Cu could induce the "Warburg effect", with increased glycolysis in the cytoplasm and decreased metabolism in the mitochondria. Therefore, P. capsici Leonian had to compensate for ATP loss in the TCA cycle by increasing the glycolysis rate. However, this metabolic shift could not prevent the death of P. capsici Leonian. To verify this hypothesis, a series of biological experiments, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), and enzyme activity measurements were carried out. The results suggest that O-CSLn-Cu causes mitochondrial injury, which consequently leads to excessive ROS levels and insufficient ATP levels, thereby killing P. capsici Leonian.

Gene expression is influenced due to 'nano' and 'ionic' copper in pre-formed Pseudomonas aeruginosa biofilms

Today, researchers across the globe suggest the use of antimicrobial coatings containing copper nanoparticles (CuNPs) complementing the traditional protocols to prevent hospital-acquired infections (HAIs). Since Pseudomonas aeruginosa is one of the commonest opportunistic pathogens, we assessed the anti-biofilm activity of CuNPs in P. aeruginosa MTCC 3541 and compared it with Cu²⁺ (copper sulphate) since the latter continues to be used as an antimicrobial-of-choice in food industries, agriculture and water treatment. In this study, we synthesized and characterized stable poly-acrylic acid (PAA) coated CuNPs with a size of 66-150 nm and zeta potential -13 mV. Pseudomonas aeruginosa MTCC 3541 biofilms were highly resistant to both CuNPs and Cu²⁺ (minimum biofilm inhibitory concentration, MBIC 300 and >600 μg/mL respectively). Scanning electron microscopy revealed alterations in cell morphology upon treatment with CuNPs. A closer analysis of the biofilm-specific gene expression (qRT-PCR) revealed that CuNPs downregulated the genes involved in biofilm matrix formation, motility, efflux, membrane lipoprotein synthesis and DNA replication. Both, CuNPs and Cu²⁺ up regulated copper resistance and biofilm dispersion genes. Copper did not affect the bacterial communication system as evidenced by downregulation of the negative regulator of quorum sensing. The gene expression analysis reveals multiple cellular targets for CuNPs and ionic Cu. The present study highlights the fact that CuNPs affect the membrane functions adversely damaging the cell surface. In pre-formed biofilms, CuNPs were more toxic and displayed distinct responses attributable due to 'nano' and 'ionic' copper. Our findings thus support the use of CuNPs for curbing HAIs.

Study on a biodegradable antibacterial Fe-Mn-C-Cu alloy as urinary implant material

Biodegradable Fe based alloys have been investigated for fracture fixation and cardiovascular support to overcome complications of permanent implants. This study was focused on the development of a new Fe-Mn-C-Cu alloy with antibacterial and anti-encrustation properties as a urinary implant material. The microstructure and mechanical properties of the alloy were studied. The degradation behavior, antibacterial and anti-encrustation properties were evaluated by immersion test, antibacterial test and encrustation test, respectively. The results showed that Fe-Mn-C-Cu alloy was a non-magnetic, biodegradable, anti-bacterial and anti-encrustation alloy that could inhibit the biofilm and stone formations on its surface through the dual effects of degradation and Cu ions release. The study revealed the preliminary mechanisms of anti-infection and anti-encrustation for Fe-Mn-C-Cu alloy due to the continuous release of Cu²⁺ ions, which provides a new idea for application of biodegradable Fe-based material and the treatment of urinary tract infections and stones in the urinary system.

Antibacterial properties and biocompatibility in vivo and vitro of composite coating of pure magnesium ultrasonic micro-arc oxidation phytic acid copper loaded

Bone infection and implant secondary removal remains a clinical challenge. We used ultrasonic micro-arc oxidation (UMAO) and conversion of phytic acid copper plating to prepare a pure magnesium polyhydric biofilm; we evaluated the surface microstructures, phase, element composition, and wettability of the film in vitro. The antibacterial activity of films with different Cu contents was confirmed by coating method, imaging examination, and microbiological cultures in vitro. The biocompatibility of biofilms was confirmed by cell proliferation, vitality, and morphology assays in vitro and histological evaluation in vivo. MC3T3-E1 cells were co-cultured with different films to assess cell viability on the films. The results showed that the mass fraction of Cu increased with increasing time of copper plating, and the surface of the Cu group was more dense and uniform. Additionally, copper coating significantly inhibited the growth of E. coli and Staphylococcus aurous. We also found that the adhesion, proliferation, and differentiation of the cells on the surface of copper plating were enhanced. Copper implantation of animals in vivo showed fine ability to promote bone growth. Antibacterial activity and biocompatibility of pure magnesium UMAO-phytic acid-Cu3min implant film are excellent, so the film has potential application value in the treatment of bone implantation.

Design and fabrication of novel thiourea coordination compounds as potent inhibitors of bacterial growth

A new thiourea ligand (HL), namely N-(4-chlorophenyl)morpholine-4-carbothioamide and its Co(III), Ni(II) and Ag(I) complexes (1a, 1b and 1c) were synthesized and investigated by Fourier-transform infrared, ¹H NMR and UV-visible spectroscopies. The compounds HL and 1c were characterized by single-crystal X-ray crystallography revealing the triclinic space group P[Formula: see text] for both compounds. The inhibitory effect of HL ligand, 1a, 1b, and 1c complexes was investigated with in vitro tests on Gram-positive and Gram-negative bacteria. For the 1c complex, the results showed that the coordination of the HL to Ag(I) ion increased its antibacterial effect especially against E. coli. The assays also indicated that for the same bacteria strains, the new complexes showed higher activity than the ligand, with the relative activity 1c > 1b > 1a > HL. Moreover, all samples were more suitable antimicrobial agents against the Gram-negative than those of the Gram-positive bacteria. Eventually, the relationship between the structure and bactericidal activities of these specimens was examined by calculating frontier molecular orbital (HOMO and LUMO) energies using density functional theory method at the 6-31 G*/LANL2DZ level of theory.

Antiparasitic Effect of Copper Alloy Surface on Cryptocaryon irritans in Aquaculture of Larimichthys crocea

Copper and alloys containing >60% copper by weight are antimicrobial. In aquaculture, copper alloys are used as part of corrosion-resistant cages or as part of copper coating. To test whether a copper alloy surface prevents the outbreak of parasitosis in the aquaculture of Larimichthys crocea, we covered the bottom of the aquaculture tank with sheets of copper alloy containing 74% to 78% copper, and we cultured L. crocea juveniles that had been artificially infected with the protozoan parasite Cryptocaryon irritans Our results showed that these copper alloy sheets effectively blocked the infectious cycle of C. irritans within a 1-week period and significantly reduced the number of C. irritans trophonts and tomonts, thereby decreasing the mortality rate of L. crocea In in vitro assays, the cytoplasmic membranes of protomonts disintegrated and the cytoplasm overflowed after just 5 minutes of contact with copper alloy surfaces. Although the same cytoplasmic membrane disintegration was not observed in tomonts, the tomonts completely lost their capacity for proliferation and eventually died following direct contact with copper alloy sheets for 1 h; this is likely because C. irritans tomonts took in >100 times more copper ions following contact with the copper alloy sheets than within the control aquaculture environment. Exposure to copper alloy sheets did not lead to excessive heavy metal levels in the aquacultured fish or in the culture seawater.IMPORTANCE Cryptocaryon irritans, a parasitic ciliate that penetrates the epithelium of the gills, skin, and fins of marine fish, causes acute suffocation and death in cultured fish within days of infection. Much of the existing research centers around the prevention of C. irritans infection, but no cure has been found. Studies demonstrate that copper has strong antimicrobial properties, and fish grown in copper-containing cages have lower rates of C. irritans infection, compared to those grown in other currently used aquaculture cages. In this study, we found that an alloy containing 74% to 78% copper by weight effectively killed C. irritans cells and prevented cryptocaryoniasis outbreaks within a 1-week period. These findings offer a new perspective on the prevention and control of cryptocaryoniasis.

Effects of a specific nutrient combination on ESBL resistance

Background and aim

Extended-spectrum beta-lactamases are the main cause of resistance in Enterobacteriaceae to beta lactam antibiotics. The aim of this study was to evaluate the antimicrobial effect of EpiQuercican supplement, combined with different antimicrobial agents, on ESBL-producing isolates and determine the underlying molecular mechanism of resistance in these isolates.

Materials and methods

Eleven ESBL producing Enterobacteriaceae isolates were collected from Saudi Arabia hospitals between 2016 and 2017 and disk diffusion test was performed in accordance with Clinical and Laboratory Standards Institute (CLSI) guidelines to determine the susceptibility of the isolates to 5 different antibiotics in the presence of EpiQuercican supplement. Polymerase chain reaction was performed for detection of ESBL genes, and efflux pump inhibitor was used to study the mechanism of resistance in these isolates.

Results

The best synergistic effect was obtained when the supplement was combined with carbapenems followed by 4th generation cephalosporins. Either no effect or antagonistic effect was seen with most of the isolates when the supplement was added to the 3rd generation of cephalosporins. Among the tested genes responsible for ESBL production in this study, our results indicated the predominance of TEM genes (73%) followed by CTX-M genes (9%). As for the mechanism of resistance in ESBL isolates, 4 isolates showed to use efflux pumps as their main mechanism of resistance.

Conclusion

The EpiQuercican supplement showed some promising results, yet its antibacterial mechanism of action needs to be elucidated further.

Surface treatment strategies to combat implant-related infection from the beginning

Orthopaedic implants are recognised as important therapeutic devices in the successful clinical management of a wide range of orthopaedic conditions. However, implant-related infections remain a challenging and not uncommon issue in patients with implanted instrumentation or medical devices. Bacterial adhesion and formation of biofilm on the surface of the implant represent important processes towards progression of infection. Given the intimate association between infection and the implant surface, adequate treatment of the implant surface may help mitigate the risk of infection. This review summarises the current surface treatment technologies and their role in prevention of implant-related infection from the beginning.

Translational potential of this article

Despite great technological advancements, the prevalence of implant-related infections remains high. Four main challenges can be identified. (i) Insufficient mechanical stability can cause detachment of the implant surface coating, altering the antimicrobial ability of functionalized surfaces. (ii) Regarding drug-loaded coatings, a stable drug release profile is of vital importance for achieving effective bactericidal effect locally; however, burst release of the loaded antibacterial agents remains common. (iii) Although many coatings and modified surfaces provide superior antibacterial action, such functionalisation of surfaces sometimes has a detrimental effect on tissue biocompatibility, impairing the integration of the implants into the surrounding tissue. (iv) Biofilm eradication at the implant surface remains particularly challenging. This review summarised the recent progress made to address the aforementioned problems. By providing a perspective on state-of-the-art surface treatment strategies for medical implants, we hope to support the timely adoption of modern materials and techniques into clinical practice.

Synthesis, Characterization, and Antimicrobial Activity of Novel Sulfonated Copper-Triazine Complexes

Metallotriazine complexes possess interesting biological and medicinal properties, and the present study focuses on the synthesis, characterization, and antimicrobial activity of four novel copper-triazine derivatives in search of potent antibacterial and antifungal drug leads. In this study, 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine-4,4′-disulfonic acid monosodium salt (L1, ferrozine) and 3-(2-pyridyl)-5,6-di(2-furyl)-1,2,4-triazine-5,5′-disulfonic acid disodium salt (L2, ferene) have been used as ligands to study the complexation towards copper(II). The synthesized complexes, [CuCl₂(ferrozine)]·7H₂O·MeOH (1), [CuCl₂(ferrozine)₂]·5H₂O·MeOH (2), [CuCl₂(ferene)]·H₂O·MeOH (3), and [CuCl₂(ferene)₂]·H₂O·MeOH (4), have been characterized spectroscopically, and preliminary bioassays have been carried out. FTIR spectroscopic data have shown that N=N and C=N stretching frequencies of complexes have been shifted towards lower frequencies in comparison with that of the ligands, confirming new bond formation between Cu and N, which in turn lowers the strength of N=N and C=N bonds. In addition, a bathochromic shift has been observed for UV-visible spectra of complexes (1), (2), (3), and (4). Furthermore, elemental analysis data have been useful to obtain empirical formulas of these complexes and to establish the purity of each complex. Complexes (1) and (2) have shown antibacterial activity for both S. aureus (ATCC® 25923) and E. coli (ATCC® 25922) at 1 mg/disc concentration, and ferrozine has shown a larger inhibition zone against the clinical sample of C. albicans at 1 mg/disc concentration in comparison with the positive control, fluconazole.

A highly selective and sensitive chemosensor forl-tryptophan by employing a Schiff based Cu(ii) complex

Construction of a new Cu(ii) complex (1) based modified glassy carbon electrode (1-GCE) for highly selective and sensitive detection ofl-tryptophan (l-Trp).

Syntheses, Characterization, Resolution, and Biological Studies of Coordination Compounds of Aspartic Acid and Glycine

Enantiomerically enriched coordination compounds of aspartic acid and racemic mixtures of coordination compounds of glycine metal-ligand ratio 1 : 3 were synthesized and characterized using infrared and UV-Vis spectrophotometric techniques and magnetic susceptibility measurements. Five of the complexes were resolved using (+)-cis-dichlorobis(ethylenediamine)cobalt(III) chloride, (+)-bis(glycinato)(1,10-phenanthroline)cobalt(III) chloride, and (+)-tris(1,10-phenanthroline)nickel(II) chloride as resolving agents. The antimicrobial and cytotoxic activities of these complexes were then determined. The results obtained indicated that aspartic acid and glycine coordinated in a bidentate fashion. The enantiomeric purity of the compounds was in the range of 22.10–32.10%, with (+)-cis-dichlorobis(ethylenediamine)cobalt(III) complex as the more efficient resolving agent. The resolved complexes exhibited better activity in some cases compared to the parent complexes for both biological activities. It was therefore inferred that although the increase in the lipophilicity of the complexes may assist in the permeability of the complexes through the cell membrane of the pathogens, the enantiomeric purity of the complexes is also of importance in their activity as antimicrobial and cytotoxic agents.

Facile synthesis of 3D flower-like Cu2−xSe nanostructures via a sacrificing template method and their excellent antibacterial activities

The flower-like Cu_2−xSe assembled from hexagonal nanosheets shows excellent antibacterial activities to S. aureus and E. coli, and its antibacterial mechanism was confirmed experimentally.

In vitro cytotoxicity and antibacterial activity of silver-coated electrospun polycaprolactone/gelatine nanofibrous scaffolds

The development of nano-sized scaffolds with antibacterial properties that mimic the architecture of tissue is one of the challenges in tissue engineering. In this study, polycaprolactone (PCL) and PCL/gelatine (Ge) (70:30) nanofibrous scaffolds were fabricated using a less toxic and common solvent, formic acid and an electrospinning technique. Nanofibrous scaffolds were coated with silver (Ag) in different concentrations of silver nitrate (AgNO₃) aqueous solution (1.25, 2.5, 5, and 10 %) by using dipping method, drying and followed by ultraviolet (UV) photoreduction. The PCL/Ge (70:30) nanofibrous scaffold had an average fibre diameter of 155.60 ± 41.13 nm. Characterization showed that Ag was physically entrapped in both the PCL and PCL/Ge (70:30) nanofibrous scaffolds. Ag⁺ ions release study was performed and showed much lesser release amount than the maximum toxic concentration of Ag⁺ ions in human cells. Both scaffolds were non-toxic to cells and demonstrated antibacterial effects towards Gram-positive Bacillus cereus (B. cereus) and Gram-negative Escherichia coli (E. coli). The Ag/PCL/Ge (70:30) nanofibrous scaffold has potential for tissue engineering as it can protect wounds from bacterial infection and promote tissue regeneration.

Antimicrobial copper alloy surfaces are effective against vegetative but not sporulated cells of gram-positive Bacillus subtilis

This study explores the role of membrane phospholipid peroxidation in the copper alloy mediated contact killing of Bacillus subtilis, a spore-forming gram-positive bacterial species. We found that B. subtilis endospores exhibited significant resistance to copper alloy surface killing but vegetative cells were highly sensitive to copper surface exposure. Cell death and lipid peroxidation occurred in B. subtilis upon copper alloy surface exposure. In a sporulation-defective strain carrying a deletion of almost the entire SpoIIA operon, lipid peroxidation directly correlated with cell death. Moreover, killing and lipid peroxidation initiated immediately and at a constant rate upon exposure to the copper surface without the delay observed previously in E. coli. These findings support the hypothesis that membrane lipid peroxidation is the initiating event causing copper surface induced cell death of B. subtilis vegetative cells. The findings suggest that the observed differences in the kinetics of copper-induced killing compared to E. coli result from differences in cell envelop structure. As demonstrated in E. coli, DNA degradation was shown to be a secondary effect of copper exposure in a B. subtilis sporulation-defective strain.

Metal nanobullets for multidrug resistant bacteria and biofilms

Infectious diseases were one of the major causes of mortality until now because drug-resistant bacteria have arisen under broad use and abuse of antibacterial drugs. These multidrug-resistant bacteria pose a major challenge to the effective control of bacterial infections and this threat has prompted the development of alternative strategies to treat bacterial diseases. Recently, use of metallic nanoparticles (NPs) as antibacterial agents is one of the promising strategies against bacterial drug resistance. This review first describes mechanisms of bacterial drug resistance and then focuses on the properties and applications of metallic NPs as antibiotic agents to deal with antibiotic-sensitive and -resistant bacteria. We also provide an overview of metallic NPs as bactericidal agents combating antibiotic-resistant bacteria and their potential in vivo toxicology for further drug development.

Survival of Escherichia coli cells on solid copper surfaces is increased by glutathione

Bacteria are rapidly killed on solid copper surfaces, so this material could be useful to limit the spread of multiple-drug-resistant bacteria in hospitals. In Escherichia coli, the DNA-protecting Dps protein and the NADH:ubiquinone oxidoreductase II Ndh were not involved in tolerance to copper ions or survival on solid copper surfaces. Decreased copper tolerance under anaerobic growth conditions in the presence of ascorbate and with melibiose as the carbon source indicated that sodium-dependent symport systems may provide an import route for Cu(I) into the cytoplasm. Glutathione-free ΔcopA ΔgshA double mutants of E. coli were more rapidly inactivated on solid copper surfaces than glutathione-containing wild-type cells. Therefore, while DNA protection by Dps was not required, glutathione was needed to protect the cytoplasm and the DNA against damage mediated by solid copper surfaces, which may explain the differences in the molecular mechanisms of killing between glutathione-containing Gram-negative and glutathione-free Gram-positive bacteria.

Susceptibility of opportunistic Burkholderia glumae to copper surfaces following wet or dry surface contact

Burkholderia glumae has been proposed to have a potential risk to vulnerable communities. In this work, we investigated the antibacterial activity and mechanism of copper surfaces against multi-drug resistant B. glumae from both patients and rice plants. The susceptibility of B. glumae to copper surfaces was noted by a significant decline in viable bacterial counts, relative to the slight reduction of stainless steel and polyvinylchloride, both of which were used as control surfaces. The mode of action of bacterial killing was determined by examing the mutagenicity, DNA damage, copper ions accumulation, and membrane damage in bacterial cells. The results indicated that the cells exposed to copper surfaces did not cause severe DNA lesions or increase the mutation frequencies, but resulted in a loss of cell membrane integrity within minutes. Furthermore, bacterial cells exposed to copper surfaces accumulated significantly higher amounts of copper compared to control surfaces. Overall, this study showed that metallic copper had strong antibacterial effect against B. glumae by causing DNA and membrane damage, cellular accumulation of copper, and cell death following DNA degradation, which could be utilized to reduce the risk of bacterial contamination and infection.

Binding of oxo-Cu2 clusters to ferric ion-binding protein A from Neisseria gonorrhoeae: a structural insight

The ferric ion-binding protein A (FbpA), a member of transferrin superfamily, is a periplasmic iron transporter employed by many Gram-negative pathogens. Our experiments indicated copper(ii) could bind with Neisseria gonorrhoeae FbpA (NgFbpA), and the binding constant reached up to (8.7 ± 0.2) × 10(8) M(-1)via UV-vis titration. The crystal structure of recombinant Cu-NgFbpA at 2.1 Å revealed that the oxo-Cu2 clusters (dinuclear centres) assembled in the iron binding cleft and were bound to the two adjacent tyrosine residues (Y195 and Y196) of the protein, two Cu ions coordinated with two tyrosines, Y195 and Y196, respectively, which was different from the binding model of Fe ion with FbpA, in which Y195 and Y196 coordinated together with one Fe ion. While this was similar to the binding of Zr and Hf ion clusters, Y195 and Y196 coordinated with two metal ions and the μ-oxo-bridges linking the metal ions. Structural superimposition demonstrated that oxo-Cu2-NgFbpA still keeping an open conformation, similar to the apo-form of NgFbpA. The structure presented additional information towards an understanding of the function of FbpA, and provided a detailed binding model for FbpA protein with the possible metal ions in a biological system.

Synthesis, characterization, and antibacterial activity of cross-linked chitosan-glutaraldehyde

This present study deals with synthesis, characterization and antibacterial activity of cross-linked chitosan-glutaraldehyde. Results from this study indicated that cross-linked chitosan-glutaraldehyde markedly inhibited the growth of antibiotic-resistant Burkholderia cepacia complex regardless of bacterial species and incubation time while bacterial growth was unaffected by solid chitosan. Furthermore, high temperature treated cross-linked chitosan-glutaraldehyde showed strong antibacterial activity against the selected strain 0901 although the inhibitory effects varied with different temperatures. In addition, physical-chemical and structural characterization revealed that the cross-linking of chitosan with glutaraldehyde resulted in a rougher surface morphology, a characteristic Fourier transform infrared (FTIR) band at 1559 cm⁻¹, a specific X-ray diffraction peak centered at 2θ = 15°, a lower contents of carbon, hydrogen and nitrogen, and a higher stability of glucose units compared to chitosan based on scanning electron microscopic observation, FTIR spectra, X-ray diffraction pattern, as well as elemental and thermo gravimetric analysis. Overall, this study indicated that cross-linked chitosan-glutaraldehyde is promising to be developed as a new antibacterial drug.

Effective bacterial inactivation and removal of copper by porous ceramics with high surface area

In this study, we present porous ceramics combining the antibacterial effect of copper with an integrated copper removal adsorbent. After preparing and characterizing the antibacterial copper-doped microbeads and monoliths (CuBs and CuMs), their antibacterial efficiency is probed against different nonpathogenic and pathogenic bacteria (Bacillus subtilis, Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa). An antibacterial efficiency of 100% is reached within 15 min to 3 h for all tested strains under static conditions. Dynamic tests with B. subtilis and E. coli showed high antibacterial efficiency up to 99.93% even at continuous flux. To avoid any adverse effects on the environment, continuous removal of released copper-ions is accomplished with porous, high surface area monolithic adsorbents (MAds). MAds are prepared similarly to the CuMs but without adding copper during the manufacturing process. MAds reduce the amount of copper released from the CuMs ≥ 99% during the first 15 min, ≥90% up to 2 h, and after 22 h of continuous filtration up to 56% of the released copper is removed.