Metallic copper corrosion rates, moisture content, and growth medium influence survival of copper ion-resistant bacteria

The rapid killing of various bacteria in contact with metallic copper is thought to be influenced by the influx of copper ions into the cells, but the exact mechanism is not fully understood. This study showed that the kinetics of contact killing of copper surfaces depended greatly on the amount of moisture present, copper content of alloys, type of medium used, and type of bacteria. We examined antibiotic- and copper ion-resistant strains of Escherichia coli and Enterococcus faecium isolated from pig farms following the use of copper sulfate as feed supplement. The results showed rapid killing of both copper ion-resistant E. coli and E. faecium strains when samples in rich medium were spread in a thin, moist layer on copper alloys with 85% or greater copper content. E. coli strains were rapidly killed under dry conditions, while E. faecium strains were less affected. Electroplated copper surface corrosion rates were determined from electrochemical polarization tests using the Stern–Geary method and revealed decreased corrosion rates with benzotriazole and thermal oxide coating. Copper ion-resistant E. coli and E. faecium cells suspended in 0.8% NaCl showed prolonged survival rates on electroplated copper surfaces with benzotriazole coating and thermal oxide coating compared to surfaces without anti-corrosion treatment. Control of surface corrosion affected the level of copper ion influx into bacterial cells, which contributed directly to bacterial killing.     

Recovery of electric energy from formate by using a recombinant strain of Escherichia coli

Recombinant Escherichia coli cells were applied for the recovery of electric energy from formate. Initially, the fdh gene, which encodes formate dehydrogenase (FDH) of Mycobacterium vaccae, was introduced into E. coli cells to allow efficient degradation of formate. The constructed microbial fuel cell (MFC) with E. coli BW25113 cells carrying fdh gene showed appreciable generation of current density in the presence of formate as a substrate. Current density and polarization curves revealed that the performance of MFC under examined conditions was limited by the electron transfer from bulk liquid to the electrode surface; accordingly, agitation resulted in an increase in the current density and achieved a coulombic efficiency of 21.7 % on the basis of formate consumed. Thus, gene recombination enables E. coli cells to utilize formate as a fuel for MFC.     

Polypropylene with embedded copper metal or copper oxide nanoparticles as a novel plastic antimicrobial agent

Aims: To develop novel polypropylene composite materials with antimicrobial activity by adding different types of copper nanoparticles. Methods and Results: Copper metal (CuP) and copper oxide nanoparticles (CuOP) were embedded in a polypropylene (PP) matrix. These composites present strong antimicrobial behaviour against E. coli that depends on the contact time between the sample and the bacteria. After just 4 h of contact, these samples are able to kill more than 95% of the bacteria. CuOP fillers are much more effective eliminating bacteria than CuP fillers, showing that the antimicrobial property further depends on the type of copper particle. Cu²⁺ released from the bulk of the composite is responsible for this behaviour. Moreover, PP/CuOP composites present a higher release rate than PP/CuP composites in a short time, explaining the antimicrobial tendency. Conclusions: Polypropylene composites based on copper nanoparticles can kill E. coli bacteria depending on the release rate of Cu²⁺ from the bulk of the material. CuOP are more effective as antimicrobial filler than CuP. Significance and Impact of the Study: Our findings open up novel applications of these ion‐copper‐delivery plastic materials based on PP with embedded copper nanoparticles with great potential as antimicrobial agents.     

Antibacterial and antibiofilm effects of silver nanoparticles against the uropathogen Escherichia coli U12

The drug-resistant bacterial strains' emergence increases day by day. This may be a result of biofilm presence, which protects bacteria from antimicrobial agents. Thus, new approaches must be used to control biofilm-related infections in healthcare settings. In such a study, biological silver nanoparticles were introduced in such a study as an anti-biofilm agent against multidrug-resistant E. coli U12 on urinary catheters. Seven different silver nanoparticles concentrations were tested for their antimicrobial activities. Also, anti-biofilm activities against E. coli U12 were tested. Using the dilution method, the silver nanoparticles concentration of 85 μg/ml was the MIC (Minimum Inhibitory Concentration) that had excellent biocompatibility and showed significant antibacterial activity against E. coli U12. Scanning electron microscopy (SEM) confirmed that the highest efficient dose of silver nanoparticles was 340 μg/ml at 144 h that reduced adhesion of E. coli U12 to the urinary catheter. E. coli U12 cells ruptured cell walls and cell membranes after being examined using transmission electron microscopy (TEM). Thus, biologically prepared silver nanoparticles could be used to coat medical devices since it is effective and promising to inhibit biofilm formation by impregnating urinary catheters with silver nanoparticles.     

The Bactericidal Effect of Dendritic Copper Microparticles,Contained in an Alginate Matrix,on Escherichia coli

Although the bactericidal effect of copper has been known for centuries, there is a current resurgence of interest in the use of this element as an antimicrobial agent. During this study the use of dendritic copper microparticles embedded in an alginate matrix as a rapid method for the deactivation of Escherichia coli ATCC 11775 was investigated. The copper/alginate produced a decrease in the minimum inhibitory concentration from free copper powder dispersed in the media from 0.25 to 0.065 mg/ml. Beads loaded with 4% Cu deactivated 99.97% of bacteria after 90 minutes, compared to a 44.2% reduction in viability in the equivalent free copper powder treatment. There was no observed loss in the efficacy of this method with increasing bacterial loading up to 10⁶ cells/ml, however only 88.2% of E. coli were deactivated after 90 minutes at a loading of 10⁸ cells/ml. The efficacy of this method was highly dependent on the oxygen content of the media, with a 4.01% increase in viable bacteria observed under anoxic conditions compared to a >99% reduction in bacterial viability in oxygen tensions above 50% of saturation. Scanning electron micrographs (SEM) of the beads indicated that the dendritic copper particles sit as discrete clusters within a layered alginate matrix, and that the external surface of the beads has a scale-like appearance with dendritic copper particles extruding. E. coli cells visualised using SEM indicated a loss of cellular integrity upon Cu bead treatment with obvious visible blebbing. This study indicates the use of microscale dendritic particles of Cu embedded in an alginate matrix to effectively deactivate E. coli cells and opens the possibility of their application within effective water treatment processes, especially in high particulate waste streams where conventional methods, such as UV treatment or chlorination, are ineffective or inappropriate.     

Characterization and antibacterial activity of the nanocomposite of half-fin anchovy (Setipinna taty) hydrolysates/zinc oxide nanoparticles

Half-fin anchovy (Setipinna taty) hydrolysates (HAHp) was conjugated with zinc oxide nanoparticles (ZnO NPs) using a hydrothermal method to develop a novel antibacterial nanocomposite. The generated supernatants of the conjugate, designated as HAHp(3.0)/ZnO NPs, were characterized by transmission electron microscopy, high resolution transmission electron microscopy, and inductively coupled plasma-optical emission spectrometer. Results showed that HAHp(3.0) was absorbed on the surface of the ZnO NPs. The total content of zinc element was 9127.4 mg/kg in HAHp(3.0)/ZnO NPs. The increased antibacterial effects were observed for the HAHp(3.0)/ZnO NPs with the minimal inhibitory concentration of 3.5 μgprotein/mL against Escherichia coli (E. coli), Pseudomonas fluorescens, Salmonella and Staphylococcus aureus, compared to the bare HAHp(3.0). The antibacterial activity of HAHp(3.0)/ZnO NPs was further evaluated using E. coli as the model strain. The incubation of HAHp(3.0)/ZnO NPs increased the outer and inner membrane permeability in E. coli cells, and the leakages of potassium ions and the cytoplasmic β-galactosidase were detected during the process. Furthermore, porous structures were observed on the membrane of E. coli cells by scanning electron microscopy. In addition, the formation of intracellular reactive oxygen species was detected using fluorescence microscopy. The results suggested that the HAHp(3.0)/ZnO NPs could be a promising antibacterial nanocomposite.     

Rapid Biosensor for Detection of Antibiotic-Selective Growth of Escherichia coli

A rapid biosensor for the detection of bacterial growth was developed using micromechanical oscillators coated in common nutritive layers. The change in resonance frequency as a function of the increasing mass on a cantilever array forms the basis of the detection scheme. The calculated mass sensitivity according to the mechanical properties of the cantilever sensor is ~50 pg/Hz; this mass corresponds to an approximate sensitivity of ~100 Escherichia coli cells. The sensor is able to detect active growth of E. coli cells within 1 h. The starting number of E. coli cells initially attached to the sensor cantilever was, on average, ~1,000 cells. Furthermore, this method allows the detection of selective growth of E. coli within only 2 h by adding antibiotics to the nutritive layers. The growth of E. coli was confirmed by scanning electron microscopy. This new sensing method for the detection of selective bacterial growth allows future applications in, e.g., rapid antibiotic susceptibility testing.     

Isolation of copper oxide (CuO) nanoparticles resistant Pseudomonas strains from soil and investigation on possible mechanism for resistance

The present study deals with isolation and characterization of copper oxide nanoparticles resistant Pseudomonas strains that were isolated from the soil collected from mining and refining sites of Sarcheshmeh copper mine in the Kerman Province of Iran. The three isolates were selected based on high level of copper oxide nanoparticles (CuO NPs) resistance. The isolates were authentically identified as Pseudomonas fluorescens CuO-1, Pseudomonas fluorescens CuO-2 and Pseudomonas sp. CuO-3 by morphological, biochemical and 16S rDNA gene sequencing analysis. The growth pattern of these isolates with all the studied CuO NPs concentrations was similar to that of control (without CuO NPs) indicating that CuO NPs would not affect the growth of isolated strains. A reduction in the amount of exopolysaccharides was observed after CuO NPs—P. fluorescens CuO-1 culture supernatant interaction. The Fourier transform infrared spectroscopy (FT-IR) peaks for the exopolysaccharides extracted from the bacterial culture supernatant and the interacted CuO NPs were almost similar. The exopolysaccharide capping of the CuO NPs was confirmed by FT-IR and X-ray diffraction analysis. The study of bacterial exopolysaccharides capped CuO NPs with E. coli PTCC 1338 and S. aureus PTCC 1113 showed less toxicity compared to uncoated CuO NPs. Our study suggests that the capping of nanoparticles by bacterially produced exopolysaccharides serve as the probable mechanism of tolerance.     

Evaluation of the microbial growth response to inorganic nanoparticles

In order to enhance the utilization of inorganic nanoparticles in biological systems, it is important to develop a fundamental understanding of the influence they have on cellular health and function. Experiments were conducted to test silica, silica/iron oxide, and gold nanoparticles for their effects on the growth and activity of Escherichia coli (E. coli). Transmission electron microscopy (TEM) and dynamic light scattering (DLS) were used to characterize the morphology and quantify size distribution of the nanoparticles, respectively. TEM was also used to verify the interactions between composite iron oxide nanoparticles and E. coli. The results from DLS indicated that the inorganic nanoparticles formed small aggregates in the growth media. Growth studies measured the influence of the nanoparticles on cell proliferation at various concentrations, showing that the growth of E. coli in media containing the nanoparticles indicated no overt signs of toxicity.     

Comparative assessment of the bactericidal effect of nanoparticles of copper oxide,silver, and chitosan-silver against Escherichia coli infection in broilers

Escherichia coli infection is considered one of the most economically important multi-systemic diseases in poultry farms. Several nanoparticles such as silver, chitosan, and copper oxide are known to be highly toxic to several microbes. However, there are no data concerning their success against in vivo experimental E. coli infection in broilers. Therefore, the present study was designed to investigate the bactericidal effect of low doses of CuO-NPs (5 mg/kg bwt), Ag-NPs (0.5 mg/kg bwt), and Ch-Ag NPs (0.5 mg/kg bwt) against E. coli experimental infection in broilers. One hundred chicks were divided into five groups as follows: (1) control; (2) E. coli (4 × 10⁸ CFU/ml) challenged; (3) E. coli +CuO-NPs; (4) E. coli +Ag-NPs; (5) E. coli +Ch-Ag NPs. The challenged untreated group, not NPs treated groups, recorded the lowest weight gain as well as the highest bacterial count and lesion score in all examined organs. The highest liver content of silver was observed in Ag-NPs treated group compared with the Ch-Ag NPs treated group. Our results concluded that Ch-Ag NPs not only had the best antibacterial effects but also acted as a growth promoter in broilers without leaving any residues in edible organs. We recommend using Ch-Ag NPs in broiler farms instead of antibiotics or probiotics.     

Differential Damage in Bacterial Cells by Microwave Radiation on the Basis of Cell Wall Structure

Microwave radiation in Escherichia coli and Bacillus subtilis cell suspensions resulted in a dramatic reduction of the viable counts as well as increases in the amounts of DNA and protein released from the cells according to the increase of the final temperature of the cell suspensions. However, no significant reduction of cell density was observed in either cell suspension. It is believed that this is due to the fact that most of the bacterial cells inactivated by microwave radiation remained unlysed. Scanning electron microscopy of the microwave-heated cells revealed severe damage on the surface of most E. coli cells, yet there was no significant change observed in the B. subtilis cells. Microwave-injured E. coli cells were easily lysed in the presence of sodium dodecyl sulfate (SDS), yet B. subtilis cells were resistant to SDS.     

Biosynthesis and antibacterial activity of ZnO nanoparticles using Trifolium pratense flower extract

Zinc oxide (ZnO) has broad applications in various areas. Nanoparticle synthesis using plants is an alternative to conventional physical and chemical methods. It is known that the biological synthesis of nanoparticles is gaining importance due to its simplicity, eco-friendliness and extensive antimicrobial activity. Also, in this study we report the synthesis of ZnO nanoparticles using Trifolium pratense flower extract. The prepared ZnO nanoparticles have been characterized by UV–Vis absorption spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM) with Energy dispersive X-ray analysis (EDX). Besides, this study determines the antimicrobial efficacy of the synthesized ZnO nanoparticles against clinical and standard strains of S. aureus and P. aeruginosa and standard strain of E. coli.     

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.     

Advantage Provided by Iron for Escherichia coli Growth and Cultivability in Drinking Water

The presence of iron, used both as a nutrient and as an electron acceptor, was demonstrated to give an advantage to Escherichia coli bacteria in drinking water. Slight additions of ferrous sulfate to water with initial low iron concentrations led to a significant increase in the number of E. coli bacteria. The presence of ferric oxide in water under anaerobic conditions increased bacterial cultivability.     

Dynamic Mechanisms of the Bactericidal Action of an Al2O3-TiO2-Ag Granular Material on an Escherichia coli Strain

The bactericidal activity of an Al₂O₃-TiO₂-Ag granular material against an Escherichia coli strain was confirmed by a culture-based method. In particular, 100% of microorganisms were permanently inactivated in 30 to 45 min. The present work aimed to investigate the mechanisms of the bactericidal action of this material and their dynamics on Escherichia coli using different techniques. Observations by transmission electron microscopy (TEM) at different times of disinfection revealed morphological changes in the bacteria as soon as they were put in contact with the material. Notably highlighted were cell membrane damage; cytoplasm detachment; formation of vacuoles, possibly due to DNA condensation, in association with regions exhibiting different levels of electron density; and membrane lysis. PCR and flow cytometry analyses were used to confirm and quantify the observations of cell integrity. The direct exposure of cells to silver, combined with the oxidative stress induced by the reactive oxygen species (ROS) generated, was identified to be responsible for these morphological alterations. From the first 5 min of treatment with the Al₂O₃-TiO₂-Ag material, 98% of E. coli isolates were lysed. From 30 min, cell viability decreased to reach total inactivation, although approximately 1% of permeable E. coli cells and 1% of intact cells (10⁵ genomic units · ml⁻¹) were evidenced. This study demonstrates that the bactericidal effect of the material results from a synergic action of desorbed and supported silver. Supported silver was shown to generate the ROS evidenced.     

Quantitative proteomic profiling of the <Emphasis Type="Italic">Escherichia coli</Emphasis> response to metallic copper surfaces

Metallic copper surfaces have strong antimicrobial properties and kill bacteria, such as Escherichia coli, within minutes in a process called contact killing. These bacteria are exposed to acute copper stress under dry conditions which is different from chronic copper stress in growing liquid cultures. Currently, the physiological changes of E. coli during the acute contact killing process are largely unknown. Here, a label-free, quantitative proteomic approach was employed to identify the differential proteome profiles of E. coli cells after sub-lethal and lethal exposure to dry metallic copper. Of the 509 proteins identified, 110 proteins were differentially expressed after sub-lethal exposure, whereas 136 proteins had significant differences in their abundance levels after lethal exposure to copper compared to unexposed cells. A total of 210 proteins were identified only in copper-responsive proteomes. Copper surface stress coincided with increased abundance of proteins involved in secondary metabolite biosynthesis, transport and catabolism, including efflux proteins and multidrug resistance proteins. Proteins involved in translation, ribosomal structure and biogenesis functions were down-regulated after contact to metallic copper. The set of changes invoked by copper surface-exposure was diverse without a clear connection to copper ion stress but was different from that caused by exposure to stainless steel. Oxidative posttranslational modifications of proteins were observed in cells exposed to copper but also from stainless steel surfaces. However, proteins from copper stressed cells exhibited a higher degree of oxidative proline and threonine modifications.     

Polysaccharide-based silver nanoparticles synthesized by <Emphasis Type="Italic">Klebsiella oxytoca</Emphasis> DSM 29614 cause DNA fragmentation in <Emphasis Type="Italic">E. coli</Emphasis> cells

Silver nanoparticles (AgNPs), embedded into a specific exopolysaccharide (EPS), were produced by Klebsiella oxytoca DSM 29614 by adding AgNO₃ to the cultures during exponential growth phase. In particular, under aerobic or anaerobic conditions, two types of silver nanoparticles, named AgNPs-EPS^aer and the AgNPs-EPS^anaer, were produced respectively. The effects on bacterial cells was demonstrated by using Escherichia coli K12 and Kocuria rhizophila ATCC 9341 (ex Micrococcus luteus) as Gram-negative and Gram-positive tester strains, respectively. The best antimicrobial activity was observed for AgNPs-EPS^aer, in terms of minimum inhibitory concentrations and minimum bactericidal concentrations. Observations by transmission electron microscopy showed that the cell morphology of both tester strains changed during the exposition to AgNPs-EPS^aer. In particular, an electron-dense wrapped filament was observed in E. coli cytoplasm after 3 h of AgNPs-EPS^aer exposition, apparently due to silver accumulation in DNA, and both E. coli and K. rhizophila cells were lysed after 18 h of exposure to AgNPs-EPS^aer. The DNA breakage in E. coli cells was confirmed by the comparison of 3-D fluorescence spectra fingerprints of DNA. Finally the accumulation of silver on DNA of E. coli was confirmed directly by a significant Ag⁺ release from DNA, using the scanning electrochemical microscopy and the voltammetric determinations.     

Binding of Escherichia coli to Functionalized Gold Nanoparticles

The molecular basis of the diversity of fimbrial lectins dictates the extent of adhesion in different types of Escherichia coli strains to mammalian cells. The mechanism of receptor binding by E. coli in eukaryotic cells differs based on the adhesin domains, patterns in the macromolecular structure and the ligand-binding groove. Current sensor technologies utilize biosensors that are based on the carbohydrate moieties that are involved in pathogen adhesion to host cells. Nanoparticles have been extensively used as carriers for pathogen detection. Gold nanoparticles (Au NPs) of 200?nm size were functionalized with two distinct glycoconjugates mannose (Mn?CAu NPs) and Neu??c(??2-3)-Gal-(??1-4)Glc?CPaa (Sg?CAu NPs) in order to investigate primary and fine sugar specificity of uropathogenic E. coli ORN178 and enterotoxigenic E. coli 13762, respectively. The UV-Vis measurement of pristine, 16-mercaptohexadecanoic acid (MHDA)/2-(2-aminoethoxy)ethanol (AEE)/sugar functionalized Au NPs showed a surface plasmon resonance band for Au. Dynamic light scattering analysis showed that the mean averages of the MHDA/AEE/Mn?CAu NP samples increased due to aggregation. The negative zeta potentials of the samples were indicative of aggregation. Fine sugar specificity was observed when Neu??c(??2-3)-Gal-(??1-4)Glc?CPaa functionalized Au NPs (Sg?CAu NPs) specifically showed binding with E. coli 13762 but not with E. coli ORN178. This specificity of E. coli strains to identify and bind to characteristic sugar moieties can be used in the development of biodiagnostic tools with Au NPs as carriers for diagnosis/treatment of human and veterinary diseases. In regards to the growing antibiotic resistance of microorganisms, gold nanoparticles can also be functionalized specifically to reverse adhesion of E. coli to host tissue and can be detected by their optical properties.     

Phyto-assisted synthesis of zinc oxide nanoparticles using Cassia alata and its antibacterial activity against Escherichia coli

Zinc oxide, an established inorganic metal oxide in nanoparticles form exhibits tremendous anti-bacterial activity. The present study focuses on determining the anti-bacterial activity of green synthesized zinc oxide nanoparticles (ZnO NPs). Results clearly validate the effective synthesis of spherical shaped nanoparticles with average size range of 60–80 nm. SEM and EDAX data buttresses the results obtained by XRD pattern in terms of size and purity. ZnO NPs exhibited dose-dependent anti-bacterial activity against Escherichia coli (E. coli) and the IC₅₀ value was calculated to be around 20 μg/mL. Growth kinetics study was conducted in the presence of nanoparticles which demonstrated the bacteriostatic effect of ZnO NPs. The study recommends the potential use of ZnO NPs in industries like food, pharmaceutical, agriculture, cosmetic industries for its anti-bacterial activity.     

Fabrication of a Bionic Needle with both Super-Hydrophobic and Antibacterial Properties

Many biological surfaces possess unusual micro-nano hierarchical structures that could influence their wettability, which provide new methods for the construction of novel materials. In this work, silver nanoparticles were successfully coated on the surface of stainless steel needle by a simple electroless replacement reaction process between the AgNO₃ solution and the activated stainless steel needle. After the replacement reaction, porous micro/nanostructures were formed on the surface of the stainless steel needle. By modifying long chains of thiol molecules, the stainless steel needle exhibited good super-hydrophobic property with a contact angle greater than 150°. Moreover, the silver coated stainless steel needle (bionic needle) showed strong antibacterial activity against the gram-negative bacterium Escherichia coli (E. coli). By calculating the area of the inhibition zone against E. coli formed on agar medium, the antibacterial activity of the bionic needle with the contact angle of 152° is much better than that with the contact angle of 138°. The as-prepared bionic needle with both super-hydrophobic and antibacterial properties has the potential to be applied in modern medical devices.