In Situ Study of the Antibacterial Activity and Mechanism of Action of Silver Nanoparticles by Surface-Enhanced Raman Spectroscopy

In Vivo and in Vitro activity of colistin-conjugated bimetallic silver-copper oxide nanoparticles against Pandrug-resistant Pseudomonas aeruginosa

BACKGROUND

Addressing microbial resistance urgently calls for alternative treatment options. This study investigates the impact of a bimetallic formulation containing colistin, silver, and copper oxide on a pandrug-resistant, highly virulent Pseudomonas aeruginosa (P. aeruginosa) isolate from a cancer patient at the National Cancer Institute, Cairo University, Egypt.

METHODS

Silver nanoparticles (Ag NPs), copper oxide nanoparticles (CuO NPs), and bimetallic silver-copper oxide nanoparticles (Ag-CuO NPs) were synthesized using gamma rays, combined with colistin (Col), and characterized by various analytical methods. The antimicrobial activity of Col-Ag NPs, Col-CuO NPs, and bimetallic Col-Ag-CuO NPs against P. aeruginosa was evaluated using the agar well diffusion method, and their minimum inhibitory concentration (MIC) was determined using broth microdilution. Virulence factors such as pyocyanin production, swarming motility, and biofilm formation were assessed before and after treatment with bimetallic Col-Ag-CuO NPs. The in vivo efficacy was evaluated using the Galleria mellonella model, and antibacterial mechanism were examined through membrane leakage assay.

RESULTS

The optimal synthesis of Ag NPs occurred at a gamma ray dose of 15.0 kGy, with the highest optical density (OD) of 2.4 at 375 nm. Similarly, CuO NPs had an optimal dose of 15.0 kGy, with an OD of 1.5 at 330 nm. Bimetallic Ag-CuO NPs were most potent at 15.0 kGy, yielding an OD of 1.9 at 425 nm. The MIC of colistin was significantly reduced when combined with nanoparticles: 8 µg/mL for colistin alone, 0.046 µg/mL for Col-Ag NPs, and 0.0117 µg/mL for Col-Ag-CuO NPs. Bimetallic Col-Ag-CuO NPs reduced the MIC four-fold compared to Col-Ag NPs. Increasing the sub-inhibitory concentration of bimetallic nanoparticles from 0.29 × 10-2 to 0.58 × 10-2 µg/mL reduced P. aeruginosa swarming by 32-64% and twitching motility by 34-97%. At these concentrations, pyocyanin production decreased by 39-58%, and biofilm formation was inhibited by 33-48%. The nanoparticles were non-toxic to Galleria mellonella, showing 100% survival by day 3, similar to the saline-treated group.

CONCLUSIONS

The synthesis of bimetallic Ag-CuO NPs conjugated with colistin presents a promising alternative treatment for combating the challenging P. aeruginosa pathogen in hospital settings. Further research is needed to explore and elucidate the mechanisms underlying the inhibitory effects of colistin-bimetallic Ag-CuO NPs on microbial persistence and dissemination.

Imidazolium-Based Ionic Liquid-Assisted Silver Nanoparticles and Their Antibacterial Activity: Experimental and Density Functional Theory Studies

The exclusive properties of ionic liquids (ILs) offer various opportunities to develop advanced materials with appreciable therapeutic applications. Imidazolium-based ILs have been frequently used as reaction media and stabilizers for the development and surface functionalization of noble metal nanoparticles (NPs). This study reports the citrate-mediated reduction of silver ions in three different ILs, that is, 1-ethyl-3-methylimidazolium methyl sulfate ([EMIM][MS]), 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM][OTf]), and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][TFSI]). The resulting Ag-ILs NPs were characterized using many analytical techniques, including UV-visible spectroscopy, dynamic light scattering (DLS), scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction (XRD). DLS and XRD characterization revealed the negatively charged Ag-[EMIM][MS] NPs, Ag-[BMIM][OTf] NPs, and Ag-[BMIM][TFSI] NPs with mean hydrodynamic sizes of 278, 316, and 279 nm, respectively, and a face-centered cubic structure. These hybrid nanomaterials were subjected to in vitro antibacterial screening against three bacterial strains. The Ag-[BMIM][OTf] NPs exhibited significant activities against Escherichia coli, Staphylococcus aureus, and Enterobacter cloacae. The lowest inhibition concentration of 62.5 μg/mL was recorded against E. coli using Ag-[EMIM][MS] and Ag-[BMIM][OTf] NPs. Further, the density functional theory calculations carried out on the computed Ag-ILs in the gas phase and water showed relatively stable systems. Ag-[BMIM][TFSI] exhibited the lowest Gibbs free energy change of -34.41 kcal/mol. The value of the global electrophilicity index (ω = 0.1865 eV) for the Ag-[BMIM][OTf] correlated with its good antibacterial activity.

Nanotechnology as an efficient and effective alternative for wastewater treatment: an overview

The increase in the surface and groundwater contamination due to global population growth, industrialization, proliferation of pathogens, emerging pollutants, heavy metals, and scarcity of drinking water represents a critical problem. Because of this problem, particular emphasis will be placed on wastewater recycling. Conventional wastewater treatment methods may be limited due to high investment costs or, in some cases, poor treatment efficiency. To address these issues, it is necessary to continuously evaluate novel technologies that complement and improve these traditional wastewater treatment processes. In this regard, technologies based on nanomaterials are also being studied. These technologies improve wastewater management and constitute one of the main focuses of nanotechnology. The following review describes wastewater's primary biological, organic, and inorganic contaminants. Subsequently, it focuses on the potential of different nanomaterials (metal oxides, carbon-based nanomaterials, cellulose-based nanomaterials), membrane, and nanobioremediation processes for wastewater treatment. The above is evident from the review of various publications. However, nanomaterials' cost, toxicity, and biodegradability need to be addressed before their commercial distribution and scale-up. The development of nanomaterials and nanoproducts must be sustainable and safe throughout the nanoproduct life cycle to meet the requirements of the circular economy.

Exploring dynamic changes of fungal cellular components during nanoemulsion treatment by multivariate microRaman imaging

Recently, essential oils (EO) have gained a lot of interest for use as antifungal agent in food and agricultural industry and extensive research is ongoing to understand their mode of action. However, the exact mechanism is not yet elucidated. Here, we integrated spectral unmixing and Raman microspectroscopy imaging to unveil the antifungal mechanism of green tea EO based nanoemulsion (NE) against Magnaporthe oryzae. The dramatic change in protein, lipid, adenine, and guanine bands indicate that NE has a significant impact on the protein, lipid and metabolic processes of purine. The results also demonstrated that the NE treatment caused damage to fungal hyphae by inducing a physical injury leading to cell wall damage and loss of integrity. Our study shows that MCR-ALS (Multivariate Curve Resolution-Alternating Least Squares) and N-FINDR (N-finder algorithm) Raman imaging could serve as a suitable complementary package to the traditional methods, for revealing the antifungal mechanism of action of EO/NE.

Disintegration and Machine-Learning-Assisted Identification of Bacteria on Antimicrobial and Plasmonic Ag-CuxO Nanostructures

Bacteria cause many common infections and are the culprit of many outbreaks throughout history that have led to the loss of millions of lives. Contamination of inanimate surfaces in clinics, the food chain, and the environment poses a significant threat to humanity, with the increase in antimicrobial resistance exacerbating the issue. Two key strategies to address this issue are antibacterial coatings and effective detection of bacterial contamination. In this study, we present the formation of antimicrobial and plasmonic surfaces based on Ag-Cu_xO nanostructures using green synthesis methods and low-cost paper substrates. The fabricated nanostructured surfaces exhibit excellent bactericidal efficiency and high surface-enhanced Raman scattering (SERS) activity. The Cu_xO ensures outstanding and rapid antibacterial activity within 30 min, with a rate of >99.99% against typical Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus bacteria. The plasmonic Ag nanoparticles facilitate the electromagnetic enhancement of Raman scattering and enables rapid, label-free, and sensitive identification of bacteria at a concentration as low as 10³ cfu/mL. The detection of different strains at this low concentration is attributed to the leaching of the intracellular components of the bacteria caused by the nanostructures. Additionally, SERS is coupled with machine learning algorithms for the automated identification of bacteria with an accuracy that exceeds 96%. The proposed strategy achieves effective prevention of bacterial contamination and accurate identification of the bacteria on the same material platform by using sustainable and low-cost materials.

Emergence of microbial resistance against nanoparticles: Mechanisms and strategies

Antimicrobial nanoparticles have gained the status of a new generation of drugs that can kill bacterial pathogens by multiple means; however, nanoparticle resistance acquired by some bacterial pathogens has evoked a cause of concern. Several reports suggested that bacteria can develop nanoparticles, specifically metal nanoparticle resistance, by mechanisms: nanoparticle transformation-induced oxidative stress, membrane alterations, reversible adaptive resistance, irreversible modifications to cell division, and a change in bacterial motility and resistance. Surface properties, concentration and aggregation of nanoparticles, biofilm forming and metal exclusion capacity, and R plasmid and flagellin synthesis by bacteria are crucial factors in the development of nanoparticle resistance in bacteria. Studies reported the resistance reversal by modifying the surface corona of nanoparticles or inhibiting flagellin production by bacterial pathogens. Furthermore, strict regulation regarding the use and disposal of nano-waste across the globe, the firm knowledge of microbe-nanoparticle interaction, and the regulated disposal of nanoparticles in soil and water is required to prevent microbes from developing nanoparticle resistance.

Prospects of Polymeric Nanocomposite Membranes for Water Purification and Scalability and their Health and Environmental Impacts: A Review

Water shortage is a major worldwide issue. Filtration using genuine polymeric membranes demonstrates excellent pollutant separation capabilities; however, polymeric membranes have restricted uses. Nanocomposite membranes, which are produced by integrating nanofillers into polymeric membrane matrices, may increase filtration. Carbon-based nanoparticles and metal/metal oxide nanoparticles have received the greatest attention. We evaluate the antifouling and permeability performance of nanocomposite membranes and their physical and chemical characteristics and compare nanocomposite membranes to bare membranes. Because of the antibacterial characteristics of nanoparticles and the decreased roughness of the membrane, nanocomposite membranes often have greater antifouling properties. They also have better permeability because of the increased porosity and narrower pore size distribution caused by nanofillers. The concentration of nanofillers affects membrane performance, and the appropriate concentration is determined by both the nanoparticles' characteristics and the membrane's composition. Higher nanofiller concentrations than the recommended value result in deficient performance owing to nanoparticle aggregation. Despite substantial studies into nanocomposite membrane manufacturing, most past efforts have been restricted to the laboratory scale, and the long-term membrane durability after nanofiller leakage has not been thoroughly examined.

Metal-Based Nanoparticles: Antibacterial Mechanisms and Biomedical Application

The growing increase in antibiotic-resistant bacteria has led to the search for new antibacterial agents capable of overcoming the resistance problem. In recent years, nanoparticles (NPs) have been increasingly used to target bacteria as an alternative to antibiotics. The most promising nanomaterials for biomedical applications are metal and metal oxide NPs, due to their intrinsic antibacterial activity. Although NPs show interesting antibacterial properties, the mechanisms underlying their action are still poorly understood, limiting their use in clinical applications. In this review, an overview of the mechanisms underlying the antibacterial activity of metal and metal oxide NPs will be provided, relating their efficacy to: (i) bacterial strain; (ii) higher microbial organizations (biofilm); (iii) and physico-chemical properties of NPs. In addition, bacterial resistance strategies will be also discussed to better evaluate the feasibility of the different treatments adopted in the clinical safety fields. Finally, a wide analysis on recent biomedical applications of metal and metal oxide NPs with antibacterial activity will be provided.

Underestimation about the Contribution of Nitrate Reducers to Iron Cycling Indicated by Enterobacter Strain

Nitrate-reducing iron(II) oxidation (NRFO) has been intensively reported in various bacteria. Iron(II) oxidation is found to be involved in both enzymatic and chemical reactions in nitrate-reducing Fe(II)-oxidizing microorganisms (NRFOMs). However, little is known about the relative contribution of biotic and abiotic reactions to iron(II) oxidation for the common nitrate reducers during the NRFO process. In this study, the typical nitrate reducers, four Enterobacter strains E. hormaechei, E. tabaci, E. mori and E. asburiae, were utilized as the model microorganisms. The comparison of the kinetics of nitrate, iron(II) and nitrite and N₂O production in setups with and without iron(II) indicates a mixture of enzymatic and abiotic oxidation of iron(II) in all four Enterobacter strains. It was estimated that 22−29% of total oxidized iron(II) was coupled to microbial nitrate reduction by E. hormaechei, E. tabaci, E. mori, and E. asburiae. Enterobacter strains displayed an metabolic inactivity with heavy iron(III) encrustation on the cell surface in the NRFOmedium during days of incubation. Moreover, both respiratory and periplasmic nitrate-reducing genes are encoded by genomes of Enterobacter strains, suggesting that cell encrustation may occur with periplasmic iron(III) oxide precipitation as well as the surface iron(II) mineral coating for nitrate reducers. Overall, this study clarified the potential role of nitrate reducers in the biochemical cycling of iron under anoxic conditions, in turn, re-shaping their activity during denitrification because of cell encrustation with iron(III) minerals.

Trehalose-Modified Silver Nanoparticles as Antibacterial Agents with Reduced Cytotoxicity and Enhanced Uptake by Mycobacteria

Silver nanoparticles (AgNPs) are potent antimicrobial agents, but their utility is limited due to their relatively high cytotoxicity. In this work, we used trehalose as the ligand to reduce the cytotoxicity of AgNPs without affecting their antimicrobial activities. Trehalose is a disaccharide that is unique to mycobacteria. We showed that trehalose-functionalized AgNPs, AgNP-Tre, drastically increased the viability of A549 cells, especially at high concentrations, for example, from 4% for AgNPs to 67% for AgNP-Tre at 64 μg/mL. The trehalose ligand slowed down the release of silver, and the amount of silver released from AgNP-Tre was less than half of that from AgNPs in the culture medium. Intriguingly, while the maltose (Mal) or tri(ethylene glycol) (TEG) ligand reduced the antibacterial activity of AgNPs against M. smegmatis (minimal inhibitory concentration (MIC) of AgNP-Mal and AgNP-TEG: 4 μg/mL for 7 nm AgNPs), the activity of AgNP-Tre was similar to that of AgNPs (MIC of AgNP-Tre: 1 μg/mL for 7 nm AgNPs). Uptake experiments revealed that the intracellular concentration of AgNP-Tre was 87 and 114% higher than those of AuNP-Mal and AgNP-TEG, respectively. The increased uptake was attributed to the enhanced interactions of AgNP-Tre with mycobacteria promoted by the trehalose ligand.

New Insights for Exploring the Risks of Bioaccumulation, Molecular Mechanisms, and Cellular Toxicities of AgNPs in Aquatic Ecosystem

Silver nanoparticles (AgNPs) are commonly used in numerous consumer products, including textiles, cosmetics, and health care items. The widespread usage of AgNPs results in their unavoidable discharge into the ecosystem, which pollutes the aquatic, groundwater, sediments, and marine environments. These nanoparticles (NPs) activate the production of free radicals reactive species in aquatic organisms that interrupt the functions of DNA, cause mitochondrial dysfunction, and increase lipid peroxidation, which terminates the development and reproduction both in vivo and in vitro. The life present in the aquatic ecosystem is becoming threatened due to the release and exploitation of AgNPs. Managing the aquatic ecosystem from the AgNP effects in the near future is highly recommended. In this review, we discussed the background of AgNPs, their discharge, and uptake by aquatic organisms, the mechanism of toxicity, different pathways of cytotoxicity, and bioaccumulation, particularly in aquatic organisms. We have also discussed the antimicrobial activities of AgNPs along with acute and chronic toxicity in aquatic groups of organisms.

Characterization of Bacteria Using Surface-Enhanced Raman Spectroscopy (SERS): Influence of Microbiological Factors on the SERS Spectra

SERS is currently being explored as a rapid method for identification of bacteria but variation in the experimental procedures has resulted in considerable variation in the spectra reported for a range of bacterial species. Here, we show that mixing bacteria with a conventional citrate-reduced silver colloid (CRSC) and drying the resulting suspension yield highly reproducible spectra. These signals were due to intracellular components released when the structure of the bacteria was disrupted during sample preparation. This reproducibility allowed us to examine the effects of variables that do not arise in SERS of simple solutions but are relevant in studies of bacteria. These included growth phase and biological variation, which occurred when the same bacterial isolates were cultured under nominally identical conditions on different days. It was found that even under optimal standardized conditions the effect of differences in experimental parameters such as growth phase was very large in some bacterial species but insignificant in others. This suggests that it is important to avoid drawing general conclusions about bacterial SERS based on studies using small numbers of samples. Similarly, discrimination between bacterial species was straightforward when a small number of isolates with distinct spectral features were investigated; however, this became more challenging when more bacterial species were included, as this increased the possibility of finding different species of bacteria with similar spectra. These observations are important because they clearly delineate the challenges that will need to be addressed if SERS is to be used for clinical applications.

Green Synthesis of Silver Nanoparticles Using Aqueous Citrus limon Zest Extract: Characterization and Evaluation of Their Antioxidant and Antimicrobial Properties

The current work concentrated on the green synthesis of silver nanoparticles (AgNPs) through the use of aqueous Citruslimon zest extract, optimizing the different experimental factors required for the formation and stability of AgNPs. The preparation of nanoparticles was confirmed by the observation of the color change of the mixture of silver nitrate, after the addition of the plant extract, from yellow to a reddish-brown colloidal suspension and was established by detecting the surface plasmon resonance band at 535.5 nm, utilizing UV-Visible analysis. The optimum conditions were found to be 1 mM of silver nitrate concentration, a 1:9 ratio extract of the mixture, and a 4 h incubation period. Fourier transform infrared spectroscopy spectrum indicated that the phytochemicals compounds present in Citrus limon zest extract had a fundamental effect on the production of AgNPs as a bio-reducing agent. The morphology, size, and elemental composition of AgNPs were investigated by zeta potential (ZP), dynamic light scattering (DLS), SEM, EDX, X-ray diffraction (XRD), and transmission electron microscopy (TEM) analysis, which showed crystalline spherical silver nanoparticles. In addition, the antimicrobial and antioxidant properties of this bioactive silver nanoparticle were also investigated. The AgNPs showed excellent antibacterial activity against one Gram-negative pathogens bacteria, Escherichia coli, and one Gram-positive bacteria, Staphylococcus aureus, as well as antifungal activity against Candida albicans. The obtained results indicate that the antioxidant activity of this nanoparticle is significant. This bioactive silver nanoparticle can be used in biomedical and pharmacological fields.

A Critical Review of the Antimicrobial and Antibiofilm Activities of Green-Synthesized Plant-Based Metallic Nanoparticles

Metallic nanoparticles (MNPs) produced by green synthesis using plant extracts have attracted huge interest in the scientific community due to their excellent antibacterial, antifungal and antibiofilm activities. To evaluate these pharmacological properties, several methods or protocols have been successfully developed and implemented. Although these protocols were mostly inspired by the guidelines from national and international regulatory bodies, they suffer from a glaring absence of standardization of the experimental conditions. This situation leads to a lack of reproducibility and comparability of data from different study settings. To minimize these problems, guidelines for the antimicrobial and antibiofilm evaluation of MNPs should be developed by specialists in the field. Being aware of the immensity of the workload and the efforts required to achieve this, we set out to undertake a meticulous literature review of different experimental protocols and laboratory conditions used for the antimicrobial and antibiofilm evaluation of MNPs that could be used as a basis for future guidelines. This review also brings together all the discrepancies resulting from the different experimental designs and emphasizes their impact on the biological activities as well as their interpretation. Finally, the paper proposes a general overview that requires extensive experimental investigations to set the stage for the future development of effective antimicrobial MNPs using green synthesis.

Metal nanoparticles assisted revival of Streptomycin against MDRS Staphylococcus aureus

The ability of microorganisms to generate resistance outcompetes with the generation of new and efficient antibiotics. Therefore, it is critically required to develop novel antibiotic agents and treatments to control bacterial infections. Green synthesized metallic and metal oxide nanoparticles are considered as the potential means to target bacteria as an alternative to antibiotics. Nanoconjugates have also attracted attention because of their increased biological activity as compared to free antibiotics. In the present investigation, silver nanoparticles (AgNPs), zinc oxide nanoparticles (ZnO NPs), copper oxide nanoparticles (CuO NPs), and iron oxide nanoparticles (FeO NPs) have been synthesized by using leaf extract of Ricinus communis. Characterization of nanoparticles was done by using UV–Vis Spectroscopy, Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, Energy Dispersive X-Ray Analyzer, X-ray Diffraction Analysis, and Dynamic Light Scattering Particle Size Analyzer. Interestingly, Streptomycin when combined with AgNPs, ZnO NPs, CuO NPs, and FeO NPs showed enhanced antibacterial activity against clinical isolates of S. aureus which suggested synergism between the nanoparticles and antibiotics. The highest enhanced antibacterial potential of Streptomycin was observed in conjugation with ZnO NPs (11 ± 0.5 mm) against S. aureus. Minimum inhibitory concentration of conjugates of AgNPs, ZnO NPs, CuO NPs, and FeO NPs with streptomycin against S. aureus was found to be 3.12, 2.5,10, and 12.5 μg/mL respectively. The considerable point of the present investigation is that S. aureus, which was resistant to streptomycin becomes highly susceptible to the same antibiotic when combined with nanoparticles. This particular observation opens up windows to mitigate the current crisis due to antibiotic resistance to combat antimicrobial infections efficiently.

Synergistically enhanced photothermal transition of a polyoxometalate/peptide assembly improved the antibiofilm and antibacterial activities

We successfully developed an antimicrobial assembly (Mo₁₅₄/TK-14) using molybdenum-polyoxometalate and a positively charged peptide of TK-14. It was characterized and assayed using zeta-potential, dynamic light scattering (DLS), and TEM measurements. The Mo₁₅₄/TK-14 assembly showed an enhanced 808 nm absorption and, therefore, improved the photothermal conversion efficiency of Mo₁₅₄ (30.3%) to 38.6%. Consequently, in comparison to 5 μM Mo₁₅₄ without irradiation, both the biofilm formation and bacterial viability of S. aureus were 24.6% and 20.2%, respectively, for the Mo₁₅₄/TK-14 assembly; the biofilm formation and bacterial viability were further decreased to 7.7% and 4.4% under 808 nm irradiation, respectively. Therefore, the Mo₁₅₄/TK-14 assembly reflects convincing antibacterial properties compared to Mo₁₅₄. This is due to the synergistic effect between the peptide-binding enhanced 808 nm absorption and the improved PTT properties. The antimicrobial assembly offers a novel strategy for the rational design of light-responsive antibacterial materials.

In Situ Monitoring of Dynamic Photocatalysis of Metal-Organic Frameworks by Three-Dimensional Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy

Metal-organic frameworks (MOFs) are promising as novel disinfectants due to the reactive oxygen species (ROS) produced in their photocatalytic processes. The optimal MOF is screened as the best disinfectant, representing high-efficacy production of ROS under photocatalytic conditions. However, current methods to screen abundant MOFs for disinfectant application are generally semiquantitative or ex situ methods [such as electron paramagnetic resonance (EPR) measurements], so achieving a strategy that can quantitatively screen an optimal MOF in situ and is reliable is demanded. Herein, we developed a three-dimensional (3D) shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) platform to study the dynamic photocatalytic processes of various MOFs (e.g., ZIF-67, ZIF-8, and UIO-66) in situ. This platform comprises silica shell-isolated gold nanoparticles (AuNPs) modified on silicon nanowire arrays (SiNWArs). The MOF is then self-assembled on the 3D-SHINERS substrate. Using this platform, we recorded dynamic spectroscopic evidence of ROS formation by various MOFs under sunlight irradiation. By dynamic comparison, ZIF-67 has the most robust photocatalytic efficiency, ∼1.7-fold stronger than that of ZIF-8 and ∼42.6-fold stronger than that of UIO-66. As expected, ZIF-67 displays the best antibacterial ability, up to 99% in the agar plate assay. This work provides a versatile platform for dynamically monitoring photocatalytic performance and screening antibacterial MOFs.

Synthesis Monitoring, Characterization and Cleanup of Ag-Polydopamine Nanoparticles Used as Antibacterial Agents with Field-Flow Fractionation

Advances in nanotechnology have opened up new horizons in nanomedicine through the synthesis of new composite nanomaterials able to tackle the growing drug resistance in bacterial strains. Among these, nanosilver antimicrobials sow promise for use in the treatment of bacterial infections. The use of polydopamine (PDA) as a biocompatible carrier for nanosilver is appealing; however, the synthesis and functionalization steps used to obtain Ag-PDA nanoparticles (NPs) are complex and require time-consuming cleanup processes. Post-synthesis treatment can also hinder the stability and applicability of the material, and dry, offline characterization is time-consuming and unrepresentative of real conditions. The optimization of Ag-PDA preparation and purification together with well-defined characterization are fundamental goals for the safe development of these new nanomaterials. In this paper, we show the use of field-flow fractionation with multi-angle light scattering and spectrophotometric detection to improve the synthesis and quality control of the production of Ag-PDA NPs. An ad hoc method was able to monitor particle growth in a TLC-like fashion; characterize the species obtained; and provide purified, isolated Ag-PDA nanoparticles, which proved to be biologically active as antibacterial agents, while achieving a short analysis time and being based on the use of green, cost-effective carriers such as water.

Tri-functional SERS nanoplatform with tunable plasmonic property for synergistic antibacterial activity and antibacterial process monitoring

Strategies integrating synergistic high-efficiency bacterial killing and antibacterial process monitoring capability are desirable. Herein, a tri-functional surface-enhanced Raman spectroscopy (SERS) nanoplatform, namely 4-mercaptobenzoic acid-encoded gold nanorods@silver coated with a layer of bovine serum albumin (AuNRs@Ag@4-MBA@BSA), with excellent biocompatibility, stability, tunable plasmonic property and activatable photothermal effect is introduced for Ag⁺/photothermal therapy (PTT) synergistic antibacterial activity and antibacterial process monitoring. An exogenous etchant is used to controllably model the physiological process of metallic silver biodegradation. Ag shell etching causes the surface plasmon resonance band of SERS nanotags to red-shift to near-infrared region, activates the photothermal conversion capability, and triggers PTT, which in turn accelerates Ag shell etching. The antibacterial rates for Staphylococcus aureus and Escherichia coli after 10 min treatment can achieve 99.5% and 99.9%, respectively. Furthermore, the near-field effect and ultrasensitive property render the SERS intensity decrease ratio is dependent on Ag shell etching as well as temperature rising and thus relevant to antibacterial activity. We have demonstrated a strong correlation between SERS signal and antibacterial effect, and have verified the possibility of antibacterial process monitoring in vitro using SERS-based methodology. We envision that our integrated strategy being used for in vivo high-efficiency bacterial killing and antibacterial process monitoring.

Nanotechnology in combating biofilm: A smart and promising therapeutic strategy

Since the birth of civilization, people have recognized that infectious microbes cause serious and often fatal diseases in humans. One of the most dangerous characteristics of microorganisms is their propensity to form biofilms. It is linked to the development of long-lasting infections and more severe illness. An obstacle to eliminating such intricate structures is their resistance to the drugs now utilized in clinical practice (biofilms). Finding new compounds with anti-biofilm effect is, thus, essential. Infections caused by bacterial biofilms are something that nanotechnology has lately shown promise in treating. More and more studies are being conducted to determine whether nanoparticles (NPs) are useful in the fight against bacterial infections. While there have been a small number of clinical trials, there have been several in vitro outcomes examining the effects of antimicrobial NPs. Nanotechnology provides secure delivery platforms for targeted treatments to combat the wide range of microbial infections caused by biofilms. The increase in pharmaceuticals' bioactive potential is one of the many ways in which nanotechnology has been applied to drug delivery. The current research details the utilization of several nanoparticles in the targeted medication delivery strategy for managing microbial biofilms, including metal and metal oxide nanoparticles, liposomes, micro-, and nanoemulsions, solid lipid nanoparticles, and polymeric nanoparticles. Our understanding of how these nanosystems aid in the fight against biofilms has been expanded through their use.

Effect of Plasmonic Gold Nanoprisms on Biofilm Formation and Heat Shock Proteins Expression in Human Pathogenic Bacteria

Gold nanoparticles have gained interest in biomedical sciences in the areas of nano-diagnostics, bio-labeling, drug delivery, and bacterial infection. In this study, we examined, for the first time, the antibacterial and antibiofilm properties of plasmonic gold nanoprisms against human pathogenic bacteria using MIC and crystal violet. In addition, the expression level of GroEL/GroES heat shock proteins was also investigated by western blot. Gold nanoparticles were characterized by TEM and EDX, which showed equilateral triangular prisms with an average edge length of 150 nm. Antibacterial activity testing showed a great effect of AuNPs against pathogenic bacteria with MICs values ranging from 50 μg/mL to 100 μg/mL. Nanoparticles demonstrated strong biofilm inhibition action with a percentage of inhibition ranging from 40.44 to 82.43%. Western blot analysis revealed that GroEL was an AuNPs-inducible protein with an increase of up to 66.04%, but GroES was down-regulated with a reduction of up to 46.81%. Accordingly, plasmonic gold nanoprisms, could be a good candidate for antibiotics substitution in order to treat bacterial infections.

Ultrasensitive Dual-Signal Detection of Telomerase and MiR-21 Based on Boolean Logic Operations

Telomerase and micro-RNAs (miRNAs) are simultaneously upregulated in a variety of tumor cells and have emerged as promising tumor markers. However, sensitive detection of telomerase and miRNAs in situ remains a great challenge due to their low expression levels. Here, we designed a Boolean logic "AND" signal amplification strategy based on functionalized ordered mesoporous nanoparticles (FOMNs) to achieve ultrasensitive detection of telomerase and miR-21 in living tumor cells. Briefly, the strategy uses telomerase as an input to enable the release of DNA3-ROX-BHQ hairpins by making the wrapping DNA1 form a DNA-a hairpin with the joint participation of dNTPs. Subsequently, DNA2-Ag, DNA3-ROX-BHQ, and the second input miR-21 participated in hybridization chain reaction to amplify fluorescence and Raman signals. Experimental results showed the intensity of output dual signals relevant to the expression levels of telomerase and miR-21. The Ag nanoparticles (AgNPs) not only enhanced the fluorescence signals but also allowed to obtain more sensitive Raman signals. Therefore, even if expression of tumor markers is at a low level, the FOMN-based dual-signal logic operation strategy can still achieve sensitive detection of telomerase and miR-21 in situ. Furthermore, FOMNs can detect miR-21 expression levels in a short time. Consequently, this strategy has a potential clinical application value in detection of tumor markers and the assessment of tumor treatment efficacy.

Preparation and characterization of a novel green tea essential oil nanoemulsion and its antifungal mechanism of action against Magnaporthae oryzae

Blast is one of the most devastating fungal diseases of rice caused by Magnaporthe oryzae. Plant essential oil (EO) can function as antifungal agents and are regarded as a safe and acceptable method for plant disease control. However, EOs are unstable and hydrophobic, which limits its use. In the present study, we aimed for the preparation and characterization of a nanoemulsion (NE) from green tea essential oil (GTO) by ultrasonication method and determined the antifungal activity of NE onM. oryzae. The particle size and zeta potential of the NE were 86.98 nm and -15.1 mV, respectively. The chemical composition and functional groups of GTO and NE were studied by using GC-MS analysis, portable Raman spectroscopy, and FTIR coupled with chemometric analysis. GC-MS analysis showed the major components in GTO and NE were n-Hexyl cinnamaldehyde and L-α-Terpineol. Both GTO and NE showed good antioxidant activity and total phenol content. Moreover, the NE showed good antifungal activity againstM. oryzae which was further confirmed by scanning electron microscopy (SEM) examination. Also, confocal Raman micro-spectroscopy (CRM) revealed the antifungal mechanism of GTO and NE on M. oryzae which proves the cell damage. To the best of our knowledge, this is the first study on the antifungal activity of GTO and NE against M. oryzae and also the use of CRM for the evaluation of the chemical changes in single fungal hyphae in a holistic approach. This study suggests that the prepared NE could be a potential candidate for use as a substitute for synthetic fungicides.

A universal automated method for determining the bacteriostatic activity of nanomaterials

The lack of analytical strategies to directly determine the bacteriostatic activity of nanomaterials in complex aqueous media (e.g., environmentally relevant scenarios) seriously hampers the harvest of reliable data for nanomaterial risk assessment. Here, we created an automated phenotypic method based on a developed multi-channel contactless conductometric sensor. Bacterial growth kinetics of E. coli and S. aureus were determined via on-line monitoring of conductivity changes in simple media (e.g., liquid LB broth) and complex media (e.g., relevant river water and seawater samples with diverse pH, salinity, conductivity, turbidity, chemical oxygen demand and total suspended solids). The high temporal resolution growth curves provide detailed information on the bacteria inhibition of the model nanomaterial - Au nanospheres, Au nanorods, Ag nanospheres and Ag nanocubes - at each growth stage, thus enabling users to directly obtain minimum inhibitory concentrations. The method highlights the advantages of universality, simplicity and affordability. It opens up possibilities for the development of a powerful analytical platform for researches in the field of nanoscience, e.g. to assess ecotoxicity of nanomaterials.

Recent Advances in the Detection of Antibiotic and Multi-Drug Resistant Salmonella: An Update

Antibiotic and multi-drug resistant (MDR) Salmonella poses a significant threat to public health due to its ability to colonize animals (cold and warm-blooded) and contaminate freshwater supplies. Monitoring antibiotic resistant Salmonella is traditionally costly, involving the application of phenotypic and genotypic tests over several days. However, with the introduction of cheaper semi-automated devices in the last decade, strain detection and identification times have significantly fallen. This, in turn, has led to efficiently regulated food production systems and further reductions in food safety hazards. This review highlights current and emerging technologies used in the detection of antibiotic resistant and MDR Salmonella.

Increased particle size of goethite enhances the antibacterial effect on human pathogen Escherichia coli O157:H7: A Raman spectroscopic study

The persistence of Escherichia coli O157:H7 in soil is one of the most common causes of the food-borne outbreaks. Nano-sized iron oxide minerals in soil, especially goethite, have been found to reduce bacterial viability, which helps to control the spread of human pathogens. However, little is known about the antibacterial effects of iron oxides with different particle sizes. Our result revealed that the micro-sized goethite exhibited a more effective antibacterial activity against E. coli O157:H7 than the nano-sized goethite. The underlying antibacterial mechanisms were further investigated via single-cell Raman microspectroscopy. The exposure to nano-sized goethite increased the levels of ribonucleoside-related substances, phenylalanine and adenosine 5'-triphosphate, while decreased those of glycogen, protein and lipopolysaccharide & outer membrane porins (LPS & OMPs). Meanwhile, micro-sized goethite triggered less variation in ribonucleoside-related substances and induced more reduction in LPS & OMPs. Therefore, the antibacterial effects of nano-sized goethite were mediated by both ROS-dependent RNA damage and cell membrane destruction, whereas micro-sized goethite induced severer membrane damage and less ROS-dependent oxidative stress. This work demonstrates the role of particle sizes in antibacterial effects of iron oxides and provides implications for the pathogen control in soil.

Antimicrobial Properties of the Ag, Cu Nanoparticle System

Microbes, including bacteria and fungi, easily form stable biofilms on many surfaces. Such biofilms have high resistance to antibiotics, and cause nosocomial and postoperative infections. The antimicrobial and antiviral behaviors of Ag and Cu nanoparticles (NPs) are well known, and possible mechanisms for their actions, such as released ions, reactive oxygen species (ROS), contact killing, the immunostimulatory effect, and others have been proposed. Ag and Cu NPs, and their derivative NPs, have different antimicrobial capacities and cytotoxicities. Factors, such as size, shape and surface treatment, influence their antimicrobial activities. The biomedical application of antimicrobial Ag and Cu NPs involves coating onto substrates, including textiles, polymers, ceramics, and metals. Because Ag and Cu are immiscible, synthetic AgCu nanoalloys have different microstructures, which impact their antimicrobial effects. When mixed, the combination of Ag and Cu NPs act synergistically, offering substantially enhanced antimicrobial behavior. However, when alloyed in Ag-Cu NPs, the antimicrobial behavior is even more enhanced. The reason for this enhancement is unclear. Here, we discuss these results and the possible behavior mechanisms that underlie them.

Facile fabrication of Tl4HgI6 nanostructures as novel antibacterial and antibiofilm agents and photocatalysts in the degradation of organic pollutants

Nano-Tl₄HgI₆ was fabricated via a co-precipitation route. It showed efficient antibacterial activity against Gram-negative and Gram-positive bacteria. Its photocatalytic activity indicated the highest degradation for RhB of around 78%.

Anti-bacterial activity of gold nanocomposites as a new nanomaterial weapon to combat photogenic agents: recent advances and challenges

Gold nanocomposites are being widely used in numerous biomedical applications owing to their excellent stability and miniaturization. Gold nanocomposites are notable because of their flexibility of functionalization and synthesis, ease of detection, and low toxicity. Cost-effectiveness, long-term stability, non-cytotoxicity, and biocompatibility are the main aspects of ideal nanocomposites. Antibacterial nanocomposites are being developed extensively in the food industry, environmental applications, and biological and medical devices. This review focuses on the applications of metal-based nanoparticles, mainly gold nanoparticles (AuNPs), as antibacterial agents in medical approaches. Additionally, the antibacterial mechanisms of AuNPs and their roles in fighting antibiotic-resistant microorganisms are highlighted in the present review.

Gold nanocomposites are being widely used in numerous biomedical applications owing to their excellent stability and miniaturization.

Applying Raman Microspectroscopy to Evaluate the Effects of Nutrient Cations on Alkane Bioavailability to Acinetobacter baylyi ADP1

Contamination with petroleum hydrocarbons causes extensive damage to ecological systems. On oil-contaminated sites, alkanes are major components; many indigenous bacteria can access and/or degrade alkanes. However, their ability to do so is affected by external properties of the soil, including nutrient cations. This study used Raman microspectroscopy to study how nutrient cations affect alkanes' bioavailability to Acinetobacter baylyi ADP1 (a known degrader). Treated with Na, K, Mg, and Ca at 10 mM, A. baylyi was exposed to seven n-alkanes (decane, dodecane, tetradecane, hexadecane, nonadecane, eicosane, and tetracosane) and one alkane mixture (mineral oil). Raman spectral analysis indicated that bioavailability of alkanes varied with carbon chain lengths, and additional cations altered the bacterial response to n-alkanes. Sodium significantly increased the bacterial affinity toward decane and dodecane, and K and Mg enhanced the bioavailability of tetradecane and hexadecane. In contrast, the bacterial response was inhibited by Ca for all alkanes. Similar results were observed in mineral oil exposure. Our study employed Raman spectral assay to offer a deep insight into how nutrient cations affect the bioavailability of alkanes, suggesting that nutrient cations can play a key role in influencing the harmful effects of hydrocarbons and could be optimized to enhance the bioremediation strategy.

The application of antimicrobial photodynamic inactivation on methicillin-resistant S. aureus and ESBL-producing K. pneumoniae using porphyrin photosensitizer in combination with silver nanoparticles

As resistance of bacterial strains to antibiotics is a major problem, there is a need to look for alternative treatments. One option is antimicrobial photodynamic inactivation (aPDI). The pathogenic cells are targeted by a nontoxic photosensitizer while the surrounding healthy tissue is relatively unaffected. The photosensitizer is activated by light of t appropriate wavelength resulting in the generation of reactive oxygen species that are cytotoxic for the pathogens. In this work, the photosensitizer TMPyP and silver nanoparticles (AgNPs) were investigated for their synergistic antibacterial effect. We tested these two substances on two bacterial strains, methicillin-resistant Staphylococcus aureus 4591 (MRSA) and extended-spectrum beta-lactamases-producing Klebsiella pneumoniae 2486 (ESBL-KP), to compare their effectiveness. The bacteria were first incubated with TMPyP for 45 min or 5 h, then irradiated with a LED source with the total fluence of 10 or 20 J/cm² and then placed in a microbiological growth medium supplemented with AgNPs. To accomplish the synergistic effect, the optimal combination of TMPyP and AgNPs was estimated as 1.56-25 μM for TMPyP and 3.38 mg/l for AgNPs in case of MRSA and 1.56-50 μM for TMPyP and 3.38 mg/l for AgNPs in case of ESBL-KP at 45 min incubation with TMPyP and fluence of 10 J/cm². Longer incubation and/or longer irradiation led to a decrease in the maximum values of the photosensitizer concentration to produce the synergistic effect. From this work it can be concluded that the combination of antimicrobial photodynamic inactivation with a treatment including silver nanoparticles could be a promising approach to treat bacterial infection.

A Review on Synthesis, Optimization, Mechanism, Characterization, and Antibacterial Application of Silver Nanoparticles Synthesized from Plants

Developments in nanotechnology and natural product research toward the search for novel antibacterial agents have drawn the interest of many scientists to the synthesis of silver nanoparticles (AgNPs) from natural product (especially plants) due to its numerous benefits over other methods of synthesis such as been easy, economical, convenient, and environmental friendly. Aside from the aforementioned advantages, the synthesis of AgNPs from medicinal plant has been reported as the best approach of synthesizing AgNPs with great biological activities due to the numerous biomolecules found in plants. Recently, the number of researches toward the improvement of the yield, morphological properties, analytical techniques, and the development of optimal conditions and exact mechanism for synthesizing AgNPs from plants have been increasing tremendously. In this review, we present a comprehensive report on the recent development in the synthesis, optimization conditions, mechanism, and characterization techniques of AgNPs synthesized from plant extracts. Furthermore, a thorough discussion on the recent advances in the application of AgNPs synthesized from plant as therapeutic agent against bacterial infections was made.

Mesoporous silica nanoparticles containing silver as novel antimycobacterial agents against Mycobacterium tuberculosis

Tuberculosis remains today a major public health issue with a total of 9 million new cases and 2 million deaths annually. The lack of an effective vaccine and the increasing emergence of new strains of Mycobacterium tuberculosis (Mtb) highly resistant to antibiotics, anticipate a complicated scenario in the near future. The use of nanoparticles features as an alternative to antibiotics in tackling this problem due to their potential effectiveness in resistant bacterial strains. In this context, silver nanoparticles have demonstrated high bactericidal efficacy, although their use is limited by their relatively high toxicity, which calls for the design of nanocarriers that allow silver based nanoparticles to be safely delivered to the target cells or tissues. In this work mesoporous silica nanoparticles are used as carriers of silver based nanoparticles as antimycobacterial agent against Mtb. Two different synthetic approaches have been used to afford, on the one hand, a 2D hexagonal mesoporous silica nanosystem which contains silver bromide nanoparticles distributed all through the silica network and, on the other hand, a core@shell nanosystem with metallic silver nanoparticles as core and mesoporous silica shell in a radial mesoporous rearrangement. Both materials have demonstrated good antimycobacterial capacity in in vitro test using Mtb, being lower the minimum inhibitory concentration for the nanosystem which contains silver bromide. Therefore, the interaction of this material with the mycobacterial cell has been studied by cryo-electron microscopy, establishing a direct connection between the antimycobactericidal effect observed and the damage induced in the cell envelope.

A Comparative Study on the Oxidation of Label-Free Silver Triangular Nanoplates by Peroxides: Main Effects and Sensing Applications

Nowadays, analytical systems based on silver triangular nanoplates (AgTNPs) have been shown as good prospects for chemical sensing. However, they still remain relatively poorly studied as colorimetric probes for sensing various classes of compounds. This study shows that these nanoparticles are capable of being oxidized by peroxides, including both hydrogen peroxide and its organic derivatives. The oxidation was found to result in a decrease in the AgTNPs' local surface plasmon resonance band intensity at 620 nm. This was proposed for peroxide-sensitive spectrophotometric determination. Five peroxides differing in their structure and number of functional groups were tested. Three of them easily oxidized AgTNPs. The effects of a structure of analytes and main exterior factors on the oxidation are discussed. The detection limits of peroxides in the selected conditions increased in the series peracetic acid < hydrogen peroxide < tert-butyl hydroperoxide, coming to 0.08, 1.6 and 24 μmol L^-1, respectively. tert-Butyl peroxybenzoate and di-tert-butyl peroxide were found to have no effect on the spectral characteristics of AgTNPs. By the example of hydrogen peroxide, it was found that the determination does not interfere with 100-4000-fold quantities of common inorganic ions. The proposed approach was successfully applied to the analysis of drugs, cosmetics and model mixtures.

Eco-friendly synthesis of silver nanoparticles by Bacillus subtilis and their antibacterial activity

Bacillus subtilis was used for biogenic of silver nanoparticles. Characterization of the prepared silver nanoparticles was done by UV-Vis spectroscopy, Transmission Electron Microscopy (TEM), and Fourier Transform Infrared Spectroscopy (FT-IR). The particle size of the prepared nanoparticles ranges from 3 to 20 nm with spherical or roughly spherical forms. The antimicrobial efficacy of the produced nanoparticles was investigated against five strains of multidrug resistant microorganisms including: Staphylococcus aureus (MRSA), Staphylococcu s epidermidis, Klebsiella. pneumoniae, Escherichia coli and Candida albicans tested as yeast. During this study, the minimum inhibitory concentrations (MICs) and the minimum lethal concentrations (MLCs) of synthesized silver nanoparticles were detected using selected strains of the genus Bacillus by a broth dilution method. The rate of MIC of the prepared silver nano-particles versus the investigated clinical isolates exhibit a massive anti-microbial efficacy; (230 µgml-1) for MRSA; 180 for Staphylococcus epidermidis, 200 for Escherichia coli and 100 µgml-1 for Candida albicans. On the other hand, the lowest anti-microbial efficacy (300 µgml-1) was appeared for Klebsiella pneumonia. The obtained results demonstrated the effectiveness of the biogenic nanoparticles and the possibility of using them as a new method in combating infectious diseases.

Green synthesis of garlic oil nanoemulsion using ultrasonication technique and its mechanism of antifungal action against Penicillium italicum

Penicillium italicum (P. italicum) can cause significant economic loss of fruits and vegetables. Although garlic oil (GO) is an effective antimicrobial agent, the unstability and hydrophobicity limit its use as an environmentally friendly alternative to the conventional antibiotics against P. italicum. In this study, we focused on the fabrication and characterization of a functional GO nanoemulsion (NE) using ultrasonic technique and revealed the antifungal mechanism of the GO NE on P. italicum based on morphological, structural and molecular analyses. The optimal hydrophilic lipophilic balance (HLB) value determined for GO was 14 through the combination of Tween 80 and Span 80. Then the Box-Benhnken Design (BBD) was applied to produce the GO NE and the effects of different fabrication parameters on the particle size were evaluated. The optimal GO NE was selected with the GO concentration of 5.5%, the Smix concentration of 10%, the ultrasonic time of 5 min and the power of 50%. This GO NE had the smallest particle size of 52.27 nm, the best antifungal effect and the most stability. Furthermore, the antifungal mechanism of the GO NE on P. italicum was evaluated by extracellular conductivity, micro-Raman spectra, fluorescence imaging and scanning electron microscopy (SEM) imaging. The results presented that the GO NE retained the antifungal active ingredients. The fungal cell structure and morphology were malformed after treated with the GO NE and the lipids, nucleic acids and protein of P. italicum were destructed. Finally, the optimal GO NE was applied in vivo and P. italicum in citrus was successfully inhibited. It indicated that the optimal GO NE had the better antifungal activity against P. italicum than the pure GO. Besides, the minimum inhibitory concentration (MIC) of GO after preparing into the NE was changed from 3.7% to 0.01265% with about 300 times improvement of bioavailability. Therefore, the synthetic GO NE which promoted the bioavailability of GO was recommended as a promising alternative to inhibit P. italicum in vegetables and fruits.

Silver Nanoparticles at Biocompatible Dosage Synergistically Increases Bacterial Susceptibility to Antibiotics

Antibiotics used to treat bacterial infections can become ineffective over time or result in the emergence of antibiotic resistant pathogens. With the advent of nanotechnology, silver nanoparticles (AgNPs) have gained significant attention as a therapeutic agent due to the well-known antimicrobial properties of silver. However, there are concerns and limited literature on the potential cytotoxicity of nanoparticles at effective antimicrobial concentrations. AgNPs prepared from silver nitrate with glucose reduction were characterized by surface plasmon resonance, dynamic light scattering, zeta potential analysis and transmission electron microscopy. The cytotoxicity of AgNPs towards human gingival fibroblasts over 7 days was determined using cell proliferation assays and confocal microscopy. AgNP MIC and antibacterial effects alone and in combination with 11 antibiotics were determined against a panel of nine microbial species including gram-positive and gram-negative bacterial species. AgNPs concentrations ≤ 1 μg/mL were non-cytotoxic but also showed no antibacterial effects. However, when combined with each of eleven antibiotics, the biocompatible concentration of AgNPs (1 μg/mL) resulted in significant inhibition of bacterial growth for multiple bacterial species that were resistant to either the antibiotics or AgNPs alone. This study presents a promising strategy with further testing in vivo, to develop novel antimicrobial agents and strategies to confront emerging antimicrobial resistance.

A sensitive and rapid bacterial antibiotic susceptibility test method by surface enhanced Raman spectroscopy

This study aims to develop a rapid bacterial antibiotic susceptibility test (AST) method by Bacteria-aptamer@AgNPs-surface enhanced Raman spectroscopy (SERS) and further evaluate the influence of different antibiotics on the Raman intensity of bacteria. The Raman intensity of Escherichia coli O157:H7 (E. coli O157:H7) and Staphylococcus aureus (S. aureus) in the presence of different concentrations of antibiotics in 2 h was detected by Bacteria-aptamer@AgNPs-SERS in this study. Our results found that the bacteria Raman signal peak at 735 cm^-1 and the minimum inhibitory concentration (MIC) value was determined in 1 h according to Raman signals. In 2 h, the bacteria Raman signal growth at sub-MIC concentrations of four different kinds of antibiotics and the bacteria colony-forming unit (CFU) have similar enhancements. SERS utilizes special functions of rough metal surfaces and offers a huge enhancement of Raman intensities with reduced fluorescence backgrounds, which makes it an ultrasensitive tool of detection. This rapid AST method and the enhancement effect should be of value in search of new antibiotic drugs.

Enhancement of A Cationic Surfactant by Capping Nanoparticles: Synthesis, Characterization and Multiple Applications

There is scarce information on cationic surfactants’ biocidal and corrosion inhbibition effects on Slime-Forming Bacteria (SFB) isolated from oil field formation water. Therefore, this work focused on the the synthesis of a cationic surfactant (CS) to increase its features by capping different metal nanoparticles (zinc, ZnNPs-C-CS; manganese, MnNPs-C-CS and tin, SnNPs-C-CS) and used them as biocides and corrosion inhibitors. The cationic surfactant was synthesized and characterized by Fourier-Transform Infrared (FTIR) and Nuclear Magnetic Resonance (NMR) spectroscopy. Afterwards, different nanoparticles were synthesized, characterized, and exploited to cap by the CS. The CS and the different nanoparticles capped by the CS were tested for their antimicrobial susceptibility against standard bacterial and yeast strains. The synthesized compounds were further evaluated as anti-biofilms agents against positively-developed bacterial biofilms. Moreover, the CS and the ZnNPs-C-CS, MnNPs-C-CS, and SnNPs-C-CS were assessed as potential biocides against SFB, particularly Pseudomonas sp. (isolated from contaminated formation water), and as corrosion inhibitors against cultivated salinity. The results revealed the great effect of the different CS-capped NPs as broad-spectrum antimicrobial and anti-biofilm agents at lower Minimum Inhibitory Concentrations (MICs), Minimum Bactericidal Concentrations (MBCs), Minimum Fungicidal Concentrations (MFCs) and Minimum Biofilm Inhibitory Concentrations (MBICs), and the activities were reported in order of SnNPs-C-CS > MnNPs-C-CS > ZnNPs-C-CS > CS. Furthermore, the ZnNPs-C-CS, MnNPs-C-CS, and SnNPs-C-CS demonstrated biocidal and corrosion inhibition effects against Pseudomonas sp. at a salinity of 3.5% NaCl, with metal corrosion inhibition efficiencies of 88.6, 94.0 and 96.9%, in comparison to a CS efficiency of 85.7%. In conclusion, the present work provides a newly synthesized cationic surfactant and has enhanced its antimicrobial and its metal corrosion inhibition effects by capping different nanoparticles, and it has been successfully applied against slime-forming bacteria at a salinity of 3.5% NaCl.

Heritable nanosilver resistance in priority pathogen: a unique genetic adaptation and comparison with ionic silver and antibiotics

The past decade has seen the incorporation of antimicrobial nanosilver (NAg) into medical devices, and, increasingly, in everyday 'antibacterial' products. With the continued rise of antibiotic resistant bacteria, there are concerns that these priority pathogens will also develop resistance to the extensively commercialized nanoparticle antimicrobials. Herein, this work reports the emergence of stable resistance traits to NAg in the WHO-listed priority pathogen Staphylococcus aureus, which has previously been suggested to have no, or very low, capacity for silver resistance. With no native presence of genetically encoded silver defence mechanisms, the work showed that the bacterium is dependent on mutation of physiologically essential genes, including those involved in nucleotide synthesis and oxidative stress defence. While some mutations were uniquely associated with resistance to NAg, the study also found common mutations that could be protective against both NAg and ionic silver. This is consistent with the observation of NAg/ionic silver cross-resistance. These mutations were detected following withdrawal of the silver exposure, denoting heritable characteristics that allow for spread of the resistance traits even with discontinued silver use. Heritable silver resistance in priority pathogen cautions that these nanoparticle antimicrobials should only be used as needed, to preserve their efficacy for treating infections.

Emerging antibacterial nanomedicine for enhanced antibiotic therapy

This review highlights the different mechanisms of current nano-antibiotic systems for combatting serious antibiotic resistance of bacteria.

A brief overview on nano-sized materials used in the topical treatment of skin and soft tissue bacterial infections

Introduction: Skin and soft tissue infections are a significant clinical problem that can happen anywhere on the body. Bacteria are the most common cause of skin and soft tissue infections in humans. Despite the fact that there is a lot of antimicrobial agents and antibiotics for elucidating bacterial infections, the prevention and control of infectious diseases continue to be one of the greatest challenges for public health worldwide. At the present time, an alarming increase in multidrug resistance instantly requests to find suitable alternatives to current antibiotics. Therefore, drug resistance has been attempted to be resolved by the development of new classes of antimicrobial agents or targeted delivery systems for antibacterial drugs using nanotechnology.Area covered: The present review summarizes the emerging topical efforts to support the use of nano-sized materials as a new opportunity to combat today's skin infectious diseases.Expert opinion: Nano-sized materials can overcome the stratum corneum barrier and deliver drugs specifically to bacterial skin infections with trivial side effects. Depending on the physicochemical characteristics of nano-scaled materials, they can specifically be selected to target bacterial pathogens and also to get into the skin layers. These systems can overcome the antibiotic-resistance mechanisms and help us to the design of novel topical formulations that will make administration of antibacterial compounds safer, easier and more convenient.

Enhancement of antibiotics antimicrobial activity due to the silver nanoparticles impact on the cell membrane

The ability of microorganisms to generate resistance outcompetes with the generation of new and efficient antibiotics; therefore, it is critical to develop novel antibiotic agents and treatments to control bacterial infections. An alternative to this worldwide problem is the use of nanomaterials with antimicrobial properties. Silver nanoparticles (AgNPs) have been extensively studied due to their antimicrobial effect in different organisms. In this work, the synergistic antimicrobial effect of AgNPs and conventional antibiotics was assessed in Gram-positive and Gram-negative bacteria. AgNPs minimal inhibitory concentration was 10–12 μg mL^-1 in all bacterial strains tested, regardless of their different susceptibility against antibiotics. Interestingly, a synergistic antimicrobial effect was observed when combining AgNPs and kanamycin according to the fractional inhibitory concentration index, FICI: <0.5), an additive effect by combining AgNPs and chloramphenicol (FICI: 0.5 to 1), whereas no effect was found with AgNPs and β-lactam antibiotics combinations. Flow cytometry and TEM analysis showed that sublethal concentrations of AgNPs (6–7 μg mL^-1) altered the bacterial membrane potential and caused ultrastructural damage, increasing the cell membrane permeability. No chemical interactions between AgNPs and antibiotics were detected. We propose an experimental supported mechanism of action by which combinatorial effect of antimicrobials drives synergy depending on their specific target, facilitated by membrane alterations generated by AgNPs. Our results provide a deeper understanding about the synergistic mechanism of AgNPs and antibiotics, aiming to combat antimicrobial infections efficiently, especially those by multi-drug resistant microorganisms, in order to mitigate the current crisis due to antibiotic resistance.