Ultrastructural changes in methicillin-resistant Staphylococcus aureus induced by positively charged silver nanoparticles

Biogenic silver nanoparticle synthesis using orange peel extract and its multifaceted biomedical application

The aim of this study was to employ an agro-industrial byproduct, specifically Citrus sinensis peels, as a reservoir of polyphenols. The natural chemicals present in C. sinensis peels serve as reducing agents in an environmentally benign method for synthesizing silver nanoparticles (AgNPs). This methodology not only provides a more environmentally friendly method for synthesizing nanoparticles but also enhances the value of agricultural waste, emphasizing the sustainable utilization of resources. In our study, AgNPs were successfully synthesized using peel aqueous exact of C. sinensis and then their various biological activity has been investigated. The synthesized AgNPs were characterized by UV-vis spectroscopy, dynamic light scattering (DLS), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and transmission electron microscopy (TEM) analysis. Furthermore, their effectiveness in inhibiting growth and biofilm formation of Escherichia coli, Staphylococcus aureus, and Candida albicans has been investigated. The minimum inhibitory concentrations (MIC) for E. coli and S. aureus were both 32 μg/mL, and for C. albicans, it was 128 µg/mL. At 250 µg/mL of AgNPs, 94% and 92% biofilm inhibition were observed against E. coli and S. aureus, respectively. Furthermore, AgNPs demonstrated significant toxic effects against human prostate cancer cell line DU145 as investigated by anti-apoptotic, 4',6-diamidino-2-phenylindole (DAPI), reactive oxygen species (ROS), and acridine orange/ethidium bromide (AO/EtBr) assays. We also conducted uptake analysis on these pathogens and cancer cell lines to preliminarily investigate the mechanisms underlying their toxic effects. These findings confirm that AgNPs can serve as a cost-effective, non-toxic, and environmentally friendly resource for green synthesis of medicinal AgNPs. Moreover, this approach offers an alternative recycling strategy that contributes to the sustainable use of biological by-products.

Controlling biofilm and virulence properties of Gram-positive bacteria by targeting wall teichoic acid and lipoteichoic acid

Wall teichoic acid (WTA) and lipoteichoic acid (LTA) are structural components of Gram-positive bacteria's peptidoglycan and cell membrane, which are mostly anionic glycopolymers. WTA confers numerous physiological, virulence, and pathogenic features to bacterial pathogens. It controls cell shape, cell division, and the localisation of autolytic enzymes and ion homeostasis. In the context of virulence and pathogenicity, it aids bacterial cell attachment and colonisation and protects against the host defence system and antibiotics. Having such a broad function in pathogenic bacteria's lifecycle, WTA/LTA become one of the potential targets for antibacterial agents to reduce bacterial infection in the host. The number of reports for targeting the WTA/LTA pathway has risen, mostly by focusing on three distinct targets: antivirulence targets, β-lactam potentiator targets, and essential targets. The current review looked at the role of WTA/LTA in biofilm development and virulence in a range of Gram-positive pathogenic bacteria. Furthermore, alternate strategies, such as the application of natural and synthetic compounds that target the WTA/LTA pathway, have been thoroughly discussed. Moreover, the application of nanomaterials and a combination of drugs have also been discussed as a viable method for targeting the WTA/LTA in numerous Gram-positive bacteria. In addition, a future perspective for controlling bacterial infection by targeting the WTA/LTA is proposed.

Topical Nanotherapeutics for Treating MRSA-Associated Skin and Soft Tissue Infection (SSTIs)

The emergence of methicillin-resistant Staphylococcus aureus (MRSA) imposes a major challenge for the treatment of infectious diseases with existing antibiotics. MRSA associated with superficial skin and soft tissue infections (SSTIs) is one of them, affecting the skin's superficial layers, and it includes impetigo, folliculitis, cellulitis, furuncles, abscesses, surgical site infections, etc. The efficient care of superficial SSTIs caused by MRSA necessitates local administration of antibiotics, because oral antibiotics does not produce the required concentration at the local site. The topical administration of nanocarriers has been emerging in the area of drug delivery due to its advantages over conventional topical formulation. It enhances the solubility and permeation of the antibiotics into deeper layer of the skin. Apart from this, antibiotic resistance is something that needs to be combated on multiple fronts, and antibiotics encapsulated in nanocarriers help to do so by increasing the therapeutic efficacy in a number of different ways. The current review provides an overview of the resistance mechanism in S. aureus as well as various nanocarriers reported for the effective management of MRSA-associated superficial SSTIs.

Regulation of Staphylococcus aureus Virulence and Application of Nanotherapeutics to Eradicate S. aureus Infection

Staphylococcus aureus is a versatile pathogen known to cause hospital- and community-acquired, foodborne, and zoonotic infections. The clinical infections by S. aureus cause an increase in morbidity and mortality rates and treatment costs, aggravated by the emergence of drug-resistant strains. As a multi-faceted pathogen, it is imperative to consolidate the knowledge on its pathogenesis, including the mechanisms of virulence regulation, development of antimicrobial resistance, and biofilm formation, to make it amenable to different treatment strategies. Nanomaterials provide a suitable platform to address this challenge, with the potential to control intracellular parasitism and multidrug resistance where conventional therapies show limited efficacy. In a nutshell, the first part of this review focuses on the impact of S. aureus on human health and the role of virulence factors and biofilms during pathogenesis. The second part discusses the large diversity of nanoparticles and their applications in controlling S. aureus infections, including combination with antibiotics and phytochemicals and the incorporation of antimicrobial coatings for biomaterials. Finally, the limitations and prospects using nanomaterials are highlighted, aiming to foster the development of novel nanotechnology-driven therapies against multidrug-resistant S. aureus.

Electrophoretic-deposited MXene titanium coatings in regulating bacteria and cell response for peri-implantitis

Background: Two-dimensional(2D)MXenes have continued to receive increasing interest from researchers due to their graphene-like properties, in addition to their versatile properties for applications in electronic devices, power generation, sensors, drug delivery, and biomedicine. However, their construction and biological properties as titanium coatings to prevent peri-implantitis are still unclear.

Materials and methods: In this work, few-layer Ti₃C₂T_x MXene coatings with different thicknesses at varied depositing voltages (30, 40, and 50 V) were constructed by anodic electrophoretic deposition without adding any electrolytic ions. In vitro cytocompatibility assay was performed on preosteoblasts (MC3T3-E1) cell lines after the characterization of the coating. Meanwhile, the antibacterial activity against bacteria which are closely related to peri-implantitis including Staphylococcus aureus (S. aureus) and its drug-resistant strain MRSA was further investigated.

Results: MXene-coated titanium models with different thicknesses were successfully assembled by analyzing the results of characterization. The compounding of Ti₃C₂T_x could significantly improve the initial adhesion and proliferation of MC3T3-E1 cells. Moreover, the coating can effectively inhibit the adhesion and cell activity of S. aureus and MRSA, and MRSA expressed greater restricting behavior than S. aureus. The ability to promote antibacterial activity is proportional to the content of Ti₃C₂T_x. Its antioxidant capacity to reduce ROS in the culture environment and bacterial cells was first revealed.

Conclusion: In summary, this work shows a new avenue for MXene-based nano-biomaterials under the clinical problem of multiple antibiotic resistance.

Silver Nanoparticle-Based Therapy: Can It Be Useful to Combat Multi-Drug Resistant Bacteria?

The present review focuses on the potential use of silver nanoparticles in the therapy of diseases caused by antibiotic-resistant bacteria. Such bacteria are known as “superbugs”, and the most concerning species are Acinetobacter baumannii, Pseudomonas aeruginosa, Staphylococcus aureus (methicillin and vancomycin-resistant), and some Enterobacteriaceae. According to the World Health Organization (WHO), there is an urgent need for new treatments against these “superbugs”. One of the possible approaches in the treatment of these species is the use of antibacterial nanoparticles. After a short overview of nanoparticle usage, mechanisms of action, and methods of synthesis of nanoparticles, emphasis has been placed on the use of silver nanoparticles (AgNPs) to combat the most relevant emerging resistant bacteria. The toxicological aspects of the AgNPs, both in vitro using cell cultures and in vivo have been reviewed. It was found that toxic activity of AgNPs is dependent on dose, size, shape, and electrical charge. The mechanism of action of AgNPs involves interactions at various levels such as plasma membrane, DNA replication, inactivation of protein/enzymes necessary, and formation of reactive oxygen species (ROS) leading to cell death. Researchers do not always agree in their conclusions on the topic and more work is needed in this field before AgNPs can be effectively applied in clinical therapy to combat multi-drug resistant bacteria.

Soil Fungi as Biomediator in Silver Nanoparticles Formation and Antimicrobial Efficacy

Introduction and Objectives

Biogenic agents in nanoparticles fabrication are gaining great interest due to their lower possible negative environmental impacts. The present study aimed to isolate fungal strains from deserts in Saudi Arabia and assess their ability in silver nanoparticles (AgNPs) fabrication and evaluate their antibacterial effect.

Methods

Soil fungi were identified using 18s rDNA, and their ability in NPs fabrication was assessed as extracellular synthesis, then UV-vis spectroscopy, dynamic light scattering (DLS), energy-dispersive X-ray spectroscopy, and transmission electron microscopy were used for AgNPs characterization. The antibacterial activity of fungal-based NPs was assessed against one Gram-positive methicillin-resistant S. aureus (MRSA) and three Gram-negative bacteria (E. coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae). Ultrastructural changes caused by fungal-based NPs on K. pneumoniae were investigated using TEM along with SDS-PAGE for protein profile patterns.

Results

The three fungal isolates were identified as Phoma sp. (MN995524), Chaetomium globosum (MN995493), and Chaetomium sp. (MN995550), and their filtrate reduced Ag ions into spherical P-AgNPs, G-AgNPs, and C-AgNPs, respectively. DLS data showed an average size between 12.26 and 70.24 nm, where EDX spectrums represent Ag at 3.0 keV peak. G-AgNPs displayed strong antibacterial activities against Klebsiella pneumoniae, and the ultrastructural changes caused by NPs were noted. Additionally, SDS-PAGE analysis of treated K. pneumoniae revealed fewer bands compared to control, which could be related to protein degradation.

Conclusion

Present findings have consequently developed an eco-friendly approach in NPs formation by environmentally isolated fungal strains to yield NPs as antibacterial agents.

First Report on the Phenotypic and Genotypic Susceptibility Profiles to Silver Nitrate in Bacterial Strains Isolated from Infected Leg Ulcers in Romanian Patients

Silver-ion-based antiseptics are widely used in treating chronic leg ulcers and, given the emergence of resistance to such compounds, the investigation of silver susceptibility and resistance profiles of pathogenic strains isolated from this type of wound is a topic of great interest. Therefore, in this study, 125 bacterial strains isolated from 103 patients with venous ulcers were investigated to elucidate their susceptibility to silver-nitrate solutions in planktonic and biofilm growth states, and the associated genetic determinants. The isolated strains, both in the planktonic and biofilm growth phases, showed high sensitivity to the standard concentration of 1/6000 silver-nitrate solution. It was noticed that even at concentrations lower than the clinical one (the first 2–3 binary dilutions in the case of planktonic cultures and the first 6–7 binary dilutions in the case of biofilms), the antiseptic solution proved to maintain its antibacterial activity. The phenotypic results were correlated with the genetic analysis, highlighting the presence of silver-resistance genes (sil operon) in only a few of the tested Staphylococcus sp. (especially in S. aureus) strains, Escherichia coli and Pseudomonas aeruginosa strains. These results demonstrate that despite its large use, this antiseptic remains a viable treatment alternative for the management of chronic leg wounds.

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.

OUP accepted manuscript

Candida auris is an emerging, multi drug resistant fungal pathogen that has caused infectious outbreaks in over 45 countries since its first isolation over a decade ago, leading to in-hospital crude mortality rates as high as 72%. The fungus is also acclimated to disinfection procedures and persists for weeks in nosocomial ecosystems. Alarmingly, the outbreaks of C. auris infections in Coronavirus Disease-2019 (COVID-19) patients have also been reported. The pathogenicity, drug resistance and global spread of C. auris have led to an urgent exploration of novel, candidate antifungal agents for C. auris therapeutics. This narrative review codifies the emerging data on the following new/emerging antifungal compounds and strategies: antimicrobial peptides, combinational therapy, immunotherapy, metals and nano particles, natural compounds, and repurposed drugs. Encouragingly, a vast majority of these exhibit excellent anti- C. auris properties, with promising drugs now in the pipeline in various stages of development. Nevertheless, further research on the modes of action, toxicity, and the dosage of the new formulations are warranted. Studies are needed with representation from all five C. auris clades, so as to produce data of grater relevance, and broader significance and validity.

Preparation, Characterization and Antimicrobial Properties of Nanosized Silver-Containing Carbon/Silica Composites from Rice Husk Waste

Rice husk, one of the main side products in the rice production, and its sustainable management represent a challenge in many countries. Herein, we describe the use of this abundant agricultural bio-waste as feedstock for the preparation of silver-containing carbon/silica nano composites with antimicrobial properties. The synthesis was performed using a fast and cheap methodology consisting of wet impregnation followed by pyrolysis, yielding C/SiO2 composite materials doped with varying amounts of silver from 28 to 0.001 wt %. The materials were fully characterized and their antimicrobial activity against ESKAPE pathogens, namely E. faecium, S. aureus, K. pneumoniae, A. baumannii, P. aeruginosa, and E. coli, and the pathogenic yeast C. albicans was investigated. Sensitivities of these strains against the prepared materials were demonstrated, even with exceptional low amounts of 0.015 m% silver. Hence, we report a straightforward method for the synthesis of antimicrobial agents from abundant sources which addresses urgent questions like bio-waste valorization and affordable alternatives to increasingly fewer effective antibiotics.

Microbial Interkingdom Biofilms and the Quest for Novel Therapeutic Strategies

Fungal and bacterial species interact with each other within polymicrobial biofilm communities in various niches of the human body. Interactions between these species can greatly affect human health and disease. Diseases caused by polymicrobial biofilms pose a major challenge in clinical settings because of their enhanced virulence and increased drug tolerance. Therefore, different approaches are being explored to treat fungal-bacterial biofilm infections. This review focuses on the main mechanisms involved in polymicrobial drug tolerance and the implications of the polymicrobial nature for the therapeutic treatment by highlighting clinically relevant fungal-bacterial interactions. Furthermore, innovative treatment strategies which specifically target polymicrobial biofilms are discussed.

Structural membrane changes induced by pulsed blue light on methicillin-resistant Staphylococcus aureus (MRSA)

BACKGROUND

In a recent study we showed that blue light inactivates methicillin-resistant Staphylococcus aureus (MRSA) by perturbing, depolarizing, and disrupting its cell membrane.

PURPOSE

The current study presents visual evidence that the observed biochemical changes also result in cell metabolic changes and structural alteration of the cell membrane.

METHODS

Cultures of MRSA were treated with 450 nm pulsed blue light (PBL) at 3 mW/cm² irradiance, using a sub lethal dose of 2.7 J/cm² radiant exposure three times at 30-min intervals. Following 24 h incubation at 37 °C, irradiated colonies and control non-irradiated colonies were processed for light and transmission electron microscopy.

RESULTS

The images obtained revealed three major effects of PBL; (1) disruption of MRSA cell membrane, (2) alteration of membrane structure, and (3) disruption of cell replication.

CONCLUSION

These signs of bacterial inactivation at a dose deliberately selected to be sub-lethal supports our previous finding that rapid depolarization of bacterial cell membrane and disruption of cellular function comprise another mechanism underlying photo-inactivation of bacteria. Further, it affirms the potency of PBL.

Lethal Mechanisms of Nostoc-Synthesized Silver Nanoparticles Against Different Pathogenic Bacteria

BACKGROUND

Increasing antibiotic resistance and the emergence of multidrug-resistant (MDR) pathogens have led to the need to develop new therapeutic agents to tackle microbial infections. Nano-antibiotics are a novel generation of nanomaterials with significant antimicrobial activities that target bacterial defense systems including biofilm formation, membrane permeability, and virulence activity.

PURPOSE

In addition to AgNO3, the current study aimed to explore for first time the antibacterial potential of silver nanoparticles synthesized by Nostoc sp. Bahar_M (N-SNPs) and their killing mechanisms against Streptococcus mutans, methicillin-resistant Staphylococcus aureus, Escherichia coli, and Salmonella typhimurium.

METHODS

Potential mechanisms of action of both silver species against bacteria were systematically explored using agar well diffusion, enzyme (lactate dehydrogenase (LDH) and ATPase) and antioxidant (glutathione peroxidase and catalase)   assays, and morphological examinations. qRT-PCR and SDS-PAGE were employed to investigate the effect of both treatments on mfD, flu, and hly gene expression and protein patterns, respectively.

RESULTS

N-SNPs exhibited greater biocidal activity than AgNO3 against the four tested bacteria. E. coli treated with N-SNPs showed significant surges in LDH levels, imbalances in other antioxidant and enzyme activities, and marked morphological changes, including cell membrane disruption and cytoplasmic dissolution. N-SNPs caused more significant upregulation of mfD expression and downregulation of both flu and hly expression and increased protein denaturation compared with AgNO3.

CONCLUSION

N-SNPs exhibited significant inhibitory potential against E. coli by direct interfering with bacterial cellular structures and/or enhancing oxidative stress, indicating their potential for use as an alternative antimicrobial agent. However, the potential of N-SNPs to be usable and biocompatible antibacterial drug will evaluate by their toxicity against normal cells.

Antimicrobial photodynamic activity of gallium-substituted haemoglobin on silver nanoparticles

Methicillin-resistant Staphylococcus aureus (MRSA), a major scourge in skin and soft-tissue infections, expresses surface-bound haemoprotein receptors that can be exploited for the targeted delivery of photosensitizers. We have developed a nanosized agent for targeted antimicrobial photodynamic therapy (aPDT), comprised of GaPpIX (a hemin analog with potent photosensitizer activity) encapsulated in haemoglobin (GaHb), mounted on 10 nm Ag nanoparticles (AgNPs). The average GaHb-AgNP contains 28 GaPpIX units stabilized by Hb αβ-dimer units. Eradication (>6-log reduction) of S. aureus and MRSA can be achieved by a 10-second exposure to 405 nm irradiation from a light-emitting diode (LED) array (140 mW cm-2), with GaHb-AgNP loadings as low as 5.6 μg mL-1 for S. aureus and 16.6 μg mL-1 for MRSA, corresponding to nanomolar levels of GaPpIX. This reduction in bacterial count is several orders of magnitude greater than that of GaHb or free GaPpIX on a per mole basis. The GaHb-AgNP platform is also effective against persister MRSA and intracellular MRSA, and can provide comparable levels of aPDT with a 15-minute irradiation by an inexpensive compact fluorescent lightbulb. Collateral phototoxicity to keratinocytes (HaCaT cells) is low at the GaHb-AgNP concentrations and fluences used for aPDT. GaHb adsorbed on 10 nm AgNPs is much more potent than that on 40 nm AgNPs or 10 nm AuNPs, indicating that both size and plasmon-resonant coupling are important factors for enhanced aPDT. Electron microscopy analysis reveals that GaHb-AgNPs are not readily internalized by S. aureus but remain attached to the bacterial cell wall, the likely target of photo-oxidative damage.

Inhibition of Mixed Biofilms of Candida albicans and Methicillin-Resistant Staphylococcus aureus by Positively Charged Silver Nanoparticles and Functionalized Silicone Elastomers

Both bacterial and fungal organisms display the ability to form biofilms; however, mixed bacterial/fungal biofilms are particularly difficult to control and eradicate. The opportunistic microbial pathogens Candida albicans and Staphylococcus aureus are among the most frequent causative agents of healthcare-acquired infections, and are often co-isolated forming mixed biofilms, especially from contaminated catheters. These mixed species biofilms display a high level of antibiotic resistance; thus, these infections are challenging to treat resulting in excess morbidity and mortality. In the absence of effective conventional antibiotic treatments, nanotechnology-based approaches represent a promising alternative for the treatment of highly recalcitrant polymicrobial biofilm infections. Our group has previously reported on the activity of pure positively charged silver nanoparticles synthesized by a novel microwave technique against single-species biofilms of C. albicans and S. aureus. Here, we have expanded our observations to demonstrate that that silver nanoparticles display dose-dependent activity against dual-species C. albicans/S. aureus biofilms. Moreover, the same nanoparticles were used to functionalize catheter materials, leading to the effective inhibition of the mixed fungal/bacterial biofilms. Overall, our results indicate the potent activity of silver nanoparticles against these cross-kingdom biofilms. More studies are warranted to examine the ability of functionalized catheters in the prevention of catheter-related bloodstream infections.

Cyanobacteria - A Promising Platform in Green Nanotechnology: A Review on Nanoparticles Fabrication and Their Prospective Applications

Green synthesis of nanoparticles (NPs) is a global ecofriendly method to develop and produce nanomaterials with unique biological, physical, and chemical properties. Recently, attention has shifted toward biological synthesis, owing to the disadvantages of physical and chemical synthesis, which include toxic yields, time and energy consumption, and high cost. Many natural sources are used in green fabrication processes, including yeasts, plants, fungi, actinomycetes, algae, and cyanobacteria. Cyanobacteria are among the most beneficial natural candidates used in the biosynthesis of NPs, due to their ability to accumulate heavy metals from their environment. They also contain a variety of bioactive compounds, such as pigments and enzymes, that may act as reducing and stabilizing agents. Cyanobacteria-mediated NPs have potential antibacterial, antifungal, antialgal, anticancer, and photocatalytic activities. The present review paper highlights the characteristics and applications in various fields of NPs produced by cyanobacteria-mediated synthesis.

Biogenic synthesis of silver nanoparticles using Gliocladium deliquescens and their application as household sponge disinfectant

The topic of this investigation was to evaluate the microbial contamination of household sponges, biosynthesize of silver nanoparticles (Ag NPs) by Gliocladium deliquescens cell-free supernatant, and estimate the efficiency of Ag NPs as an acceptable disinfectant. The 2³ factorial design was applied for the optimization of Ag NPs synthesis. Silver nitrate (AgNO₃) concentration was the main positive impact on Ag NP biosynthesis. Various gamma irradiation doses were used in Ag NP production where the highest yield production was at 25.0 kGy. Ag NPs were characterized by UV-Vis. spectroscopy, The Fourier-transform infrared spectroscopy analysis (FTIR), dynamic light scattering (DLS), X-ray diffraction (XRD), and transmission electron microscope (TEM). Ag NPs were monodispersed spherical-shaped with 9.68 nm mean size. Two hundred sponge samples that were collected from different Egyptian household furniture and kitchens were highly contaminated by various contaminants including Salmonella spp., Staphylococcus spp., coliform bacteria, Gram-negative bacteria, yeasts, and molds. Ag NPs showed functional antimicrobial activity against all the microbial contaminants; Salmonella spp. was completely inhibited by Ag NP (50.0 μg/mL) treatment. The Ag NPs have the maximum inhibition zone against Salmonella spp. (14 mm) compared with the Staphylococcus spp. (12.3 mm). The minimum inhibitory concentration (MIC) of Ag NPs against Salmonella spp. and Staphylococcus spp. were 6.25 μg/ mL and 12.5 μg/ mL, respectively. The antibiofilm activity of Ag NPs was the highest at the concentration of 50.0 μg/mL recording 63.3 % for Salmonella spp. and 54.5 % for Staphylococcus spp. Ag NPs may find potent disinfectant applications for household purposes.

Silver Nanoantibiotics Display Strong Antifungal Activity Against the Emergent Multidrug-Resistant Yeast Candida auris Under Both Planktonic and Biofilm Growing Conditions

Candida auris is an emergent multidrug-resistant pathogenic yeast with an unprecedented ability for a fungal organism to easily spread between patients in clinical settings, leading to major outbreaks in healthcare facilities. The formation of biofilms by C. auris contributes to infection and its environmental persistence. Most antifungals and sanitizing procedures are not effective against C. auris, but antimicrobial nanomaterials could represent a viable alternative to combat the infections caused by this emerging pathogen. We have previously described an easy and inexpensive method to synthesize silver nanoparticles (AgNPs) in non-specialized laboratories. Here, we have assessed the antimicrobial activity of the resulting AgNPs on C. auris planktonic and biofilm growth phases. AgNPs displayed a strong antimicrobial activity against all the stages of all C. auris strains tested, representative of four different clades. Under planktonic conditions, minimal inhibitory concentration (MIC) values of AgNPs against the different strains were <0.5 μg ml⁻¹; whereas calculated IC₅₀ values for inhibition of biofilms formation were <2 μg ml⁻¹ for all, but one of the C. auris strains tested. AgNPs were also active against preformed biofilms formed by all different C. auris strains, with IC₅₀ values ranging from 1.2 to 6.2 μg ml⁻¹. Overall, our results indicate potent activity of AgNPs against strains of C. auris, both under planktonic and biofilm growing conditions, and indicate that AgNPs may contribute to the control of infections caused by this emerging nosocomial threat.

Toxicity evaluation of nanocrystalline silver-impregnated coated dressing on the life cycle of worm Caenorhabditis elegans

In recent times, however, due to the emergence of bacterial strains with resistance to conventional antibiotics, silver has again gained attention as an alternative for developing new efficient bactericides, including the use of silver nanoparticles (AgNPs). However, the improper disposal of these items after use may cause toxicological effects on organisms in the environment. To evaluate the potential environmental hazard of nanosilver-coated dressings, the nematode Caenorhabditis elegans was chosen as a test organism. The assays were conducted in 24-well plates that contain four different sizes of coated dressing to obtain different concentrations. L1 and L4 C. elegans larval stages were exposed to these nanosilver concentrations. Dressing cutouts were arranged between two layers of agar for 3 days and Escherichia coli (OP 50 strain) was added as food source for the worms. After the exposure period, growth, reproduction, fertility, silver concentration in the medium and the concentration of reactive oxygen species (ROS) in the worms were evaluated. Scanning and transmission electron microscopy analyses were performed on the coated dressings, as well as analyses of zeta potential, ionic release and antibacterial power in two bacterial strains (Pseudomonas aeruginosa and Staphylococcus aureus). It was verified the antibacterial power of the coated dressing, in both bacteria strains tested. Characterization of the coated dressing indicated heterogeneous nanoparticles, as well as distinct zeta potentials for the medium in water and saline medium (0.9% NaCl). L1 larval worms exposed to nanosilver-coated dressing showed a high ROS concentration and reductions in growth, fertility and reproduction. Worms exposed to the coated dressing during the L4 stage showed almost no response. Overall, the obtained results indicate the potential environmental hazard of nanosilver-coated dressings.

Cytotoxic effect of green silver nanoparticles against ampicillin-resistant Klebsiella pneumoniae

Considering the harmful effects and high spread of drug-resistant Klebsiella pneumoniae, many researchers have been trying to produce new antibacterial agents to combat the emergence of multidrug-resistant (MDR) strains of this bacterium. Recent progress in the nanomedicine field has provided opportunities for synthesizing unique nanoagents to battle MDR bacteria by targeting virulence and resistance signalling. The biocidal effects of 14.9 nm silver nanoparticles fabricated using Nostoc sp. Bahar M (N-SNPs) and AgNO3 were examined against drug-resistant K. pneumoniae using the agar well diffusion method. Transmission electron microscopy (TEM) was used to detect the ultrastructural changes caused by N-SNPs and AgNO3. To address the mode of action of N-SNPs and AgNO3, CAT, GPx, LDH and ATPase levels were assessed. The toxicity of N-SNPs and AgNO3 was evaluated against the mfD, flu, hly, 23S, hns, hcp-1, VgrG-1 and VgrG-3 genes as well as cellular proteins. N-SNPs showed the greatest inhibitory activity against K. pneumoniae, with MIC and MBC values of 0.9 and 1.2 mg mL-1, respectively. Furthermore, N-SNPs and AgNO3 induced apoptotic features, including cell shrinkage and cell atrophy. N-SNPs were more potent bactericidal compounds than AgNO3, causing increased leakage of LDH and GPx activities and depletion of ATPase and CAT activities, resulting in induced oxidative stress and metabolic toxicity. Compared to AgNO3, N-SNPs exhibited the highest toxicity towards the selected genes and the greatest damage to bacterial proteins. N-SNPs were the most potent agents that induced bacterial membrane damage, oxidative stress and disruption of biomolecules such as DNA and proteins. N-SNPs may be used as effective nanodrugs against MDR bacteria.

Novel Biogenic Silver Nanoparticle-Induced Reactive Oxygen Species Inhibit the Biofilm Formation and Virulence Activities of Methicillin-Resistant Staphylococcus aureus (MRSA) Strain

Emerging antibiotic-resistant bacteria result in increased mortality and have negative economic impacts. It is necessary to discover new strategies to create alternative antibacterial agents that suppress the bacterial resistance mechanism and limit the spread of serious infectious bacterial diseases. Silver nanoparticles may represent a new medicinal agents as alternative antibiotics affect different bacterial mechanisms such as virulence and resistance. In addition to that of silver nitrate (AgNO₃) and ampicillin, for the first time, the inhibitory effect of silver nanoparticles synthesized using Desertifilum sp. (D-SNPs) was evaluated against five pathogenic bacteria using the agar well diffusion method. Also, the influence of D-SNPs and AgNO₃ on bacterial antioxidant and metabolic activities was studied. The antibacterial activity of D-SNPs and AgNO₃ against methicillin-resistant Staphylococcus aureus (MRSA) strains was studied at the morphological and molecular level. D-SNPs and AgNO₃ have the ability to inhibit the growth of the five bacterial strains and resulted in an imbalance in the CAT, GSH, GPx and ATPase levels. MRSA treated with D-SNPs and AgNO₃ showed different morphological changes such as apoptotic bodies formation and cell wall damage. Moreover, both caused genotoxicity and denaturation of MRSA cellular proteins. Additionally, TEM micrographs showed the distribution of SNPs synthesized by MRSA. This result shows the ability of MRSA to reduce silver nitrate into silver nanoparticles. These data indicate that D-SNPs may be a significant alternative antibacterial agent against different bacteria, especially MDR bacteria, by targeting the virulence mechanism and biofilm formation, leading to bacterial death.

Inhibition of Candida auris Biofilm Formation on Medical and Environmental Surfaces by Silver Nanoparticles

Candida auris is an emerging pathogenic fungus implicated in healthcare-associated outbreaks and causes bloodstream infections associated with high mortality rates. Biofilm formation represents one of the major pathogenetic traits associated with this microorganism. Unlike most other Candida species, C. auris has the ability to survive for weeks on different surfaces. Therefore, there is an urgent need to develop new effective control strategies to combat the threat of C. auris. Advances in nanotechnologies have emerged that carry significant potential impact against Candida biofilms. We obtained pure round silver nanoparticles (AgNPs) (1 to 3 nm in diameter) using a microwave-assisted synthetic approach. When tested against C. auris, our results indicated a potent inhibitory activity both on biofilm formation (half maximal inhibitory concentration (IC₅₀) of 0.06 ppm) and against preformed biofilms (IC₅₀ of 0.48 ppm). Scanning electron microscopy images of AgNP-treated biofilms showed cell wall damage mostly by disruption and distortion of the outer surface of the fungal cell wall. In subsequent experiments AgNPs were used to functionalize medical and environmental surfaces. Silicone elastomers functionalized with AgNPs demonstrated biofilm inhibition (>50%) at relatively low concentrations (2.3 to 0.28 ppm). Bandage dressings loaded with AgNPs inhibited growth of C. auris biofilms by more than 80% (2.3 to 0.017 ppm). Also, to demonstrate long-lasting protection, dressings loaded with AgNPs (0.036 ppm) were washed thoroughly with phosphate-buffered saline, maintaining protection against the C. auris growth from cycles 1 to 3 (>80% inhibition) and from cycles 4 to 6 (>50% inhibition). Our results demonstrate the dose-dependent activity of AgNPs against biofilms formed by C. auris on both medical (silicone elastomer) and environmental (bandage fibers) surfaces. The AgNPs-functionalized fibers retain the fungicidal effect even after repeated thorough washes. Overall these results point to the utility of silver nanoparticles to prevent and control infections caused by this emerging pathogenic fungus.

Evaluation of Antibacterial and Cytotoxicity Properties of Silver Nanowires and Their Composites with Carbon Nanotubes for Biomedical Applications

In this work, we prepared silver nanowires (AgNWs) via the polyol method in the presence or absence of single wall carbon nanotubes (CNTs) and tested their physicochemical, antibacterial and cytotoxic properties. Results showed that the introduction of CNTs lead to the formation of AgNWs at lower temperature, but the final product characteristics of AgNWs and AgNWs-CNT were not significantly different. AgNWs exhibited antibacterial properties against all the studied bacterial species via the formation of oxygen reactive species (ROS) and membrane damage. Furthermore, AgNWs exhibited a dose-dependent and time-dependent toxicity at concentrations ≥ 10 µg/mL. Fibroblasts appeared to be more resistant than human colorectal adenocarcinoma (Caco-2) and osteoblasts to the toxicity of AgNWs. The cytotoxicity of AgNWs was found to be related to the formation of ROS, but not to membrane damage. Overall, these results suggest that AgNWs are potential antibacterial agents against E. coli, S. aureus, MRSA and S. saprophyticus, but their dosage needs to be adjusted according to the route of administration.

Synthesis of Silver Nanoparticles Using a Novel Cyanobacteria Desertifilum sp. extract: Their Antibacterial and Cytotoxicity Effects

BACKGROUND

The emergence of multi drug-resistant (MDR) bacterial infections and cancer has necessitated the development and discovery of alternative eco-safe antibacterial and anticancer agents. Biogenic fabrication of metallic nanoparticles is an emerging discipline for production of nanoproducts that exert potent anticancer and antibacterial activity, and do not suffer from the limitations inherent in physiochemical synthesis methods.

METHODOLOGY

In this study, we isolated, purified, and characterized a novel cyanobacteria extract (Desertifilum IPPAS B-1220) to utilize in biofabrication of silver nanoparticles (D-SNPs). D-SNPs were produced by adding Desertifilum extract to silver nitrate solution under controlled conditions. Biofabrication of D-SNPs was confirmed using a UV-Vis spectrophotometer. The resultant D-SNPs were characterized using XRD, FTIR, SEM, and TEM. The toxicity of D-SNPs against five pathogenic bacteria and three cancer cell lines (MCF-7, HepG2, and Caco-2) was evaluated.

RESULTS

Formation of D-SNPs was indicated by a color change from pale yellow to dark brown. The peak of the surface plasmon resonance of the D-SNPs was at 421 nm. The XRD detected the crystallinity of D-SNPs. FTIR showed that polysaccharides and proteins may have contributed to the biofabrication of D-SNPs. Under SEM and TEM, the D-SNPs were spherical with diameter ranges from 4.5 to 26 nm. The D-SNPs significantly suppressed the growth of five pathogenic bacteria, and exerted cytotoxic effects against MCF-7, HepG2, and Caco-2 cancer cells with IC50 values of 58, 32, and 90 µg/mL, respectively.

CONCLUSION

These findings showed for the first time the potentiality of novel cyanobacteria strain Desertifilum IPPAS B-1220 to fabricate small SNPs that acted as potent anticancer and antibacterial material against different cancer cell lines and pathogenic bacterial strains. These findings encourage the researchers to focus on cyanobacteria in general and especially Desertifilum sp. IPPAS B-1220 for synthesizing different NPs that opening the window for new applications.

Activating a Silver Lipoate Nanocluster with a Penicillin Backbone Induces a Synergistic Effect against S. aureus Biofilm

Many antibiotic resistances to penicillin have been reported, making them obsolete against multiresistant bacteria. Because penicillins act by inhibiting cell wall production while silver particles disrupt the cell wall directly, a synergetic effect is anticipated when both modes of action are incorporated into a chimera cluster. To test this hypothesis, the lipoate ligands (LA) of a silver cluster (Ag29) of known composition (Ag29LA12)[3-] were covalently conjugated to 6-aminopenicillanic acid, a molecule with a β-lactam backbone. Indeed, the partially conjugated cluster inhibited an Staphylococcus aureus biofilm, in a dose-response manner, with a half-maximal inhibitory concentration IC50 of 2.3 μM, an improvement over 60 times relative to the unconjugated cluster (IC50 = 140 μM). An enhancement of several orders of magnitude over 6-APA alone (unconjugated) was calculated (IC50 = 10 000 μM). Cell wall damage is documented via scanning electron microscopy. A synergistic effect of the conjugate was calculated by the combination index method described by Chou-Talalay. This hybrid nanoantibiotic opens a new front against multidrug-resistant pathogens.

Protocol optimization for a fast, simple and economical chemical reduction synthesis of antimicrobial silver nanoparticles in non-specialized facilities

OBJECTIVE

Silver nanoparticles (AgNPs) can be difficult or expensive to obtain or synthesize for laboratories in resource-limited facilities. The purpose of this work was to optimize a synthesis method for a fast, facile, and cost-effective synthesis of AgNPs with antimicrobial activity, which can be readily implemented in non-specialized facilities and laboratories.

RESULTS

The optimized method uses a rather simple and rapid chemical reduction process that involves the addition of a polyvinylpyrrolidone solution to a warmed silver nitrate solution under constant vigorous stirring, immediately followed by the addition of sodium borohydride. The total synthesis time is less than 15 min. The obtained AgNPs exhibit an aspect ratio close to 1, with an average size of 6.18 ± 5 nm. AgNPs displayed potent antimicrobial activity, with Minimal Inhibitory Concentration values of ≤ 4 µg mL^-1 for Staphylococcus aureus and ≤ 2 µg mL^-1 for Candida albicans. The resulting method is robust and highly reproducible, as demonstrated by the characterization of AgNPs from different rounds of syntheses and their antimicrobial activity.

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.

Influence of AgVO3 incorporation on antimicrobial properties, hardness, roughness and adhesion of a soft denture liner

The objective of this in vitro study was to investigate the effect of nanostructured silver vanadate decorated with silver nanoparticles (AgVO₃) on antimicrobial activity, hardness, roughness, and adhesion of a soft denture liner. The antimicrobial efficacy of the Trusoft (Boswoth) liner incorporated with different concentrations of AgVO₃ against Enterococcus faecalis, Pseudomonas aeruginosa, Candida albicans, and Staphyloccocus aureus (n = 5) was evaluated by the agar diffusion method. Roughness, hardness, and adhesion properties were also evaluated. The data were analyzed by analysis of variance (ANOVA) and Tukey's multiple comparison test with significance at the p < 0.05 level. At concentrations of 1 and 2.5%, AgVO₃ incorporation was effective only against E. faecalis, and at 5 and 10%, against E. faecalis, P. aeruginosa, and C. albicans. None of the concentrations was effective against S. aureus. A decrease in hardness was found for the 1, 2.5, and 10% AgVO₃ concentrations (p < 0.001) and at 5%, hardness was not affected. None of the concentrations affected the roughness of the material. A significant increase in tensile values was observed between the liner and heat-curing acrylic resin for 2.5% (p < 0.001) and 10% (p = 0.042) concentrations. AgVO₃ incorporation to a soft denture liner promoted antimicrobial activity against E. faecalis, P. aeruginosa, and C. albicans without affecting roughness, maintaining the hardness properties recommended for soft and extra soft liners, and improving the adhesion between the liner and the acrylic resin used for dentures.

Superior antibacterial activity of ZnO-CuO nanocomposite synthesized by a chemical Co-precipitation approach

Synthesis of highly efficient antibacterial agents has become highly important due to emergence of antibiotic resistance. Herein, Pristine ZnO and ZnO-CuO nanocomposite has been synthesized by simple chemical co-precipitation method and characterized by X-ray diffraction (XRD), microscopic and spectroscopic techniques. The prepared ZnO-CuO nanocomposite is composed of two dimensional nanosheets consisting of hexagonal ZnO and monoclinic CuO crystal phases present in coexistence. Moreover, a minute presence of Cu₅Zn₈ cubic phase has been evident in the XRD pattern of ZnO-CuO nanocomposite. Fourier Transform Infrared Spectroscopy (FTIR) spectrum of the prepared nanocomposite has revealed the presence of vibrational modes related to both Zn-O and Cu-O. Photoluminescence (PL) investigations depicted the formation of huge amounts of surface defects in ZnO-CuO nanocomposite as compared to pristine ZnO nanostructures. The prepared ZnO-CuO nanocomposite has efficiently killed Methicillin resistant Staphylococus aureus (s. aureus) bacterium by producing 24 mm of zone of inhibition (ZOI) comparing to 8 mm ZOI produced by pristine ZnO. The superior antibacterial activity of ZnO-CuO nanocomposite has been attributed to oxidative stress generated by electron transfer pathway and reactive oxygen species (ROS) generation.

Preparation and antibacterial behaviour of nanostructured Ag@SiO2–penicillin with silver nanoplates

Preparation of Ag@SiO₂–penicillin NPs with superior synergistic and antibacterial properties against methicillin-resistant Staphylococcus aureus.

Review of the effects of silver nanoparticle exposure on gut bacteria

Gut bacteria are involved in regulating several important physiological functions in the host, and intestinal dysbacteriosis plays an important role in several human diseases, including intestinal, metabolic and autoimmune disorders. Although silver nanoparticles (AgNPs) are increasingly being incorporated into medical and consumer products due to their unique physicochemical properties, studies have indicated their potential to affect adversely the gut bacteria. In this review, we focus on the biotoxicological effects of AgNPs entering the gastrointestinal tract and the relationship of these effects with important nanoscale properties. We discuss in detail the mechanisms underlying the bactericidal toxicity effects of AgNPs and explore the relationships between AgNPs, gut bacteria and disease. Finally, we highlight the need to focus on the negative effects of AgNPs usage to facilitate appropriate development of these particles.

Tetrahedral (T) Closed-Shell Cluster of 29 Silver Atoms & 12 Lipoate Ligands, [Ag29(R-α-LA)12](3-): Antibacterial and Antifungal Activity

Here we report on the identification and applications of an aqueous 29-atom silver cluster stabilized with 12 lipoate ligands, i.e. Ag₂₉(R-α-LA)₁₂ or (29,12), wherein R-α-LA = R-α-lipoic acid, a natural dithiolate. Its uniformity is checked by HPLC-ESI-MS and analytical ultracentrifugation, which confirms its small dimension (~3 nm hydrodynamic diameter). For the first time, this cluster has been detected intact via electrospray ionization mass spectrometry, allowing one to confirm its composition, its [3-] charge-state, and the 8-electron shell configuration of its metallic silver core. Its electronic structure and bonding, including T-symmetry and profound chirality in the outer shell, have been analyzed by DFT quantum-chemical calculations, starting from the known structure of a nonaqueous homologue. The cluster is effective against Methicillin-Resistant Staphylococcus aureus bacteria (MRSA) at a minimum inhibitory concentration (MIC) of 0.6 mg-Ag/mL. A preformed Candida albicans fungal biofilm, impermeable to other antifungal agents, was also inhibited by aqueous solutions of this cluster, in a dose-response manner, with a half-maximal inhibitory concentration (IC₅₀) of 0.94 mg-Ag/mL. Scanning electron micrographs showed the post-treatment ultrastructural changes on both MRSA and C. albicans that are characteristic of those displayed after treatment by larger silver nanoparticles.

Unexpected insights into antibacterial activity of zinc oxide nanoparticles against methicillin resistant Staphylococcus aureus (MRSA)

Zinc oxide nanoparticles (ZnO-NPs) are attractive as broad-spectrum antibiotics, however, their further engineering as antimicrobial agents and clinical translation is impeded by controversial data about their mechanism of activity. It is commonly reported that ZnO-NP's antimicrobial activity is associated with the production of reactive oxygen species (ROS). Here we disprove this concept by comparing the antibacterial potency of ZnO-NPs and their capacity to generate ROS with hydrogen peroxide (H2O2). Then, using gene transcription microarray analysis, we provide evidence for a novel toxicity mechanism. Exposure to ZnO-NPs resulted in over three-log reduction in colonies of methicillin resistant S. aureus with minimal increase in ROS or lipid peroxidation. The amount of ROS required for the same amount of killing by H2O2 was much greater than that generated by ZnO-NPs. In contrast to H2O2, ZnO-NP mediated killing was not mitigated by the antioxidant, N-acetylcysteine. ZnO-NPs caused significant up-regulation of pyrimidine biosynthesis and carbohydrate degradation. Simultaneously, amino acid synthesis in S. aureus was significantly down-regulated indicating a complex mechanism of antimicrobial action involving multiple metabolic pathways. The results of this study point to the importance of specific experimental controls in the interpretation of antimicrobial mechanistic studies and the need for targeted molecular mechanism studies. Continued investigation on the antibacterial mechanisms of biomimetic ZnO-NPs is essential for future clinical translation.

Mechanisms of antibiotic resistance in bacteria mediated by silver nanoparticles

Silver nanoparticles (AgNPs) are widely used in industry, consumer products, and medical appliances due to their efficient antimicrobial properties. However, information on environmental toxicity and bacterial impact of these particles is not completely elucidated. Results showed that AgNPs produced growth inhibition and oxidative stress in bacteria Escherichia coli (gram negative) and Staphylococcus aureus (gram positive), with half-maximal inhibitory concentrations (IC₅₀) of 12 and 7 mg/L, respectively. Surprisingly, bacteria pre-exposed to sublethal dose of AgNPs exhibited increased resistance toward antibiotics (ampicillin and Pen-Strep) with IC₅₀ elevated by 3-13-fold. Further, AgNP pre-exposure raised the minimal inhibitory concentration and minimal biocidal concentration by two- to eightfold when cells were challenged with antibiotics with diverse mechanisms of action (penicillin, chloramphenicol, and kanamycin). Interestingly, we found that upon exposure to ampicillin, strains pretreated with AgNPs exhibited lower levels of membrane damage and oxidative stress, together with elevated levels of intracellular ATP relative to untreated cells. Bacterial reverse mutation assay (Ames test) showed that AgNPs are highly mutagenic, consistent with further assays demonstrating abiotic reactive oxygen species (ROS) generation and intrinsic DNA cleavage activity in vitro of AgNPs. Overall, our results suggest that AgNPs enhance bacterial resistance to antibiotics by promoting stress tolerance through induction of intracellular ROS. Our data suggest potential consequences of incidental environmental exposure of bacteria to AgNPs and indicate the need to regulate use and disposal of AgNPs in industry and consumer products.

Non-cytotoxic effect of green synthesized silver nanoparticles and its antibacterial activity

Silver nanoparticles (AgNPs) were green synthesized using ethanolic extract of fenugreek leaves and characterized using UV-Vis spectroscopy, Fourier transform infra-red spectroscopy (FTIR), X-ray diffraction (XRD), high resolution transmission electron microscopy HRTEM and energy dispersive X-ray analysis (EDX) techniques. The HRTEM results revealed the formation of highly stable, mono dispersed, spherical shaped AgNPs with the size ranging from 20 to 30nm. The presence of flavonoids and their interaction with the AgNPs were confirmed using FTIR. Antibacterial activities of the AgNPs were studied against pathogenic gram-positive Staphylococcus aureus (S. aureus) and gram negative Escherichia coli (E. coli) bacteria. The synthesized AgNPs displayed the enhancement of antibacterial activity against E. coli. The morphological changes in the bacterial cell membrane was observed using SEM analysis. Leakage of protein from the bacterial cells increased at every time intervals (2 and 4h). MTT assay was carried out for the AgNPs against human skin cell line (HaCaT). Interestingly, cytotoxicity of the synthesized AgNPs was less toxic to HaCaT cells as compared to bacteria cells, which suggests that the synthesized AgNPs by this method is eco-friendly in nature.

Biosynthesized silver nanoparticles: are they effective antimicrobials?

BACKGROUND

Silver nanoparticles (AgNPs) are increasingly being used in medical applications. Therefore, cost effective and green methods for generating AgNPs are required.

OBJECTIVES

This study aimed towards the biosynthesis, characterisation, and determination of antimicrobial activity of AgNPs produced using Pseudomonas aeruginosa ATCC 27853.

METHODS

Culture conditions (AgNO₃ concentration, pH, and incubation temperature and time) were optimized to achieve maximum AgNP production. The characterisation of AgNPs and their stability were evaluated by UV-visible spectrophotometry and scanning electron microscopy.

FINDINGS

The characteristic UV-visible absorbance peak was observed in the 420–430 nm range. Most of the particles were spherical in shape within a size range of 33–300 nm. The biosynthesized AgNPs exhibited higher stability than that exhibited by chemically synthesized AgNPs in the presence of electrolytes. The biosynthesized AgNPs exhibited antimicrobial activity against Escherichia coli, P. aeruginosa, Salmonella typhimurium, Staphylococcus aureus, methicillin-resistant S. aureus, Acinetobacter baumannii, and Candida albicans.

MAIN CONCLUSION

As compared to the tested Gram-negative bacteria, Gram-positive bacteria required higher contact time to achieve 100% reduction of colony forming units when treated with biosynthesized AgNPs produced using P. aeruginosa.

Control of biofilm-associated infections by signaling molecules and nanoparticles

As the severe infections caused by resistant pathogens and biofilm embedded bacteria continue to emerge, alternative antimicrobial strategies could represent a solution. Recent studies support the development of molecular approaches (through signaling molecules) aiming to fight infections by modulating the virulence, behavior and formation of resistance structures such as biofilms. The utilization of such formulations would offer the advantage of reducing the selection of resistant isolates, since most of the proposed molecules do not interfere with the population fitness if utilized in low amounts. Despite the promising results, these therapies are delaying to be applied in the clinical context mainly because of the following: (i) limited knowledge regarding their long and medium term effect, (ii) specific properties that make most of these molecules difficult to be utilized in pharmacological formulations, (iii) low stability, (iv) difficulty to reach a target within the host body, and (v) limited availability. For reducing most of these disadvantages, nanotechnology seem to offer the best option through the development of nanostructured materials and nanoparticles able to improve the efficiency of molecular virulence modulators and novel antimicrobial compounds and to ensure their targeted delivery and controlled release.